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EPE 2002

1. 99 plus VAT Deluxe Development Kit 99 plus VAT and on line help included Institutional 10 user Network Licence 199 plus VAT Del E tVersion lus VAT D eluxe Export Version 96 plus Price 19 95 inc VAT Deluxe PiCtutor Hardware UK and EU customers add VAT at 17 5 to plus VAT prices ELECTRONIC CIRCUITS amp COMPONENTS V2 0 Provides an introduction to the principles and application of the most common types of electronic components and shows how they are used to form complete circuits The virtual laboratories worked examples and pre designed circuits allow students to learn experiment and check their understanding Version 2 has been considerably expanded in almost every area following a review of major syllabuses GCSE GNVQ A level and HNC It also contains both European and American circuit symbols Sections or include Fundamentals units amp multiples electricity Circuit simulation screen electric circuits alternating circuits Passive Components resistors capacitors inductors transformers Semiconductors diodes transistors op amps logic gates Passive Circuits Active Circuits The Parts Gallery will help students to recognise common electronic components and their corresponding symbols in circuit diagrams Selections include Components Components Quiz Symbols Symbols Quiz Circuit Technology Included in the Institutional Versions are multiple choice questions exam style q
2. Everyday Practical Electronics April 2002 and placing it in a separate small holder which is plugged into the appropriate out put socket It would be a good idea to buy a second battery so that the phone may be kept in use while the other one is on charge In fact it would be best to buy two inexpensive com patible non manufacturer s batteries and keep the original one for home use This is because charging by the present unit is not as sophisticated as that provided by the phone itself and a conventional plug in charger If carelessly used overcharging could occur which might damage the battery CIRCUIT DESCRIPTION The complete circuit diagram for the Solar Charge and Go is shown in Fig 1 X1 and X2 are the solar panels which provide a nominal 3V at 80mA each based on bright light conditions These are con nected in series to give nominally 6V at 80mA Tests show that the specified units will supply about 20mA under reasonably bright conditions and around 100mA in full sunlight ME1 0 TO 100A CHARGE 2 Low 14001 HIGH On E l 0 5W E SEE TEXT J gt BACKUP ON B2 4 5V AA x 3 ALK l R4 SEE TEXT 102 FOR 3 6V 33Q FOR 2 4V PHONE BATTERY OUTPUT 2 5mm JACK DIRECT OUTPUT POWER JACK a Fig 1 Complete circuit diagram for the Solar Charge and Go power unit As they stand the solar panels would make a poor supply The vo
3. FOROFOFOFO OFOFOROROPOPOPFoOHO O L ogo dG QQ 0 00 00000000000000000000000000 lOO OO 0000000000000000000000000 000 H jO O 000000008000000008000008800000 H GlIO000008 00000000800000000800800000 G Fi 0 00Q0000040000000080 000000000 000 0 EG O O 0000000000000000000000000000 0 F DIG O00 0000000000000000000000000000 0 D ClO 0 0 00 00 0000000000000 00 00004000 GC BIO O00 0000000000000000000000000000 8 A JO O00000000000000000000000000000 0 A OF OPOPFOFOFOFOPOPOROROFOTO Ofegogo OgFoseqogo F O O O Fig 4 Electric Guitar Tuner stripboard topside component layout interwiring to off board components and details of breaks required in the underside copper tracks The complete circuit board is shown above left 238 Everyday Practical Electronics April 2002 for C4 so that any frequency drift with changes in temperature is minimised A polycarbonate capacitor is probably the best choice but a good quality polyester component should give good results Most ceramic types have inadequate short and long term stability and should not be used Practically any small or medium size instrument case is suitable for this project Alternatively a diecast aluminium box is a good choice if maximum toughness is required The exact layout of the unit is not important but try to arrange things so that the wiring from socket SK1 to the circuit board is no more than a few centimetres long Due to the high gain of IC1 plus
4. TRIAXIAL CABLE Fig 6 8 Guarded resistance measurement a non guarded set up b non guarded equivalent circuit c guarded set up d guarded equivalent circuit 250 Everyday Practical Electronics April 2002 Fig 6 9 Guard signal for instrumentation amplifier Batteries create electric current through electrochemical effects Similar processes can occur if contaminants are present on circuit boards and terminals Variations in humidity can affect sensor systems with very high impedances Contaminants e g from handling cables and connectors can also reduce insulation resistance leading to errors High precision circuits and sensors must be kept clean RANDOM NOISE The electronic components and sensors used to build circuits generate noise from within themselves that is random in nature This means that we can never predict the actual instantaneous value of the noise volt age or current although the overall statistics of how the noise behaves is known however Fig 6 10 Example of random noise illustrated via the Picoscope Fig 6 11 sinewave heavily contaminated by noise Picoscope display of a Everyday Practical Electronics April 2002 A typical random noise signal is shown in Fig 6 10 A sine wave suffering from a significant amount of random noise is shown in Fig 6 11 The fact that the components i
5. 400 pages 96 pages 200 pages Music Audio and Video QUICK GUIDE TO ANALOGUE SYNTHESIS lan Waugh Even though music production has moved into the digi tal domain modern synthesisers invariably use ana logue synthesis techniques The reason is simple analogue synthesis is flexible and versatile and it s rel atively easy for us to understand The basics are the same for all analogue synths and you ll quickly be able to adapt the principles to any instrument to edit exist ing sounds and create exciting new ones This book describes How analogue synthesis works The essen tial modules every synthesiser has The three steps to synthesis How to create phat bass sounds How to generate filter sweeps Advanced synth modules How to create simple and complex synth patches Where to find soft synths on the Web If you want to take your synthesiser of the hardware or software variety past the presets and program your own sounds and effects this practical and well illustrated book tells you what you need to know ls Tve Tele H eab T 7 45 QUICK GUIDE TO MP3 AND DIGITAL MUSIC lan Waugh MP3 files the latest digital music format have taken the music industry by storm What are they Where do you get them How do you use them Why have they thrown record companies into a panic Will they make music easier to buy And cheaper Is this the future of music All these questions and more are answered in thi
6. This follow on to Bebop to the Boolean Boogie is a multimedia extravaganza of information about how computers work It picks up where Bebop left off guiding you through the fascinat ing world of computer design P i x P CRO and you ll have a few chuckles if not belly laughs along the way In addition to over 200 megabytes of mega cool multimedia the CD ROM contains a virtual microcomput er simulating the motherboard and standard computer peripherals in an extremely realistic manner In addition to a wealth of technical information myriad nuggets of triv ia and hundreds of carefully drawn illustrations the CD ROM contains a set of lab experiments for the virtual microcomputer that let you recreate the experiences of early computer pioneers If you re the slightest bit inter ested in the inner workings of computers then don t dare to miss this Over 800 pages in Adobe Acrobat format 21 95 Order code BEB2 CD ROM ELECTRONICS MADE SIMPLE lan Sinclair Assuming no prior knowledge Electronics Made Simple presents an outline of modern electronics with an empha sis on understanding how systems work rather than on details of circuit diagrams and calculations It is ideal for students on a range of courses in electronics including GCSE C amp G and GNVQ and for students of other subjects who will be using electronic instruments and methods Contents waves and pulses passive component
7. Vol 31 No 4 OO St ie IT x M73 56193 wo 2 Be E wo i Printed in the UK 4 i aga t f a Copyright 2001 2002 Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND UK and Maxfield amp Montrose Interactive Inc PO Box 857 Madison Alabama 35758 USA All rights reserved WARNING The materials and works contained within EPE Online which are made available by Wimborne Publishing Ltd and Maxfield amp Montrose Interactive Inc are copyrighted You are permitted to make a backup copy of the downloaded file and one 1 hard copy of such materials and works for your personal use International copyright laws however prohibit any further copying or reproduction of such materials and works or any republication of any kind Maxfield amp Montrose Interactive Inc and Wimborne Publishing Ltd have used their best efforts in preparing these materials and works However Maxfield amp Montrose Interactive Inc and Wimborne Publishing Ltd make no warranties of any kind expressed or implied with regard to the documentation or data contained herein and specifically disclaim without limitation any implied warranties of merchantability and fitness for a particular purpose Because of possible variances
8. Creating an Event Counter By Clive Max Maxfield and Alvin Brown INTERGRAPH COMPUTER SYSTEMS 3D GRAPHICS A chapter from Intergraph s book that explains computer graphics technology in an interesting and understandable way with full colour graphics EXTRA ARTICLE ON VOL 1 amp 2 THE LIFE amp WORKS OF KONRAD ZUSE a brilliant pioneer in the evolution of computers A bonus article on his life and work written by his eldest son including many previously unpublished photographs NOTE These mini CD ROMs are suitable for use on any PC with a Send a copy of this form or order by letter if you do not wish to CD ROM drive They require Adobe Acrobat Reader available free cut your Issue from the Internet www adobe com acrobat yt a ic a Card NO 646 6 6 45 6946650 455 0041 688d bed l Expiry Date 22s ecnacnuee nee es Switch Issue No l l I I I I l l l SEND TO Everyday Practical Electronics l Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND I Tel 01202 873872 Fax 01202 874562 I i E mail orders epemag wimborne co uk 1 Payments must be by card or in Sterling cheque or bank I draft drawn on a UK bank l Normally supplied within seven days of receipt of order I I Everyday Practical Electronics April 2002 211 SURFING THE INTERNET NET WORK ALAN WINSTANLEY Wie to this month s Net Work our column specially writ t
9. based simulation tool and to design printed circuit boards CADPACK is made up of three separate software modules These are restricted versions of the full Labcenter software ISIS Lite which provides full schematic drawing features including full control of drawing appearance automatic wire routing and over 6 000 parts PROSPICE Lite integrated into ISIS Lite which uses unique animation to show the operation of any circuit with mouse operated switches pots etc The animation is compiled using a full mixed mode SPICE simulator ARES Lite PCB layout software allows professional quality PCBs to be designed and includes advanced features such as 16 layer boards SMT components and an autorouter operating on user generated Net Lists C FOR PICMICRO MICROCONTROLLERS C for PICmicro Microcontrollers is designed for students and professionals who need to learn how to use C to program embedded microcontrollers This product contains a complete course in C that makes use of a virtual C PlICmicro which allows students to see code execution step by step Tutorials exercises and practical projects are included to allow students to test their C programming capabilities Also includes a complete Integrated Development Environment a full C compiler Arizona Microchip s MPLAB assembler and software that will program a PIC16F84 via the parallel printer port on your PC Can be used with the P Ctutor hardware see oppos
10. 5V supply with the built in switching power supply generating plus and minus 10V supplies for the line driver Handshaking Serial interfacing has a reputation for being awkward to implement and one reason for this is the difficulties involved When handshaking is required Fortunately it should not be necessary to use handshaking when using a serial link to your projects The relatively low TTLICMOS a RS232C Input Output TTL CMOS 4 RS232C Output Input Fig 4 Circuit for a simple line driver and receiver using the MAX202 speed of an RS232C port means that there is little risk of the add on or the PC receiving data at a rate that it cannot handle However you do have to be careful that data is not generated at a rate that is too high for the link to handle Serial interfacing is not the right choice if high data transfer rates are needed The interface s absolute maximum rate of 1 920 bytes per second must not be exceeded 259 Constructional Project PIC CONTROL INTRUDER AL JOHN BECKER A sophisticated multi zone intruder detection system that offers deluxe monitoring facilities EN Editor Mike suggested that Wi author might be interested in designing a PIC controlled intrud er alarm the suggestion was accepted in the knowledge that to do the job properly would make a worthwhile challenge The author has designed alarms before but none having the sophistication that appeare
11. AM FM 1 5MHz 2GHz Datron 1061 High Quality 5 5 Digit Bench Multimeter True RMS 4 wire Res Current Converter IEEE Datron 1061A High Quality 6 digit Bench Multimeter True RMS 4 wire Current Converter Racal Receiver RA1772 50kHz 30MHz L E D Display Basically working NOW ONLY MARCONI 893C AF Power Meter Sinad Measurement MARCONI 893B No Sinad MARCONI 2610 True RMS Voltmeter Autoranging 5Hz 25MHz 19 GOULD J3B Sine Sq Osc 10Hz 100kHz low distortion AVO 8 Mk 6 in Every Ready case with leads etc Other AVOs from GOODWILL GVT427 Dual Ch AC Millivoltmeter 10mV 300V in 12 ranges Freq 10Hz 1MHz 100 125 SOLARTRON 7150 DMM 6 2 digit Tru RMS IEEE SOLARTRON 7150 Plus HIGH QUALITY RACAL COUNTERS 9904 Universal Timer Counter 50MHz 9916 Counter 10Hz 520MHz 9918 Counter 10Hz 560MHz 9 digit WAYNE KERR B424 Component Bridge RACAL AIM 9343M LCR Databridge Digital Automeasurement of R C L Q D HUNTRON TRACKER Model 1000 FLUKE 8050A 4 5 Digit 2A True RMS FLUKE 8010A 3 5 Digit 10A FLUKE 8012A 3 5 Digit 2A SOLARTRON 7045 Bench Multimeter ONLY 4 5 Digit Bright L E D with leads Portable Appliance Tester CD Megger Pat H P 6012B DC PSU 0 60V 0 50A 1000W 1000 FARNELL AP60 50 1KW Autoranging FARNELL H60 50 0 60V 0 50A FARNELL H60 25 0 60V 0 25A Power Supply HPS3010 0 30V 0 10A FARNELL L30 2 0 30V 0 2A FARNELL L30 1 0 30V 0 1A Many other Power Supplies avai
12. Free 2 CD ROMs Microchip 2001 Tech Library NOV 01 PROJECTS e Capacitance Meter Pitch Switch e Lights Needed Alert e Teach In 2002 Power Supply FEATURES e Teach In 2002 Part 1 Practically Speaking Circuit Surgery New Technology Update Ingenuity Unlimited Net Work The Internet Page Free 16 page Supplement PIC Toolkit TK3 For Windows DEC 01 PROJECTS e Ghost Buster PIC Polywhatsit Twinkling Lights Mains Failure Alarm FEATURES e Teach In 2002 Part 2 Marconi The Father of Radio Interface Ingenuity Unlimited Circuit Surgery New Technology Update Net Work The Internet Page 2001 Annual Index Jan 02 PROJECTS e PIC Magick Musick Time Delay Touch Switch Versatile Bench Power Supply Forever Flasher FEATURES e Teach In 2002 Part 3 Practically Speaking Ingenuity Unlimited New Technology Update Circuit Surgery Net Work The Internet PROJECTS e PIC Spectrum Analyser Guitar Practice Amp HT Power Supply Versatile Current Monitor FEATURES e Teach In 2002 Part 4 Ingenuity Unlimited Russian Space Shuttle Revisited Circuit Surgery Interface New Technology Update Net Work The Internet Page PROJECTS MK484 Shortwave Radio PIC Virus Zapper RH Meter PIC Mini Enigma FEATURES e Teach In 2002 Part 5 Ingenuity Unlimited Programming PIC Interrupts Circuit Surgery P
13. MOVWE TMRO BCF INTCON TOIF BSF INTCON TOIE BSF INTCON GIE main loop MAIN ensure timer flag is clear enable timer wrap interrupt enable global interrupts bump the main loop counter BTFSS STATUS Z Skip if it has wrapped to zero GOTO MAIN else repeat main loop every 256 times round flash the led briefly MOVE ISRCL W copy ISR low byte counter Al BSF PORTA 0 turn LED on MOVWE COUNTL A3 INCF LOOPCT F bump the counter MOVE ISRCH W copy ISR high byte counter BTFSS STATUS Z _ till it wraps to zero again MOVWE COUNTH GOTO A3 subtract last counter value from this counter value BCF PORTA 0 then turn off the LED check that the result is positive or zero produces no borrow GOTO MAIN and resume MOVE LASTL W load last counter low byte check has failed put on the LED and loopstop into W FAIL BSF PORTA O SUBWEF COUNTL W subtract current low byte STOP GOTO STOP MOVE LASTH W into W BTESS STATUS C borrow ADDLW 1 borrow MOVE COUNTH F BTFSS STATUS Z GOTO A2 MOVE LASTH F load last counter high byte C set if last subtraction did not C clear so add 1 to W for the test if high byte is zero Z clear so high byte not zero COUNTH is zero so test if BANKO Interrupt service routine ISR MOVWF SAVEW SWAPF STATUS W MOVWE SAVES gt save W save STATUS ensure Bank U set BTFSS INTCON TOIF test TOIF GOTO POP not a timer interrupt there is a timer i
14. Receiver Register Clock Q7 Data Received Reset Data Received 19 Receiver Register Input d UART The 6402 is the industry standard UART and as such it is readily available It has a 40 pin d il encapsulation and the pin assignments are shown in Fig 1 The transmitter and receiver sections are largely independent and they can oper ate at different baud rates However a common set of inputs determines the word format for both sec tions This is not a major drawback since practical applications would normally require a common word format Pin 34 is taken high to load the control register with the bit pattern on pins 35 to 39 It can be pulsed high to latch momentary data into the control register or simply held high if the control inputs are hard wired A wide range of formats are available with from five to eight bits one or two stop bits and parity checking enabled or disable All formats have the standard sin gle start bit The best format for general interfacing is eight data bits one stop bit and no parity checking Full eight bit transfers are provided but the number of bits in each word is kept to a minimum This format is obtained by taking pin 36 low and tying the other four control inputs high There are separate clock inputs for the transmitter pin 40 and the receiver pin 17 but in most applications a single clock generator agl Transmitter Clock Ground del Receiver Register Disable 4 37 C
15. Scratch Blanker Flashing Snowman Multi project PCB x Video Cleaner FEB 00 251 Find It 252 x Teach In 2000 Part 4 253 High Performance Regenerative Receiver x EPE Icebreaker PCB257 programmed PIC16F877 and floppy disc Parking Warning System x Micro PICscope Garage Link Transmitter Receiver Versatile Mic Audio Preamplifier PIR Light Checker x Multi Channel Transmission System Transmitter Receiver Interface SEPT 99 241 7 51 7 64 3 50 7 88 3 00 6 93 6 78 7 82 7 85 3 96 4 44 5 63 4 20 4 52 APR 00 x Canute Tide Predictor PIC Gen Frequency Generator Counter Q Meter EPE Moodloop AUG 00 271 Quiz Game Indicator 272 Handy Amp 273 Active Ferrite Loop Aerial SEPT 00 Remote Control IR Decoder PIC Dual Channel Virtual Scope Handclap Switch x PIC Pulsometer Twinkling Star Festive Fader Motorists Buzz Box x PiCtogram x PIC Monitored Dual PSU 1 PSU Monitor Unit Static Field Detector Multi project PCB Two Way Intercom UFO Detector and Event Recorder Magnetic Anomaly Detector Event Recorder Audio Alarm Using PICs and Keypads Ice Alarm Graphics L C D Display with PICs Supp Using the LM3914 6 L E D Bargraph Drivers Multi purpose Main p c b Relay Control L E D Display PC Audio Power Meter Doorbell Extender Transmitter MAR 01 292 Receiver 293 Trans Remote 294 Rec Relay 295 EPE Snug bug Heat Control for Pets A
16. These are finished in blue p v c printed with the magazine logo in gold on the spine Price 5 95 plus 3 50 p amp p for overseas readers the postage is 6 00 to everywhere except Australia and Papua New Guinea which cost 10 50 Normally sent within seven days but please allow 28 days for delivery more for overseas Payment in sterling only please Visa Amex Diners Club Switch and MasterCard accepted minimum card order 5 Send fax or phone your card number and card expiry date with your name address etc Or order on our secure server via our UK web site Overseas customers your credit card will be charged by the card provider in your local currency at the existing exchange rate Everyday Practical Electronics April 2002 Editor MIKE KENWARD Deputy Editor DAVID BARRINGTON Technical Editor JOHN BECKER Business Manager DAVID J LEAVER Subscriptions MARILYN GOLDBERG Administration FAY KENWARD Editorial Admin 01202 873872 Advertisement Manager PETER J MEW Frinton 01255 861161 Advertisement Copy Controller PETER SHERIDAN 01202 873872 On Line Editor ALAN WINSTANLEY EPE Online Internet version Editors CLIVE MAX MAXFIELD and ALVIN BROWN READERS ENQUIRIES E mail techdept epemag wimborne co uk We are unable to offer any advice on the use purchase repair or modification of commercial equipment or the incorporation or modification of designs published in the magazine We regre
17. a place FROM THE DAYS of Maxwell Hertz Lodge and Marconi to what was the state of the art just a few short years ago THERE IS ALSO a selection of free readers For Sale and Wanted advertisements in every issue Radio Bygones covers it all THE MAGAZINE is published six times a year and is only available by postal subscription It is not available at newsagents TO TAKE OUT a subscription or to order a sample copy please contact RADIO BYGONES Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND Tel 01202 873872 Fax 01202 874562 Web sites www radiobygones co uk 280 www radiobygones com Everyday Practical Electronics April 2002 READOUT E mail editorial epemag wimborne co uk John Becker addresses some of the general points readers have raised Have you anything interesting to say Drop us a line WIN A DIGITAL MULTIMETER A 31 5 digit pocket sized I c d multime ter which measures a c and d c volt age d c current and resistance It can also test diodes and bipolar transistors Every month we will give a Digital Multimeter to the author of the best Readout letter X LETTER OF THE MONTH amp LIFE INTHE ELECTRONIC WORLD Dear EPE In the October 01 issue you asked for any positive observations on employment in British Industry My experience is now out of date but ve no complaints I checked and found that my first electronics book Basic Radio was g
18. and we are guaranteed that COUNTH and COUNTL will be a consis tent and correct copy of ISRCH and ISRCL Once ISRCH is loaded into W we can safely re enable interrupts because the ISR does not affect anything else used by the main loop Any interrupt events that occurred during the critical section will cause the ISR to be run at this point but the ISR will preserve W If you make the above changes to INT PROG6 and rerun it you will probably find that it runs OK i e with the dim 1 e d on indefinitely So are we finally done Well maybe not quite Murphy may still have one more trick up his sleeve and it s a subtle one If we want to make our code really bomb proof we should protect against this too MURPHY S LAST TRICK Earlier versions of the PIC16x84 data sheets identified a possibility that we shall now discuss The relevant note has disap peared from later versions and is not in the 87x data sheets In various tests the author has been unable to reproduce the behaviour described in this section with a PICI6F84 even using an external oscillator that is not synced to the instruction clock as interrupt source It would therefore appear that Microchip have fixed this feature in later versions of their microcontrollers But since it s still possible that you might be using an old PIC perhaps a 16C84 that behaves this way it s as well to be aware of this prob lem and how to get around it For safety it
19. for the inclusive price of 10 each overseas add 1 p amp p They are also able to supply a suitable 2 line x 16 characters per line alphanumeric display module at a very reasonable price The software is available on a 3 5in PC compatible disk EPE Disk 5 from the EPE Editorial Office for the sum of 3 each UK to cover admin costs for over seas charges see page 301 It is also available Free from the EPE web site ftp ftp epemag wimborne co uk pubs PICS PiCalarm The alarm printed circuit board is available from the EPE PCB Service code 339 Finally the alarm fittings such as PIR sensors bell and strobe etc can be purchased from most DIY superstores Solar Charge and Go The 3V solar panels used in the Solar Charge and Go model came from Maplin amp 0870 264 6000 or www maplin co uk code CJ37S They also supplied the dummy AA cells code YX92 and the single hole fixing 2 5mm panel mounting power socket code JK10L A suitable plug is coded HH62S For the 6 way tagboard you could try Greenweld 01277 811042 or www greenweld co uk and Chevet Supplies 01253 751858 If problems do arise finding a local source for the tagboard Maplin see above list one as code FL11 You will need to cut it down to size The Shottky diode 1N5817 is also listed by them as code JA46A The miniature edgewise 1004A f s d panel meter was purchased from Farnell 0113 263 6311 or www farnell com code 143 509 Everyday Practical E
20. loaded free from our Internet FTP site ftp ftp epemag wimborne co uk EPE PRINTED CIRCUIT BOARD SERVICE Order Code Project Quantity Price cheque PO in sterling only to r Lit t VISA Everyday D Practical Electronics 9 Switch Issue No MasterCard Amex Diners Club Visa or Switch Minimum order for cards 5 Card No Signature Card Exp Date NOTE You can also order p c b s by phone Fax E mail or via our Internet site on a secure server http www epemag wimborne co uk shopdoor htm 301
21. that seems interesting I ll add it to the PIC Tricks ftp and disk TK3 AND PICTUTOR Dear EPE I am sure you had no intention of misleading Tomas Henry in your reply Jan 02 but I have tried using your brilliant TK3 software with the PICtutor board and apart from being confined to 14 pin PICs of the 16x84 variety and not being able to disassemble to ASM it worked perfectly without any modification to the hardware Pat Alley via email Thanks Pat but I took it that Tomas wanted to know if TK3 was fully usable with PICtutor which it is not Providing PICtutor users perform the correct on board switch operations at appro priate points before and after programming TK3 can indeed send programs to PIC16x84 devices on the Tutor board 283 ELECTRONICS CD ROMS ELECTRONICS PROJECTS Logic Probe testing Electronic Projects is split into two main sections Building Electronic Projects contains comprehensive information about the components tools and techniques used in developing projects from initial concept through to final circuit board production Extensive use is made of video presentations showing soldering and construction techniques The second section contains a set of ten projects for students to build ranging from simple sensor circuits through to power amplifiers A shareware version of Matrixss CADPACK schematic capture circuit simulation and p c b design software is included The projects on the CD ROM a
22. the appropriate window for Signals that topic However in most cases it is only the first page for that topic that appears Others are avail able from the pop down menu at the bottom of the screen as shown in Fig 3 There are so many pages available that a second method of accessing them Fig 2 Many of the pages can be has been included An accessed via the menu system Index window opens Everyday Practical Electronics April 2002 automatically when the program is launched see Fig 1 and this provides an easy way to search for the exact topic that you require The eight tabs at the top of the window are used to select the general area of interest such as electronics or components A scrollable list of all the relevant pages then appears In order to launch the required page it is merely necessary to double click on its entry in the Index window Using the menu system provides the quickest means of access ing pages but with so many pages available the Index window is the more practical means of navigating the program In addition some of the pages can only be accessed via the Index window Some of the lists in the index are very long but the use of sub headings makes it easier to find the required topic Considering the huge range of topics and pages on offer finding your way around the program is remarkably easy Interactivity Some of the pages are in HTML and consist of a colour photo graph plus some text For examp
23. Allows monitoring of fewer zones than are available Automatically recognises whether a sensor should be moni tored for an open circuit or a closed circuit Allows open circuit or closed circuit sensors to be used without system modification Recognises that a sensor is incorrectly open or closed prior to monitoring being activated and indicates which sensor is incor rect i e door open when it should be closed Allows users to preview zone sensor status Allows the bell on time to be set for a shorter period than the 20 minutes permitted in the UK Prevents the bell on time exceeding the UK limit Allows users to check the system by means of indicator lights without activating the bell etc Allows indicator lights to display the status of the power supply and bell etc Provides anti tamper warning of interference with the system Provides a Panic button that immediately activates the bell etc even if the system is not set for full zone monitoring Provides passive advice e g buzzer that a zone has been entered even if the system is not set for full monitoring and for the advice to be terminated once the zone has been vacated e g to monitor shop door opening closing Accepts all conventional types of switched output commercial sensor including magnetic catches pressure pads passive infra red PIR devices vibration detectors etc and for any mixture of these to be used Provides an o
24. Fig 1 The opening screen The program is less convention al than it first appears 278 should proceed reasonably quickly and reliably The minimum requirements to run this program are not very demanding and practically any PC running Windows 95 or later is suitable This is useful for educational establishments where the computers are something less than state of the art The program is fully installed onto the computer s hard disk This avoids the need to have the CD ROM in the drive when the program is in use and ensures that everything runs smoothly and quickly About 45 megabytes of hard disk space is required which makes the program quite compact by current standards You will not spend hours learning to use this program before you can actually start learning from it Keeping Tabs A screen like the one shown in Fig 1 appears when the program is first run and it offers two ways of selecting the required pages At the top of the screen there is the usual Windows style menu bar but this does not have the usual headings such as File and Tools Instead it provides menus for Op Amps Digital Computing etc For example Fig 2 shows the A C menu which offers subjects such as inductance a c theory and active filters Selecting J Electronics and Computing Prinaples 1 REL Parallel Circuits neti Chemica Ineduchowns Le unan a menu option brings up Communication System
25. If the unit requires less than 100mA under such fault conditions it could prove destructive To give an extra margin of safety a 3 9V Zener diode D5 is included excl case meter amp batts SK1 2 5mm panel mounting socket SK2 power in type panel mounting socket S1 s p s t toggle switch S2 d p d t toggle switch B1 AA size nickel metal hydride cells 3 off B2 AA size alkaline cells 3 off see text Tag board two rows of 6 tags or alter native method of construction plastic box size 254mm x 203mm x 40mm max height x 20 mm height holders for three AA cells 2 off battery connectors 2 off 3mm l e d clip power in type line plug 2 5mm line plug possible dummy AA cells see text Fig 3 materials for phone battery charging unit see text small hardware Even so this over voltage could prove too much so to be safe only cheap equipment should be connected to this unit CONSTRUCTION The tag board method of construction shown in Fig 2 was used in the prototype However a stripboard layout could also be used In view of the small number of com ponents a printed circuit board p c b was not considered necessary Solder the components on to the board taking particular care over the polarity of the four diodes Solder resistor R1 directly across the meter MEI terminals and resistor R2 across switch S1 normally open make contacts Prototype interior layout and
26. Principles However it was merged back into one program at Version 7 1 and it is currently sold as Electronic and Computing Principles The program is not fundamentally different from Version 5 or even earlier variants and it is a collection of screens that provide tutorials on various aspects of computing electronics mathe matics basic physics etc The main difference from one version to the next is the range of topics covered and the number of screens in each section The range covered by V7 1 is vast but it remains reasonably easy to navigate your way to the desired topics Getting Started The program is supplied on a single CD ROM and it is installed via the usual Setup program Provided you have a suitable PC this C Electronics and Computing Principles V7 1 DC AC Electrical Semi Conductors Op Aamps Maths Digital Computing Test ka Electronics and Compuling Principles Vi Index fs comping Toobor Logics Mars Topic Hydrogen Alori Electron Shells Carbon Atom gt Sibcon Atom Copper Atom gt Genmanium Atom Conductor Ineulator Measuring an Electric Curent gt Finding Circuit Voltages Measuring Vollage and Current Venable Resistance Select Random Value Three Resistors in Sanes Two Parallel Resistors Potential Drader Loading a Fotental Drader Pull Up Pull Down Resistors Push Swich Change over Switch Staircase Switch Relay Switch DG Voltage
27. a blow by blow guide to the use of EASY PC Professional XM a schematic drawing and printed circuit board design computer package The guide also con ducts the reader through logic circuit simulation using Pulsar software Chapters on p c b physics and p c b production techniques make the book unique and with its host of project ideas make it an ideal companion for the integrative assignment and common skills components required by BTEC and the key skills demanded by GNVQ The principal aim of the book is to provide a straightfor ward approach to the understanding of digital electronics Those who prefer the Teach In approach or would rather experiment with some simple circuits should find the book s final chapters on printed circuit board produc tion and project ideas especially useful 88 pages 250 pages large format WROL GRZ A X 17 99 50 SIMPLE LED CIRCUITS R N Soar Contains 50 interesting and useful circuits and applica tions covering many different branches of electronics using one of the most inexpensive and freely available components the light emitting diode LED Also includes circuits for the 707 common anode display Order code BP42 2 99 A BEGINNER S GUIDE TO TTL DIGITAL ICs R A Penfold This book first covers the basics of simple logic circuits in general and then progresses to specific TTL logic integrated circuits The devices covered include gates oscillators
28. a switching Hall effect device B NEGATIVE MAGNETIC FIELD B POSITIVE B mT Fig 6 14 Output graph for a latching Hall effect device 252 PANEL 6 1 Magnetic Fields We can define a magnetic field as a region in which a magnetic force exists and is produced by movement of electric charges A conductor carrying a current will produce a magnetic field Fig 6 15 Permanent magnets are different in that the magnetic fields of their atoms are lined up this is in contrast to most materials where the magnetic fields are random DIRECTION OF FIELD CURRENT Fig 6 15 Current to magnetic field relationship Permanent magnets are made of iron or ferrite but stronger magnetic fields can be obtained using Neodymium Iron Boron NIB Samarium Cobalt SmCo Aluminum Nickel Cobalt AINiCo alloys Magnets have north and south poles and we all know that like poles repel while opposites attract The magnetic field is visualized as lines of flux that indicate the direction of the field and in the SI system is measured in webers Wb which is the field strength present Unipolar devices have an output voltage to magnetic field relationship as indicated in Fig 6 13 showing hysteresis where the operating point Bop is different from the release point Bgp The amount of hysteresis depends on the device chosen and provides a clean switching characteris tic for the output Note that Bop and Bp are both positive indicating t
29. been made if the passive mode is in operation The buzzer is also activated along with the strobe and bell in the event of an unauthorised intrusion being detected when the system is in full monitoring mode The bell is automatically turned off after a preset delay via line RE2 and tran sistor TR3 The strobe and buzzer though remain active until an authorised user resets the alarm The auxiliary output option controlled via line RBS is only activated for the maximum period that has been set for it more later Fig 3 Circuit diagram for alarm output device drivers The PIC is capable of supply 25mA from each output pin but it has a maxi mum total output current capability of 200mA which must not be exceeded The 25mA current is capable of directly driving a warning buzzer of the type that has its own in built oscillator It could also trigger alarm devices such as bells or strobes that have their own control circuit built in to them Most external devices though are likely to require driving at voltages and currents greater than the PIC can supply For this reason each of the REO RE2 RBS5 outputs are connected to power Darlington transistors TR1 to TR4 as illustrated in D3 D4 1N4001 1N4001 T a Rk 6 TO BACKUP BATTERY Fig 2 Power supply circuit diagram 262 In addition to controlling their respective transistors if installed the four output lines each have an l e d resistor pair The l e d
30. c across the terminals of capacitor C3 and 12V at the output of IC2 Adjust VR2 until a voltage of about 13 5V or the recharging voltage specified by the back up battery manufacturer is present across the battery terminal block pins Disconnect the mains power insert the PIC and reconnect the battery which should be in a reasonably fully charged state when first put into use If the PIC has not been programmed yet you can do this in situ now using Toolkit Mk2 or Mk3 via connector TB2 POWERING UP When powering up with the pro grammed PIC in place your first need is to adjust the I c d s screen contrast using pre set VRI Ignore any information which then becomes apparent it depends on the existing contents of the PIC s data EEPROM Having set the contrast put the program into Engineer s Mode by holding down keypad D bottom right then pressing and releasing Reset switch S4 mounted sepa rately on the p c b and then releasing key D This action allows an authorised engi neer i e you to change the main PIN code without previously knowing the cor rect one On other occasions it also resets the alarm if it has been activated turning off the bell etc Additionally it resets various default factors Zones to be monitored 1 and 8 Entry exit zone 1 Entry exit time 30 seconds Bell on time 15 minutes Keypad 2 entry time out 30 seconds Normally the PIN code and other fac tors c
31. can be changed at any time Zone detection will be discussed shortly Alarm Outputs Four audio visual alarm control outputs are provided three via pins REO RE2 and one via RB5 When activated these pins go high and are specifically intended for driving an internal buzzer REO external strobe RE1 external bell RE2 and any device of the user s choice RB5 As will be discussed in relation to Fig 3 the out puts can activate these devices depending on their type either directly or via power transistors TR1 to TR4 In any alarm condition the bell strobe if fitted and buzzer are all activated The bell remains active for a period preset and automatically stored by the user through the software with a maximum duration of 20 minutes The software prevents the bell from restarting again irrespective of fur ther unauthorised zone entries but see Panic Switches later Once activated the alarm system can normally also see later only be reset by keying in the correct PIN code Display A liquid crystal display l c d module X2 is controlled via pins RAO RAS oper ated in output mode Pin RA4 is an open collector output and is biased high to the 5V power line via resistor R2 The l c d displays a variety of messages in respect of the several control and status modes that can be selected via the pushbutton key pad s It is used in conventional 4 bit con trol mode and its contrast is adjustable
32. compliments on my Spectrum Analyser Timewise designing pro jects for EPE is a hobby I greatly enjoy because it keeps me out of the cold during the winter but I m longing for outdoors and summer In fact designing does not take as long as some of you might suppose If you study my designs you are likely to find that there are aspects that might have originated in an earlier project either as hardware or software As I ve frequently commented much of electronics is based on building blocks That s one reason why EPE is so popular many readers know that even if they do not want to build a design in its entirety it can Still be a useful source of ideas for other circuits that readers want to design It s really no different for my designs and I often re vamp some aspects as library material This is especially true with software Having worked out a routine for something it can easily be used in another program that has a similar requirement sometimes without modifi cation at other times with a variety of tweeks to tailor it to the new conditions Regarding MPASM yes that s the dialect route I would recommend to anyone newly get ting into PICs The use of TASM is historical as that s the dialect introduced to us in the first PIC programmer design we did in Feb 96 Having learned PICs through that article TASM contin ues to be the dialect I prefer for myself and I know lots of other pe
33. component identification legends and a solder mask assists reliable soldering during assembly Turned pin connectors are used at strategic points to allow easy link wire connection between the p c b and an external breadboard The kit includes components p c b breadboard I c d and a choice of PIC microcon troller The prices are 34 99 for the PIC16F84 version and 39 99 for the F877 UK post and packing is 3 For more information contact Magenta Electronics Dept EPE 135 Hunter Street Burton on Trent Staffs DE14 2ST Tel 01283 565435 Fax 01283 546932 Everyday Practical Electronics April 2002 243 PIC AND MIX MICROCHIP S new PICDEM MSC1 demonstration board has been designed to simplify the design of mixed signal applications that use the PIC16C781 2 configurable analogue microcontrollers The board allows users to configure the PIC s multiple digital and analogue peripherals and download the configura tion for quick evaluation The system includes an evaluation package with an easy to use graphical user interface and code generator Designers can configure the inputs and outputs of each peripheral module load and view the contents of the Special Purpose Registers operate a dynamic conversion loop for scoping the DAC module output or continuously monitor the ADC input channels For more information www microchip com browse QUASAR TIMES SEVEN E e Lo B Lm Tr Mi z B QU
34. effect sensor instead of a reed switch BOUNCY SWITCHES One major concern with reed switches and all switches is switch bounce that occurs when a switch is closed because the switch contacts are springy they will bounce open and closed for several milli seconds before remaining closed This may be OK for turning lights on and off but causes problems if we wish to connect a switch to a logic circuit In Fig 6 12 is shown a screenshot of a reed switch bouncing captured using the Picoscope You can imagine a circuit designed to count the number of times a door is opened The circuit is straightfor ward a reed switch connected to the input of a counter device which may display the count value on l e d s Every time the Switch is activated it will bounce three or possible four times causing the counter to count three or four times Fig 6 12 Picoscope display of switch bounce 291 We need a switch debouncing circuit to stop this Lab 6 1 illustrates switch bounce using reed switches and Lab 6 2 shows how we can use a switch debouncing circuit to overcome this You can use these circuits to debounce any switch If switches are con nected directly to the input of a microcon troller then we can design software to provide debounce instead of hardware SEMICONDUCTING SENSORS Semiconducting magnetic sensors use the Hall Effect which was discovered by Edwin Hall in 1879 He was working on the effects of a magne
35. electronics products supplying retailers nationwide with over 3000 exclu sive RadioShack branded products It is also actively seeking the involvement of other retailers We have recently received Radio Shack s latest catalogue At over 440 pages the cat alogue well illustrates why it is that the company s products are well respected In addition to a very wide range of consumer electronic products from amplifiers to weather stations the catalogue contains a range of accessories such that any home electronics constructor is likely to need from capacitors and resistors to transistors and i c s etc The catalogue costs 1 99 plus P amp P which is refundable with your next order valued at 10 or over For information on your nearest RadioShack stockist or to order a cata logue call 01543 468855 Email info rs rusk com Web www radioshack com WORKBENCH DEAL FOR STUDENTS ADEPT Scientific tell us that Multisim and Ultiboard the award winning electronics software from Electronics Workbench is now available to students in a suite for only 65 excluding VAT and delivery Multisim 2001 is the latest version of the renowned circuit simulation software used extensively in both industry and teaching Adept say that it is the ideal tool for students to develop their skills in electronic circuit design With this soft ware students can create circuits analyse pre built circuits work through virtual laboratory assi
36. example Through this mode you can set the time for which the bell is turned on if unautho rised entry to a zone occurs There is a legal limit in the UK of 20 minutes maxi mum You may set a time between 1 and 20 minutes In the above example the previously set bell on time is shown as 12 minutes with the MAX20 reminding that 20 minutes is the maximum On line 2 is where your newly selected time is displayed when you press the permitted numeric keys The first digit the tens of minutes can only have a value between 0 and 2 A value between O and 9 can be keyed for digit 2 the units The following condi tions apply though If digit 1 has a value of 2 only 0 can be entered for digit 2 If digit 1 has a value of 0 a value of 0 cannot be keyed in for digit 2 This ensures that only a time between 1 and 20 minutes can be selected MODE 6 Auto zone assess On entry to Mode 6 a 2 line message will be displayed of which the following is an example This mode allows the system to assess whether it should be monitoring individual zones as normally open or normally closed The letter C in any of the eight positions on line 2 indicates that a zone sensor is currently closed letter o shows that it is currently open In this example zones 1 4 and 6 are shown as having normally closed logic Zones 2 3 5 7 and 8 have normally open logic The settings shown in line 2 can be stor
37. fish to get as close to nature as they can So what self respecting independent traveller would carry a mobile phone Apparently many do Some simply wish to maintain contact with family and friends at home Others see it as an important piece of safety equipment that may be used to summon help in an emergency However there is a problem Once the phone battery has run flat it may be impossible to charge it With no mains or 12V car supply available use of the phone may be restricted to emergency use only and kept switched off most of the time Even so the battery depending on type will self discharge fairly quickly On a long trip it may be found that it has dis charged whether the phone has been used or not O SOLAR MIO This solar operated circuit will charge a nominal 2 4V or 3 6V nickel cadmium or nickel metal hydride mobile phone battery It may also be used to power an inexpen sive 3V personal cassette player the type that normally use two AA size cells You could listen to music or learn the local lan guage Note however that the unit will probably not be successful at operating the cassette player and charging the mobile phone battery at the same time Many mobile phones use the batteries above For example the popular Nokia 3210 and 5110 models use a 2 4V and a 3 6V type respectively Before starting any construction work check the voltage of your battery by look ing at the label attached to i
38. if it s not H byte must have wrapped Z clear so LASTH not zero skip the check SUBWF COUNTH W subtract LASTH from COUNTH C set if there was no borrow C clear so an error has occurred RETFIE eventually overflow and allowance has to be made for this The main loop periodically turns the l e d on and off briefly as a visual check that it is running OK It does this too fast for it to be perceived by the eye as flashing the l e d appears to be dimly illuminated if all is well Read through Listing 6 and make sure you understand it then load and run INTPROG6 By now you will not be too surprised to see that the le d comes on dimly then after a few seconds is fully illuminated as the program detects an error in the counter Murphy s Law has struck again but exactly where and how What is the bug in INTPROG6 Give up OK look at the four instruc tions following the label MAIN which copy ISRCL and ISRCH to COUNTL and COUNTH Consider what happens if an interrupt occurs after COUNTL has been copied but before COUNTH has been copied On first thoughts it would seem there is no problem Let s assume for the sake of argument that ISRCL and ISRCH contain some arbitrary count like H 1234 The first two instructions will copy H 34 into COUNTL Then an interrupt occurs and ISRCL is incremented to H 35 COUNTL will stay at H 34 and the main loop will then copy H 12 i
39. if this is connected in any way but how does a sim ple twisted pair reject radio interference Again it is a matter of loops acting like transformer secondaries or antennae The smaller the area of any loops then the smaller the interference pick up must be Put simply a twisted cable has smaller loops than two individual wires that could potentially form a very large loop SOURCE OF INTERFERENCE A e LJ _ EG DIGITAL CLOCK UNE SOURCE OF e l l INTERFERENCE E G DIGITAL CLOCK LINE O SIGNAL WIRE Fig 3a Capacitive coupling of interfer ence and b equivalent circuit for screened cable with capacitively cou pled interference grounded by the screen On Screen Gerard s final question is How does screening work and does it only work if the negative or earth is on the outside Well capacitive coupling can pick up interference when there is in effect a form of capacitor created which links a source of interference to the wire carrying the sig nal This is illustrated in Fig 3 When we screen a cable by surrounding it with a braid then the interference is coupled to the screen instead The screen is equivalent to inserting a capacitance in series with the interference coupling capacitance and connecting the centre point to ground The interference picked up by the screen is therefore harm lessly shorted to ground see Fig 3b For this to work the screen obviousl
40. important classes of filter filter order filter impedance and impedance matching and effects of different filter types Advanced Theory which covers the use of filter tables mathematics behind filter design and an explanation of the design of active filters Passive Filter Design which includes an expert system and filter synthesis tool for the design of low pass high pass band pass and band stop Bessel Butterworth and Chebyshev ladder filters Active Filter Design which includes an expert system and filter synthesis tool for the design of low pass high pass band pass and band stop Bessel Butterworth and Chebyshev op amp filters DIGITAL WORKS 3 0 Digital Works Version 3 0 is a graphical design tool that enables you to construct digital logic circuits and analyze their behaviour It is so simple to use that it will take you less than 10 minutes to make your first digital design It is so powerful that you will never outgrow its capability Software for simulating digital logic circuits Create your own macros highly scalable Create your own circuits components and i c s Easy to use digital interface Animation brings circuits to life Vast library of logic macros and 74 series i c s with data sheets Powerful tool for designing and learning ELECTRONICS CAD PACK PCB Layout Electronics CADPACK allows users to design complex circuit schematics to view circuit animations using a unique SPICE
41. is advised that all programs for all PICs use the workaround Remember the quiz show Mastermind When the time up pinger went in the middle of a question Magnus Magnusson would announce his catchphrase Tve started so I ll finish and the contestant could complete the answer to that question So itis with the PIC if an interrupt event occurs when an instruction has started the interrupt is held pending until the instruc tion in progress has completed and then the transfer of control to the ISR takes place Instructions are sometimes said to be atomic with respect to interrupts where atomic is used in its original Greek mean ing of indivisible TURNING OFF INTERRUPTS Now instructions take some time to complete typically four clock cycles on the PIC The instruction has to be fetched from program memory parsed and the opcode decoded In the case of the BCF instruction the operand has to be fetched from register memory the appropriate bit cleared and the result written back to regis ter memory An interrupt can occur at any time dur ing this procedure In the processing of the BCE INTCON GIE instruction there could be a time window after the instruction has started and before the PIC has determined that the GIE bit is to be cleared when an interrupt event can occur If it does the interrupt will be taken and held pending till the clear GIE instruction completes Then the ISR will run and will terminate with a R
42. operate the personal stereo They also have an important voltage stabilising effect which will be explained later On the rear panel of the unit are two switches and two output sockets One socket is used for mobile phone battery charging and the other to power the per sonal stereo The sockets are of different types so make sure only the correct one is used for the job because they are not interchangeable One switch sets a high or low charge rate for the re chargeable batteries the purpose of this will be explained later and the other selects normal or backup mode for the mobile phone bat tery When the backup supply is switched on the light emitting diode on top glows to remind the user that this has been done BACKUP SUPPLY The backup supply is provided by the alkaline cells These enable the mobile phone battery to be kept sufficiently charged for an emergency call to be made This will be useful when there has been insufficient light to keep the battery charged using solar energy alone or if the phone has been used excessively Regarding mobile phone battery charg ing initial tests were made using the exist ing charger input on the phone This proved unreliable due to the voltage drop of the internal voltage regulator and the checks made by the phone circuit Also all the various models of phone could not be tested However good results are obtained by removing the battery from the phone
43. operation at input test point A by connecting the Picoscope to the circuit and set to trigger on a negative sig nal using the fastest timebase available The Picoscope should capture the waveform when you bring a magnet close to the switch You can capture a single trace if the trigger is set to once or repeat The waveform should look like that in Fig 6 12 earlier where you can see the bounce clearly 253 Fig 6 18 Reed switch and interface gate Fig 6 19 Switch bounce observed at point B in Fig 6 18 Now observe the output of the gate test point B If you are using an inverting gate as shown in Fig 6 18 then the trigger should be set to positive Bring up the mag net and you should see the switch bounce converted to a short series of alternating logic levels before settling down as shown in Fig 6 19 Lab 6 2 Debouncing a Reed Switch There are several ways of debouncing a switch If you look in circuit books you will most likely see the circuit in Fig 6 20 which uses a flip flop to cause the output to change state when the switch is first closed Any subsequent bounces will not cause the flip flop to change state again Note that this needs a changeover switch which is 254 Breadboard assembly for the circuit in Fig 6 18 Note the disk magnet alongside the reed switch 3 IAA P lt j U e g eo ET Aa AN A E KLL x n gt ee L i Un A ern a Se ee ey ee ee P te gt gt lt
44. operation of the circuit is straight forward The magnetic sensor ICI is placed close to the magnet which is attached to the shaft and its output is con nected to the negative edge trigger input of a 4098 monostable C2 The monostable is set up to be non retriggerable i e once triggered any subse quent negative edges at the input won t restart it until its time period has elapsed The time constant is determined by the for mula 0 5R2C1 and is set to about 60ms This value determines the highest speed that can be measured in this case about 16 revolutions per second 16Hz The output of the monostable is passed into a low pass filter R3 C2 whose average output voltage is proportional to shaft speed Finally an OP177 op amp IC3 is used to amplify the output by up to seven times to produce a more usable voltage Fig 6 25 shows typical waveforms generated There are a number of changes that can be made Firstly the time constant of the monostable determines the highest speed but if the pulses are narrow high speed then the energy added to the low pass filter will be small so the output will be very low for low speeds Secondly the value of the low pass filter determines the response time try chang ing the values and see what the effects are Low values will give a fast response but you will see rapid decay between pulses Conversely large values will give a slow response and this can be seen if the shaft
45. phase As they do so the l e d varies from maximum brightness with the two signals 180 degrees out of phase to fully switched off with the sig nals in phase This produces the flashing from the l e d at a rate equal to the difference in the two frequencies or the beat rate as it is known A lack of activity from the L e d whether it is fully switched on turned off or anywhere in between indicates that the two frequencies are accurately matched CIRCUIT OPERATION The full circuit diagram for the Electric Guitar Tuner is shown in Fig 3 The ampli fier uses operational amplifier IC1 in the Everyday Practical Electronics April 2002 Resistor R7 provides one of the timing resistances and the other one is made up from series resistor R6 and whichever of the six preset potentiometers VR1 to VR6 is switched into circuit using rotary switch S1 The six presets provide the six reference frequencies with VR6 and VR1 being used for the top and bottom EF notes respectively The value of R7 is kept low in comparison to the other timing resistances in order to give an output waveform at pin 3 of IC2 that has a mark space ratio of approximately 1 to 1 Indicator D1 is the l e d and R3 is the current limiter resistor The l e d current is about 4mA but as the l e d is never switched on for more than about 50 per cent of the time the average current never exceeds about 2mA It is therefore advis able to use a high bri
46. runs flat make sure sufficient charge is put back from the backup supply if necessary to enable an emergency call to be made at any time It would be best to drain the phone battery by no more than can be put back during the course of one day With the phone simply switched on standby the current requirement is much less than while actually talking It will be best to experiment with all this before you leave home It would also be a good idea to carry a spare set of back up batteries When setting out on a trip start with the re chargeable battery pack fully charged Remember to replace the alkaline cells before your next trip especially if they have been used Enjoy your holiday L with David Barrington PIC Controlled Intruder Alarm The miniature 4x4 matrix data entry keypad used in the prototype PIC Controlled Intruder Alarm came from RS and can be ordered through any bona fide stockists code 331 304 including some of our component advertisers You can order direct credit card only from RS on 01536 444079 or through the web at rswww com A post and packing charge will be payable Other keypads can be used but you will need to make sure the pin numbering corresponds with the Circuit diagram or be prepared to change the wiring For those readers unable to program their own PICs a ready programmed PIC16F877 microcontroller can be purchased from Magenta Electronics 01283 565435 or www magenta2000 co uk
47. set up properly Where any set ting up is required the procedures are very straightforward and they are described in detail Projects covered Simple MIIDI tester Message grabber Byte grabber THRU box MIDI auto switcher Auto manual switcher Manual switcher MIDI patchbay MIDI controlled switcher MIDI lead tester Program change pedal Improved program change pedal Basic mixer Stereo mixer Electronic swell pedal Metronome Analogue echo unit Order code PC116 10 95 124 pages THE INVENTOR OF STEREO THE LIFE AND WORKS OF ALAN DOWER BLUMLEIN Robert Charles Alexander This book is the definitive study of the life and works of one of Britain s most important inventors who due to a cruel set of circumstances has all but been overlooked by history Alan Dower Blumlein led an extraordinary life in which his inventive output rate easily surpassed that of Edison but whose early death during the darkest days of World War Two led to a shroud of secrecy which has covered his life and achievements ever since His 1931 Patent for a Binaural Recording System was so revolutionary that most of his contemporaries regard ed it as more than 20 years ahead of its time Even years after his death the full magnitude of its detail had not been fully utilized Among his 128 patents are the princi pal electronic circuits critical to the development of the world s first elecronic television system During his short working life Blumle
48. some time and it is the subject of this month s Interface article Many serial interface designed for use on the buses of a microprocessor making them unusable in simple add on projects For relatively simple projects a UART uni versal asynchronous receiv er transmitter is a more prac tical proposition The word format etc of a UART can be controlled by hard wiring the control pins to the appropriate logic lev els This avoids the need to base projects on microproces sors and enables the control logic to be kept as simple as possible PIC microcontrollers offer another means of interfacing to serial ports In the past it was necessary to program the chip to provide the serial decoding but some of the more recent PIC chips have a built in UART This greatly simplifies matters and makes PIC chips well suited to intelligent serial port add ons This article will deal with the straightforward UART approach to serial interfacing but the use of PIC chips in this role will be covered in a later article chips are 258 Positive Supply Cif No Connection d2 Receiver Buffer Register 7 Ts Receiver Buffer Register 6 Ue Receiver Buffer Register 5 d7 Receiver Buffer Register 4 del Receiver Buffer Register 3 qe Receiver Buffer Register 2 Cio Receiver Buffer Register 1 11 Receiver Buffer Register 0 Lz Parity Error dral Framing Error Q4 Overrun Error 15 Status Flags Disable tsj
49. standard baud rate In some applications it might be possi ble to avoid using any control logic If the outputs are used to control lights motors etc these will respond to changes in the output states as each new byte of data is received In other applications it will be necessary for the main circuit to be trig gered when fresh data is available for processing The Data Received output at pin 19 going high is then used to trigger the main circuit Pin 18 must be pulsed low to reset this output before the next byte of data is received The eight outputs are at normal 5V CMOS logic levels but in practice they seem to work well with 74LS devices in addition to 74HC and 4000 series CMOS chips Although the 6402 UART is a com plex device its current consumption is very low at no more than a milliamp or two The current consumption of the entire circuit is no more than about 4mA to 5mA Transmitter Circuit The circuit diagram for a Serial Transmitter based on the 6402 is shown in Fig 3 The clock and reset circuits are the same as those in the receiver If the UART is being used to send and receive data the same reset and clock cir cuits are used for both sections of the device The output signal at pin 9 of IC1 then connects to pins 17 and 40 of UART IC2 A pulse is applied to the Send input in order to transmit a byte of data This input is normally held high and data is loaded into the transmitter buffer register o
50. the Comprehensive Radio Valve Guides five books with a Free copy of the Master Index for just 15 Also Jonathan Hill s excellent Radio Radio a comprehensive book with hun dreds of photos depicting the develop ment of the British wireless set up to the late 1960s The three volumes of our own Wireless For the Warrior by Louis Meulstee are also available These are a technical his tory of radio communication equipment in the British Army from pre war through to the 1960s For details see the shop on our UK web site at www epemag wimborne co uk or contact us for a list of Radio Bygones books BOOK ORDERING DETAILS All prices include UK postage For postage to Europe air and the rest of the world surface please add 1 per book For the rest of the world airmail add 2 per book Send a PO cheque international money order sterling only made payable to Direct Book Service or card details Visa Mastercard Amex Diners Club or Switch minimum card order is 5 to DIRECT BOOK SERVICE WIMBORNE PUBLISHING LTD 408 WIMBORNE ROAD EAST FERNDOWN DORSET BH22 9ND Books are normally sent within seven days of receipt of order but please allow 28 days for delivery more for overseas orders Please check price and availability see latest issue of Everyday Practical Electronics before ordering from old lists For a further selection of books see the next two issues of EPE Tel 01202 873872 Fax 01202 874562 E mai
51. the first place But holding interrupts off is likely to be undesirable for any length of time because the reason you made things interrupts is in order to get the fastest response to them So there s a trade off between minimising the delay to processing interrupts and getting your program to work robustly That s why in INTPROG6 and INT PROG7 ISRCH and ISRCL are copied to COUNTH and COUNTL and then COUNTH and COUNTL are used in the calculation This keeps the critical section down to three instructions while the copy is made If ISRCH and ISRCL had been used directly the critical section would have been most of the main loop Interrupts could only have been safely enabled for a short period at its end If multiple interrupts had occurred dur ing the critical section then all but one would have been lost Indeed there would then not have been much point in using interrupts at all such a program might just as well have polled the TOIF flag at the end of the loop Critical sections are necessary whenever more than one variable set by the ISR needs to be accessed consistently by the main program or where repeated access to the same single variable is needed If only one variable is set by the ISR and the main program accesses it exactly once it is probably safe not to use a critical section This is because as we saw above instructions are atomic an interrupt can only occur between instructions so a sin gl
52. the main latch to open but once the door itself were open would activate the countdown timing of the main system s authorised entry mode The children would thus need to use the house hold s main PIN to deactivate the alarm within its allocated entry time Everyday Practical Electronics April 2002 It would be permissible but perhaps unwise from a security point of view to give the same PIN code to both keypads PANIC SWITCHES As referred earlier two options for Panic switches have been included The first can be made using Zone 8 which is never allowed to be turned off through the software A normally open or normally closed pushbutton switch can be used mounted at a strategic location When the switch is pressed changing the status of its contacts an alarm condition is sensed and the full bell strobe buzzer system is acti vated as with other zones with the bell still subject to time out and non retriggering The other option is via pin RB4 This is normally held high via its internal pull up resistor When normally open pushswitch S3 is pressed the pin is shorted to OV Again an alarm condition is sensed and acted upon In this mode the bell is still subject to the preset time out period but can be reactivated if the Panic button is pressed again It seems reasonable that if someone real ly is in a Panic situation that they should be allowed to reactivate the bell at will Unlike the fi
53. thin silicon fin that enables the short channel effects to be overcome raised polysilicon drain and source to reduce parasitic effects two gates that are self aligned to each other and to the source and drain regions The other advantage is that the FinFET has been produced in both n and p channel varieties allowing FinFET CMOS i c s to be manufactured si Hn Bady Fig 2 FinFET structure Courtesy www ecedha org The gate of the latest FinFETs are around 18 nanometers long and this corre sponds to the dimensions of just 100 atoms This is about ten times shorter than the standard dimensions used in transis tors For the future it is hoped to cut the FinFET dimensions by about half although further work will be required to achieve this Advantages The miniaturisation that the FinFET will provide can be utilised by chip designers to pack even more into future designs As the new transistor is ten times smaller than existing ones it will allow 100 times as many devices to be packed into the same space and will allow chip makers to significantly improve the func tionality of microprocessors or to shrink chip designs to improve yields and reduce prices It is expected that existing CPUs may be remodelled using the new transistor design so it is possible that the new tran sistor will appear in new versions of exist ing processors In this way the new tech nology can be introduced into production as soon as possibl
54. turn on the LED about 10 bumps sec at 2MHz clock sets C if COUNT W gt test C C clear so COUNT lt SPEED reset the wrapped count wraps COUNT SPEED so toggle RAO repeat main loop and repeat main loop gt save W save STATUS ensure bank U set bump interrupt count test INTE not an RBO interrupt try timer NOP nothing to do for this demo BCF INTCON INTE TMR BTFSS INTCON TOIF GOTO POP timer interrupt INCF COUNT F BCF INTCON TOIF POP SWAPF SAVES W MOVWE STATUS SWAPF SAVEW F SWAPF SAVEW W RETFIE ISR BREVITY ISRs should be kept as short as possible too This is partly because in their turn ISRs disrupt the main program Timings in the main loop become difficult to predict if a lengthy ISR is going off all the time Also interrupts are disabled while YOU T in the ISR so other interrupts and repeat occurrences of the same interrupt will all be held pending and not handled until the ISR completes processing the cur rent interrupt At worst interrupts could be lost As much processing as possible should be left to the main program loop But the main reason for keeping ISRs short is that they are next to impossible to debug If you have a bug in an ISR then you will find that simulators and CD in circuit development tools give you little if any help When testing it s hard to control exact ly when an ISR runs and as we ve seen that can be very im
55. wire connection to keypad 2 as dis cussed earlier you can only use those keys for which wiring exists All others will be ignored MODE 9 Set keypad 2 entry time On entry to Mode 9 a 2 line message will be displayed of which the following is an example after the new entry time 15 secs has been keyed in This mode sets the time during which the auxiliary output transistor TR4 and the buzzer are activated when the correct PIN code has been keyed in via keypad 2 At the end of the time out TR4 and the buzzer are turned off This mode is used identically to Mode 2 MODE Activate passive monitor mode An eleventh mode is available entered by pressing the decimal point key On entry to this mode a 2 line message will be displayed of which the following is an example When in this mode all zones are moni tored and if any are found to have their 267 sensors in the opposite logic to that expect ed e g open instead of closed the buzzer sounds until all sensors return to their nor mal expected status The appropriate zone numbers are displayed on line 2 with the number being replaced by a dash when no longer triggered In the example zone 6 has been entered This facility can be used for example in a shop when it desirable to know if a cus tomer has opened a door or removed an object from where it should be Passive monitoring is terminated by keying in
56. 1 inch stripboard having 32 holes by 28 strips 8 pin d i l socket 2 off control knob multistrand wire solder pins 11 excluding batt amp case Approx Cost Guidance Only 251 circuit by way of a voltage regulator One advantage of a 555 oscillator is that its method of operation ensures that there is no significant change in output frequency even with quite large variations in the sup ply potential CONSTRUCTION The Electric Guitar Tuner circuit is buillt on a piece of stripboard and the top side component layout interwiring and details of breaks required in the underside copper tracks are shown in Fig 4 A board having 32 holes by 28 copper strips is required and this is not one of the L V E e e L 2 ls a 24 6 SRS 8 wee Lie a standard sizes A larger piece of strip board must therefore be trimmed to size using a small hacksaw The breaks in the copper strips can be made with a handheld twist drill bit of about 5mm in dia Make sure that the strips are cut properly with no fine tracks of cop per left behind The two mounting holes are 3mm in diameter and they will accept M2 5 mounting bolts The board is now ready for the compo nents and link wires to be added Neither of the two integrated circuits are sensitive to static charges but it is still a good idea to fit them on the board via i c holders Ideally the six preset potentiometers would be mul
57. 16 are tied low to permanently enable the outputs The data to be transmitted is placed on pins 26 to 33 and pin 23 is then pulsed low to load the data into the transmitter buffer The transmitter shift register is loaded immediately if it is empty The byte of data is otherwise held in the transmitter buffer until the transmitter register is empty This method of buffering is normal with serial chips and it is designed to reduce the risk of one byte being loaded before the previous one has been sent However in order to avoid mishaps it is still necessary to ensure that the control logic operates effectively High Status Status outputs at pins 22 and 24 respectively go high when the transmitter buffer register and the transmitter register are empty One or other of these can be used to provide a hold off until the relevant register is empty or a clock circuit can control the transmission rate If the second option is cho sen the rate at which bytes are transmitted must be kept within the maximum that is supported by the baud rate in use Dividing the baud rate by 10 gives the theoretical maximum for the number of bytes that can be transmitted per second At 19 200 baud for example the theoretical maximum is 1 920 bytes per second but in practice it would be advisable to settle for a slightly lower rate A rate of about 1500 to 1600 bytes per second should give totally reliable results Everyday Practical Electron
58. 2 Power Supply Lights Needed Alert Pitch Switch Capacitance Meter Main Board double sided Display Board double sided K amp PIC Toolkit TK3 Software onl 4 Channel Twinkling Lights Ghost Buster Mic Main X PIC Polywhatsit Digital Analogue JULY 01 AUG 01 5 94 8 24 3 00 DEC 01 Forever Flasher JAN 02 Time Delay Touch Switch X PIC Magick Musick Versatile Bench Power Suppl PIC Spectrum Analyser Versatile Current Monitor Guitar Practice Amp x PIC Virus Zapper RH Meter PIC Mini Enigma Software only AX Programming PIC Interrupts Software onl FEB 02 7 13 4 75 5 39 MAR 02 339 6 50 EPE SOFTWARE Software programs for EPE projects marked with a single asterisk are available on 3 5 inch PC compatible disks or free from our Internet site The following disks are available PIC Tutorial Mar May 98 PIC Toolkit Mk2 V2 4d May Jun 99 EPE Disk 1 Apr 95 Dec 98 EPE Disk 2 1999 EPE Disk 3 2000 EPE Disk 4 2001 EPE Disk 5 Jan 2002 issue to current cover date EPE Teach In 2000 EPE Spectrum EPE Interface Disk 1 October 00 issue to current cover date PIC Toolkit TK3 software Nov 01 is on CD ROM The 3 5 inch disks are 3 00 each UK the CD ROM is 6 95 UK Add 50p each for overseas surface mail and 1 each for airmail All are available from the EPE PCB Service All files can be down
59. 4V or 3 4V NiCad and nickel metal hydride mobile phone batteries Series and Features NEW TECHNOLOGY UPDATE by lan Poole 240 FinFET devices feature ultra thin silicon fins that further reduce chip sizes TEACH IN 2002 6 Magnetic Sensors Interference and Noise 248 with experiments by lan Bell and Dave Chesmore INTERFACE by Robert Penfold 258 PC Serial Port Interfacing NET WORK THE INTERNET PAGE surfed by Alan Winstanley 273 Java applets speed EPE online ordering JBMail helps reduce spam ELECTRONIC PRINCIPLES V7 1 REVIEW by Robert Penfold 278 The range of V7 1 is vast offering tutorials on various aspects of computing electronics maths physics etc with interactive screens PROGRAMMING PIC INTERRUPTS 2 by Malcolm Wiles 291 How to use interrupts successfully with your PIC programs CIRCUIT SURGERY by Alan Winstanley and lan Bell 299 More on grounded and floating supply lines Charging Yaesu transceiver batteries Eco Warrior battery charging Regulars and Services ELECTRONICS MANUALS 230 Essential reference works for hobbyists students and service engineers EDITORIAL 235 ELECTRONICS VIDEOS Our range of educational videos 242 NEWS Barry Fox highlights technology s leading edge 243 Plus everyday news from the world of electronics BACK ISSUES Did you miss these Many now on CD ROM 270 READOUT John Becker addresses general points arising 282 CD ROMS FOR ELECTRONICS 284 A wide range of CD ROMs for hobbyists stude
60. 591E 1MHz 1 8GHz 75 Ohm H P 853A with 8559A 100kHz 21GHz H P 8558B with Main Frame 100kHz 1500MHz H P 3585A 20Hz 40MHz H P 3580A 5Hz 50kHz ADVANTEST R4131B 10kHz 3 5GHz EATON AILTECH 757 0 001 22GHz MARCONI 2382 100Hz 400Mkz high resolution 2000 MARCONI 2370 30Hz 110MHz from 500 H P 182 with 8557 10kHz 350MHz H P 141T SYSTEMS 8553 1kHz 110MHz 8554 500kHz 1250MHz 8555 10MHz 18GHz TEKTRONIX 491 10MHz 12 4GHz H P 8443 Tracking Gen Counter 110MHz H P 8444 OPT 059 B amp K 2033R Signal Analyser H P 5372A Frequency amp Time Interval Analyser H P 8754A Network Analyser 4MHz 1300MHz H P 3557A Network Analyser 5Hz 200MHz H P 53310A Mod Domain Analyser Opt 001 003 ONO SOKKI CF300 Portable FFT Analyser from 500 from 750 Used Equipment GUARANTEED Manuals supplied This is a VERY SMALL SAMPLE OF STOCK SAE or Telephone for lists Please check availability before ordering CARRIAGE all units 16 VAT to be added to Total of Goods and Carriage 211 Special Report ELECTRONIC PRINCIPLES V7 7 REVIEW ROBERT PENFOLD Robert tries the Soft approach to electronics and computing and finds it well thought out and easy to use HE Electronic Principles software package has undergone a few changes since Version 5 was reviewed in a 1998 issue of EPE At Version 7 it was actually split into two separate pro grams called Electronic and Computing Principles and Computer Science and Mathematics
61. 6 24 Simple rotational speed sensor circuit Everyday Practical Electronics April 2002 0 7277 ARUN Rotational sensor used in Lab 6 5 It will be discussed more fully next month The output is an open collector type and needs to be connected to the power supply via a resistor see the device s data sheet We have added an 1 e d to show when the output is on sinking current Construct the circuit in Fig 6 22 and switch on Bring a magnet close to the sen sor and the l e d should light Monitor the output of the sensor using the Picoscope and capture the signal when the magnet is brought close You should get an output similar to that in Fig 6 23 which shows a clean transition no bounce A stronger magnet will cause the output to go on when it is further away You can try this by magnetizing a screwdriver by stroking it in the same direction a number of times against a magnet the more strokes the stronger the magnet produced Also test the circuit s response to a mag netic north pole being brought up to the front of the sensor and then the south pole Lab 6 4 Bipolar Hall Effect Device Simply replace the switching sensor SS441 in Fig 6 22 with an SS411 latching sensor and try the same experiments as in Lab 6 1 The difference between a 255 Fig 6 25 Waveforms monitored by the Picoscope with the circuit in Fig 6 24 Left Pulse train from the output of the monostable IC2 at pin 6 Centre
62. 657A Synth sig gen 100kHz 1040MHz H P 8656B Synth sig gen 100kHz 990MHz H P 8656A Synth sig gen 100kHz 990MHz R amp S APN62 Synth 1Hz 260kHz sig gen balanced unbalanced output c d display PHILIPS PM5328 sig gen 100kHz 180MHz with 200MHz freq counter IEEE RACAL 9081 Synth AM FM sig g en 5kHz 1024MHz H P 3325A Synth function gen 21MHz MARCONI 6500 Amplitude Analyser H P 4192A Impedance Analyser H P 4275A LCR Meter 10kHz 10MHz H P 8903A Distortion Analyser WAYNE KERR 3245 Inductance Analyser H P 8112A Pulse Generator 50MHz MARCONI 2440 Frequency Counter 20GHz H P 5350B Frequency Counter 20GHz H P 5342A 10Hz 18GHz Frequency Counter H P 1650B Logic Analyser 80 channel MARCONI 2035 Mod Meter 500kHz 2GHz RADIO COMMUNICATIONS TEST SETS MARCONI 2955 2995A ROHDE amp SCHWARZ CMT 0 1 1000MHz SCHLUMBERGER 4040 KEITHLEY 2010 DMM 7 digit KEITHLEY 617 Programmable Electrometer H P 4338B Millionmmeter RACAL Counter type 1999 2 6GHz H P Counter type 53131A 3GHz H P AGILENT 33120A Func Gen ARB 100uHz 15MH 900 1000 SONY TEKTRONIX AFG320 Arbitary Func Gen H P 8904A Syn Function Gen DC 600kHz 1000 1250 BLACK STAR JUPITOR 2010 Func Gen 0 2Hz 2MHz with frequency counter H P 8116A Pulse Generator 1mH 50MHz H P 8657B Syn Sig Gen 0 1 2080MHz CO AXIAL SWITCH 1 5GHz IEEE CABLES H P 8561B 50Hz 6 5GHz H P 8560A 50Hz 2 9GHz synthesised H P 8594E 9kHz 2 9GHz H P 8
63. 900 9 0 A 0 0 0 9 0 0 90 00 E D C Q BLOG 000000000 00000006 06 000 0 A Q O O O O 0 O 0 O 0 Fig 3 Stripboard component layout and interwiring for the Manual Stepper Motor L L Controller Rotary switch S1 MUST be a make before break type 276 Everyday Practical Electronics April 2002 header plug which then plugs onto the p c b type header SK2 The ribbon cable is taken to the stepper motor and the author again used a crimp terminal at the far end of the ribbon cable to attach it to the motor sol dering the motor s leads directly to a p c b header In this way cables and motors can be fairly easily swapped in and out A magnet is mounted on the motor s shaft or on whatever mechanism may be attached to the shaft in such a way that it will close reed switch S2 as the magnet passes by If a more powerful stepper motor is to be used you may increase the rating of the rotary switch S1 by wiring every solder tag of the switch s three poles in parallel and SPECIAL OFFERS TEKTRONIX 2445A s a t 4 ch 150MHz delay L cursors etc Supplied m with 2 Tektronix probes ii L Bei e N ela TEKTRONIX 2232 Digital Storage Scope Dual Trace 100MHz 100M S with probes 525 H P 54501A Dig Oscilloscope 100MHz 4 Ch 425 MARCONI 2019A AM FM SYNTHESISED SIGNAL GENERATOR 80 kHz 1040MHz TRA 7 increasing the value of capacitor C1 In this way the switch can manage curre
64. ANKO BCF 0x03 5 DEFINE BANK BSF 0x03 5 Enter_Critical_ Section MACRO LOCAL CS __CS1 BCF INTCON GIE BTEFSC INTCON GIE GOTO _ CSI ENDM Leave_Critical_ Section BSF INTCON GIE ENDM LISTING 7b MAIN Enter_Critical_ Section MOVE ISRCL W MACRO copy ISR low byte counter MOVWE COUNTL MOVE ISRCH W high byte counter Leave_Critical_ Section MOVWE COUNTH copy ISR LISTING 7c CS1 BCF INTCON GIE BTFSC INTCON GIE GOTO CS1 MOVE ISRCL W low byte counter MOVWE COUNTL MOVE ISRCH W high byte counter BSF INTCON GIE MOVWE COUNTH copy ISR copy ISR 293 Can you think why this has been done If you can t or if you can and want to prove that you re right change this test in INTPROG8 back to how it is in INT PROGS reassemble INTPROG8 and re run Experiment 3 Hint if the PIC appears to stop working don t immedi ately reset it to try again leave it for a minute or so A detailed explanation is left as an exercise for the student as they say in the best textbooks but if you can fully account for what you observe it s all to do with equality then you have probably got a good understanding of interrupt loops multiple interrupts and the PIC instruction set MORE ON CRITICAL SECTIONS Critical sections should be kept as short as possible While a program is in a critical section interrupts will be held off after all that s why you had the critical section in
65. ASAR Electronics comment that no one can call themselves an electronics hob byist unless they have built a timer From this assertion we assume that your hobby ist attributes will increase 7 fold when you build Quasar s new Multi Mode Timer kit which features seven timers The seven different timing modes of Quasar Kit 3141 are microcontrolled Four crystal controlled timing periods are pro vided covering the ranges to 255 and 10 to 2550 in seconds or minutes Trigger options range from simple push button to electrically isolated voltage sources The trigger inputs are optoisolat ed Output is to a high quality mains rated relay Timing modes and delay ranges are set using on board DIP switches and there are screw terminals for all connections Available by mail order KIT 3141 is just 14 95 or 23 95 ready assembled including VAT UK postage is 2 For more information contact Quasar Electronics Ltd Dept EPE PO Box 6935 Bishops Stortford CM23 4WP Tel 01279 467799 Fax 07092 203496 Email epesales quasarelectronics com Web www quasarelectronics com 244 MATHS AND BROOKLANDS ARE you anxious about algebra Do sym bols and equations confuse you Can you make sense of Boolean logic Brooklands College in Surrey has asked these probing questions and believe they have the solu tion if you answer yes to them This renowned college has produced a new on line course designed to provide you wit
66. C3 2200u radial elect 25V C4 to C6 100n ceramic 5mm pitch 3 off Semiconductors D1 D6 to D9 1N4148 signal diode 5 off D2 D5 D10 to D13 red l e d 6 off See text D3 D4 1N4001 rectifier diode 2 off REC1 W005 50V 1A bridge rectifier TR1 to TR4 TIP120 npn Darlington transistor 4 off See text IC1 PIC16F877 microcontroller pre programmed see text IC2 7812 12V 1A voltage regulator IC3 7805 5V 1A voltage regulator Miscellaneous 1 2 16 key 4 x 4 data entry keypad 2 off see text S3 push to make Panic switch extra large palm activated wall mounting S4 push to make switch p c b mounting 0 2in pitch 1A fuse slow blow with panel mounting holder 2 off T1 mains transformer 12V secondary 1A rating or higher TB1 10 way pin header strip 0 1in pitch 1mm dia TB2 4 way pin header strip 0 1in pitch 1mm dia see text X1 3 2768MHz crystal X2 2 line 16 character per line alphanumeric I c d module FS1 FS2 Printed circuit board available from the EPE PCB Service code 339 40 pin d i l socket 2 way terminal blocks p c b mounting side by side stacking 0 2in pitch screw connections quantity to suit application see text metal or plastic case to suit application 12V heavy duty sealed lead acid back up battery ribbon cable 9 way for keypad s see text 9 pin pin header strips and connectors 0 1in pitch 1mm dia 2 off optional see te
67. D Tel 01202 873872 Fax 01202 874562 Email subs epemag wimborne co uk Order online www epemag wimborne co uk 256 Post code If you do not wish to cut your issue send a letter or a copy of this form Everyday Practical Electronics April 2002 INTERFACE Robert Penfold G F C ae Pea ee Fi j Tey ee a bL l PC SERIAL PORT INTERFACING Revs seem to send a steady flow of enquiries regarding the subject of PC serial interfacing Many PCs have the par allel port occupied by a printer PIC pro grammer or some other gadget but have one or both serial ports free for use with electronic projects On the face of it the serial ports are then the obvious choice for interfacing your projects to the PC In practice how ever the RS232C ports are not necessarily the best choice Interfacing to serial ports is less straightforward than using a parallel port and the maximum rate for data transfers is much lower Adding a parallel port card to the PC might be a better option On the plus side serial interfaces are designed for two way operation so independent 8 bit input and output ports can be provided by each serial interface Take Your PIC Directly controlling the serial port hardware was covered not too long ago in the October 1999 issue of EPE Consequently this aspect of serial inter facing will not be considered further here The hardware side of serial interfacing has not been covered for
68. EOUS VT501 58 minutes Fibre Optics From the fundamentals of fibre optic technology through cable manufacture to connectors transmitters and receivers Order Code VT501 VT502 57 minutes Laser Technology A basic introduction covering some of the common uses of laser devices plus the operation of the Ruby Rod laser HeNe laser CO gas laser and semiconductor laser devices Also covers the basics of CD and bar code scanning Order Code VT502 Each video uses a mixture of animated current flow in circuits plus text plus cartoon instruc tion etc and a very full commentary to get the points across The tapes are imported by us and originate from VCR Educational Products Co an American supplier We are the worldwide distributors of the PAL and SECAM versions of these tapes All videos are to the UK PAL stan dard on VHS tapes unless you specifically request SECAM versions Everyday Practical Electronics April 2002 A roundup of the latest Everyday News from the world of electronics FAST TRACK IDENTITY RECOGNITION Body language detectors can replace fingerprints for identification Barry Fox reports INGERPRINTS face pattern recognition iris scans and signatures are already old hat says Spinnaker International of Plymouth in a patent for a completely different type of security check GB 2 359 890 A cash in transit box contains an accelerometer which continually senses motion up and down and side to side
69. ER AUDIO AMPLIFIER CONSTRUCTION R A Penfold Practical construction details of how to build a number of audio power amplifiers ranging from about 50 to 300 400 watts r m s includes MOSFET and bipolar transistor designs Order code BP277 4 49 96 pages 291 Circuits Data and Design PRACTICAL ELECTRONIC FILTERS Owen Bishop This book deals with the subject in a non mathematical way It reviews the main types of filter explaining in sim ple terms how each type works and how it is used The book also presents a dozen filter based projects with applications in and around the home or in the constructor s workshop These include a number of audio projects such as a rythm sequencer and a multi voiced electronic organ Concluding the book is a practical step by step guide to designing simple filters for a wide range of purposes with circuit diagrams and worked examples Order code BP299 5 49 DIGITAL ELECTRONICS A PRACTICAL APPROACH FREE With FREE Software Number One Systems EASY PC Professional XM and Pulsar Limited Functionality Richard Monk Covers binary arithmetic Boolean algebra and logic gates combination logic sequential logic including the design and construction of asynchronous and synchro nous circuits and register circuits Together with a consid erable practical content plus the additional attraction of its close association with computer aided design including the FREE software There is
70. ETFIE But as we saw earlier RETFIE sets the GIE bit So when the main program resumes at the instruc tion after the BCF INTCON GIE then GIE will be set and it will be as if the BCF instruction had not executed We will be into our critical section with interrupts still enabled The bottom line is that a BCF INT CON GIE instruction cannot be guaranteed to succeed if interrupts are enabled as they usually will be if you re clearing GIE The workaround is simple after a BCF INTCON GIE you need to test GIE to ensure it really is clear and if not go back and repeat the clear Eventually it will suc ceed unless you re in an ISR loop The fol lowing sequence does the job MAIN BCF INTCON GIE BTFSC INTCON GIE GOTO MAIN Note that it s not just a BCF INT CON GIE instruction that will be affected it can be any instruction sequence that has the effect of clearing GIE e g the fol lowing is also vulnerable MOVLW H 7F ANDWE INTCON F INTPROG7 is the final corrected version of INTPROG6 It uses two macros Enter_Critical_Section and Leave_Critical_Section which expand to the necessary code sequences see Listing 7a The author prefers to use these as they make it very clear in the source listing what is going on the code is almost self docu menting Listing 7b shows how the macros are used in INTPROG7 Readers who use MPASM are welcome to copy these macros and use them in their own programs Diehard TASM u
71. Eco Charger with micro processor control available from CPC Part No BT00283 approximately 35 telephone 08701 202530 This desktop unit will discharge and recharge a mixture of different sizes AA to D size on its four channels all at the same time it has a useful l c d display and most importantly it actually recharges zinc carbon and alkaline bat teries several times over as well An alternative type is the Goodmans GBC1150 Part No BT02327 approx 26 although I have not tested it Regular readers know how I feel about throwing toxic batteries especially NiCads into the ordinary domestic waste due to the pathetic state of UK recycling facilities so anything that helps the envi ronment in this way is extremely welcome ARW CIRCUIT THERAPY Circuit Surgery is your column If you have any queries or comments please write to Alan Winstanley Circuit Surgery Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND E mail no attach ments alan epemag co uk Please indicate if your query is not for publica tion A personal reply cannot be guaranteed but we will try to publish rep resentative answers in this column Everyday Practical Electronics April 2002 PCB SERVICE Printed circuit boards for most recent EPE constructional projects are available from the PCB Service see list These are fabricated in glass fibre and are fully drilled and roller tinned All prices include VAT
72. Electronics April 2002 A COMMON C D COMMON B Fig 2 Unipolar drive Table 2 Full step Control Step A B C D 1 ON OFF OFF ON 2 ON ON OFF OFF 3 OFF ON ON OFF 4 OFF OFF ON ON CONSTRUCTION The specified rotary switch S1 has an external adjustable rotation limit stop metal washer which prevents full rotation We need full rotation for this project so the metal washer is discarded Certain types of rotary switches may need further butchering and this means you must carefully prise open the switch observing where each part fits At the bot tom of its black well at the side is an internal rotation limit stop a small plastic notch which is integral to the plastic COMPONENTS Resistors S R1 D i All 0 25W 5 carbon film TALK Capacitors page C1 1000u radial elect 16V Semiconductors D1 to D8 1N4001 50V 1A rect diode 8 off D9 5mm red l e d D10 5mm green l e d Miscellaneous M1 12V d c four phase unipolar stepper motor S1 3 pole 4 way make before break rotary switch see text S2 small reed switch with magnet or flush mount alarm switch combination S3 S p s t rocker switch SK1 2 1mm power socket single hole fixing 6 way straight p c b header with crimp terminal plug 2 off SK2 SK3 Stripboard O 1in matrix size 24 holes by 16 strips 6 way multicoloured ribbon cable plastic case size to choice 15cm length of flexible wire 3 off knob wit
73. IRCUIT 2 GROUND ALTERNATIVE CONNECTION CIRCUIT 1 GROUND VIA SCREEN USEFUL FOR FLOATING SENSORS Fig 6 1 Capacitively coupled interference a and the use of screening to inhibit it b Everyday Practical Electronics April 2002 CIRCUIT 1 k gt SCREENED CABLE GROUND Fig 6 2 above Screened differential signal Fig 6 3 right Large wiring loops a make a circuit suscep tible to voltages generated by magnetic fields Reducing loop size b helps to combat the problem CIRCUIT 2 CIRCUIT 1 a CIRCUIT 2 CIRCUIT 1 EES SSS BS E E A E b Rsuppty1 2 R gt GROUND1 gt Rsuppty2 SUPPLY SUPPLY CIRCUIT 1 CIRCUIT 2 Fig 6 4 Voltage drops in the supply line a caused by the line s inherent resistance can be reduced by point to point wiring b is implemented using coaxial screened cable to link for example a sensor to a cir cuit and by enclosing the sensitive circuits in a grounded screening box The source of interference can also be screened to reduce its effect on other cir cuits Choice of where the screened cable is grounded may have an effect on circuit per formance due to the possibility of creating grounding loops if the screen signal return path is grounded at both ends more on this a little later For differential signals we can also use screened wires the two signal wires form a twisted pair and are enclosed by the screen see Fig 6 2 He
74. MHz as set by crystal X1 It is this rate which deter mines the accuracy of the software clock that controls the bell on duration and entry exit timing In order to comply with the allocated timings a different frequency must not be used with this design PIC Programming During development the author pro grammed the PIC via his Toolkit TK3 sys tem Oct Nov 0O1 and terminal block TB2 Resistor R1 and diode D1 allow cor rect operation of the MCLR pin during and after programming This facility may be used by those who wish to program their own PIC in situ Pre programmed PICs are available as stated later POWER SUPPLY The design is intended to be mains pow ered with battery back up Referring to Fig 2 mains transformer T1 provides a 12V a c secondary output at about 1A This is rectified by REC1 and smoothed by capacitors C3 and C4 Light emitting diode le d D2 buffered by resistor R15 provides a power on indication when a voltage of about 18V d c is present across C3 A mains input fuse is not used but could be included if preferred The raw d c voltage is fed to regulator IC2 whose nominal 12V d c output can be adjusted upwards by preset VR2 The intention is to set C2 s output voltage to the level that best suits the charging of the external 12V back up battery typically about 13 5V Current at the required voltage is fed to the back up battery via diode D3 which prevents the battery from dischar
75. Memory in the box stores information on the motion pattern created when an authorised security guard is carrying the box If someone else grabs the box or if the guard behaves unnaturally running when chased or being driven off in a vehicle the signals from the accelerome ter no longer match the stored gait pat tern The box then detonates a dye pack to spoil the contents The system can also be used to protect portable computers which disable if car ried by someone unfamiliar or provide early warning of suspect vibration in a car suspension or engine The Massachussetts General Hospital in Charlestown also has no confidence in SCIENCE EXHIBITION ONCE a year the Royal Society the UK s independent academy of science makes sure that you have the chance to meet some of the scientists and engineers working on the UK s most innovative research This year you can come face to face with cutting edge science and engineering at the Society s Summer Science Exhibition from 2 to 4 July and entry is free Among the 20 exhibits will be malaria vaccines cryptog raphy and mapping of the oceans in respect of ocean forecasting and climate change monitoring For more information phone the Royal Society on 020 7451 2574 or browse www royalsoc ac uk Neon String A SMALL British business Inntact Electronics seems to be attracting interna tional attention including NASA Inntact specialise in electroluminescent EL p
76. NCIPLES AND TECHNOLOGY lan Poole Radio technology is becoming increasingly important in today s high technology society There are the traditional uses of radio which include broadcasting and point to point radio as well as the new technologies of satellites and cellular phones All of these developments mean there is a growing need for radio engineers at all levels Assuming a basic knowledge of electronics this book provides an easy to understand grounding in the topic Chapters in the book Radio Today Yesterday and Tomorrow Radio Waves and Propagation Capacitors Inductors and Filters Modulation Receivers Transmitters Antenna Systems Broadcasting Satellites Personal Communications Appendix Basic Calculations 263 pages Order code NE30 15 99 PROJECTS FOR RADIO AMATEURS AND S W L S R A Penfold This book describes a number of electronic circuits most of which are quite simple which can be used to enhance the performance of most short wave radio systems The circuits covered include An aerial tuning unit A simple active aerial An add on b f o for portable sets A wavetrap to combat signals on spurious responses An audio notch filter A parametric equaliser C W and S S B audio filters Simple noise limiters A speech processor A volume expander Other useful circuits include a crystal oscillator and RTTY C W tone decoder and a RTTY serial to parallel converter A full range of interesting and useful cir
77. ODEL amp CRAFT TOOLS A COMPREHENSIVE RANGE OF MINIATURE HAND AND POWER TOOLS AND AN EXTENSIVE RANGE OF ELECTRONIC COMPONENTS FEATURED IN A FULLY ILLUSTRATED 528 PAGE MAIL ORDER CATALOGUE 2002 ISSUE Note If you have ordered from 2001 copy you will receive the new catalogue automatically SAME DAY DESPATCH FREE POST AND PACKAGING Catalogues FREE OF CHARGE to addresses in the UK Overseas CATALOGUE FREE postage at cost charged to credit card Squires 100 London Road Bognor Regis West Sussex PO21 1DD TEL 01243 842424 FAX 01243 842525 SHOP NOW OPEN DISTANCE LEARNING SHORT COURSES with BTEC CERTIFICATION Analogue and Digital Electronics Fibre Optics Fault Diagnosis Mechanics Mathematics and Programmable Logic Controllers Suitable for beginners and those wishing to update their knowledge and practical skills Courses are very practical and delivered as self contained kits No travelling or college attendance Learning is at your own pace Each course can stand alone or be part of a modular study programme Tutor supported and BTEC certified For information contact NCT Ltd P O Box 11 Wendover Bucks HP22 6XA Telephone 01296 624270 Fax 01296 625299 Web http www nct ltd uk a VISA 2000 CD ROM The whole of the 12 part Teach n 2000 series by John Becker published in EPE Nov 99 to Oct 2000 is now available on CD ROM Plus the Teach In 2000 interac tive so
78. PR 01 296 6 50 Intruder Alarm Control Panel Main Board 297 6 97 External Bell Unit 298 4 76 Camcorder Mixer MAY 01 299 6 34 300 5 07 PIC Graphics L C D Scope JUNE 01 301 Hosepipe Controller Magfield Monitor Sensor Board 302 Dummy PIR Detector 303 PIC16F87x Extended Memory Software only 5 47 4 52 4 52 4 67 Software only DEC 00 JAN 01 Software only Software only Everyday Practical Electronics April 2002 JAN 00 250 4 83 932 3 00 PIC Controlled Intruder Alarm APR 02 JUNE 00 3 05 JULY 00 268 5 07 269 4 36 OCT 00 5 15 NOV 00 270 3 96 Software only Order Code PROJECT TITLE Stereo Surround Sound Amplifier Perpetual Projects Uniboard 1 Solar Powered Power Supply amp Voltage Reg MSF Signal Repeater and Indicator Repeater Board Meter Board PIC to Printer Interface Lead Acid Battery Charger Shortwave Loop Aerial X Digitimer Main Board R F Board Perpetual Projects Uniboard 2 L E D Flasher Double Door Buzzer Perpetual Projects Uniboard 3 SEPT 01 Loop Burglar Alarm Touch Switch Door Light and Solar Powered Rain Alarm L E D Super Torches Red Main Display Red White L E D Sync Clock Driver Water Monitor Camcorder Power Supply OCT 01 318 PIC Toolkit Mk3 319 Perpetual Projects Uniboard 4 Gate Sentinel Solar 305 powered Bird Scarer and Solar Powered Register Teach In 200
79. R usually in decibels dB and based on the ratio of noise power hence the v terms in the equation y2 SNR 10log 9 5 V n Where v is the r m s signal voltage and v 1s the r m s noise voltage When using or quoting SNR values the bandwidth range of signal and noise frequencies considered should be quoted because noise power is frequency dependent and noise may be pre sent well outside the range of signal fre quencies of interest Next month we will continue to look at random noise meanwhile let us turn our attention to magnetic sensors REED SWITCHES The simplest magnetic sensor is the reed switch which usually consists of two con tacts made of ferrous metal housed in a sealed glass tube For most reed switches the contacts are usually open but when a magnet is brought sufficiently close the two strips of metal become magnetized and will attract each other closing the switch Typical example of a reed switch Such a simple device has many applica tions ranging from detecting when doors open and close to detecting the rate of rota tion of an object such as an axle In the first case the switch is placed on the wall close to the door and the magnet is attached to the door while in the second case the mag net is placed on the axle and causes the reed switch to periodically close as the axle rotates We will be using this approach to measure wind speed in Lab Work where the sensor will be a Hall
80. RVICE MANUAL plus a FREE SUPPLEMENT Printed version only Road East Ferndown Dorset BH22 9ND l I enclose payment of 24 95 for one Manual or 39 90 for both Manuals saving another We offer a 30 day MONEY BACK GUARANTEE 10 by ordering both together plus postage if applicable Offers end May 31st 2002 on ESM see the panel above for details i l also require the appropriate Supplements four times a year These are billed separately and can be discontinued at any time Please delete if not required POSTAGE CH ARG ES FOR ESM I i MEM CD ROM POST FREE TO ALL COUNTRIES FOLL NAME cs 46 fA ARES OE RET EER WA A AE EE OR A hae nd Note we use the VAT portion of the MEM CD ROM payment l PLEASE PRINT to pay for overseas postage l ADDRESS s s s s sss ss s s nnn nnn nnn nn nnn n s ss s s s s s ss ss s s s ss ss s s s s ss s s s s s sss s s s Price PER ESM PRINTED MANUAL l Postal Region Surface Air l l nnn nu n n un n n n n n nu n nnn n2 n nnn nnn nnn nnuaunnnnannnnnnnnnnnnnnnnnnnnman Mainland UK FREE I Scottish Highlands PO eens POSICODE 244 sheds weae scans UK Islands amp Eire 6 each l Europe EU 22 each j SIGNATURE o0 e ewstece cent odernee 6ecw ew eaatierneseeen Cees ee MES eo Ree wees Europe Non EU 22 each 29 each i a eae USA amp Canada 26 each 36 each l _ enclose cheque PO in UK pounds payable to Wimborne Publishing Ltd Fa
81. Series TEACH IN 2002 Part Six Magnetic Sensors Interference and Noise IAN BELL AND DAVE CHESMORE Making Sense of the Real World Electronics to Measure the Environment VER the last couple of months we have looked at differential signals and circuits which help us reduce the effects of electrical interference drift and temperature dependence in sensor circuits To fully protect our circuits from interfer ence though we must also consider practical matters related to wiring and construction such as shielding and grounding Electrical interference is not the only noise effect you may need to consider when designing sensor systems So we will also look at some other sources of interference and at the random noise that is generated within the circuits and sen sors themselves On the sensor side of things this month we study magnetic sensors problems with switch bouncing in mechanical sensors and building a simple wind speed meter using a magnetic sensor NOISE ANNOYS The unwanted signals present in elec tronic systems are known as noise Noise is important in sensor systems because it lim its measurement of low level signals and degrades accuracy of measurement Noise also limits maximum gain for amplifiers as sufficiently high gain will result in the amplifier saturating simply due to the noise from the source or the input stage Noise may be present as part of an input signal e g it may come
82. Update 6 Circuit Surgery Practically Speaking Ingenuity Unlimited e CIRSIM Shareware Review Net Work The Internet FEB 01 PROJECTS e Ice Alert Using LM3914 6 Bargraph Drivers Simple Metronome e PC Audio Power Meter FEATURES e The Schmitt Trigger Part 4 Ingenuity Unlimited Circuit Surgery e New Technology Update Net Work The Internet e Free 16 page supplement How To Use Graphics L C D s With PICs PROJECTS e Doorbell Extender Body Detector e DIY Tesla Lightning Circuit Tester FEATURES e Understanding Inductors The Schmitt Trigger Part 5 Circuit Surgery Interface New Technology Update Net Work The Internet Page APRIL 01 PROJECTS e Wave Sound Effect Intruder Alarm Control Panel Part 1 Sound Trigger EPE Snug Bug Pet Heating Control Centre FEATURES e The Schmitt Trigger Part 6 e Practically Speaking Ingenuity Unlimited 6 Circuit Surgery 6 Net Work The Internet Page e FREE supplement An End To All Disease MAY 01 PROJECTS e Camcorder Mixer PIC Graphics L C D Scope D C Motor Controller Intruder Alarm Control Panel Part 2 FEATURES e The Schmitt Trigger Part 7 Interface Circuit Surgery Ingenuity Unlimited New Technology Update Net Work The Internet Page JUNE 01 PROJECTS Hosepipe Controller In Circuit Ohmmeter Dummy PIR Detector s Magfield Monitor FEATURES e Controlling Jodrell Bank e PIC1687x Ex
83. VR1 for the lowest flash rate from the l e d indicator D1 If the out put frequency of IC2 is well away from the correct figure the flash rate will be so high that the l e d will seem to light up contin uously Adjust VR1 to produce a percepti ble flash rate first and then carefully adjust it for the lowest possible rate The same basic procedure is then used to give the other five preset potentiometers suitable settings There should be no diffi culty in matching the frequency of C2 to within 0 1Hz of each reference note In use the Electric Guitar Tuner is used in much the same way but each note of the guitar is adjusted for the lowest possible flash rate The initial tuning error might be quite large when a new string is fitted and the guitar must then be adjusted to produce perceptible flashing from the l e d indica tor first It can then be adjusted for the low est flash rate The simple flashing light indicator does not show the direction of any tuning error but with a little practice it is still quite easy to home in on the correct setting New Technology FinFET devices feature ultra thin silicon fins that enable short channels to be used in CMOS production yet again reducing chip sizes lan Poole reports on their pending introduction HERE are many stories around about how semiconductor technology as we know it today is reaching the end of the road It is only possible to miniaturise the technolo
84. Varying wind speed monitored at the output of IC3 using long time constant averaging Right As centre using short time constant Anemometer assembly to be described next month switching and a latching sensor is that in a latching sensor the output will go on and stay on until a magnetic field of the oppo site polarity is sensed Lab 6 5 Simple Rotation Sensor Measuring Wind Speed In this experiment we will be building a very simple wind speed meter anemome ter using an SS441 unipolar sensor and a magnet to detect the speed of rotation of a shaft Note that we will be returning to this next month when we will be designing a higher quality combined wind speed and direction indicator This Lab illustrates the principle of operation of rotation sensing and gives a very simple circuit to generate an analogue voltage proportional to speed of rotation Fig 6 24 is the circuit for the sensor It uses a frequency to voltage converter based on the humidity sensor in Part 3 The wind speed sensor is shown in the accompanying photographs and consists of three cups attached to a shaft Wind causes the cups to go round and the speed of rota tion is proportional to wind speed Don t worry about the design of the anemometer as we will be designing one next month In the meantime you can simulate the opera tion of the circuit using any shaft that can be rotated at a low speed the turntable of a record deck for instance The
85. WIRING UP Prepare three lengths of flexible wire each about 15cm long Strip the ends and tin them with solder These leads are taken from the board to power socket SK1 and on off switch S3 as shown in Fig 3 Prepare a 15cm length of 5 way ribbon cable stripping the ends and tinning them with solder This is also taken from the stripboard to rotary switch S1 as shown Finally prepare a length of 6 way ribbon cable of any desired length inserting the six ends into a six way female crimp terminal MOTOR CONTROL L B s F E R amp P P T 4 a R hal oe G VL gt o anp M N TO STEPPER MOTOR S3 5 AND REED SWITCH ON OFF P 1 10 15 20 24 P O 6600000000000060 O ojo 0 Oo 0086000009090000 0 O NIO O 0000860009000006 0 O O O ofo O 0000860000008 OO Q Q 00000006 00086 00 O 0000008 00008 Q Q O0O0O000000 8808000 OoO0O00 000000 800 OoO0O0O00000000 8000 e oo0o00o0000008 00 oee Q 0000008 Q Q O O 008 00 QQQ Q Q Q Q 0086 QQQ QQ Q Q OQ 0008 QQQ Q Q OoO0O00 08 0000 Q O QQ QQQ QQQ Q ofo OFOFOFOFOFOFO O O ls les Lel lel C1 Lel L e Ls Le les Les Le Les le L lt Ls Le OFOFOFOTOFOFOFOTOFOIOF m le ls Le Le le Le Le Le Les Lel Le Le OOO ofofo ojojo ojojo ls Ls Le ofo OFOFOFOFOFOFOPFOFOPTOFOFOFOFO OFOFOFOFOFOFOFO FOPOFOIO OFOFOFOPFOFOTO FOFTOFO OFOFOFOFOFOFOTOTO s Lel U Ls Ls Lel L ls Lel Ls Ls Le L K J H G F 0299 0990
86. YOUR BACK ISSUES ON MINI CD ROMS hiya 1 2 45 each including VAT A great way to buy EPE Back Issues our mini CD ROMs contain back issues from our EPE Online website plus bonus articles all the relevant PIC software and web links Note no free gifts are included All this for just 12 45 each including postage and packing VOL 1 CONTENTS BACK ISSUES November 1998 to June 1999 all the projects features news IUs etc from all eight issues Note No advertisements are included PIC PROJECT CODES All the available codes for the PIC based projects published in these issues VOL 2 CONTENTS BACK ISSUES July 1999 to December 1999 all the projects Order on line from features news IUs etc from all six issues Note No advertisements www epemag wimborne co uk shopdoor htm are included PIC PROJECT CODES All the available codes for the or www epemag com USA prices PIC based projects published in these issues or by phone Fax E mail or Post VOL 3 CONTENTS ee ang N BACK ISSUES January 2000 to June 2000 all the projects features BACK ISSUES MINI CD ROM ORDER FORM news lUS etc from all six issues PIC PROJECT CODES All the available codes for the PIC based projects published in these issues Please send me quantity BACK ISSUES CD ROM VOL 1 VOL 4 CONTENTS Please send me quantity BACK ISSUES CD ROM VOL 2 I l I I l I I I I I l l l l BACK ISSUES July 2000 t
87. ake the connections for pins to 8 Pin 9 is simply for grounding the key pad s metal frame to earth and can possi bly be ignored but consider any possible mains electrical safety aspects first any metal item that could potentially come into undesirable electrical contact with a mains supply must be earthed It would also be reasonable to use just four connections so that only four keys are active The same degree of code security would remain since all 16 keys would still appear to be available TESTING To assist bench testing temporarily con nect one or more switches to various zones to simulate sensors Fully check your p c b assembly for errors and poor soldering before applying power Do not connect mains power to the system until you have checked the rest of the system using a 12V battery or bench power supply Connect the battery to the allocated ter minals and check that 5V is present at the output of regulator IC3 and that around 11 4V is present at the cathode k of 265 diode D4 i e about 0 6V below the bat tery s actual output voltage L E D D5 should be on If all is well disconnect the battery Connect the secondary winding of trans former T1 to the terminals provided Set preset VR2 for minimum resistance between the common pin of regulator C2 and the OV line Ensuring satisfactory safety precautions are observed connect mains power to the transformer There should about 18V d
88. allotted anti tamper terminals zone 7 Anti tamper wiring could be connect ed in series between all required zones Alternatively the zones could be treated as separate anti tamper connections with each cable pair commoned into the zone 7 terminal block The latter tech nique may make it easier to trace an open circuit should one occur Anti tam per wiring should always be normally closed It is debatable as to whether anti tamper monitoring is required in a normal domes tic security system UNAUTHORISED ENTRY If one more zones are entered without authority the bell strobe and buzzer are all activated A clock is started from zero 268 WAOIDNRWNEO when the first zone is entered The screen changes to display a message showing which zone has been triggered plus the clock read out e g In this example zone is shown to have been entered and that it is 1 hour 28 min utes and 15 seconds since that event The clock continues counting until the alarm is reset via your PIN code The elapsed time can reach 99 59 59 Gust over four days a long week end for example and then restarts from zero The bell is automatically turned off after the preset delay period has elapsed as dis cussed earlier The strobe and buzzer remain on until reset by keying in your PIN code If a second unauthorised entry is made following the first the bell is not reactivat ed nor does this event affect the clock s cur
89. amming skills KEEP YOUR MAGAZINES SAFE RING US NOW This ring binder uses a special system to allow the issues to be easily removed and re inserted without any damage A nylon strip slips over each issue and this passes over the four rings in the binder thus holding the magazine in place The binders are finished in hard wearing royal blue p v c with the magazine logo in gold on the spine They will keep your issues neat and tidy but allow you to remove them for use easily The price is 5 95 plus 3 50 post and packing If you order more than one binder add 1 postage for each binder after the initial 3 50 postage charge overseas readers the postage is 6 00 each to everywhere except Australia and Papua New Guinea which costs 10 50 each Send your payment in s sterling cheque or PO Overseas readers send sterling bank draft or cheque drawn on a UKbank or pay by card to Everyday Practical Electronics Wimborne Puublishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND Tel 01202 873872 Fax 01202 874562 E mail editorial epemag wimborne co uk Web site http www epemag wimborne co uk Order on line from www epemag wimborne co uk shopdoor htm We also accept card payments Mastercard Visa Amex Diners Club or Switch minimum card order 5 Send your card number and card expiry date plus Everyday Practical Electronics April 2002 295 Switch Issue No with your order SWITCH a VISA SQUIRES M
90. an els and EL string sometimes called neon string and the inverters that power them EL products produce a very even light and generate no heat resulting in improved illumination and significant power saving NASA are replacing the l e d systems of their escape guidance systems with these EL devices BAE have also approached Inntact with regard to powering the EL dis plays in the Euro Fighter simulators The neon string is so flexible you can tie it in knots and it is just 2 5mm in diameter producing a bright crisp light without heat It can produce green or blue light and be operated at 12V for automotive use A trial kit is available consisting of one metre of string with connectors and power pack for 29 99 including delivery and VAT For more information contact Inntact Electronics Dept EPE Unit 5 Butterley Croft Whiteley Road Ripley Derbys DES 3QL Tel 01773 570008 Email inntact aol com Web www inverter solu tions co uk Also see the advert in this issue conventional biometrics and is patenting a way of using the human anatomy as a pass word WO 01 73680 The object is to identify individuals without close inspec tion A pair of video cameras simultane ously record a series of images of the sub ject walking naturally Arm leg and torso length are then mapped into reference graphics together with characteristic body shape and motion such as a head roll arm swing leg stride and shoulder postur
91. an be amended from within the run ning system but only after the correct PIN has been keyed in On entry to Engineer s mode you will be greeted by the 1 line message Enter your chosen 4 character PIN code using any of keys 0 to 9 and A to C for example 123A The other three keys blank decimal point and D cannot be used for the PIN code Each keypress is accom panied by a beep of the buzzer and its asso ciated l e d being briefly turned on Each accepted keypress digit will be shown on line 2 If you make a mistake press the blank key to clear line 2 allow ing you to start again Pressing blank when no digits are shown exits this mode 266 When all four digits have been entered press D The word STORED will now appear briefly telling you that the code has been stored in the PIC s data EEPROM for future recall All data EEPROM values are retained even after power has been disconnected The screen then displays ALL OFF on line 1 with line 2 clear From here on access to all modes must be prefixed by your PIN code being keyed in Key it in now If you enter a wrong digit nothing will happen There is no screen confirmation of which key is pressed for obvious security reasons When the correct PIN has been entered line 1 displays the message SELECT MODE You now have a choice of eleven modes selected by pressing one of the following keys 0 Activate alarm and start exit delay count d
92. and postage and packing Add 1 per board for airmail outside of Europe Remittances should be sent to The PCB Service Everyday Practical Electronics Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND Tel 01202 873872 Fax 01202 874562 E mail orders epemag wimborne co uk On line Shop www epemag wimborne co uk shopdoor htm Cheques should be crossed and made payable to Everyday Practical Electronics Payment in sterling only NOTE While 95 of our boards are held in stock and are dispatched within seven days of receipt of order please allow a maximum of 28 days for delivery overseas readers allow extra if ordered by surface mail Back numbers or photostats of articles are available if required see the Back Issues page for details Please check price and availability in the latest issue Boards can only be supplied on a payment with order basis PROJECT TITLE Order Code JULY 99 233 6 78 L E D Stroboscope Multi project PCB 932 3 00 AUG 99 237 8 88 932 3 00 EPE Mood PICker x 8 Channel Analogue Data Logger Freezer Alarm Multi project PCB Child Guard Variable Dual Power Supply 242 Micro Power Supply OCT 99 243 x Interior Lamp Delay 244 Mains Cable Locator Multi project PCB 932 Vibralarm NOV 99 230 Demister One Shot 245 x Ginormous Stopwatch Part 1 246 x Ginormous Stopwatch Part 2 DEC 99 Giant Display 247 Serial Port Converter 248 Loft Guard 249
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94. arel price includes postage to most 1 L C For PiCmicro Microcontrollers site licence anns countries in the world O PiCtutor op EU residents outside the UK add 5 _ Electronic Circuits amp Components V2 0 Dba Cuh wd for airmail postage per order i i L PiCtutor Development Kit Standard Note The CD ROM is not included 1 L PiCtutor Development Kit Deluxe LC Deluxe Export Tn the Development Kit prices I a i C Electronic Components Photos L Electronics In Control Single User Note The software on each version is L Electronics In Control Multiple User the same only the licence for use varies 1 L Modular Circuit Design Single User i LI Modular Circuit Design Multiple User i FUILNaME sers co cows e E oe hh ech eae E E E A eh a oe hs dee l ec CS en eee eee a ea a a aa ee eee ee ee ccc I Seeeheguwenhs eo ee he seo ee he Post code nannaa ceed oa Tal NG K ar 974 0 ar ia cowed SNAUE aa araea E E R RER sw gh E HEE ER ee L enclose cheque PO in sterling payable to WIMBORNE PUBLISHING LTD for L Please charge my Visa Mastercard Amex Diners Club Switch Card expiry date ee50b Constructional Project SOLAR CHARGE AND GO TERRY DE VAUX BALBIRNIE Keep mobile while enjoying the outdoor life OME people shun traditional sun Sess holidays to seek the inde pendent life Carrying a small tent and a minimum of equipment on their back they walk climb camp and
95. arm condition to exist MODE 1 Change main PIN code Discussed previously MODE 2 Change entry exit time On selection of Mode 2 the screen dis plays a 2 line message such as where the value following PREV is the previously set time out period in seconds Everyday Practical Electronics April 2002 Any value between 01 and 99 may be selected note the prefix O for values below 10 Each digit entered is displayed at the bottom left of line 2 If you make a mis take press the blank key to clear the value just entered allowing you to start again Note that you are returned to the SELECT MODE display if blank is pressed when only one digit has been entered If more than two digits are keyed in suc cession the others will be ignored MODE 3 select entry exit zone On entry to Mode 3 a 2 line message will be displayed such as where in this instance the numeral 1 indi cates that Zone 1 is currently the selected entry exit zone As MAX 6 states one of six zones can be nominated as the entry exit zone Pressing any key between 1 and 6 selects that zone and the chosen digit appears replacing the appropriate dash and with a dash now replacing the previous digit Zones 7 and 8 cannot be selected for entry exit as these are regarded by the soft ware as being for anti tamper and Panic zone use MODE 4 select zones to be monitored On entry to Mode 4 a 2 line message will
96. be displayed of which the following is an example This example shows that zones and 8 have been selected for unauthorised access monitoring If any of these zones are entered when zone monitoring is active an alarm condition will exist accompanied by the bell and buzzer sounding and the strobe flashing if installed The exception is when the zone entered is that allocated as the entry exit zone If this zone is entered during active monitor ing the entry exit countdown timer will start with the buzzer sounding If the cor rect PIN code is keyed in within the allot ted time see Mode 2 the system will be deactivated and the buzzer silenced If the entry exit delay is exceeded then the bell and strobe will be activated When in Mode 4 pressing any key between 1 and 7 will toggle that zone between active watched and ignored When selected the zone number will be displayed otherwise a dash will be shown Note the following however Zone 8 cannot be deselected as the soft ware regards this as being a Panic zone Zone 7 nominally allocated as an anti tamper zone can be selected deselected Any zone nominated as the entry exit zone cannot be deselected When in Mode 2 set entry exit zone the selected zone automatically causes the same Watch zone to be activated MODE 5 Set bell on t me On entry to Mode 5 a 2 line message will be displayed of which the following is an
97. ble Send your circuit ideas to Alan Winstanley Ingenuity Unlimited Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND We do not accept sub missions for U via E mail Your ideas could earn you some cash and a prize WIN A PICO PC BASED OSCILLOSCOPE WORTH 586 100MS s Dual Channel Storage Oscilloscope 50MHz Spectrum Analyser Multimeter Frequency Meter Signal Generator If you have a novel circuit idea which would be of use to other readers then a Pico Technology PC based oscilloscope could be yours Every 12 months Pico Technology will be awarding an ADC200 100 digital storage oscilloscope for the best IU submission In addition a DrDAQ Data Logger Scope worth 69 will be presented to the runner up on when making portable devices there is a need for a regulated 5V supply typically to power either logic or a microcontroller Usually a linear regulator such as a 7805 is used to derive this supply Such regula tors are quite wasteful because the current into such a regulator is always greater than the current out of it and there is a voltage drop across the reg ulator as well When running 5V logic from a 9V supply the regulator is wasting almost as much power as the whole device is using If running the system from a 12V battery such as a key fob battery then more power is wasted than is used For example with an input of 9V an output 5V 500mA using P IV the i
98. ble for any modern PC Requires Adobe Acrobat Reader which is included on the MEM CD ROM Price of the Basic Work 29 95 OFFER PRICE 24 95 POST FREE Offer ends May 31st 2002 ELECTRONICS SERVICE MANUAL PRINTED VERSION ONLY EVERYTHING YOU NEED TO KNOW TO GET STARTED IN The essential work for REPAIRING AND SERVICING ELECTRONIC EQUIPMENT servicing and repairing SAFETY Be knowledgeable about Safety Regulations Electrical Safety and First Aid electron ic equipment UNDERPINNING KNOWLEDGE Specific sections enable you to Understand Electrical e Around 900 pages and Electronic Principles Active and Passive Components Circuit Diagrams Circuit Measurements Radio Computers Valves and Manufacturers Data etc e Fundamental principles PRACTICAL SKILLS Learn how to identify Electronic Components Avoid Static N Troubleshooting techniques Servicing techniques Choosing and using test equipment Reference data Easy to use format Clear and simple layout Vital safety precautions Professionally written Regular Supplements Sturdy gold blocked ring binder Hazards Carry Out Soldering and Wiring Remove and Replace Components TEST EQUIPMENT How to Choose and Use Test Equipment Assemble a Toolkit Set Up a Workshop and Get the Most from Your Multimeter and Oscilloscope etc SERVICING TECHNIQUES The regular Supplements include vital guidelines on how to Service Audio Amplifiers Radio Receivers TV Receivers Cassette Rec
99. bouts small variations matter little for our purposes here A regulated 12V sup ply is recommended since an unregulat ed supply may rise substantially above 12V and cause the motor to heat unnec essarily or even burn out The power sup ply should provide 6W or 500mA for smaller motors 3cm to 4cm dia The next step is to wire up the motor s common lead to the positive terminal of a 12V regulated supply Now take the negative OV lead of the 12V supply and apply it to the motor s four spare leads in various sequences Once you have found a sequence that advances the motor in small steps in a clockwise direction label these leads A to D What you have just achieved is wave control see Table 1 Finally the windings A to D need to be energised in the sequence shown in Table 2 which is full step control A pic torial representation of the windings or phases A to D is shown in Fig 2 Data sheets may present Table 2 in dif ferent ways and at first sight such tables might seem incompatible with each other The table drawn here is the most logically coherent way so that you will be able to appreciate the shifting of the binary sequence 1 0 0 1 across the stepper motor s leads STEPPER MOTOR S2 MAGNETIC REED SWITCH CEE REG So s K1 OTO 12V REGULATED SURRIY Fig 1 Complete circuit diagram for the Manual Stepper Motor Controller Switch S1 must be a make before break type Everyday Practical
100. ch Mode Regulator capacitor The Schottky diode provides a path for the inductor current when the switch which produces the square wave is off Regulation is achieved by feeding back the output voltage via a resistor divider back into the device Inside the i c the voltage on pin 1 is compared with a 1V reference If the volt age on pin is too high then the output volt age must be too high and so the i c reduces the duty cycle of the square wave which drops the output voltage a classical applica tion of negative feedback We can now see why the circuit is efficient If the input voltage is double that of the out put voltage then the square wave s duty cycle will be about 0 5 50 This means that the circuit is only drawing current half the time In addition the only major losses in the circuit are in the switch which produces the square wave and in the diode These losses are small owing to the low voltage drops across the devices when in their on state So next time an efficient power sup ply is needed consider using these simple switch mode devices in your application Samuel Ginsberg Everyday Practical Electronics April 2002 Lottery Predictor ts A Rollover A number generator which has been designed to give a numerical display of numbers between 0 and 49 is shown in the circuit diagram Fig 2 It is ideal for choosing those six all important lottery numbers and it is based on a number of traditi
101. ctors see Fig 1 The two enhancement mode devices are fabricated on a silicon chip and connected in a push pull configuration Whilst the level of heat produced by CMOS circuits is dramatically less than OXIDE GATE N SCURCE N DRAIN P SOURCE P DRAIN N SUBSTRATE Fig 1 CMOS structure 240 that generated by other technologies this does come at the cost of an increase in the level of fabrication complexity However this is more than compensated for by the increase in the level of integra tion that can be achieved Also early devices were not as fast as other technolo gies but since then their performance has been very considerably improved The CMOS process has been particular ly successful being used for very many years Feature sizes have steadily been reduced to enable it to meet the require ments for today s technology but now it appears that the limit is in sight for the standard technology in terms of providing for the very latest chips with their minute feature sizes Resolving the Problems There are a number of ways that have successfully been used to overcome the problems that occur with CMOS One is to make the channel depletion region more effective by increasing the level of doping However this also has the effect of increasing the on resistance for the device In turn this degrades the overall perfor mance and in particular the frequency response Another alternative that is bein
102. cuits for short wave enthusiasts Order code BP304 4 45 92 pages AN INTRODUCTION TO AMATEUR RADIO I D Poole Amateur radio is a unique and fascinating hobby which has attracted thousands of people since it began at the turn of the century This book gives the newcomer a com prehensive and easy to understand guide through the subject so that the reader can gain the most from the hobby It then remains an essential reference volume to be used time and again Topics covered include the basic aspects of the hobby such as operating procedures jar gon and setting up a station Technical topics covered include propagation receivers transmitters and aerials etc Order code BP257 5 49 150 pages VALVE RADIO AND AUDIO REPAIR HANDBOOK Chas Miller This book is not only an essential read for every profes sional working with antique radio and gramophone equipment but also dealers collectors and valve tech nology enthusiasts the world over The emphasis is firm ly on the practicalities of repairing and restoring so technical content is kept to a minimum and always explained in a way that can be followed by readers with no background in electronics Those who have a good grounding in electronics but wish to learn more about the practical aspects will benefit from the emphasis given to hands on repair work covering mechanical as well as electrical aspects of servicing Repair techniques are also illustrated throughout A
103. d cheque or money order drawn on a UK bank Make cheques payable to Direct Book Service Visa Mastercard Amex Diners Club and Switch orders accepted please give card number card expiry date and Switch Issue No Orders are normally sent within seven days but please allow a maximum of 28 days longer for overseas orders Send your order to Direct Book Service Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND Tel 01202 873872 Fax 01202 874562 E mail dbs epemag wimborne co uk Online store www epemag wimborne co uk shopdoor htm 242 RADIO VT401 61 minutes A M Radio Theory The most complete video ever produced on a m radio Begins with the basics of a m trans mission and proceeds to the five major stages of a m reception Learn how the signal is detected converted and reproduced Also covers the Motorola C QUAM a m stereo system Order Code VT401 VT402 58 minutes F M Radio Part 1 FM basics including the functional blocks of a receiver Plus r f amplifier mixer oscillator i f amplifier limiter and f m decoder stages of a typical f m receiver Order Code VT402 VT403 58 minutes F M Radio Part 2 A con tinuation of f m technology from Part 1 Begins with the detector stage output pro ceeds to the 19kHz amplifier frequency dou bler stereo demultiplexer and audio amplifier stages Also covers RDS digital data encoding and decoding Order Code VT403 MISCELLAN
104. d l e d IC1 S8441 magnetic sensor Miscellaneous Magnet any type Lab 6 4 Resistor R1 470Q 0 25W 5 carbon film Semiconductors D1 red l e d IC1 SS411 magnetic sensor Lab 6 5 Resistors R1 6k8 R2 120k R3 470k R4 1k5 0 25W 5 carbon film Potentiometer VR1 10k min preset Capacitors C1 1u radial elect 16V C2 15u radial elect 16V Semiconductors IC1 SS441 magnetic sensor IC2 4098 dual monostable IC3 OP177 op amp sensor this is because the combination of R3 and Cl acts as a low pass filter which stops rapid changes the larger the values of R3 and Cl the slower the circuit We will be returning to the idea of filters in a later part of Teach In Approx Cost Guidance Only Everyday Practical Electronics April 2002 The values chosen for Fig 6 21 are suffi cient for our experiments but it is worth increasing the value of Cl by say 10 times to see the overall effect Construct the cir cuit and observe the output of the gate as you did earlier This time the output should be clean without any bounces If your switch is particularly bouncy then you may see one bounce in this case increase C1 until the bounce stops Lab 6 3 Unipolar Hall Effect Device Connecting a SS441 switching sensor is very simple it has three pins supply ground and output as shown in Fig 6 22 Fig 6 23 Cleanly switching output from the circuit in Fig 6 22 SEE TEXT Rext Cext Cext ext Fig
105. d possible through using a PIC microcontroller It seemed that an ideal system should have the features itemised in Panel 1 It is believed that all the requirements listed in the Panel have been met in this design How they are implemented will be discussed as we progress CONCEPTUAL LOGIC Designing an intruder alarm system is based on the simple Boolean logic concept that a sensor s switch contacts can be either open or closed If the contacts are found to be in the opposite condition to that in which they should be e g open when they should be closed then an alarm condition exists and appropriate action should be taken Everything else follows on from this logical argument but as is illustrated through Panel 1 there are many factors that make a considerable difference between a 1 gate circuit that simply detects an open closed condition and a system that provides a great many other security aiding facilities as well there are around 1900 program commands in the controlling soft ware for this design CIRCUIT DIAGRAM The main circuit diagram for the PIC Controlled Intruder Alarm is shown in Fig l The principal functions are as follows Main Zones PIC16F877 microcontroller C1 is in charge of the entire system Via port pins RDO RD3 and RCO RC3 which are used in input mode the PIC can monitor between one and eight sensor zones plus an extra Panic zone via RB4 The quan tity is selected by the user and
106. e This problem can be very significant for example when one sub circuit has a digital clock signal that is coupled via the supply into a sensitive amplifier The solution is to wire the supply and ground connections separately to a single point rather than using the same point to point wire for all the connections see Fig 6 4b This approach applies equally to the wiring inside the cabinet of an instrument and to Everyday Practical Electronics April 2002 CIRCUIT 2 GROUND CIRCUIT 2 GROUND Fig 6 5 Ground loops between circuits a can be avoided by using a single ground connection the supply connections on an integrated circuit Noise can also find its way from the a c power lines through your power supply and into your circuit Power line noise can be quite substantial if your circuit is on the same mains connection as equipment such as cookers or power tools A power line filter can help reduce power line noise GROUND LOOPS When two circuits sub circuits instru ments or other equipment are grounded at two separate points on a ground bus we have a situation known as a ground loop or earth loop see Fig 6 5a The ground bus may be a circuit board track the chas sis of the equipment point to point wiring or most commonly the mains earth con nected at different outlets This situation does not only occur in measurement and instrumentation systems many people have suffered unnecessary le
107. e The reference images are stored and compared with images from cameras mounted by a secure area If the image characteristics match access is authorised MAGENTA TK3 KIT UP IG a D G Zh DCC Oo T m R 16 E afa ba 4399391999719199 se oo oe H Pe a a HOW TO BE KEENE Keene Electronics 2002 catalogue seem ingly contains everything that you could possibly want in the way of audio visual equipment and accessories The company tell us that they sell interesting useful and sometimes hard to find bits and pieces designed to make your life easier whether you re a camcorder enthusiast home cine ma fan or general gadget addict Their catalogue is nicely produced in full colour A4 with around 100 pages It can be obtained free of charge by anyone that asks for it says Alan Quinby of Keene Contact Keene Electronics Dept EPE Unit 9 Old Hall Mills Business Road Little Eaton Derbyshire DE21 5DN Tel 0870 990 9000 Fax 01332 830551 Email sales keene co uk Web www keene co uk os Mail order specialists Magenta Electronics have launched their own printed circuit board and kit for EPE Toolkit Mk3 TK3 Based on the authors original p c b as published in Oct 01 the Magenta board has been somewhat redesigned to include a d c power socket with a reverse polarity protec tion diode Facilities for adding a 9 way p c b mounted serial connector have been added as well The board is printed with
108. e 0 40V 0 40V 0 40V 0 40V 0 40V task and it requires a high current to set or Max Output Current 20mA 20mA 20mA 20mA 20mA reset 1ts magnetic field As you can imag Output Switching Time 0 O05us typ 0 O05us typ O O5us typ 0 05us typ 0 O05us typ ine this makes the circuitry more complex Risetime 1 5us max 1 5us max 1 5us max 1 5uS max 1 5us max and in some applications the circuit V 12V R 1 6k includes feedback from the sensor to con Output Switching Time 0 15us typ 0 15us typ 0 15us typ 0 15us typ 0 15us typ trol the strap in order to minimise ambient Falltime 1 5us max 1 5us max 1 5us max 1 5us max 1 5us max fields We will not be going into this part V 12V R 1 6k y o ee SE of the circuits Max Operating Field 6 OmT 14 0mT 11 5mT 18 OmT 39 0mT ut mainly because the sensors are Very Min Release Field 6 0mT 14 0mT 2 0mT 7 5mT 23 5mT expensive TEACH IN 2002 Lab Work 6 DAVE CHESMORE Magnetic Switch Experiments Lab 6 1 Reed Switch and Switch Bounce N this Lab we illustrate the use of a reed switch and how switch bounce can occur in its use Construct the circuit in Fig 6 18 on your breadboard The reed switch is connected between ground and 5V via resistor R1 The switch is also con Everyday Practical Electronics April 2002 nected across the input of a NAND gate any gate will do such as AND OR NOR buffer or inverter and could be from the 74xx or 40xx series Observe the switch s
109. e format WOCE CA 08 14 99 MORE ADVANCED ROBOTICS WITH LEGO MINDSTORMS Robert Penfold Covers the Vision Command System Shows the reader how to extend the capabilities of the brilliant Lego Mindstorms Robotic Invention System RIS by using Lego s own accessories and some sim ple home constructed units You will be able to build robots that can provide you with waiter service when you clap your hands perform tricks see and avoid objects by using bats radar or accurately follow a line marked on the floor Learn to use additional types of sensors including rotation light temperature sound and ultrasonic and also explore the possibilities provid ed by using an additional third motor For the less experienced RCX code programs accompany most of the featured robots However the more adventurous reader is also shown how to write programs using Microsoft s VisualBASIC running with the ActiveX con trol Spirit OCX that is provided with the RIS kit Detailed building instructions are provided for the fea tured robots including numerous step by step pho tographs The designs include rover vehicles a virtual pet a robot arm an intelligent sweet dispenser and a colour conscious robot that will try to grab objects of a specific colour Order code BP902 298 pages ANDROIDS ROBOTS AND ANIMATRONS John Lovine Build your own working robot or android using both off the shelf and workshop constr
110. e on subscription anywhere in the world see below from all UK newsagents distributed by COMAG and from the following electronic component retailers Omni Electronics and Yebo Electronics S Africa EPE can also be pur chased from retail magazine outlets around the world An Internet on line version can be purchased and downloaded for just 9 99 US approx 7 70 per year available from www epemag com SUBSCRIPTIONS Subscriptions for delivery direct to any address in the th Tt nann 1 i RHH l UK 6 months 15 12 months 28 50 two years 52 Overseas 6 months 18 standard air service or 27 express airmail 12 months 34 50 standard air service or 52 express airmail 24 months 64 standard air service or 99 express airmail Online subscriptions for downloading the magazine via the Internet 9 99 US approx 7 70 for one year available from www epemag com Cheques or bank drafts in sterling only payable to Everyday Practical Electronics and sent to EPE Subs Dept Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND Tel 01202 873872 Fax 01202 874562 Email subs epemag wimborne co uk Also via the Web at http Awww epemag wimborne co uk Subscriptions start with the next available issue We accept MasterCard Amex Diners Club Switch or Visa For past issues see the Back Issues page BINDERS Binders to hold one volume 12 issues are available from the above address
111. e standards of educational software Electronics and Computing Principles V7 1 is very reasonably priced at 119 99 inclusive of VAT A multi user network version is also available The software is also available from Maplin Electronics and read ers can now play with a copy in their stores product code RR63 There is a Free trial Electronics and Computing Principles OnLine demonstration version available from the EPTsoft web site Students and hobbyists can extend this to 12 months unlimited use by taking out a subscription for the sum of 29 95 plus VAT For more details contact EPTsoft Ltd Dept EPE Pump House Lockram Lane Witham Essex CM8 2BJ UK Tel 44 0 1376 514008 Fax 44 0 8700 509660 Email info eptsoft com Web address www eptsoft com WHETHER your interest is in domestic radio and TV or in amateur radio in military aeronautical or marine communications in radar and radio navigation in instruments in broadcasting in audio and recording or in professional radio systems fixed or mobile RADIO BYGONES is the magazine for you ARTICLES on restoration and repair history circuit techniques personalities reminiscences and just plain nostalgia you ll find them all Plus features on museums and private collections and a full colour photo feature in every issue IT S MOSTLY about valves of course but solid state whether of the coherer and spark gap variety or early transistors also has
112. e subject of digital electronics up to the operation and architecture of microprocessors The virtual laboratories allow users to operate many circuits on screen Covers binary and hexadecimal numbering systems ASCII basic logic gates monostable action and circuits and bistables including JK and D type flip flops Multiple gate circuits equivalent logic functions and specialised logic functions Introduces sequential logic including clocks and clock circuitry counters binary coded decimal and shift registers A D and D A converters traffic light controllers memories and microprocessors architecture bus systems and their arithmetic logic units Sections on Boolean Logic and Venn diagrams displays and chip types have been expanded in Version 2 and new sections include shift registers digital fault finding programmable logic controllers and microcontrollers and microprocessors The Institutional versions now also include several types of assessment for supervisors including worksheets multiple choice tests fault finding exercises and examination FILTERS Filters is a complete course in designing active and passive filters that makes use of highly interactive virtual laboratories and simulations to explain how filters are designed It is split into five chapters Revision which provides underpinning knowledge required for those who need to design filters Filter Basics which is a course in terminology and filter characterization
113. e variable will either have been accessed or it will not Nevertheless the author always uses a critical section whenever any ISR variable single or otherwise is accessed by the main program The hard part about critical sections is understanding the notion behind them and getting their placement right Once you ve managed that critical sections are easy to implement and involve minimal overhead Even if they are not strictly necessary they are good practice using them is a good habit to get into there s no harm in a measure of belt and braces safety and should a program ever need modifying in the future such that one becomes neces sary the structure is already there 294 LISTING 8 Section of INTPROG8 which illustrates the use of two interrupt sources Interrupt setup BSF INTCON INTE CLRF TMRO CLRF COUNT BCF INTCON TOIF BSF INTCON TOIE BSF INTCON GIE data initialisation BSF PORTA 0 main loop MAIN MOVLW SPEED Enter_Critical_ Section SUBWE COUNT W BTESS STATUS C GOTO A2 CLRF COUNT Leave_Critical_ Section MOVLW 1 XORWE PORTA F GOTO MAIN A2 Leave_Critical_ Section GOTO MAIN Interrupt service routine ISR MOVWE SAVEW SWAPE STATUS W MOVWE SAVES BANKO INCF ICOUNT F BTEFSS INTCON INTF GOTO TMR INTF interrupt enable INTF interrupt Clear internal clock count up clear clock wrapped count clear the TMRO wrapped flag enable timer interrupts enable global interrupts
114. e without the need to wait for the development of the next gen eration of processors with completely new designs As such it should be possible to see the new technology hitting the markets before too long Everyday Practical Electronics April 2002 VIDEOS ON ELECTRONICS A range of videos selected by EPE and designed to provide instruc tion on electronics theory Each video gives a sound introduction and grounding in a specialised area of the subject The tapes make learning both easier and more enjoyable than pure textbook or magazine study They have proved particularly useful in schools colleges training departments and electronics clubs as well as to general hobbyists and those following distance learning courses etc BASICS VT201 to VT206 is a basic electronics course and is designed to be used as a complete series if required VT201 54 minutes Part One D C Circuits This video is an absolute must for the begin ner Series circuits parallel circuits Ohms law how to use the digital multimeter and much more Order Code VT201 VT202 62 minutes Part Two A C Circuits This is your next step in understanding the basics of electronics You will learn about how coils transformers capacitors etc are used in common circuits Order Code VT202 VT203 57 minutes Part Three Semicon ductors Gives you an exciting look into the world of semiconductors With basic semicon ductor theory Plus 15 different semiconduc tor devic
115. easy work of the hard wiring construction meth ods including stripboard custom printed circuit boards plain matrix boards surface mount boards and wire wrap ping finishing off and adding panel labels getting prob lem projects to work including simple methods of fault finding In fact everything you need to know in order to get start ed in this absorbing and creative hobby Order code BP392 5 49 135 pages PRACTICAL FIBRE OPTIC PROJECTS R A Penfold While fibre optic cables may have potential advantages over ordinary electric cables for the electronics enthusiast it is probably their novelty value that makes them worthy of exploration Fibre optic cables provide an innovative interesting alternative to electric cables but in most cases they also represent a practical approach to the problem This book provides a number of tried and tested circuits for projects that utilize fibre optic cables The projects include Simple audio links F M audio link P W M audio links Simple d c links P W M d c link P W M motor speed control RS232C data links MIDI link Loop alarms R P M meter All the components used in these designs are readily available none of them require the constructor to take out a second mortgage Order code BP374 5 45 132 pages RADIO BYGONES We also carry a selection of books aimed at readers of EPE s sister maga zine on vintage radio Radio Bygones These books include
116. ed The system can be configured later in software via keypad S1 to suit the entry zones you ve decided to use Nor do you have to instal all output con trolling transistors if their higher power capability or control functions are not needed e g omission of the strobe or sec ond keypad facility similarly with their terminal connectors Note that the output 263 264 AUX BUZZER STROBE BELL BATTERY D13 a E TBI Ee S i cTR4 TB2 k a b al S nd MCLR 2 DATA RB7 E gt CLK RB6 5 k ERS ov C C O k a b D11 G R18 ven E LT HH la lel TR2 k a b ET a i 21 S N STs C2 k b ra R23 E OUT C G a BE k a INIC3 D4 D4 E TI RM1 1 12V AC R aul 7 Ke K is eR R R R R R N Gu 12lh alh al 10 COM 4 IN IC2 RM2 6 o oe o ooo 5 6 7 8 1 2 3 4 S3 PANIC ZONES 4 5IN 114 3mm Fig 5 Printed circuit board component layout and full size track master pattern Everyday Practical Electronics April 2002 W Qu Resistors R1 R15 R2 to R6 Si 1k 2 off R21 to R2410k 9 off See JOP R7toR14 100k soff TALK R16 R17 page to R20 470Q 5 off RM1 8 x 47k common 9 pin s i l resistor module RM2 8 x 1k common 9 pin s i l resistor module R1 to R24 0 25W 5 carbon film or better Potentiometers VR1 10k min preset round VR2 1k min preset round Capacitors Ci C2 10p ceramic 5mm pitch 2 off
117. ed in our pages cannot be legally used in the UK Readers should check the law before buying any transmitting or telephone equipment as a fine confiscation of equipment and or imprisonment can result from illegal use or ownership The laws vary from country to country readers should check local laws 225 Constructional Project ELECTRIC GUITAR TUNER ROBERT PENFOLD Strike a chord with your group UITAR tuner projects range from G simple devices having l e d dis plays to highly complex units using signal processing stages frequency to volt age converters and sophisticated displays This unit is very much in the cheap and cheerful category but it nevertheless works very well Guitar tuning is an application where the more sophisticated approaches tend to generate problems that take ever more electronics to solve Most problems stem from the fact that the output waveform from a guitar tends to change quite dra matically during the course of a sustained note with some of the harmonics becom ing very strong at times True frequency measuring devices can have problems due to harmonics multiples of the fundamental frequency being measured at times rather than the fundamental frequen cy itself Without suitable signal processing Fig 1 Block diagram for the Electric Guitar Tuner 236 the tuning indicator can jump around making precise adjustment very difficult IN COMPARISON The guitar tu
118. ed to know if you can t tell your EMS from your EGA Order code BP282 5 45 270 pages 13 99 128 pages Everyday Practical Electronics April 2002 Theory and Reference Bebop To The Boolean Boogie By Clive call me Max Maxfield Specially imported by EPE Excellent value An Unconventional Guide to Electronics Fundamentals Components and Processes This book gives the big picture of digital electronics This indepth highly readable up to the minute guide shows you how electronic devices work and how they re made You ll discover how transistors operate how printed circuit boards are fabricated and what the innards of memory ICs look like You ll also gain a working knowledge of Boolean Algebra and Karnaugh Maps and understand what Reed Muller logic is and how it s used And there s much MUCH more including a recipe for a truly great seafood gumbo Hundreds of carefully drawn illustrations clearly show the important points of each topic The authors tongue in cheek British humor makes it a delight to read but this is a REAL technical book extremely detailed and accurate A great reference for your own shelf and also an ideal gift for a friend or family member who wants to understand what it is you do all day BR OPE 409 470 pgs large format H al Td oele 8 1 f 26 95 BEBOP BYTES BACK and the Beboputer Computer Simulator CD ROM Clive Max Maxfield and Alvin Brown
119. ed to the data EEPROM by pressing D they will then be the settings that the sys tem checks are correct when in active mon itoring mode Should any sensor be found to be in a different condition and that zone is one of those selected to be monitored see Mode 4 then an alarm condition exists The system then behaves as described under Mode 4 bells etc Before pressing D to store the data physically visit all zones and ensure that the sensors are in the required condition 1 6 doors and windows closed the cat not sitting on the pressure mat wife not mov ing around in front of the PIR sensor etc Except for blank all other keys are ignored in this mode Everyday Practical Electronics April 2002 MODE 7 View normal zone logic On entry to Mode 7 a 2 line message will be displayed of which the following is an example This mode is for information only It simply shows the normally open and nor mally closed logic for each sensor as stored in the data EEPROM in this case they are all shown as normally open MODE 8 Set second keypad PIN On entry to Mode 8 the following line 1 message will be displayed but with line 2 blank Mode 8 is used in the same way as Mode 1 but allowing you to enter the required 4 digit PIN for use with the optional keypad 2 It may be the same PIN as used with keypad 1 but it does not provide access to the main system Note that if you have chosen to use just a 4
120. efficiency 69 Output 5V 360mA Input 12V 220mA efficiency 68 Output 5V 540mA Input 12V 380mA efficiency 59 Output 5V 720mA Input 12V 600mA efficiency 50 In addition the circuit can output 500mA for long periods without any need for a heatsink The minimum input voltage that the circuit needs to produce regulated 5V output is about 7 3V The circuit is generally not recommended for sensitive analogue circuitry 246 as it does have a small amount of ripple on the output The circuit is straightforward to build The inductor current rating should be about the same as the load current for best operation and inductors can be connected in series or in parallel to achieve the desired value The diode D1 should be a Schottky type as the cir cuit runs at high frequency It is possible to add current limiting by inserting a resistor into the circuit between pin 8 and pins 7 and 6 Imaginative The circuit s operation may be understood intuitively Imagine a square wave with a 50 duty cycle the average voltage out of such a circuit is half the peak voltage of the square wave All that is needed to convert such a square wave to d c is a circuit that takes the average of its input a low pass fil ter is such a circuit Many low pass filters use resistors and capacitors but resistors are not desirable in power circuitry and therefore in the SMPSU the low pass filter uses an inductor and a Fig 1 Circuit diagram for a Swit
121. egisters or tons of output ports 32 bits just happens to be perfect for clock numerals and with free samples avail able from Allegro Microsystems www alle gromicro com or www allegromicro com sf 58184 index htm you can bet that a nixie clock will be my first project once I get my Mk3 built Say that might make for a great project writeup or submission to Ingenuity Unlimited Warren Parks Fort Collins Colorado via email Great effusion and great to hear from you Warren I ve passed your comments to Robert and added you to my fan club list welcome aboard I remember nixies very well and had lots of fun with them even believing that by using four in a display plus some flip flops built using many discrete transistors etc copying a circuit in a Mullard book I was on my way to designing a computer very early 60 s I think how naive Ingenuity Unlimited is always pleased to receive interesting offerings TK3 AND PARTITIONED DRIVES Dear EPE I notice through various Readouts that some readers have tried to install TK3 on a partitioned drive but failed I had problems trying to get TK3 to run on my second of two hard drives D with the following results and fixes When trying to run the program on D from a shortcut on the desktop I kept getting a path not found error when the program tried to open its first text file i e TK3Settings txt I eventual ly found that the default drive and
122. en for users of the Internet Remember that you can buy most of EPE s books back issues p c b s videos and CD ROMs online via our Online shop at www epemag wimborne co uk shop door htm and you can also subscribe for 6 months or 2 years by taking out a subscription online at subrates htm Of course you can download the source code for nearly all our PIC projects by hopping over to our FTP site ftp ftp epemag wimborne co uk pub links are provided on the home page of our web site and a mirror web site of our PIC codes is maintained by Thomas Stratford at http homepages nildram co uk star bug epepic htm Also on our FTP site are several other files and folders supporting Robert Penfold s Interface column A Catalog of Problems Recently my phone rang and it was a UK sales manager for Actinic Software who busied himself describing their latest pack ages support contracts and upgrades for their e commerce software systems Some readers may be aware of the problems that we sud denly experienced in January 2002 when our own system based on Actinic Catalog failed to update itself properly and some key fea tures were corrupted This disruption resulted in a lot of hair pulling and a major out age that lasted nearly two weeks while different servers and operat ing systems were tested and double checked After a lot of hard work by both ourselves and our ISP we re pleased to see the system fully restored and working
123. epper motor control system Thanks to high school student Stuart Shapiro for asking the question l JUST IN H P 6063B DC Electronic Load 3 240V 0 10A 250W H P 66312A PSU 0 20V 0 2A H P 66311B PSU 0 15V 0 3A H P 66309D PSU Dual 0 15 0 3A 0 12 0 1 5A H P 6632B PSU 0 20V 0 5A H P 6623A PSU triple output ranging from 0 7V 0 5A to H P AGILENT 34401A DMM 672 digit H P 3478A DMM 5 digit FLUKE 45 DMM dual display H P 3312A Function Gen 0 1Hz 13MHz AM FM Sweep Tri Gate Brst etc 300 FARNELL Dual PSU XA35 2T 0 35V 0 2A Twice QMD I c d Display CIRRUS CRL254 Sound Level Meter with Calibrator 80 120dB LEQ 15 EDDYSTONE 1002 Receiver 150kHz 30MHz Brooadcast FM unused 125 FARNELL AMM255 Automatic Mo Meter 1 5MHz 2GHz unused FARNELL DSG1 Low Frequency Syn Sig Gen 0 001Hz 99 99kHz low distortion TTL Square Pulse Outputs etc 9 FLUKE 8060A Handheld True RMS DMM 4 2 digit As new 150 used 95 BECKMAN HD110 Handheld 3 digit DMM 28 ranges with battery leads and carrying case 40 H P 3310A Function Gen Sine Sq Tri Ramp Pulse FARNELL LFM4 Sine Sq Oscillator 10Hz 1MHz low distortion TTL output Amplitude Meter 125 H P 545A Logic Probe with 546A Logic Pulser and 547A Current Tracer FLUKE 77 Multimeter 3 2 digit handheld FLUKE 77 Series 11 HEME 1000 L C D Clamp Meter 00 1000A in carrying case Racal 9008 0 005Hz 5MHz ONLY Automatic Modulation Meter
124. ers use It s the flux that helps the solder flow properly and it s already inside the solder wire That s the brown stuff you see bubbling off the solder It takes roughly 0 5 seconds or less to melt an average solder joint you shouldn t keep heating the joint or you ll damage the board by making the copper foil tracks lift away from the circuit board If you re scorching or blackening it then you re overheating it way too much It takes practice I would get an old board and practice taking parts off and soldering new parts in You ll get the hang of it Remember you re only using the iron to briefly heat up the place where you re going to dab the solder onto noth ing else Alan Winstanley SHORTENED DIVISION Dear EPE Thanks to Peter Hemsley for his comments Cheats Again Readout Feb 02 There is always a trade off in either performance or mem ory when making code generic but I m sure most Everyday Practical Electronics April 2002 people will agree that usually the benefits in flexibility outweigh the performance deficits Therefore the full 16 bit division routine would be more useful as generic code than a 10 bit Granted if you were only going to use it for pro cessing the 10 bit ADC on the PIC16F877 it is worth making a specific routine However the following piece of code helps to optimise the full 16 bit division routine when being passed numbers less than 16 bit I ve taken the lib er
125. es explained Order Code VT203 VT204 56 minutes Part Four Power Supplies Guides you step by step through different sections of a power supply Order Code VT204 VT205 57 minutes Part Five Amplifiers Shows you how amplifiers work as you have never seen them before Class A class B class C op amps etc Order Code VT205 VT206 54 minutes Part Six Oscillators Oscillators are found in both linear and digi tal circuits Gives a good basic background in oscillator circuits Order Code VT206 34 95 2 inc VAT amp postage Order 8 or more get one extra FREE Order 16 get two extra FREE VCR MAINTENANCE VT102 84 minutes Introduction to VCR Repair Warning not for the beginner Through the use of block diagrams this video will take you through the various circuits found in the NTSC VHS system You will follow the signal from the input to the audio video heads then from the heads back to the output Order Code VT102 VT103 35 minutes A step by step easy to follow procedure for professionally clean ing the tape path and replacing many of the belts in most VHS VCR s The viewer will also become familiar with the various parts found in the tape path Order Code VT103 DIGITAL Now for the digital series of six videos This series is designed to provide a good ground ing in digital and computer technology VT301 54 minutes Digital One Gates begins with the basics as you learn about seven of the most comm
126. et period to prevent annoy ance to neighbours Allows timed zone entry exit time out for users without trig gering the full alarm Allows full monitoring of required zones once time out has ended Allows users to terminate time out procedure Allows users to control the monitoring system by means of a unique alphanumeric personal identity code PIN entered via a keypad Allows users to change the PIN code Allows users to access the control system without using a PIN code in the event of system failure or servicing Normally powered from a mains power source Instantaneously switches over to being powered by a heavy duty back up battery if mains power fails Keeps the battery fully charged when mains power is present the battery should be capable of keeping the monitoring system and any activated alarms operational for a reasonable period Allows the system to resume active monitoring should power totally fail but subsequently resume Indicates that there has been a total power failure even after power has been resumed Prevents the bell from being activated when power is resumed Indicates for later viewing whether zones have been entered even though there may also have been a power failure and resumption VE VE La RAO ANO RA1 AN1 RA2 AN2 VREF RA3 AN3 VREF RA4 TOCK1 RA5 AN4 SS L C D MODULE PSPO0 RDO PSP1 RD1 PSP2 RD2 PSP3 RD3 T10SO T1CKI RCO T10SI CCP2 RC1 CCP1 RC2 SCK SCL RC3
127. everal other jobs I became a freelance pro grammer and started work on a project assem bly level programming a microcontroller rather similar to a present day PIC Suffering from ill health I retired at 56 and took up woodturning and largely forgot about electronics but kept on some computing Following a triple bypass operation I made the minor mistake of trying to go back to wood turning too soon I should just have waited a few more weeks but I bought a copy of EPE instead and I ve never got back to woodturning Maybe I was lucky but I got four electron ics jobs when it was supposed to be almost impossible because of my age The industry really did quite well for me As well as my interest in electronics I m researching that first piece of engineering technology to ever enter the home the spin ning wheel I certainly have no intention of giving up learning Alan S Raistrick Oxfordshire Thanks Alan that s great to hear of how elec tronics has served you so well over the years sorry there was not enough space for your full letter You might be interested to know I started out in the film industry too at Elstree Borehamwood as a trainee film editor Hobbyist electronics eventually led me into full time electronics and I too have no regrets It s a great technology to be involved in in whatever capacity Should I team up with you in doing a PIC controlled spinning wheel clock without separate shift r
128. faster than ever before One important change with the online system is that a Java applet is now used at the order encryption phase The applet is based on 128 bit security to encrypt credit card information in your browser and it is much faster than waiting for a lengthy Perl script on a slow secure server to run One drawback is that Windows XP users may not be able to run the Java applet without first downloading the Java Virtual Machine from the Microsoft web site The reasons why Microsoft offers you this Internet download rather that include it on the XP CD are spelt out in their Open Letter to Sun Microsystems at www microsoft com java issues openletter htm Unfortunately those operating behind a firewall that prohibits applets from running will not be able to place an order This is a rare occurrence but we are unable to offer any other way of accepting or processing online payments for goods bought via the online shop Every cloud has a silver lining though and the faster server final ly enable users to run a search quickly so simply type any keywords such as PIC Toolkit into the Search box and all instances of books p c b s CDs and back issues containing this expression will be listed Full terms and conditions are available online under the Info button and if you want a clearer way of navigating the shop try using the Site Map function instead You Have Junk Mail In the November 2001 issue I outlined ways i
129. fectly ADJUSTMENT AND USE If a suitable frequency meter is available it can be used to set the correct output fre quencies from IC2 In order to obtain ade quate accuracy an instrument having a gate time of 10 seconds and a resolution of 0 1Hz is required The correct output fre quencies to the nearest 0 1Hz are shown in Table 1 Table 1 Output Tuning Frequencies Note Frequency Preset E 82 4 VR1 A 110 VR2 D 146 8 VR3 G 196 VR4 B 246 9 VR5 E 329 6 VR6 Everyday Practical Electronics April 2002 L R gy x i L 5 6 L L 7 L L i E R a U v s a i a E a d 7 a FEF i F gt oe a i ais m E u a Se 6 9 i s 7 a i t 6 s ai Interwiring from the circuit board to the front panel mounted components Another method is to monitor the output of IC2 using an earphone connected to socket SK2 and then tune the presets by ear Either pitch pipes or an accurately tuned instrument is needed to provide ref erence notes that the unit can be tuned against A third method is to connect an accu rately tuned guitar to socket SK1 and then use this as the tuning reference An elec tronic keyboard instrument can be used in the same way but make sure it is set for a normal musical scale with middle A at 440Hz A normal screened jack lead is used to connect the electric guitar or other instrument to SK1 With preset potentiometer VR1 selected using rotary switch S1 play the lower E note and adjust
130. from a sensor along with the wanted sensor signal or it may be introduced by the circuitry e g amplifier used to process the signal Noise may also come from outside or elsewhere in the sys tem coupled or picked up inadvertently and added to the signal being processed this is often called interference Noise generated within components is generally random in nature and has a wide frequency range whereas interference may produce unwanted signals at very specific frequencies Examples of interference that you may be familiar with include poorly suppressed ignition in cars which interferes with the car radio and mains hum picked up in hi fi equipment In some fields notably the mil itary interference may be deliberate to jam radio signals 248 ELECTRICAL INTERFERENCE Sensor systems and other electronic cir cuits can be adversely affected by signals from other parts of the system or from out side being inadvertently picked up and added in with the wanted signal External signals may get into your circuit through electrostatic electromagnetic and mag netic coupling In electrostatic coupling a high imped ance part of your circuit acts like one plate of a capacitor In magnetic coupling a loop in your circuit acts like the secondary of a transformer In electromagnetic coupling parts of your circuit act like antennae Mains hum signals at 50Hz 60Hz and radio frequency interference from other elect
131. ftware covering all aspects of the series and Alan Winstanley s Basic Soldering Guide including illustrations and Desoldering Teach In 2000 covers all the basic principles of elec tronics from Ohm s Law to Displays including Op Amps Logic Gates etc Each part has its own section on the inter active software where you can also change component values in the various on screen demonstration circuits The series gives a hands on approach to electronics with numerous breadboard circuits to try out plus a sim ple computer interface which allows a PC to be used as a basic oscilloscope ONLY 12 45 including VAT and p amp p Robotics INTRODUCING ROBOTICS WITH LEGO MINDSTORMS Robert Penfold Shows the reader how to build a variety of increasingly sophis ticated computer controlled robots using the brilliant Lego Mindstorms Robotic Invention System RIS Initially covers fundamental building techniques and mechanics needed to construct strong and efficient robots using the various click together components supplied in the basic RIS kit Then explains in simple terms how the brain of the robot may be programmed on screen using a PC and zapped to the robot over an infra red link Also shows how a more sophisticated Windows programming language such as Visual BASIC may be used to control the robots Details building and programming instructions provided including numerous step by step photographs 288 pages larg
132. g them first I searched for Yaesu UK s web site www yaesu co uk from which I ob tained an email address My thanks to Sam Ruddy of Yaesu UK Technical Support who was extremely helpful replying by return with some suggestions Sam explained that their original NC 26 was a simple wall charger which plugged into the side of the FBA 8 battery pack that held the NiCads There is no charging circuit built into the battery pack itself so you really need a proper external NiCad charger As the NC 26 is no longer available they recommend the basic RS plug top NiCad charger part number 250 1397 phone 01536 444079 or see http rswww com This provides a constant current of 60mA and can handle 1 to 12 cells It has l e d charge status and short circuit reverse polarity protection Also available is an RS charger code 250 1252 which has an adjustable current of 50mA to 400mA and a proper quick charge unit code 250 1404 with a built in timer and automatic sensing and switch ing to trickle charge Yaesu UK agrees that the trouble with using the 700mA adaptor is making sure it does not overcharge those expensive bat teries It s your choice personally I think the basic RS unit although slow will be the kindest on your batteries or go for the fast charge with timer Eco Warrior Lastly something I have been itching to say for months for all my NiCad or NiMH battery charging I am very pleased with my Saitek
133. g used by some manufacturers is to use an insulating substrate in a process known as silicon on insulator SOI Using this approach the substrate is depleted of all electrons and in this way the electrons are forced to move through the very thin channel This ensures that all the current is forced through the relevant areas of the chip Further developments of this technology have made the channel very thin In this way what is known as the floating body effect is eliminated This effect is an unwanted feature of SOI devices One team has reported a 50nm thick channel whilst another has reported reducing the channel thickness to just 7nm However for this very thin channel a gate oxide layer that was four times as thick as most gate oxide layers today was used FinFET Another method that can be used to over come the problem is to use a double gate This normally entails placing a gate on top and below the channel In this way the bulk silicon is not able to be a problem Achieving this is not easy though The tech niques required in the i c fabrication process dramatically increase the overall cost A novel approach has been adopted to overcome the problem By rotating the structure through ninety degrees gates can be placed on either side of the channel Despite its rather novel approach the FinFET as it is known is very close to the traditional double gate FET structure seen in the textbooks It features the ultra
134. ghtness l e d that is designed for operation on low currents Socket SK2 can be used to monitor the output of C1 using a crystal earphone and resistor R8 attenuates the output sig nal to a suitable level The circuit can drive medium impedance headphones as used with personal stereo units if R8 is reduced to a value of 10 kilohms For best results the phones should be driven in series The actual voltage from a 9V battery varies significantly during its operating life but there is no need to power the Resistors See R1 R2 39k 2 off R3 1k5 SHOP R4 2M2 R5 R7 2k2 2 off TALK R6 4k7 page R8 100k All 0 25W 5 carbon film Potentiometers VR1 VR2 47k min enclosed carbon preset horiz 2 off VR3 VR4 22k min enclosed carbon preset horiz 2 off 10k min enclosed carbon preset horiz 2 off VR5 VR6 Capacitors C1 100u radial elect 10V C2 100n polyester 5mm lead spacing C3 1u radial elect 50V C4 220n polyester or polycarbonate 5mm lead spacing Semiconductors D1 5mm or 3mm low current 2mA red I e d with panel mounting clip IC1 LF351N bi f e t op amp IC2 TS555CN low power timer i c Miscellaneous S1 6 way 2 pole rotary switch only one pole used S2 s p s t min toggle switch SK1 standard 6 35mm mono jack socket SK2 3 5mm mono jack socket B1 9V battery PP3 size with connector clips Small instrument case size to suit 0
135. ging back into IC2 during a mains power failure A C MAINS INPUT The voltage at the D3 battery junction is fed via diode D4 to provide approximately 12V d c to power external sensor and alarm warning devices up to a total current of about 900mA allowing a reasonable headroom for battery charging currents and that required by the control board Fuses FS1 and FS2 prevent transformer overload and battery discharging in the event of a short circuit between the 12V and OV lines It is recommended that panel mounting fuseholders are used The voltage at the D3 D4 junction is regu lated down to 5V by IC3 This provides power for the PIC microcontroller IC1 and l c d X2 neither of which must be powered at a higher voltage The presence of an output voltage from IC3 is displayed by l e d D5 ALARM DEVICES As previously said there are four outputs through which the PIC can activate external alarm devices either directly or indirectly depending on their type Fig 3 Each transistor is capable of sinking 1A sourced from the 12V d c power line but remember that this line can only supply about 900m lt A as said earlier Because of the way in which the software is written external audio visual alarm devices should only be connected in the order shown The buzzer is frequently used to indi cate a variety of functions such as keypad presses to indicate that entry exit timing is in progress and that an entry has
136. gnments and simulate circuit behaviour Ultiboard 2001 is the latest version of the highly successful p c b layout software also from Electronics Workbench It provides a comprehensive design flow from board set up and component trace placement to file report generation for manufacturing and assembly It includes a large library and built in autorouting It has powerful visuali sation tools which enable students to easily view and navigate board designs For more information contact Adept Scientific plc Deplt EPE Amor Way Letchworth Herts SG6 1ZA Tel 01462 480055 Fax 01462 480213 Email ewb adeptscientific co uk Web www adeptscience co uk Everyday Practical Electronics April 2002 INGENUITY UNLIMITED Our regular round up of readers own circuits We pay between 10 and 50 for all material published depending on length and technical merit We re looking for novel applications and circuit designs not simply mechanical electrical or software ideas Ideas must be the reader s own work and must not have been submitted for publication elsewhere The circuits shown have NOT been proven by us ngenuity Unlimited is open to ALL abilities but items for consideration in this column should be typed or word processed with a brief circuit description between 100 and 500 words maximum and full circuit diagram showing all relevant component values Please draw all circuit schematics as clearly as possi
137. gt y 1 ed ANT Lad a L i K L y g Ea k B b 4 4 4 y w t d KM p 4 F b e gt om Pat Z et ort a 0 Ne Kr Sie m 5 L R aA _ 4 lt Fig 6 20 Switch debouncing flip flop circuit Fig 6 21 Simple switch debounce cir cuit It is further improved if a Schmitt trigger gate is used not always practical Most reed switches are not changeover although they can be purchased Another simpler way of debouncing is shown in Fig 6 21 which uses a capacitor to effectively slow down the change in voltage to the input of the gate In this case the gate must however be a CMOS logic gate as we need a higher input impedance than a TTL gate provides Also using a Schmitt trigger gate such as inverters 4106 or 4584 will improve mat ters because it shows hysteresis Selection of R3 and C1 is important especially if we are going to activate the switch often as may occur in a rotation COMPONENTS N B Some components are repeated between Lab Works 4k7 0 25w See 5 carbon iS Fa e film Semiconductor IC1 4011 quad NAND gate see text Miscellaneous S1 reed switch Lab 6 2 Resistors R1 R2 1k 2 off R3 10k 0 25W 5 carbon film Capacitor C1 470n ceramic disc Semiconductor IC1 4011 quad NAND gate see text Miscellaneous s p d t min toggle switch S2 reed switch Lab 6 3 Resistor R1 470Q 0 25W 5 carbon film Semiconductors D1 re
138. gy to a given point beyond which no further improvements are possible For the most part it has been possible to over come the limitations that were thought to exist but now it does seem that the devel opment of the standard form of CMOS is reaching its final limits It has been found that since gate lengths went into sub micron sizes the drain of the CMOS MOSFET has given rise to prob lems When gate lengths fall to below about 0 5 microns the electric field around the drain can easily rise to the levels where the source drain leakage increases consid erably In extreme cases it can give rise to a punch through effect whereby the device permanently fails CMOS devices have been the mainstay of i c technology for very many years Only a few years after the introduction of 1 c s it was feared that the limits of integra tion would soon be reached because the heat dissipated in the conventional circuits used could not be removed in such a way that chip operating temperatures could be kept within satisfactory limits Whilst work was undertaken to improve the ways in which heat was removed the real breakthrough occurred with the devel opment of CMOS technology that dramat ically reduced the current drawn by the cir cuits in the i c and accordingly the level of heat produced was also reduced Complementary metal oxide semicon ductor or CMOS is formed by the combi nation of PMOS and NMOS p type and n type channel semicondu
139. h fixing nut solder etc Approx Cost Guidance Only excluding case amp stepper motor PE MANUAL STEPPER MOTOR CONTROLLER moulding Cut this out then test to see that there is smooth 360 rotation of the switch before carefully snapping it back together again This simple Manual Stepper Motor Controller project is built on a single piece of 0 lin matrix stripboard measuring 24 holes by 16 strips The topside component layout and interwiring is shown in Fig 3 There are no breaks in the underside cop per tracks A length of 6 way multi coloured ribbon cable attached at each end with female pin header plugs is used to interlink the circuit board to the stepper motor Commence construction by soldering in position the two link wires the p c b head er SK2 the leads to the stepper motor are plugged on here and the two resistors continuing with the eight diodes the two l e d s and the capacitor The cathodes k of diodes D1 to D8 are banded The cath odes of l e d s D9 and D10 have the short est leads and have a flat on the body near est these leads Be sure also to observe the correct polar ity of capacitor Cl L E D s D9 and D10 are mounted on the stripboard in such a POWER D10 INPUT a IOO nn m DOD TE R Components mounted on the completed circuit board way that they will protrude through the front panel of the case when the board is slotted into place
140. h the maths skills that are essential to developing a good understanding of electronics The course aims to develop Skills in the use of mathematical notation formulae equations graphs trigonometry Boolean algebra logarithms and exponen tials all of which subjects are essential to a higher understanding and practice of electronics On line tutor support is available throughout the course and assessment is based on seven tutor marked assessments Successful students will be awarded a Brooklands College Certificate that will record the total assessment mark and the grade awarded Pass Merit or Distinction The first part of the course can be sam pled before you enrol and further on line electronics courses are currently being developed The full course costs only 29 99 To find out more http online brooklands ac uk browse Spicing Up Electronics RD Research have introduced B Spice AD Version 4 replacing the widely used B Spice 2000 Version 4 uses what they describe as the Berkeley 3F5 simulation engine to accurately simulate the way electronic circuits work Users can design analogue and digital circuits quickly and easily This new version also includes the design of r f circuits The software is priced at 229 and comes complete with a model library of over 8000 parts Complex circuits can easily and rap idly be designed on screen and subjected to a range of tests The results are displayed in graph
141. haracter Length Select 2 3J Stop Bit Select fas Parity Inhibit 232D Master Reset Fig 1 Pin assignments for the 6402 UART The Receiver and Transmitter are largely independent 2D Even Parity Enable sD Character Length Select 1 D Control Register Load sD Transmitter Buffer Register 7 2D Transmitter Buffer Register 6 aiD Transmitter Buffer Register 5 Sol Transmitter Buffer Register 4 2s Transmitter Buffer Register 3 2 Transmitter Buffer Register 2 zD Transmitter Buffer Register 1 D Transmitter Buffer Register 0 sD Transmitter Register Output SD Transmitter Register Empty 2D Transmitter Buffer Register Load 2D Transmitter Buffer Register Empty drives them The baud rate is one six teenth of the clock frequency Grabbing Bytes Received bytes are clocked into a shift register and then latched onto pins 5 to 12 The data on these lines therefore remains valid while the next byte of data is clocked into the shift register This gives a clean switch from one byte of data to the next The Data Received output pin 19 goes high when a new byte of data is placed on the outputs and this output is reset by briefly taking pin 18 low There are three error outputs associat ed with the receiver pins 13 to 15 but these are of little use in the current con text The receiver outputs are all tristate types but this ability is not normally needed unless the UART is interfaced to a microprocessor Pins 4 and
142. hat the device will switch on in the presence of a field as opposed to its absence A bipolar device is different and will turn on in the presence of a positive field and off in the presence of a negative field as shown in Fig 6 14 Its output will only change state when the field is reversed and acts like a normal on off switch and once activated will not change state even when the field is removed UNIPOLAR AND BIPOLAR There are a number of unipolar and bipo lar Hall effect sensors available the most common are from Honeywell and the char acteristics of the SS400 series are given in Table 6 1 We will use two of these devices in Labs 6 1 and 6 2 to act as simple switch es Data sheets for the SS400 series can be downloaded from the Honeywell web site multiplied by the area through which the field passes The tesla T is the SI unit of magnetic flux density equal to one weber per square metre or 10 gauss Finally the gauss G is an older measure of flux den sity The Earth s magnetic field varies with locality but is approximately 0 6G at the poles and 0 3G at the equator We sometimes need to know the force exerted by a magnetic field given the directions of movement of a charge and the magnetic field s direction It turns out that they are all perpendicular to each other and can be remembered by Fleming s Right Hand Rule If you hold your right hand as shown in Fig 6 16 then your thumb po
143. i ine Fig 5 Most of the pages are interactive and permit some form of user input Everyday Practical Electronics April 2002 a A range of high quailty bight LED s are available to the constructor with red Green and yelga with herp lens in two sites Imm and fmm The optical constuction ensures that they gwe a good visible ight output low drive current and fast response ime LED s are also suitable for pulsed operation the irequency and mark space ratio of which wil effect ihe visible ight oufpul as for a ere ee will be switched off T S URN The renrennmenrieri anemi AM in 12T inaari amend 15 i in AmA hea miwa SI Fig 4 One of the HTML pages this one covers l e d s light emitting diodes voltage etc see Fig 6 Most interactive pages use the same method of altering parameters and displaying the changes that are produced The range covered by Version 7 1 is vast but it remains reasonable easy to navigate your way to the desired topics In Control Although most pages rely on buttons and dialogue boxes for user input the method of control is altered slightly to suit certain types of circuit In particular the method of control is slightly dif ferent for most logic circuits With the D type flip flop for exam ple two buttons enable the logic states of the Data and Clock inputs to be toggled The onscreen logic indicators change in response to these input signals In o
144. ics April 2002 Receiver Circuit The circuit diagram for a Serial Receiver based on the 6402 UART is R5 Z 2 1 134 35 37 38 39 shown in Fig 2 The UART requires a rela 2k7 tively long reset pulse at switch on and capacitor C4 and resistor R6 provide this X1 Serial interfaces do not operate at nor 2 4576MHz mal 5V logic levels but instead use 12V i to represent logic 0 and 12V to represent S C1 17 9 R3 fy 2 logic 1 A circuit that provides level shift 330k 4024BE pa ing and an inversion must therefore pre 10 5 cede the serial input of IC2 TRI 6 There are special line receiver chips BC547 ul that can handle this task but in this cir 12 cuit a simple inverter stage based on tran sistor TR2 is used Proper line receivers 3s lielse islig are preferable if the serial link must oper DR ate over long distances but a simple inverter is perfectly adequate where short connecting cables are used o OV A crystal controlled clock generator ensures that an accurate baud rate is obtained Transistor TR1 is used in a sim ple crystal oscillator operating at 2 4576MHz and this signal is divided by 8 in IC1 The 4024 is actually a seven stage binary counter but in this circuit only three stages are used This gives a clock frequency of 307 2kHz and a baud rate of 19 200 It is advisable to use a high baud rate in order to obtain a DR Reset reasonably high maximum transfer rate and 19200 is the highest
145. in any money with it which proves that writing for Ingenuity Unlimited is a whole lot more lucrative than gambling on the National Lottery ARW Ian Hill Plymouth Devon Y DISPLAY EMABLE CLOCK INHIBIT COMMUN CATHODE level meter s Ideal for balancing speaker levels in PA or industrial use mm Includes Case 3302055 Plus P amp Pt Tiis home cinema audio RadioShack f You ve il ww We ve got answers Ideal for home cinema Reads to 126dB SPL Includes Case 3302050 2499 Plus PSP wa EE eee ee 7 range sound level meter audio PA or industrial use RadioShack Catalogue x Features over 3000 products x Over 400 pages GG ONLY 1 99 Pus PEP gt Electronics Mini Audio 14 Piece Cleaner Amplifier gre Computer 77 with Speaker Tool Kit Brush s Volume s Demagnetised 6404327 poses 6401990 ELEY Bi For th address of you nearest 699 1199 1099 LEZE SE or order direct Pus PAP Plus Ps Pt Plus PAP CALL Huge Range of RadioShack Products now Available in the U K Bt LE ESITTEET Cost of catalogue refunded or e mail info rs rusk com P amp P if applicable costs from E2 00 per package orders with next order valued at E10 over E100 Free Retailer Enquiries Welcome or over Excludes P amp P RuSk Limited is the Licenced Distributor for RadioShack Corporation in the U K Everyday Practical Electronics April 2002 247 EPE Tutorial
146. in produced patent after patent breaking entirely new ground in electronic and audio engineering During the Second World War Alan Blumlein was deeply engaged in the very secret work of radar development and contributed enormously to the system eventually to become H25 blind bombing radar Tragically during an experi mental H2S flight in June 1942 the Halifax bomber in which Blumlein and several colleagues were flying crashed and all aboard were killed He was just days short of his thirty ninth birthday Order code NE32 15 99 420 pages Everyday Practical Electronics April 2002 VIDEO PROJECTS FOR THE ELECTRONICS CONSTRUCTOR R A Penfold Written by highly respected author R A Penfold this book contains a collection of electronic projects specially designed for video enthusiasts All the projects can be simply con structed and most are suitable for the newcomer to project construction as they are assembled on stripboard There are faders wipers and effects units which will add sparkle and originality to your video recordings an audio mixer and noise reducer to enhance your sound tracks and a basic computer control interface Also there s a useful selection on basic video production techniques to get you started Complete with explanations of how the circuit works shop ping lists of components advice on construction and guid ance on setting up and using the projects this invaluable book will save y
147. in the quality and condition of materials and workmanship used by readers EPE Online its publishers and agents disclaim any responsibility for the safe and proper functioning of reader constructed projects based on or from information published in these materials and works In no event shall Maxfield amp Montrose Interactive Inc or Wimborne Publishing Ltd be responsible or liable for any loss of profit or any other commercial damages including but not limited to special incidental consequential or any other damages in connection with or arising out of furnishing performance or use of these materials and works ISSN 0262 3617 PROJECTS THEORY NEWS COMMENTS POPULAR FEATURES VOL 31 No 4 APRIL 2002 www epemag wimborne co uk Cover illustration by Jonathan Robertson EPE Online www epemag com Projects and Circuits ELECTRIC GUITAR TUNER by Robert Penfold 236 Six fixed frequencies and an l e d help you to stay in tune INGENUITY UNLIMITED hosted by Alan Winstanley 246 Switch Mode Regulators Lottery Predictor PIC CONTROLLED INTRUDER ALARM by John Becker 260 A sophisticated multi zone intruder detection system that offers deluxe monitoring facilities MANUAL STEPPER MOTOR CONTROLLER by Thomas Scarborough 274 Illustrates how a 4 phase stepper motor can be controlled bi directionally using a conventional rotary switch SOLAR CHARGE AND GO by Terry de Vaux Balbirnie 286 Use solar power to charge your 2
148. ints in the direction of charge motion the fore finger represents the direction of magnetic lines of force from the north pole to the south pole and the middle finger represents the direction of conventional current flow positive to negative Nw Field middle finger current thuMb Motion Fig 6 16 Fleming s Right Hand Rule http content honeywell com 80 sens ing prodinfo solidstate catalog c20008 pdf or just generally search via http con tent honeywell com These 3 pin sensors operate over a very wide supply range from 3 8V to 30V and are temperature compensated Since they have a current switching output they need a suitable resistor connected from the out put to the supply In Lab Work we use a 470Q2 resistor connected to an 1 e d to illus trate their operation The resistor can be any suitable value as long the operating current 20mA is not exceeded Examples of Hall effect switching devices Everyday Practical Electronics April 2002 One other thing to be noticed from Table 6 1 is that they have a very fast switching time 1 5us or faster which means they can detect rapid changes in magnetic field Applications of bipolar sensors range from simple detection of the presence of a magnetic field and sensing doors opening and closing to measurement of rotation We will be looking at their use in rotation sensing in Lab 6 5 LINEAR SENSORS Linear sensors produce an output pro portiona
149. is suddenly stopped the output will take some time to change NEXT MONTH Next month we will look at how this simple anemometer can be improved We also look at digital optical sensing comparators positioning and direction discrimination If you have any queries directly related to this series you can write to the authors c o the Editorial address or you can email them to teach in epemag demon co uk no file attachments or general electronic queries please MAKE IT A GIFT EVERY MONTH AND SAVE UP TO 68p AN ISSUE LUA WAAL ISC pG red enclose payment of SUBSCRIPTION ORDER FORM cheque PO in sterling only payable to Everyday Practical Electronics T13 hs MAGAZINE FOR ELECTRONICS TECHNOLOGY amp COMPUTER PROJECTS SUBSCRIPTION ORDER FORM Annual subscription rates 2002 Signature 6 Months UK 15 Overseas 18 standard air service 27 express airmail Card Ex Date 1 Year UK 28 50 Overseas 34 50 standard air service 52 express airmail My card number is Please print clearly and check that you have the number correct Switch Issue NO sasecenonan Subscriptions can only start with the next available issue For back numbers see the Back Issues page 2 Years UK 52 00 Overseas 64 00 standard air service 99 express airmail To Everyday Practical Electronics Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9N
150. ise to some 4 1V when fully charged and off load Unless conditions are very cloudy the voltage available from the solar panels even tak ing into account the forward voltage drop of diode D1 will exceed that of the re chargeable cells The cells will therefore charge up over a period of time Diode D1 prevents them discharging back through the solar panels when there is insufficient illumination When switch S1 is set to the low posi tion the current from the solar panels must now flow through resistor R2 and this limits it to a smaller value This may pass continuously through B1 cells and will simply maintain the charge Everyday Practical Electronics April 2002 PHONE OUTPUT With switch S2 in the normal posi tion current will pass from the solar panels meter MEI S2a contacts diode D2 and resistor R4 to a mobile phone battery plugged into socket SK1 The battery will then charge in a time dependent on the light available Diode D2 is a Schottky barrier diode which has a smaller forward voltage drop 0 3V rather than 0 7V for a conventional silicon diode so involves less loss in the charging process Assuming switch S1 is set to high the voltage appearing at diode D1 anode and hence at D2 anode will be some 0 7V ts forward voltage drop higher than that at B1 positive terminal It will therefore lie in the range 4 3V to 4 9V assuming sufficient light reaches the solar panels to allow this to ha
151. ite Although the course focuses on the use of the PlCmicro series of microcontrollers this product will provide a relevant background in C programming for any microcontroller PRICES Prices for each of the CD ROMs above are FIODDYV ISU SLUG IN ococctc seseccecceserccuccecesiesendesiniaedecenees 45 inc VAT Institutional Schools HE FE Industry 99 plus VAT Institutional 10 user Network Licence 199 plus VAT Site Bc 499 plus VAT UK and EU customers add VAT at 17 5 to plus VAT prices Interested i in programming PIC microcontrollers Learn with PlCtutor ELECTRONIC easy to follow logical sequence HARDWARE unit comes with a battery holder a reduced number of switches and no displays This version will allow users to complete 25 of the 39 Tutorials The Deluxe Development Kit is supplied with a plug top power supply the Export Version has a COMPONENTS This highly acclaimed CD ROM by John Becker together with the PlCtutor experimental and development board will teach you how to use PIC microcontrollers PHOTOS with special emphasis on the PIC16x84 devices The board will also act as a development test bed and programmer for future projects as your programming skills develop This interactive presentation uses the specially developed Virtual PIC Simulator to show exactly what is happening as you run or step through a program In this way the CD provides the easiest and best ever in
152. iven to me as a school prize in 1945 I trained as a chemist and found employ ment in the 1950s when there was no problem about finding a job in an Industrial Research Association I kept up my interest in electron ics by reading the magazines such as Radio Constructor and Practical Wireless We were expected to be minor geniuses supposedly being able to find the answer to any problem our industry threw at us My elec tronics came in useful from time to time and as the years passed I read things like Practical Electronics After a variety of related jobs I returned to the Research Association to work on a discrete germanium transistor logic process controller because I was capable of understanding both the electronics and the process we were trying to control There had been a complete break down of communication between the non chemical electronic equipment supplier and the non electronic chemical users The crunch came some years later when changes in funding and industry reorganisation caused the transfer of the job to over a hundred miles away There was no other organisation in the country where my particular specialised experience fitted so I decided to try applied electronics By now I was over 40 and even then we were supposed to be over the hill and unemployable Working for an instrumentation company I quickly found I was fully at home in the envi ronment and when I saw a development job in the film industry I a
153. key If the alarm was previously in monitor ing mode and there has been no unautho rised zone entry a 2 line message similar to following is shown This indicates that no zones have been intruded and that it is 6 seconds and count ing since the power was restored If one or more zones have been intruded the message might appear as indicating that zonel has been entered and that panic has been pressed again show ing the elapsed time since power restora tion The message PSU ERR or the earlier POWER ERROR means that you should check the condition of your battery To clear either of the last two messages you must reset the alarm by keying in your PIN code and pressing blank to return to ALL OFF AUTHOR S EXIT The PIC Monitored Intruder Alarm has not been tested in active service However it has been extensively bench tested with a variety of switches and sen sor simulation devices It is believed that it lives up the specifications outlined earlier but this cannot be guaranteed and no legal responsibility can be accepted for it However if you have any suggestions for how the system could be improved please advise us at Editorial HQ not via the Chat Zone since we do not visit this regularly May you live without intrusion RESOURCES Software for this design is available on 3 5 inch disk for which a nominal han dling charge applies It is also available for free download fro
154. l dbs epemag wimborne co uk Order from our online shop at www epemag wimborne co uk shopdoor htm BOOK ORDER FORM i Teu Address 00 ce cecceceececcececceeeeceececeeeeeeceeeeceeeesaeeeesesaeees Post code Signature eee ee eee ee nee ean eee C enclose cheque PO payable to DIRECT BOOK SERVICE for _ Please charge my card Card Number S Telephone NO eee Please continue on separate sheet of paper if necessary If you do not wish to cut your magazine send a letter or copy of this form Everyday Practical Electronics April 2002 Regular Clinic ALAN WINSTANLEY and IAN BELL CIRCUIT pa SURGERY Vb Za R ni ull In this month s column we examine the principles of screening of signal wires and the problems caused by ground loops A new transceiver has battery problems too Potential Problems Our thanks to Gerard Galvin who emailed to ask a few questions about earth ing and shielding topics which we will look at in turn His first point concerns the provision that some bench power supplies e g Andy Flind s Versatile Bench Power Supply in EPE Jan 2002 have for a choice of positive negative or floating earth ground output terminals so that other earthed equipment such as oscilloscopes can be safely connected to any circuit on test Gerard asks If both circuit and test equipment are at the same potential why can there be a problem There are two
155. l connection Signal guarding uses triaxial cables and connectors see Fig 6 6 which have an inner conductor carrying the signal of interest and two layers of shielding The inner shield is connected to a signal of equal voltage to the signal provided by a unity gain amplifier see Fig 6 7 This means that there is a zero voltage differ ence between the signal and inner shield so the leakage currents and capacitance effects are minimised The outer shield is usually grounded and provides interference protection for the guard signal As an example of how guarding works consider the schematic in Fig 6 8a for which an equivalent circuit is shown in Fig 6 8b Here we are trying to measure the resistance of a sensor Rg which has a very high resistance value and therefore leakage through the cable insulation resistance Rc is significant We apply Vm and measure I this should give the value of Rg as Vw but actually gives us this parallel combination of R and Rc due to the leakage current I Using a guard Figs 6 8c and 6 8d means that the voltage across Ro between the inner conductor and guard is zero and hence no leakage current flows The buffer amplifier has no difficulty in supplying the guard to ground leakage current I and this does not disrupt the measurement Differential signals can also be guarded by applying a buffered common mode sig nal to the guard shield Obviously the cable requires two central conduc
156. l to the magnetic field and the Honeywell SS490 series is a good exam ple The SS495A operates from 5V to 10V and produces an output at 3 125mV per G with a range of 600G to 600G More complex linear devices exist which have two axes perpendicular to each other these can measure direction of magnetic field and can be used for electronic compasses Honeywell have several highly sensitive devices e g the HMC1022 which are mag netoresistive and made of a Permalloy nick el iron thin film deposited on a silicon wafer and patterned as four resistors in a bridge for mat The presence of a magnetic field causes the resistance to change We have already used bridges in previous circuits and they can be used for these sensors These sensors also have an offset strap which is used to cancel out any pre existing magnetic fields For example suppose we are designing an electronic compass for use in a car The car is made of ferrous metal PANEL 6 2 Hall Effect The illustration in Fig 6 17 shows a thin wafer of semiconductor thickness d with current I flowing in the X direction an applied magnetic field By in the Y direction and a voltage E generated in the Z direction across the wafer The size of the voltage is proportional to the prod uct of the magnetic flux density and the current If we consider how current flows in a semiconductor it is made up of charge carriers electrons and holes the current I is given by I n
157. l unit a drive card and a dedicated power supply unit as well as of course the motor itself The author perceived in this a basic problem The barrier between owning a stepper motor and actually using it is fair ly great Contrast this with the easy avail abilty of stepper motors today particularly from cast off Lain disk drives and fax machines and you clearly have a problem waiting for a solution HOW IT WORKS The present article describes a simple way to rotate a four phase unipolar stepper motor with the help of a single rotary switch just eight inexpensive rectifier diodes and some incidental components The full circuit diagram for the Manual Stepper Motor Controller is shown in Fig 1 Turn the rotary switch S1 clockwise and the stepper motor turns clockwise Turn the rotary switch anticlockwise and the stepper motor turns anticlockwise Bring the rotary switch to rest and the stepper motor comes to rest at full torque called holding torque This mimics the basic control features available from standard stepper motor con troller i c s with the exception that the Manual Stepper Motor Controller is oper ated entirely by hand It also incorporates basic feedback in the form of light emitting diode l e d D10 and magnetic reed switch S2 so that if the 274 motor is mounted out of sight the user may know when it has completed one full rotation Possible applications include the remote positio
158. la uand ra doped BPE aoa rh ih Aire piani Lir dain od milesi hirad Pee nar pies art RHS MAT RZ of our brd ga fer Bn Brk aan aii dsn tad p aei Pia Wis kD h 10 fisi i 1 oiii 93 03 MOT ey cee Di KS X 314 pins EPE s Online Shop where you can buy books PCBs back issues and more all conveniently online However many users are not aware that it is possible to access mail on the server without needing to download it into your own mail client e g Outlook Express or Eudora first Nor do you need to ask your ISP s technical support you can handle this easily for yourself One package I suggest is JBMail which will poll multiple mail boxes automatically so that you can manually screen out unwanted mail This morning one of my mailboxes contained nearly 50 junk emails that arrived overnight from the USA but they were all delet ed satisfyingly at a stroke using JBMail Another mailbox started to fill before my very eyes with junk just after I had cleaned it out The downside is that it is easy to overlook legitimate mails needing your attention so care is needed when sifting through the debris A new Version 3 of JB Mail has now been launched which includes the very significant upgrade of multiple address books e g work friends This data can be imported as a tab delimited file and you can also create your own address books as well New blacklist filters are included and one of JBMail s most valuable fea tures is its ability to
159. lable Isolating Transformer 240V In Out 500VA 40 STEWART of READING za 110 WYKEHAM ROAD READING BERKS RG6 1PL nie Telephone 0118 9268041 Fax 0118 935169 www stewart of reading co uk Callers welcome 9am 5 30pm Monday to Friday other times by arrangement Everyday Practical Electronics April 2002 TEKTRONIX TDS310 dual trace 50MHz 200M S LECROY 9400A dual trace 175MHz 5G S HITACHI VC 6523 d trace 20MHz 20M S delay etc Unused 600 PHILIPS PM3092 2 2 ch 200MHz delay etc 800 as new 950 PHILIPS PM3082 2 2 ch 100MHz delay etc 700 as new 800 TEKTRONIX TAS465 dual trace 100MHz delay etc 750 TEKTRONIX 2465B 4 ch 400MHz delay cursors etc 1500 TEKTRONIX 2465 4 ch 300MHz delay cursors etc 900 TEKTRONIX 2445 A B 4 ch 150MHz delay cursors etc 500 900 TEKTRONIX 468 Dig Storage dual trace 100MHz delay 450 TEKTRONIX 466 Analogue Storage dual trace 100MHz 250 TEKTRONIX 485 dual trace 350MHz delay sweep TEKTRONIX 475 dual trace 200MHz delay sweep TEKTRONIX 465B dual trace 100MHz delay sweep PHILIPS PM3217 dual trace 50MHz delay GOULD 0S1100 dual trace 30MHz delay HAMEG HM303 dual trace 30MHz component tester HAMEG HM203 7 dual trace 20MHz component tester FARNELL DTV20 dual trace 20MHz component tester 125 Many other Oscilloscopes available MARCONI 2022E Synth AM FM Sig Gen 10kHz 1 01GHZz l c d display etc H P 8
160. large reference section provides a range of infor mation compiled from many contemporary sources and includes specialist dealers for valves components and complete receivers Order code NE34 288 pages 20 50 Computers and Computing MULTIMEDIA ON THE PC lan R Sinclair In this book you ll find out what a CD ROM is how it works and why it is such a perfect add on for a PC allowing you to buy programmes text graphics and sound on a CD It also describes the installation of a CD ROM drive and a sound card pointing out the common problems that arise and then shows how to use them to create a complete multimedia presentation that con tains text photos a soundtrack with your own voice recorded as a commentary even animation and edited video footage Order code PC112 HOW TO BUILD YOUR OWN PC Morris Rosenthal More and more people are building the own PCs They get more value for their money they create exactly the machine they want and the work is highly satisfying and actually fun That is if they have a unique begin ner s guide like this one which visually demonstrates how to construct a state of the art computer from start to finish Through 150 crisp photographs and clear but minimal text readers will confidently absorb the concepts of computer building The extra big format makes it easy to see what s going on in the pictures For non special ists there s even a graphical glossary that clearly illust
161. le even if it is in the garage etc It is battery powered and does not require any modification to the appliance thus using the Indicator will not invalidate any manufacturer s warranty se ONE DOES IT BETTER Everyday Practical Electronics April 2002 DON T MISS AN ISSUE PLACE YOUR ORDER NOW Demand is bound to be high PRA THE MODERN ELECTRONICS MANUAL CD ROM VERSION ONLY Over 800 pages In depth theory Projects to build Detailed assembly instructions RICE 9002 Full components checklists R and Extensive data tables en more Manufacturers web links Easy to use Adobe Acrobat format Clear and simple layout Comprehensive subject range Professionally written Regular Supplements EVERYTHING YOU NEED TO GET STARTED AND GO FURTHER IN ELECTRONICS The revised CD ROM edition of the Modern Electronics Base Manual MEM contains practical easy to follow information on the following subjects Electronic Components and their Characteristics 16 sections from Resistors and Potentiometers to Crystals Crystal Modules and Resonators Circuits Using Passive Components 10 sections Power Supplies The Amateur Electronics Workshop The Uses of Semiconductors Digital Electronics 6 sections Operational Amplifiers Introduction to Physics including practical experiments Semiconductors 5 sections and Digital Instruments 3 sections There s nothing to beat the satisfaction of creating your own project
162. le all those in the Components and Equipment sections fall into this category The general idea is to provide familiarity with real world equipment and components which should make life easier for those who progress to designing and building real circuits A good range is covered in both cate gories In the components section for instance there is everything from fuses and battery holders to l e d s and displays Part of the page covering l e d s light emitting diodes is shown in Fig 4 Se Pee ees ee ee ee ee ey ee eee I ee ee Fig 3 Further pages on the same basic topic can be accessed via a pop down menu Most of the pages consist of a diagram or diagrams plus some explanatory notes Where appropriate formulae and calculations are also included The vast majority of these pages are interactive in some way and this makes the learning process easier and more fun As a simple example Fig 5 shows the window for an active low pass filter The input voltage and the values of important compo nents can be changed by operating the appropriate button The dia logue box that appears when the button for resistor R2 in the filter circuit is pressed is shown in Fig 5 The new value is typed into the textbox and then the OK but ton is operated The figures in the circuit then change to suit the new value as do the calculated cut off frequency output Fo ibs Poe fae G CZ s liar BI Ti RZ s bik S erl PER IR Zn Gh get oot 3
163. lectronics April 2002 Electric Guitar Tuner We do not expect any problems to be encountered when sourcing the com ponents for the Electric Guitar Tuner project Certainly the op amp and timer i c s are stock items carried by most component advertisers However to keep the battery drain low you need to order a low power version of the 555 timer chip To keep frequency drift due to temperature changes to a minimum a high qual ity capacitor must be purchased for C4 A polycarbonate type would be the best choice here but a polyester capacitor should give good results Ceramic types tend to have inadequate short and long term stability and should not be used The 2 pole 6 way rotary switch used in the prototype is a Lorlin type and came from Maplin amp 0870 264 6000 or www maplin co uk code FF74R Most of our component advertisers should be able to offer a similar type Teach In 2002 Lab 6 Only the Hall effect sensor devices could cause sourcing problems in this month s Teach In 2002 Lab Work 6 demonstration circuits The Honeywell SS441A unipolar and the SS411A bi polar magnetic sensors were ordered from Farnell 0113 263 6311 or www farnell com codes 311 1477 and 311 1465 respectively The rest of the semiconductors should be readily available from most of our regular components advertisers Manual Stepper Motor Controller We cannot foresee any buying problems when shopping for parts for the Manual Steppe
164. limited experience of electronics Chapter 1 covers the basics of analogue and digital multimeters discussing the relative merits and the limitations of the two types In Chapter 2 various methods of component checking are described including tests for transistors thyristors resis tors capacitors and diodes Circuit testing is covered in Chapter 3 with subjects such as voltage current and continuity checks being discussed In the main little or no previous knowledge or experi ence is assumed Using these simple component and cir cuit testing techniques the reader should be able to con fidently tackle servicing of most electronic projects Order code BP239 4 49 DIGITAL GATES AND FLIP FLOPS lan R Sinclair This book intended for enthusiasts students and techni cians seeks to establish a firm foundation in digital elec tronics by treating the topics of gates and flip flops thor oughly and from the beginning Topics such as Boolean algebra and Karnaugh map ping are explained demonstrated and used extensively and more attention is paid to the subject of synchronous counters than to the simple but less important ripple counters No background other than a basic knowledge of elec tronics is assumed and the more theoretical topics are explained from the beginning as also are many work ing practices The book concludes with an explanation of microprocessor techniques as applied to digital logic Order code PC106 9 95
165. ltage and cur rent delivering capability would vary greatly with the brightness of the light reaching them In fact it is quite likely that the output would be insufficient to operate a cas sette player direct those tested needed 150mA approximately The re charge able battery pack will make up the short fall and enable several hours of use per day depending on the available light It will also enable the user to listen to music in the evenings Assume that Charge switch S1 is closed for the moment high position Assume also that nothing is plugged into either out put socket SK1 or SK2 Resistor R2 is bypassed by S1 contacts so has no effect The current from the solar panels passes through milliammeter MEI resistor R1 connected between its terminals provides the correct full scale reading and this point will be explained later It then flows through diode D1 to battery pack B1 com prising three nickel metal hydride cells NiMH Cells made using this technology unlike the nickel cadmium variant do not suffer from the memory effect This is a gradual loss of capacity when they are not completely discharged before re charging Due to the nature of this circuit nickel metal hydride cells are more appropriate because they are more likely to be partially charged and discharged BATTERY VOLTAGE The nominal voltage developed by the battery pack B1 is 3 6V that is 1 2V per cell although this will r
166. m out ftp site See PCB Service page Read this month s Shoptalk page for additional details on obtaining the soft ware plus pre programmed PICs and gen eral information on buying components for this PIC Controlled Intruder Alarm S Everyday Practical Electronics April 2002 ELECTRONICS TODAY INTERNATIONAL THE Meni MAGAZINE FOR ELECTRONICS TECHNOLOGY amp COMPUTER PROJECTS We can supply back issues of EPE by post most issues from the past three years are available An EPE index for the last five years is also available see order form Alternatively indexes are published in the December issue for that year Where we are unable to provide a back issue a photostat of any one article or one part of a BACK ISSUES series can be purchased for the same price Issues from Jan 2001 onwards are also available to download from www epemag com DEC 00 PROJECTS e PIC Monitored Dual PSU Part1 Static Field Detector Motorists Buzz Box Twinkling Star Christmas Bubble e Festive Fader e PlCtogram FEATURES e The Schmitt Trigger Part 2 Ingenuity Unlimited e Interface Circuit Surgery New Technology Update Quasar Kits Review Net Work The Internet e 2000 Annual Index JAN 01 PROJECTS Versatile Optical Trigger UFO Detector and Event Recorder Two Way Intercom PIC Monitored Dual PSU Part 2 FEATURES e Using PICs and Keypads The Schmitt Trigger Part 3 New Technology
167. mail Editor Mike says that we ll see what we can do about an ESR meter There is also a build yourself one in Supplement S57 of our sister publication Electronics Service Manual Stay reading good publications PIC SPECTRUM ANALYSER Dear EPE The PIC Spectrum Analyser is yet another really excellent project from John Becker how does he find the time I have been a PE and then EPE reader since the first one in 1964 when I was 14 and it real ly does lead all other publications in that it is fully informative has excellent projects includes all software to allow user modification which is what good projects are all about unlike your competition You keep a nice blend of starter through to high end type of projects such as this month s Spectrum Analyser I especially like the PIC projects as I use PICs throughout one constructive comment if I may I would really recommend using MPASM as it includes a good IDE text editor software emulation etc I know you can transfer from TASM but why re invent the development tools when Microchip provide them for free and update as necessary I fully appreciate the need to put the magazine on the web However in the future please do not stop the option of still purchasing it in its current form as a paper magazine can be carried around read on the bus train etc I know you can do a printout but it is not the same Stephen H Alsop via email Nice of you to offer
168. ment or sub circuits This voltage is a source of mains hum in hi fi components or mea surement errors in test equipment CIRCUIT 2 CIRCUIT 2 EARTH IN MAINS LEAD CONNECTION LEAD SIGNAL WIRE CONNECTION LEAD EARTH WIRE CIRCUIT 1 CIRCUIT 1 RG MAINS EARTH IN MAINS LEAD O MAINS EARTH HOUSE LAB EARTH WIRING Fig 2 A mains ground loop formed from a resistance in the wire Re Connecting an oscilloscope ground probe onto a regulator tab If a grounded power supply is being used care is need ed to ensure damage will not be caused by shorting any part of the circuit under test e g the regulator tab to the OV rail via the scope probe and earth 299 Hum Bug Two possible solutions to this problem were actually given by Gerard in his ques tion The first is to reduce the effective value of Rg by providing a very low resis tance path between the earth connections of the two circuits by linking the chassis or casings in this case The second is to break the loop by con necting only one of the circuits to mains earth in practice by disconnecting the Earth from one of the appliance s 3 pin plugs It might not always be recommend ed to disconnect an earth terminal in this way because of possible safety implica tions however a lot of equipment today is double insulated and runs from a twin core power cord with no separate earth being used anyway Gerard goes on to ask I don t know
169. microcontrollers will feature in future projects and indeed have featured in one or two past projects but we do not feel it is sensible to start investigating too many software languages and their intracacies We will stick to project building as our main area of interest and introduce the specialist PIC program ming areas where we can like this month s Programming PIC Interrupts article Having said that let me assure those readers who do not want to go down the chip programming route that we will continue to cater for them Not everything has to be programmed fascinating and versatile though this technology is So we have a varied content lined up for future issues including a wide range of easy to build projects using both simple transistor and simple digital i c circuitry VARIETY I think this issue is a good example of the variety of material we will continue to pub lish Even if you are not into programming your own chips John s PIC Controlled Intruder Alarm is an excellent and versatile project and as with virtually all our PIC based designs is one that can be built without the need to understand the programming just buy the pre programmed chip for an easy to build project Both the Solar Charge And Go and the Electric Guitar Tuner articles show the wide range of projects that can be built using very simple circuitry So why not drag out that soldering iron and get stuck in AVAILABILITY Copies of EPE are availabl
170. n any elec tronic circuit or system generate random noise means that there is always a certain level of noise even with no signal present This is known as the noise floor which is important because the circuit cannot mean ingfully process sensor signals that are smaller than the noise floor As the noise floor relates to noise within the circuit this is different from noise with in the input signal If the properties of the required signal are known there are tech niques which can extract signals that are smaller than noise present within the sig nal for example due to interference The random noise generated within elec tronic components and sensors is fundamen tally due to the discrete nature of electricity at the atomic level 1 e electric charge in cir cuits is carried in packets of fixed size on electrons Random noise may be classed according to the frequency or range of fre quencies present White noise has the same power throughout the frequency spectrum whereas 1 f noise or pink noise decreases in proportion to frequency For 1 f noise there is the same amount of noise power in the bandwidth of say 100Hz to IkHz are there is in 1kHz to 10kHz whereas for white noise there would be 10 times as much power in the bandwidth 1kHz to 10kHz as 100Hz to 1kHz because it is 10 times larger The difference between the signal and the noise is often of great importance This is expressed as the signal to noise ratio SN
171. n one direction in the windings hence the designation unipolar and this considerably simplifies identification The first step is to find the common lead or leads A six lead four phase unipolar motor has two common leads and these are most likely to be in the centre of two rows of three It is frequently used in print ers or fax machines A five lead motor has a single common lead This kind of motor is commonly used in 5 in disk drives We shall omit eight lead motors from our discussion here since these are far less common and their leads more difficult to identify COMMON LEAD It is easy to test with a multimeter which is the common lead If there are six leads measure the resis tances across every possible combination of leads e g green white green red white red but ignore any measure ments that indicate open circuit an infi nitely great resistance Which leads were always involved where the lowest resis tances were measured These are the com mon leads Twist or solder these two leads together into one Q MOTOR CONTROL 1 SEE TEXT Table 1 Wave Control Step A B C D 1 ON OFF OFF OFF 2 OFF ON OFF OFF 3 OFF OFF ON OFF 4 OFF OFF OFF ON In the case of five leads just one lead will be found to be consistently involved where the lowest resistances are measured This is the common lead IN CONTROL Most four phase unipolar stepper motors use a 12V power supply or there a
172. n the high to low transition Provided it is empty the transmitter register is loaded on the low to high transition As explained previously loading is delayed if this register is full and data in the transmitter register will not be over written by new data The same is not true of data in the buffer register so it is essen tial not to feed the circuit with data at an excessive rate The two status outputs of Everyday Practical Electronics April 2002 x1 BC549 2 4576MHz U R Fig 3 Circuit diagram for the Serial Transmitter Pulsing the Send input results in a byte of data being transmitted IC2 s transmitter section are available should they be needed but it is usually easier to have the control logic operating at a low enough speed to avoid any problems The serial output signal should be at nominal signal voltages of plus and minus 12V in order to guarantee that the circuit will drive the PC s serial port correctly However in practice most ser ial inputs will work reliably with nor mal 5V logic levels provided a short connecting cable is used In this circuit transistor TR2 is used as a simple invert ing buffer stage at the serial output of IC2 There are special chips that make life easier if proper line drivers and receivers are needed The circuit diagram of Fig 4 provides a simple line driver and a receiv er and the driver provides proper RS232C voltages The circuit is powered from a single
173. n which you can take better control of your email Spam or junk mail is getting worse all the time and readers are reminded that posting any message into Usenet is a surefire way of getting your email address onto spam mer s mailing lists so never use a critical work email address when posting into newsgroups unless you relish the taste of spam Various come on tactics are used to try to get you to read incom ing junk mail The subject line is the first thing you see so it may say Hi Here s the info you asked for 38954 the randomised number is there to beat any spam filters It is easy enough to filter out anything containing say a sign or the word mortgage but no matter how much you relish the challenge of configuring your mail s filtering rules unwanted mail is sometimes best dealt with by deleting it manually from the mailserver Everyday Practical Electronics April 2002 Theat Dee Serve Gur a pecial 8816 T of Hah wi ba of tere ee reed eco 198 6 coe puny design epee 999 merece oF titiis aiher Cur foes me feed bo deo eee rih he world Ues nui srera Ee gs faci 1 reete a brd buria by et oF aii CEL Dark ewes Deck eee md meis of Deedee Proc Deco EPEC con mew De bruy e se MME FS emia on peck ete CD Ode Yia ran alen f tsp EPE Bech bole buri caiie yei oi anama Ye Lai ee prime De oe fn pee he ee ee ee eee Er Vd ZT Kg LEZ 9 41 Ha T Aiai be il PLD ari Guilty pote tE Ha nE Kp mare EFE arsm la Mad
174. ndication of how much cur rent they can supply before the voltage fell to too low a level and it was time to recharge An individual 1 2V cell should be con sidered flat when its voltage has dropped to about 0 9V or so The term mA is sim ply short for milliamperes or 1 1 000 amp a measurement of current flow Putting your nine cells in series creates a 10 8V 2500mAh battery pack with a capacity of 2 5 amps for one hour Be Constant The general rule is to charge a NiCad battery with a constant current of capacity divided by 10 for a period of say 14 to 16 hours maximum You mentioned a manu facturer s rating of 165mA which sounds about right However I am very concerned about using the suggested 700mA battery charger as it sounds like a brutal fast charger One fast 2 hour charger in my possession is intended for eight AA cells at a time but when I measured the cell s tempera tures they were an astonishing 65 C which is 30 per cent higher than the battery s maximum rating the charger and batteries were way too hot I have had several fast chargers overheat and fail altogether tak ing the batteries with them Excessive temperature is a real killer of cells and overcharging can cause serious damage so matching your batteries charge current and time is very important and using an intelligent charger is recommend ed The better ones will cycle the batter ies properly by dischargin
175. ner featured here uses a very simple frequency comparison circuit that works just as well whether the input to the comparator is at the fundamental fre quency or a harmonic This avoids the need for any signal processing other than a sim ple input amplifier The display is just a single l e d light emitting diode that flashes at a rate equal to the difference between the guitar s fre quency and the correct frequency Correct tuning is therefore indicated by a steady state from the l e d indicator The unit is powered from a small 9V battery and it is fully portable This project is simple enough to be tack led by a complete beginner at electronic project construction No test equipment is AMPLIFIER OUTPUT OSCILLATOR OUTPUT AMPLIFIER OUTPUT OSCILLATOR OUTPUT AMPLIFIER OUTPUT OSCILLATOR OUTPUT AMPLIFIER OUTPUT OSCILLATOR OUTPUT needed to set up the finished unit but an accurately tuned instrument or pitch pipes are needed to provide reference frequencies HOW IT WORKS The block diagram for the Electric Guitar Tuner project appears in Fig l and as will be apparent from this the circuit is basically just an amplifier and an audio oscillator An l e d is connected between the outputs of these two stages The ampli fier has a high level of voltage gain so that its output signal will normally be a square wave signal The audio oscillator also has an output waveform that is more or less squa
176. ning of lights or vents the manual rotation of the hands of a wall mounted clock or the remote control of robots and robotic toys CIRCUIT THEORY A four phase unipolar stepper motor may typically be controlled in four differ ent ways all of which have advantages and disadvantages Wave control This is the simplest form of control as it energises only one winding or phase at a time Its main drawback is poor torque Full step control This is a simple means of control with good torque util ising two windings of the motor at a time Half step control This is a more com plex form of control combining wave control with full step control it there fore has twice as many steps It has good torque and stabilises motor oper ation However it is not suitable for our purposes here above all for its loss of torque under manual control Micro stepping control This is a com plex form of control with sophisticated circuitry which enables countless in between in between steps and great precision It is frequently used in industry The method of control which best suits our purposes here is full step control since it is both easy to implement and has good torque This requires a 4 bit binary control sequence to be shifted right or left across a stepper motor s leads A single pole four way rotary switch would accomplish this task with the help of eight multiplexing diodes Howe
177. nisable as logic 1 In Fig 4b with the sensor in a normal ly closed condition the voltage at the junction of the 100k and 47k resistors is recognisable as logic 1 see previous para graph If a zone is intruded the sensor s contacts open and the voltage fed to the PIC falls to OV The 1k resistor in the chain protects the 12V power line in the event of the sensor s cable being cut and shorted to OV It was felt to be unreasonable to attempt to protect the system against very high voltages being maliciously applied across sensor cables Several sensors may be used in each zone For a normally open zone they must the S drive a load such as a relay or solenoid consequently it could be used to activate an automatic door latch such as the type used in response to inter NORMALLY CLOSED SENSORS ARE WIRED IN SERIES be wired in parallel Fig 4c For a normal ly closed zone they must be wired in series Fig 4d Do not mix normally open and normal ly closed sensors in the same zone KEYPADS The first of the keypads S1 is for keyed control of the total alarm system including responding to a unique PIN code when keyed in rejecting any code that is not recognised Facilities for a second optional keypad S2 have been included following a read er s request During development of this alarm system David Mynatt of Manchaca Texas emailed us to say that he wished to instal a system that would allow his pre s
178. nput power 4 5Watts output power 2 5W Wasted power 2W efficiency 2 5 4 5 55 If the input is 12V then the input power 6W the wasted power is 3 5W and the efficiency falls to 42 The wasted power is dissipated as heat and so the regulator must be mounted on a heatsink Switch mode power supplies SMPSUs convert one voltage to another voltage much more efficiently Under the right conditions they can draw less current at a higher voltage than they supply to the load at lower volt age In the past switch mode supplies have been extremely tricky devices to use requiring specialist knowledge but now several manufacturers pro duce switch mode chips which have everything needed to make switch mode converters The datasheets for these devices give very good applica tion data to assist designers and some manufacturers even give out soft INPUT CURRENT LIMIT COLLECTOR EMITTER ware to design the whole circuit according to user input parameters As an example the circuit diagram of Fig l is based on National Semiconductor s LM3578 switch mode con verter The entire circuit costs about half as much as a 9V PP3 alkaline battery The cir cuit s efficiency is summarised below Output 5V 180mA Input 9V 14ImA efficiency 71 Output SV 360mA Input 9V 290mA efficiency 69 Output 5V 540mA Input 9V 450mA efficiency 67 Output 5V 720mA Input 9V 620mA efficiency 65 Output 5V 180mA Input 12V 108mA
179. nterrupt LASTH is zero BTFSS STATUS Z GOTO A5 BTESS STATUS C gt so OK GOTO FAIL and there are specialist cases when this might have uses However setting GIE in an ISR would invalidate some of the tech niques discussed in this article e g Context preserving The PIC is not well suited to writing re entrant code as it lacks any support for structures such as dynamic data stacks which would be needed This article is not going there and readers are strongly advised not to either EXPERIMENT 4 INTPROG6 uses the PIC s internal timer to generate interrupts at quite a high rate about 5kHz though not so fast that it causes looping in the ISR Each time the ISR is entered it bumps increments a counter which is 16 bits 2 bytes long because a 1 byte counter would overflow very quickly The program s main loop monitors and checks this counter Because of the high interrupt rate it is possible that the main loop is interrupted several times each iteration so the counts it reads are not necessarily contiguous Therefore the check is that the value just read is greater than the value read on the previ ous loop It does this by subtracting the previous value from the current value If the result of the subtraction is not positive or zero then something has gone wrong If a counter error is found the main loop loopstops with the l e d fully illuminat ed Of course the 16 bit counter will 292
180. nto COUNTH The program then checks the value H 1234 which will be found to be at least as large as the previous value The last value INCF ISRCL F BTFSC STATUS Z INCF ISRCH F bump interrupt count low byte test if it wrapped to zero skip if not bump high byte if low byte wrapped MOVLW INTTMR MOVWE TMRO BCF INTCON TOIF SWAPE SAVES W MOVWE STATUS SWAPE SAVEW F SWAPF SAVEW W reset the timer clear the interrupt restore STATUS restore W gt exit ISR will be set at H 1234 and the next iteration will read the value H 1235 or larger which will also check out successfully But now consider what will happen if ISRCL and ISRCH contain not an arbi trary value but one where the low byte is just about to wrap e g H 12FF COUNTL will be copied as H FF Now the ISR runs and ISRCH L are bumped to be H 1300 So COUNTH is copied as H 13 The main loop checks that H 13FF is greater than the last value it read some thing like H 12FE maybe and indeed it will be But it will set the last value read to H 13FP On the next iteration it will read some thing like H 1300 or H 1301 but unless there have been 256 or more interrupts during one iteration of the main loop which can t happen with the parameters of Experiment 4 then it will read a value less than the last one it has stored This is what is happening to INT PROG6 i
181. nts and engineers SHOPTALK with David Barrington 290 The essential guide to component buying for EPE projects PLEASE TAKE NOTE PIC Virus Zapper Dog and Cat Scarer I U 290 DIRECT BOOK SERVICE 296 A wide range of technical books available by mail order plus more CD ROMs PRINTED CIRCUIT BOARD AND SOFTWARE SERVICE 301 Wimborne Publishing Ltd 2002 Copyright in all PCBs for EPE projects Plus EPE software drawings photographs and articles published in EVERYDAY PRACTICAL ELECTRONICS is fully ADVERTISERS INDEX 304 tected and ducti imitations in whol in part are expressly forbidden n P FREE GIANT OP AMP DATA CHART Between pages 264 265 Our May 2002 issue will be published on Thursday 11 April 2002 See page 227 for details Readers Services Editorial and Advertisement Departments 235 Everyday Practical Electronics April 2002 225 NEXT MONTH PIC BIG DIGIT DISPLAY RECENTLY Display Electronics acquired several thousand individual electromechanical big digits These had previously graced the platforms of British Rail in 6 digit 7 segment clocks The digits measure 12in high Yin wide and 2 25in deep 30 5cm x 23cm x 5 5cm The angled display area is effectively 10in high x 7in wide 25 5cm x 18cm and comprises seven bright yellow hinged segments This EPE design provides a versatile interface that can control the digits It is capable of driving from one to eight digits with expansion up to 64 digits p
182. nts of almost 0 5A Finally the control circuitry may be fitted into a suitable case The specified case allows the stripboard to be slotted into place so that l e d s D9 and D10 protrude through the front panel see photographs IN USE All that remains is to apply power 12V 500mA and turn the rotary Motor Control switch All being well the stepper motor will turn with it Do not reverse the power supply polar ity Whilst reverse voltages hold little OSCILLOSCOPES GOULD OS300 Dual Trace 2OMHz Tested with Manual TEKTRONIX TDS350 dual trace 200MHz 1G S Unused 1500 TEKTRONIX TDS 320 dual trace 100MHz 500M S c MANUAL STEPPER MOTOR CONTROLLER Power input socket is located in the rear of the case Top left Using a crimp terminal and header plug socket to connect the motor to the circuit board Left The small glass encapsulated reed switch danger for the stepper motor which would simply refuse to turn it could severely damage capacitor Cl Although most 12V unipolar stepper motors are rated 12V continuous they may generate an uncomfortable amount of heat If full torque is not required a simple solu tion is to insert a 15 ohm 10W or other suit able resistor in one of the supply lines The pull of a small four phase unipolar stepper motor is fairly strong between the fingers and such motors could find many uses all for an outlay which is many times less than that of a typical st
183. o Dec 2000 all the projects features 1 Please send me quantity BACK ISSUES CD ROM VOL 3 news lUS etc from all six issues PROJECT CODES All the available l Please send me quantity BACK ISSUES CD ROM VOL 3 I I I l I l l l l l I l I I codes for the programmable projects in these issues Please send me quantity BACK ISSUES CD ROM VOL 5 VOL 5 CONTENTS Price 12 45 each includes postage to anywhere in the world BACK ISSUES January 2001 to June 2001 all the projects features news lUS etc from all six issues PROJECT CODES All the available codes for the programmable projects in these issues including those for Interface AdAESS chase cases wataeehoneake bw oe bea ee Koes on oS l EXTRA ARTICLES ON ALL VOLUMES R BASIC SOLDERING GUIDE Alan Winstanley s internationally l E eee O ee Post Code l acclaimed fully illustrated guide i i UNDERSTANDING PASSIVE COMPONENTS Introduction to the I enclose cheque P O bank draft to the value of I basic principles of passive components I I HOW TO USE INTELLIGENT L C Ds By Julyan Ilett An utterly practi l _ Please charge my Visa Mastercard Amex l cal guide to interfacing and programming intelligent liquid crystal display Diners Club Switch i modules l PhyzzyB COMPUTERS BONUS ARTICLE 1 Signed and Unsigned Binary Numbers By Clive Max Maxfield and Alvin Brown PhyzzyB COMPUTERS BONUS ARTICLE 2
184. ome extent and as high as some 3 3V that is 1 65V per cell which is the approximate voltage devel oped by new cells The supply at socket SK2 should therefore operate the cassette player correctly MODIFIED READING Returning to meter MEI the specified unit has a full scale deflection of 100UA yet the maximum current in the circuit is likely to exceed 100mA The full scale reading therefore needs to be modified and this is the purpose of shunt resistor R1 A shunt is a low value resistor which allows most of the current to flow through itself and only a small amount through the meter By choosing a suitable value it can be arranged for a total current of say 120mA rather more than the maximum delivered by the solar panels to allow 100uA to flow through the meter and so give a full scale reading The value of the resistor required depends on the basic full scale deflection f s d of the meter and its resistance The specified unit has a resistance of 1750 ohms Calculation shows that for a full scale deflection of 120mA a suitable value for the shunt resistor is 1 5 ohms The value may be modified to make it suitable for other meters and solar panels This can be done by trial and error and is described at the end When switch S2 is in the backup posi tion S2a connects the reserve supply to socket SK1 At the same time S2b contacts connect backup 1 e d D3 in circuit with current limited by resis
185. on Some guitar pickups produce much higher output levels than others and the closed loop voltage gain of ICI has therefore been set very high so that strong clipping is produced at the output even when it is used with a low output pickup Negative feedback resistors R4 and R5 set the voltage gain at just over 60dB 1000 times Resistors R1 and R2 bias the input of the amplifier and set the input impedance at just under 20 kilohms 20k This produces a good match for most gui tar pickups The oscillator uses IC2 in the standard 555 oscillator mode A low power version of the 555 timer i c is used in order to keep the battery drain quite low and the total current consumption of the circuit is only about 8mA Fig 3 Complete circuit diagram for the Electric Guitar Tuner switched on continuously It is at less than full brightness but it is much brighter than with the signals 90 degrees out of phase The drive current is set high enough to give reasonable brightness with the l e d switched on for 50 per cent of the time In the final pair of waveforms the sig nals are 270 degrees out of phase and the l e d is again switched on for 25 per cent of the time A further phase shift of 90 degrees would take things back to the beginning with the signals in phase and the l e d switched off With the guitar slightly off tune so that there is a small mismatch in the two fre quencies the output signals gradually slip in and out of
186. on gates which are used in almost every digital circuit plus Binary notation Order Code VT301 VT302 55 minutes Digital Two Flip Flops will further enhance your knowledge of digital basics You will learn about Octal and Hexadecimal notation groups flip flops counters etc Order Code VT302 VT303 54 minutes Digital Three Registers and Displays is your next step in obtaining a solid understanding of the basic circuits found in today s digital designs Gets into multiplexers registers display devices etc Order Code VT303 VT304 59 minutes Digital Four DAC and ADC shows you how the computer is able to communicate with the real world You will learn about digital to analogue and ana logue to digital converter circuits Order Code VT304 VT305 56 minutes Digital Five Memory Devices introduces you to the technology used in many of today s memory devices You will learn all about ROM devices and then proceed into PROM EPROM EEPROM SRAM DRAM and MBM devices Order Code VT305 VT306 56 minutes Digital Six The CPU gives you a thorough understanding in the basics of the central processing unit and the input output circuits used to make the system work Order Code VT306 ORDERING Price includes postage to anywhere in the world OVERSEAS ORDERS We use the VAT portion of the price to pay for airmail postage and packing wherever you live in the world Just send 34 95 per tape All payments in sterling only sen
187. on the positive one in each case The photograph shows the completed inte rior of the prototype unit BATTERY HOLDER To charge the mobile phone battery you will need to make a small separate unit which will allow the connections to be made to it The photograph shows a Nokia 3210 battery but the exact details will depend on the unit used and will need to be modified with regard to its dimensions and the position of the terminals The unit is made from a thin plastic box rather larger than the size of the battery Place the battery on the top panel and draw round its outline Mark the position of the six circular plastic p c b spacers 5mm long or as appropriate which act as location pegs They should be positioned so that when attached the battery is held firmly When satisfied about the positions drill the holes and attach the spacers Check that the battery will locate accurately and make adjustments as necessary Remove the bat tery measure and mark the position of its terminals and make a small slot in the lid to correspond MAKING CONTACT Contact with the battery terminals may be made in various ways However there should be some form of spring loading to ensure reliable contact In the prototype unit two sub miniature lever arm microswitches were used It was only the spring action and ease of mount ing which was required not the actual switches The levers were carefully bent through right angles to pro
188. onal 4000 series logic chips The circuit is based around two 4026 7 segment display drivers IC2 and IC3 and their accompanying 7 segment common cath ode l e d displays X1 and X2 When the Draw switch S1 is pressed the output pin 3 from the NE555 astable multivibrator IC1 is fed into the input of IC2 The frequency of ICI is controlled by resistors R1 R2 and capacitor Cl which can be changed as desired Resistor R3 holds the clock input of IC2 low when S1 is open in order to prevent any false triggering The carry out output pin 5 of IC2 is fed to the clock input of IC3 pin 1 and also the input pin 14 of IC4 a 4017 decade counter This chip is configured to reset IC3 when the display reaches 50 i e X1 shows 5 Therefore when switch S1 is opened a random number between 00 and 49 inclusive is displayed The only minor problem with this circuit is that the number OO cannot of course be used for the national lottery in this case the number DISPLAY ENABLE E CAARY OUT f sl CLOCK INHIBIT w IC2 Fig 2 Circuit diagram for the Lottery Predictor should be discarded and another one chosen The circuit can run from a standard 9V bat tery or a mains adaptor If desired the con figuration of C4 can be altered to allow a number between 0 10 0 20 0 30 etc to be selected Although this circuit was designed to choose winning numbers the author confess es that he has yet to actually w
189. ople are also more familiar with TASM That s why my TK3 caters for both dialects it s also faster than I find Microchip s program to be There s room for many PIC dialects and readers no doubt choose the ones that are best suited to themselves Many readers much prefer to write PIC programs in C for example We thoroughly share your view that EPE should continue to be paper based SOLDERING Dear EPE I found your web site on soldering and I think its great Tm a novice to this and I fix Playstations I have a 30W iron but I seem to have a bad habit of scorching the circuit boards and once I accidentally removed a transistor that I wasn t supposed to from the heat of the iron I m wondering if I should go to a lower wattage iron or if there is something else I m doing wrong Although I just found out my mistake in using the iron to move the solder I also have no stand for the iron I use a metal plate but I do use flux Angela Mcgann via email Circuit Surgeon Alan is our soldering guru and replies 30 watts is a little on the high side especially if it s not temperature controlled It s not too bad but 15 watts would be fine for delicate Playstation type work I used a 15W iron for years till I could afford a proper soldering station A cheap stand would be a good idea Electronics solder already contains its own flux and you must NEVER add flux separately espe cially acid flux that e g plumb
190. or the ISR to read PORTB to latch the changed value in order to clear the RBIF flag but we glossed over what would happen if this was not done Another ISR loop is the answer The PIC will continue to assert RBIF while it detects that there has been a change even if software tries to clear it and so the ISR will be called continually So if you do have a play with interrupts and find that you have an apparently dead PIC on your hands check to see whether an ISR loop could be the cause RE ENTRANCY Readers who have followed the plot so far may be wondering if interrupt events are happening faster than the ISR can process them is the ISR itself interrupted when the next interrupt event occurs The answer is no almost When the PIC takes an interrupt and transfers control to Location 4 as part of this procedure it also clears the GIE bit Thus although the interrupt events still occur and the flag bit s still get set no fur ther interrupts can be caused The RETFIE instruction used to exit from the ISR sets the GIE bit again So under normal circumstances the ISR is not re entered if another interrupt occurs while it is being executed It would be possible for an ISR to set the GIE bit and so potentially be re entered 291 LISTING 6 Section of INTPROGGE MOVE COUNTL W MOVWE LASTL MOVF COUNTH W MOVWE LASTH INCF LOOPCT F Interrupt setup AS copy this counter to last counter MOVLW INTTMR set the timer
191. orders Video Recorders Personal Computers etc TECHNICAL NOTES Commencing with the IBM PC this section and the regular Supplements deal with a very wide range of specific types of equipment radios TVs cassette recorders amplifiers video recorders etc REFERENCE DATA Detailing vital parameters for Diodes Small Signal Transistors Power Transistors Thyristors Triacs and Field Effect Transistors Supplements include Operational Amplifiers Logic Circuits Optoelectronic Devices etc ELECTRONICS SERVICE MANUAL ESM Printed version only Basic Work Contains around 900 pages of information Edited by Mike Tooley BA Regular Supplements Unlike a book or encyclopedia this Manual is a living work continuously extended with new material If requested Supplements are sent to you on approval approximately every three months Each Supplement contains around 160 pages all for only 23 50 2 50 p amp p You can of course return any Supplement within ten days which you feel is superfluous to your needs You can also purchase a range of past Supplements to extend your Base Manual on subjects of particular interest to you Presentation Durable looseleaf system in large A4 format Price of the Basic Work 39 95 SALE PRICE 24 95 to include a recent Supplement FREE Offer ends May 31st 2002 Our 30 day money back guarantee gives you complete peace of mind If you are not entirely happy with the Electronics Service M
192. ossible They can be controlled via a standard 4 x 4 data entry keypad or via a PC compatible computer running under MS DOS or Win95 98 ME A PIC 16F84 microcontroller is the controlling device between the PC or keypad and the multiplexed digits The PC software is written in QBasic QuickBASIC but can be run as a stand alone program without the need for QB to be installed The digits are ideal for use in any situation that requires a large electronically controlled display where the data is to be input intermittently Applications that come to mind are sporting score boards ticket draw results display of outdoor temperature in public arenas well you ve seen where large digits can be used think up your own applications NEW SERIES SIMPLE AUDIO CIRCUITS A selection of practical pick n mix low cost audio circuits Part 1 describes six different power amplifiers using five different i c s Part 2 covers pre amplifiers tone control and filters with seven different projects whilst Part 3 is all about power supplies loudspeakers crossover networks and filters Finally Part 4 describes loudspeaker enclosures and includes practical designs for a simple low frequency tuning oscillator and a resonance detector Seventeen different p c b designs providing dozens of project combinations all with full constructional details WASHING READY INDICATOR This little unit will tell you when the washing machine has finished its cyc
193. ou a small fortune Circuits include video enhancer improved video enhancer video fader horizontal wiper improved video wiper negative video unit fade to grey unit black and white keyer vertical wiper audio mixer stereo headphone amplifier dynamic noise reducer automatic fader pushbut ton fader computer control interface 12 volt mains power supply co ele H od Om k L 10 95 124 pages PC MUSIC THE EASY GUIDE Robin Vincent How do make music on my PC Can record music onto my PC What s a sequencer How can get my PC to print a music score What sort of a soundcard do need What hardware and software do need How do connect a key board to my PC Just a few of the questions you ve probably asked Well you ll find the answers to all these questions and many more in this book It will show you what can be done what it all means and what you will need to start creating your own music on your PC It s an easy read it s fully illustrated and it will help you understand how a computer can be used as a creative music tool It covers soundcards sequencers hard disk digital audio recording and editing plug ins printing scores with notation software using your PC as a synthesiser getting music onto and off the Internet using Windows sample PC music set ups FAQs a glossary advice on hardware and software and a list of industry contacts 116 pages Order code PC117 11 95 HIGH POW
194. own 1 Change main PIN code 2 Change entry exit time time out 3 Set zone to be regarded as the sole main entry exit point 4 Set zones required to be monitored when the alarm is active 5 Set bell on time between 1 and 20 minutes 6 Automatically assess zones for sensor status normally open or normally closed 7 Display normal zone logic sensors n o or n c for information only 8 Select second PIN code as required for second optional keypad 9 Set entry time for zone covered by second keypad decimal point Set passive mode in which any zone entry is displayed and a buzzer sounded terminated when zone entry ceases When new data has been keyed in press D to store it in the data EEPROM con firmed by STORED appearing and a return to SELECT MODE All modes except Passive see later may be exited by pressing the blank key but any changed data is NOT stored if you do so Having escaped from a mode or hav ing completed any changes permitted by it and stored them by pressing D the screen returns to displaying SELECT MODE and another mode selection can be made Pressing the blank key when SELECT MODE is shown fully exits the mode selection facility followed by ALL OFF again being displayed It is necessary to key in your main PIN code keypad 1 to re enter the mode selection facility Next time a data mode is entered the data displayed is that previously keyed in and s
195. path were still pointing to drive C The way I got around this was to insert the following two statements in the TK3MainProgram Form Load sub after the third line ChDrive App Path Change to the drive on which the application is running ChDir App Path Change to the application s directory This change allowed the program to be loaded on either drive and to run in that drive provided that there was a copy of the program on the respective drive There is more information in VB help under App There was also a problem when trying to change drive from within the TK3 Check Toolkit PCB Functions screen Changing to drive A was OK but trying to change back to C or D gave Runtime error 76 Path not found This I even tually traced to the fact that Drivel Drive in the case of hard drives returns both the drive and its label The solution seems to be to change the first line in TK3CheckToolkit sub Drivel_Change to DefaultDrive Left Ucase Drivel Drive 2 amp thus picking up only the drive letter and not the Volume id There is information in VB help under DriveListBox control drive property and then scan to Fixed Media Thank you for pointing out the existence of NoteTab I have not used it very much as yet but it seems to be just what is wanted Now the main point of my visit to your site was to see if there was any help about running TK3 under Windows XP I found your compila tion notes on the s
196. poll multiple mailboxes at once Remember that you re dealing directly with the mailserver so if you want to keep any correspondence you must save it out as a file Any mail deleted from the server is gone for ever if you save that session when exiting the software It can be ideal for firing off quick replies in real time rather than using your regular offline mail client You can contact the writer at alan epemag co uk Ei BII Eon Plus 3 0 Fie Help Li Account POPS options Send aras Fiters Gisbai Fil in account data name and rave profile top ol windoz chek Connect Heb Connect Boll Pol al F ifotava polie on Connect T Enter only i mabor was modiied POPS host mailserver tom Farot manna Kp JBMail Version 3 now has a built in address book and other improvements 213 Constructional Project MANUAL STEPPER MOTOR CONTROLLER THOMAS SCARBOROUGH Keep in step with this novel low cost controler HIGH SCHOOL student recently con A the author for help in building a robotic arm for a school project He had some stepper motors on hand and was looking for a simple way to utilise them Unfortunately there didn t seem to be any really simple way to do it nor could the author find any published design to help at least not any that fitted the description of simplicity itself A typical stepper motor control system incorporates a microprocessor contro
197. portant You generally cannot put much debug into an ISR without disrupting things so much that your prob lem is masked or changes or simply can t be reproduced Bugs in the ISR will tend to produce symptoms varying from the just strange to the totally bizarre clear the interrupt test INTE not a timer interrupt bump clocks wrapped count clear the interrupt restore STATUS restore W gt exit ISR By far the best approach is to keep ISRs short sweet and above all simple so that you don t create problems in the first place Prevention is much much better than cure here A good ISR should do the following and only the following save Context establish its own Context test the flags thoroughly to be sure which event s have occurred increment a counter or two maybe set a Boolean flag to record that it has run take emergency action only e g if an endstop microswitch has been triggered turn off the motor clear the interrupt s that have occurred restore Context exit STACK The mechanism used by the PIC when the ISR is entered is rather like a CALL instruction The address of the next instruction to be executed when the ISR exits is pushed onto the Stack and popped from the Stack by the RETFIE instruction Everyday Practical Electronics April 2002 So it is worth noting that if you use inter rupts you effectively lose one level of Stack That won t affect mo
198. possible problems with earthing on supplies and test equipment one relates to interference and measure ment accuracy which we will return to ina moment The other problem relates to the possibility of short circuits An oscilloscope probe will usually have its outer wire screen connected directly to the chassis and therefore to the mains Earth This means that if you clip the scope probe ground anywhere in a circuit you will connect that part of the circuit directly to mains earth In the USA and elsewhere the term ground is used instead of earth If the power supply OV rail is also grounded to mains earth in the apparatus then the oscilloscope probe s ground ter minal will cause that part of the circuit to be shorted to the circuit s OV rail affecting its operation or even damaging it see SCOPE PROBE GROUND CONNECTION J IS AT OV Fig 1 A grounded OV connection can affect circuits under test sometimes a floating supply is preferable Everyday Practical Electronics April 2002 CIRCUIT Fig 1 If the power supply output is float ing or isolated so that there is no d c path to mains earth then connecting a single scope ground should not cause a short Ground Loops The interference problem is caused by earth loops Gerard also asked us to explain this commenting Why was it sometimes necessary to link the casings of one s stereo deck and amplifier together I think I wa
199. ppen This provides a reasonably stable supply to charge the phone battery The value of resistor R4 is chosen according to whether a 2 4V or a 3 6V bat tery is being charged This limits the cur rent to a reasonable value In the prototype unit this was some 50mA to 60mA This is kept on the low side on purpose to prevent damage 287 WIRED FOR SOUND Approx Cost A personal cassette player is operated by Guidance Only 29 plugging it into socket SK2 The unit receives some current from the solar panels which is then topped up by battery pack B1 If the ambient light level is low say at night all the current is supplied by the batteries The current flows through fuse FS1 and diode D4 In the event of a short circuit re chargeable cells can deliver a very large current and this could cause the wiring to become hot and possibly for the insulation to burn The fuse FS1 is included to pre vent this happening Since the nickel metal hydride cells B1 lock the voltage appearing across them to 4 1V there will be some 34V available at output socket SK2 taking into account the forward voltage drop of diode D4 However this falls to 3V or less 2 6V in the prototype unit under the load of the cassette player Equipment normally powered using two AA size cells should be designed to oper ate with an applied voltage as low as 2 4V or less allowing it to be used when the bat teries have run down to s
200. pplied and got the job of development engineer I was designing and 32 BIT OUTPUT Dear EPE Just want to say great magazine the Toolkit Mk3 TK3 project is so exciting I just had to sign up for an Online subscription after buy ing my first paper edition here in the States Great service I also want to direct a comment to Robert Penfold on his 32 bit Output Port project Interface Oct 01 using the UCN5818AF As he mentioned this chip was designed for fluo rescent displays but I want to add that this chip also opens up exciting possibilities for designing nixie tube projects you remember nixie tubes those orange neon numeric display tubes so pop ular for a brief time before l e d s came out Before this chip and those like it were avail able either high voltage transistors 10 per tube or the ultra illusive and high power 7441 i c s were needed to pull the high voltage cathodes down to light the numerals The 5818 not only provides this ability but its simple serial inter face makes it a snap to design a nixie display or 282 building specialised interfaces for Data General Nova and Eclipse computers using TTL logic The small team that I was the elec tronics part of received a Technical Oscar from the American Motion Picture Academy and an award from the British Kinematograph Sound and Television Society Unfortunately I developed an allergy to film processing chemicals and had to get out After s
201. projects Version 3 includes data and circuit modules for a range of popular PICs includes PICAXE circuits the system which enables a PIC to be programmed without a programmer and without removing it from the circuit Shows where to obtain free software downloads to enable BASIC programming Essential information for anyone undertaking GCSE or A level electronics or technology and for hobbyists who want to get to grips with project design Over seventy different Input Processor and Output modules are illustrated and fully described together with detailed information on construction fault finding and components including circuit symbols pinouts power supplies decoupling etc Single User 19 95 inc VAT Multiple User 34 plus VAT UK and EU customers add VAT at 17 5 to plus VAT prices Minimum system requirements for these CD ROMs Pentium PC CD ROM drive 32MB RAM 10MB hard disk space Windows 95 98 NT 2000 ME XP mouse sound card web browser pee eee ee eee ee ee ee ee ee eee eee Please send me CD ROM ORDER FORM ORDERING l Electronic Projects Note The software on each C Analogue Electronics Version required version is the same unless ALL PRICES INCLUDE UK Digital Electronics V2 0 C Hobbyist Student are e the POSTAGE l L Filters L Institutional l L Digital Works 3 0 O Institutional 10 user Student Single User Standard Version i L Electronics CAD Pack O Institutional VISA vaste C
202. ptional slave keypad with separate PIN for addi tional access to a selected zone Inherently stable and most unlikely to be triggered except via the installed sensors Inexpensive to construct R3 TO R6 10k TO D3 D4 RM2 1k Santee PSP4 RD4 PSP5 RD5 PSP6 RD6 INT BUZZER EXT STROBE EXTe BEER REO ANS5 RD RE1 AN6 WR RE2 AN7 CS PSP7 RD7 SDI SDA RC4 SDO RC5 TX CK RC6 D1 CONTRAST 1N4148 C1 RX DT RC7 MATRIX 10p INT RBO OSC1 CLKIN X1 3 2768MHz ie PIC16F877 4P C2 RB1 RB2 PGM RB3 RB4 UNALLOCATED OUTPUT 39 UNDER S2 CONTROL PGCLK RB6 OSC2 CLKOUT PGDA RB7 OV Vpp DATA CLK PROGRAMMER Fig 1 Main control unit for the PIC Controlled Intruder Alarm Everyday Practical Electronics April 2002 261 Immediate Panic Port pin RB4 can be used as an alterna tive to using one of the eight main zones for Panic switch monitoring The pin is used in input mode internal pull up acti vated and when Panic switch S3 is pressed to short this pin to the OV line an interrupt is generated in the PIC and a flag is set In response to this flag the software trig gers the full alarm system bell strobe and buzzer see Unauthorised Entry later This occurs whether or not the rest of the alarm is in active or passive mode The flag is then reset The bell on time is subject to the nor mal bell on time out but also see later Timing The PIC is operated at 3 2768
203. quency of 15kHz could be totally useless even open circuit if test ed at that frequency It should be pointed out that a fresh new capacitor does not exhibit this phenomenon to such a large degree it may only fall in capaci tance by a few microfarads Old worn capacitors are also very temperature dependant such a capacitor may test OK at room temperature but cool it down with a can of freezer and it can fall to zero While your design may be good in prin cipal it cannot be considered as an accurate test to apply to an electrolytic capacitor A much better test to apply to an electrolytic capacitor is to measure the capacitor s effective series resistance ESR in ohms using a special ist tester This test is usually applied by the tester at a frequency of 100kHz and is a measure of the capacitor s goodness The test is applied to the capacitor in circuit and can give an early indica tion of capacitor failure In my job as a TV video engineer I quite often find that a faulty electrolytic removed from a switchmode power supply can read OK when checked on my professional digital capacitance meter In circuit capacitor ESR testers are readi ly available from various sources from around 130 Once you ve used one you will wonder how you ever managed without it Perhaps you should consider an ESR meter project Incidentally I started reading your magazine in 1976 at the age of 11 Michael Dranfield Buxton Derbys via e
204. qvA Where n number of charge carriers per unit volume A cross sectional area of the wafer q charge on an electron v average velocity of the charge car riers through the wafer If we apply a magnetic field By the charge carriers experience a force caus ing the carriers to move towards one side of the wafer e g the top leaving a deficit on the other side This creates an electric field E which creates another force on the carriers which Fig 6 17 The Hall effect principle opposes the force caused by the mag netic field An equilibrium occurs when these two forces are equal i e the force due to the electric field F E q and the force due to the magnetic field Fz Byqv so E Byv The resulting voltage V is V Ezd Byvd Byl d ngA where d is the thickness of the wafer In other words V is proportional to Byly which has a significant effect on the magnet Table 6 1 Honeywell SS400 Series of Digital Hall Effect Sensors ic field inside the vehicle If the compass is SS411A SS413A SS441A SS443A SS449A fixed in the car then the magnetic field effect Type Bipolar Bipolar Unipolar Unipolar Unipolar is approximated by a shift in the Earth s magnetic field and if this shift can be deter Supply Voltage 3 8V to 30V 3 8V to 30V 3 8V to 30V 3 8V to 30V 3 8V to 30V mined it can be cancelled Max Supply Current 10mA 10mA 10mA 10mA 10mA The offset strap is used to perform this Max Output Voltag
205. r East amp Australasia GRS each 40 Gach l _ Please charge my Visa Mastercard Amex Diners Club Switch Switch Issue No Rest of World 26 each 48each_ I I I I the world Each ESM weighs about 4kg when packed L a oy me ee ee e H mm ee i a r t en em bn r r en e pe d mem cd IZ AL LOT ELECTRONICS TODAY INTERNATIONAL THEE Ha hr Editorial Offices EVERYDAY PRACTICAL ELECTRONICS EDITORIAL WIMBORNE PUBLISHING LTD 408 WIMBORNE ROAD EAST FERNDOWN DORSET BH22 9ND Phone 01202 873872 Fax 01202 874562 Email epe wimborne co uk Web Site http www epemag wimborne co uk EPE Online www epemag com EPE Online Shop www epemag wimborne co uk shopdoor htm See notes on Readers Enquiries below we regret lengthy technical enquiries cannot be answered over the telephone Advertisement Offices EVERYDAY PRACTICAL ELECTRONICS ADVERTISEMENTS MILL LODGE MILL LANE VOL 31 No 4 APRIL 2002 THORPE LE SOKEN ESSEX C016 OED Phone Fax 01255 861161 Email epeads aol com WAY TO GO With so many developments in both electronics and computing plus the combination of these areas to allow such things as microcontroller programming etc it s more and more difficult to try to keep EPE on track in our major areas of interest Should we do more on programming languages and on programming microcontrollers from ranges other than the PIC devices from Microchip There is no doubt that other
206. r Motor Controller project A good range of low voltage stepper motors are stocked by Magenta amp 01283 565435 or www magenta2000 co uk The 4 way 3 pole rotary switch MUST be a make before break type The one in the model came from RS see earlier code 320 736 PLEASE TAKE NOTE PIC Virus Zapper Mar 02 Page 187 Fig 7 and components list It has come to light that the PIC Virus Zappers voltage regulator IC1 has the wrong type number two digits being transposed it should be LP2950CZ If any readers have trouble finding this device it is listed by ESR Components Tel 0191 251 4363 or http Awww esr co uk code LP2950CZ 5 0 Rapid Electronics Tel 01206 751166 code 82 0680 and Farnell Tel 0113 263 6311 code 412 478 also stock this device Mar 02 Dog and Cat Scarer Ingenuity Unlimited Page 163 Fig 2 The output pin 3 and the trigger pin 2 designations of IC2 should be swapped over 290 Special Feature PROGRAMMING PIC INTERRUPTS MALCOLM WILES How to use Interrupts successfully with your PIC programs concepts of using interrupts and showed a simple circuit using a PIC16F84 which would allow you to experiment with them We conclude with further examples of what you need to know to use interrupts successfully EXPERIMENT 3 Load INTPROGS into the PIC and reconnect your flying lead to pin RBO This is a simple program to flash the 1 e d on RAO at about 1 Hz It also has the INTF inter
207. ractically Speaking New Technology Update Net Work The Internet Page BACK ISSUES ONLY 3 30 each inc UK p amp p Overseas prices 3 80 each surface mail 5 25 each airmail We can also supply issues from earlier years 1998 except Jan to May July Nov Dec 1999 2000 except Feb July 2001 except Oct Where we do not have an issue a photostat of any one article or one part of a series can be provided at the same price ORDER FORM BACK ISSUES PHOTOSTATS INDEXES L Send back issues dates L Send photostats of article title and issues date L Send copies of last five years indexes 3 30 for five inc p amp p Overseas 3 80 surface 5 25 airmail L_ I enclose cheque P O bank draft to the value of L Please charge my Visa Mastercard Amex Diners Club Switch On ING oi ainsi eae ha eae a eae yd eee ae Switch Issue No Card Expiry Date Note Minimum order for cards 5 SEND TO Everyday Practical Electronics Wimborne Publishing Ltd 408 Wimborne Road East Ferndown Dorset BH22 9ND Tel 01202 873872 Fax 01202 874562 E mail orders epemag wimborne co uk On line Shop www epemag wimborne co uk shopdoor htm Payments must be in sterling cheque or bank draft drawn on a UK bank Normally supplied within seven days of receipt of order Send a copy of this form or order by letter if you do not wish to cut your issue Everyday Practical Electronics April 2002 STORE
208. rates technical terms The author goes under the hood and shows step by step how to create a socket 7 Pentium and non intel chipsets and a Slot 1 Pentium Il computer covering What first time builders need to know How to select and purchase parts How to assemble the PC How to install Windows 98 The few existing books on this subject although badly outdated are in steady demand This one delivers the expertise and new technology that fledgling computer builders are eagerly looking for 224 pages large format H elv Td ose 128 C1 a Yam 21 99 184 pages 12 95 PIC YOUR PERSONAL INTRODUCTORY COURSE SECOND EDITION John Morton Discover the potential of the PIC micro controller through graded projects this book could revolutionise your electronics construction work A uniquely concise and practical guide to getting up and running with the PIC Microcontroller The PIC is one of the most popular of the microcontrollers that are transforming electronic project work and product design Assuming no prior knowledge of microcontrollers and introducing the PIC s capabilities through simple projects this book is ideal for use in schools and col leges It is the ideal introduction for students teachers technicians and electronics enthusiasts The step by step explanations make it ideal for self study too this is not a reference book you start work with the PIC straight away The revised second edition covers
209. re A simple CR oscillator is used and this has six switched resistors that provide output frequencies that are the same as the six open string notes of a guitar The polarity of the indicator l e d is such that it is switched on when the output of the amplifier is low and the oscillator s output is high It is switched off with any other set of output states Fig 2 Output waveforms with various phase relationships between the two output signals The dotted lines indicate when the l e d is turned on Everyday Practical Electronics April 2002 In Fig 2 the top pair of waveforms rep resents the output signals from the ampli fier and oscillator with the same output frequencies and the two signals in phase With the two signals always at the same state the l e d is never switched on In the next pair of waveforms the two signals are still at the same frequency but they are now 90 degrees out of phase This results in the l e d being switched on for 25 per cent of each cycle The pulses from the l e d are at too high a frequency for the individual pulses to be perceived and the l e d seems to be switched on continuous ly but at less than full brightness In the third pair of waveforms the sig nals are 180 degrees out of phase and the l e d is now switched on for 50 per cent of each cycle Again the individual pulses cannot be seen and the l e d appears to be C2 R2 S ak standard non inverting configurati
210. re Logic Probe Light Heat and Moisture Sensor NE555 Timer Egg Timer Dice Machine Bike Alarm Stereo Mixer Power Amplifier Sound Activated Switch Reaction Tester Full parts lists schematics and p c b layouts are included on the CD ROM ANALOGUE ELECTRONICS 1 d Soc C e Complimentary output stage bzh tee Dk ee A a o A har hE 1 Counter project Analogue Electronics is a complete learning resource for this most difficult branch of electronics The CD ROM includes a host of virtual laboratories animations diagrams photographs and text as well as a SPICE electronic circuit simulator with over 50 pre designed circuits Sections on the CD ROM include Fundamentals Analogue Signals 5 sections Transistors 4 sections Waveshaping Circuits 6 sections Op Amps 17 sections covering everything from Symbols and Signal Connections to Differentiators Amplifiers Single Stage Amplifiers 8 sections Multi stage Amplifiers 3 sections Filters Passive Filters 10 sections Phase Shifting Networks 4 sections Active Filters 6 sections Oscillators 6 sections from Positive Feedback to Crystal Oscillators Systems 12 sections from Audio Pre Amplifiers to 8 Bit ADC plus a gallery showing representative p c b photos DIGITAL ELECTRONICS V2 0 Digital Electronics builds on the knowledge of logic gates covered in Electronic Circuits amp Components opposite and takes users through th
211. re grounding at both ends is not a problem as the ground does not carry the signal Magnetic interference is worse when physically large loops occur in the circuit e g see Fig 6 3a and can therefore be reduced by avoiding such loops for cables the use of twisted pairs of wires is an effective approach e g see Fig 6 3b For circuit boards use a ground plane on one side of the board For ribbon cables make sure each signal has an adjacent return wire Circuits can be shielded against magnet ic fields but this is not used as commonly as shielding for capacitive coupling as it GROUND requires special high permeability materi als such as Mu Metal These materials are expensive and as they may need to be quite thick the screening may be bulky Supply Based Interference The circuit in Fig 6 4 illustrates how supply resistance Fig 6 4a may lead to errors or interfer ence The supply current taken by a circuit causes a voltage drop across the supply wiring so for example the ground volt age at each sub circuit will not actually be at OV This will obviously cause problems if we are trying to make accurate voltage mea surements with reference to ground The error in the ground voltage is not necessar ily constant as the supply current of one sub circuit varies then the supply voltage drop and hence the ground error voltage at this and other sub circuits fluctuates this is sometimes called ground bounc
212. rent counting It is the elapsed time since the first entry occurred that continues to be shown The display though is updat ed to show the number of the second zone or more as well as the first When Panic mode is triggered via switch S3 the clock is always reset to Zero If the bell time out has not completed following zone triggering and a total power failure occurs the bell is NOT reactivated when power is resumed although the buzzer and strobe are re triggered When entering the correct PIN code to stop an alarm condition and turn off the bell strobe and buzzer as appropriate all zone and timing information remains on screen until blank is pressed to cause a return to ALL OFF mode Be assured that even if the alarm is in active monitoring mode and use of the key pad is made full system scanning contin ues preventing unauthorised users from fooling the system by holding down a key indefinitely TOTAL POWER LOSS If there is a total power loss through a mains failure and lack of battery power and then one or the other is restored the software restarts from a Reset condition In doing so it notes this fact and displays one of three messages If the system has not been set into active monitoring mode the following 2 line message appears The second line is cleared when you enter your PIN code and enter SELECT MODE from which you can immediate ly escape if you wish press blank
213. ronic systems such as phones and computers are obvious examples of exter nal interference The amount of external noise a circuit or sensor is subject to will vary greatly depending on its location The problem will obviously be worse close to power lines electrical machines and equip ment such as TV sets Signals in one part of your circuit can find their way into other parts of the circuit where they cause problems A common example of this is the clock of a digital sec tion of the circuit getting into an analogue section via the power supply lines or by capacitive coupling to high impedance points Careful circuit design and construc tion can greatly reduce these problems SHIELDING AND GROUNDING In the following discussion the boxes labelled Circuit 1 and Circuit 2 in the accompanying schematics may be any sub sections of the circuit of interest Typically in the case of this series Circuit 1 will be a sensor possibly with associated circuitry power supply potential divider bridge cir cuit etc and Circuit 2 may be an amplifier However the implications of our discus sion are wider than this and apply to other situations too Capacitively coupled interference see Fig 6 la can be reduced using screening which effectively grounds the interference coupling capacitance Fig 6 1b Screening e SOURCE OF INTERFERENCE E G DIGITAL CLOCK LINE a SCREENED CABLE CIRCUIT 1 a a ae CIRCUIT 2 l C
214. rst option this Panic mode is triggered whether or not the main alarm is in monitoring mode The condition once triggered needs to be reset in the usual way Be aware however that this interrupt driven option is potentially a weak link in the system s stability All other alarm zone monitoring is done via software polling of the zones Interrupts via RB4 though are automatically generated by the PIC in response to any OV going change of logic status at this pin Whereas it is believed that the power supply and other zones are likely to be largely immune to external electrical inter ference such as caused by electrical storms an RB4 interrupt might conceiv ably be triggered under such conditions Reader feedback on this would be welcomed If this Panic interrupt is not required connect a link between the pins of the S3 connector so holding RB4 permanently low CONSTRUCTION This design is mains powered and its construction should only be undertaken by those who are suitably experienced or supervised Printed circuit board component and track layout details are shown in Fig 5 This board is available from the EPE PCB Service code 339 Assemble the components in order of size and use a socket for the PIC Do not insert the PIC or connect the l c d until the correctness of the power supply has been confirmed It is not necessary to instal all the zone terminals shown Just solder in those that are actually requir
215. rupt enabled When this is running OK take the wire connected to RBO and hold it on PIC pin 15 CLKOUT i e connect together pins 6 and 15 The Le d will stop flashing and remain either on or off depending on how it was l AST month we discussed the basic when the wire was connected Remove the wire from CLKOUT and the Le d will start flashing again Take a moment to think what might be happening here before reading on The code section relevant to this experiment is shown in Listing 5 Actually this one isn t so difficult CLKOUT is generating a clock output that is running at the same rate as the instruc tion processing rate Interrupts are there fore being generated at the instruction processing rate Since there are 14 instruc tions in the ISR interrupts are being gen erated at 14 times the rate that the PIC can process them LOOPING IN THE ISR If interrupts are allowed to occur faster than the PIC can process them then as LISTING 5 Main loop and ISR code for INTPROGS CLRF TMRO CLRF COUNT BCF INTCON TOIF BTFSS INTCON TOIF GOTO Al INCF COUNT F MOVLW SPEED XORWE COUNT W BTFSS STATUS Z GOTO A2 MOVLW 1 XORWE PORTA F GOTO MAIN Interrupt service routine ISR MOVWE SAV EW SWAPF STATUS W MOVWE SAVES BANKO BTFSS INTCON INTF GOTO POP there is an INTF interrupt clear internal clock count up clear ticks count clear the TMRO wrapped flag has TMRO wrapped yet no loop till it ha
216. s bump count of wraps about 10 bumps sec at 2MHz clock gt sets Z if COUNT W test Z Z not set so COUNT lt gt SPEED wraps COUNT SPEED so toggle RAO and repeat main loop gt save W save STATUS ensure Bank U set test INTF not an RBO interrupt NOP nothing to do for this demo CLR BCF INTCON INTF INCF ICOUNT F POP SWAPE SAVES W MOVWE STATUS SWAPE SAVEW F SWAPEF SAVEW W RETFIE clear the interrupt bump count of interrupts restore STATUS restore W gt exit ISR Everyday Practical Electronics April 2002 Part 2 soon as one interrupt has been processed and the PIC exits its ISR another interrupt will be pending and the ISR is immediate ly entered again Since interrupts pre empt the main program the main program never runs and the PIC effectively loops in the ISR Externally the PIC will appear to be dead or to have hung The same thing will happen if due to a software bug the ISR fails to clear the interrupt flag bit for the event which caused the interrupt On exit from the ISR the PIC will see the flag bit still set and will think that another interrupt is pending So it will immediately enter the ISR again ad infinitum If you want to try this as an experiment in INTPROGS replace the instruction CLR BCF INTCON INTF by CLR NOP and see what happens Last month when discussing INTPROG4 we said that it was necessary f
217. s active components and ICs linear circuits block and circuit diagrams how radio works disc and tape record ing elements of TV and radar digital signals gating and logic circuits counting and correcting micro processors calculators and computers miscellaneous systems Order code NE23 13 99 SCROGGIE S FOUNDATIONS OF WIRELESS AND ELECTRONICS ELEVENTH EDITION S W Amos and Roger Amos Scroggie s Foundations is a classic text for anyone work ing with electronics who needs to know the art and craft of the subject It covers both the theory and practical aspects of a huge range of topics from valve and tube technology and the application of cathode ray tubes to radar to digital tape systems and optical recording techniques Since Foundations of Wireless was first published over 60 years ago it has helped many thousands of readers to 199 pages become familiar with the principles of radio and electronics The original author Sowerby was succeeded by Scroggie in the 1940s whose name became synonymous with this classic primer for practitioners and students alike Stan Amos one of the fathers of modern electronics and the author of many well known books in the area took over the revision of this book in the 1980s and it is he with his son who have produced this latest version Order code NE27 21 99 GETTING THE MOST FROM YOUR MULTIMETER R A Penfold This book is primarily aimed at beginners and those of
218. s From basic principles like soldering and making printed circuit boards to the tools needed for circuit building the Modern Electronics Manual and its Supplements describe clearly with appropriate diagrams how to assemble a radio loudspeaker circuits amplifiers car projects a computer interface measuring instruments workshop equipment security systems medical and musical circuits etc The Base Manual describes 12 projects including a Theremin and a Simple TENS Unit Extensive tables on diodes transistors thyristors and triacs digital and linear i c s Should you come across a technical word phrase or abbreviation you re not familiar with simply look up the glossary included in the Manual and you ll find a comprehensive definition in plain English The Manual also covers component and equipment The most comprehensive reference work ever produced at a price you can afford the CD ROM edition of THE MODERN ELECTRONICS MANUAL provides you with all the essential information you need and provides web links to Revised CD ROM Edition of Basic Work Contains over 800 pages of information in Adobe Acrobat format Edited by John Becker Regular Supplements Additional CD ROMs each containing four 160 page Supplements of additional material will be available for 19 95 each to MEM buyers Information on the availability and content of each Supplement CD ROM will be sent to you as they become available Presentation CD ROM suita
219. s concise and practical book which explains everything you need to know about MP3s in a simple and easy to understand manner It explains How to play MP3s on your computer How to use MP3s with handheld MP3 players Where to find MP3s on the Web How MP3s work How to tune into Internet radio stations How to create your own MP3s How to record your own CDs from MP3 files Other digital audio music formats Whether you want to stay bang up to date with the lat est music or create your own MP3s and join the on line digital music revolution this book will show you how 60 pages Order code PC119 7 45 60 pages ALL PRICES INCLUDE UK POST AND PACKING ELECTRONIC MUSIC AND MIDI PROJECTS R A Penfold Whether you wish to save money boldly go where no musi cian has gone before rekindle the pioneering spirit or sim ply have fun building some electronic music gadgets the designs featured in this book should suit your needs The projects are all easy to build and some are so simple that even complete beginners at electronic project construction can tackle them with ease Stripboard layouts are provided for every project together with a wiring diagram The mechanical side of construction has largely been left to individual constructors to sort out simply because the vast majority of project builders prefer to do their own thing in this respect None of the designs requires the use of any test equip ment in order to get them
220. s tables or on virtual meters For more information contact RD Research Dept EPE Research House Norwich Road Eastgate Norwich NR10 AHA Tel 01603 872331 Fax 01603 879010 Email rd research paston co uk Web www looking co uk New Ham Licence THE DTI Radiocommunications Agency has introduced a new ham radio licence called the Foundation Licence It is aimed at young people to help get them interested in radio electronics communications and com puters with a view to them possibly pursu ing a career in the subjects The youngest person so far taking the Foundation Licence course is an 8 year old girl To view the Foundation Licence syllabus and for more information on the new licence visit www qsl net RADIO SHACK RADIO Shack has been a household name for many years especially to those living in the USA or who used to frequent the Tandy stores in the UK Radio Shack was founded in 1921 and has become one of the world s largest retailers of consumer elec tronics products with over 5000 company owned stores in the USA and in excess of 2000 in over 38 other countries RUSK Ltd has become the licensed dis tributor for Radio Shack in the UK It was established as a UK company in the year 2000 to service the requirements of an existing network of ex Tandy dealers and to develop new exciting business opportu nities within the retail electronics market The company is said to be a one stop shop for
221. s are turned on whenever the respec tive PIC line is high regardless of whether a transistor is also connected to that output Each transistor has a diode connected between its collector and the 12V line This is to inhibit back e m f pulses in the event that an inductive load is being driven via the transistor It is permissible to control solenoids or relays INTRUSION DEFINITIONS Returning to zone intrusion sensing via pins RDO RD3 and RCO RC 3 refer to Fig 4 This shows the equivalent circuits for the zone components when used with sensors that are normally open or normally closed To clarify a possible source of confusion the following definitions are used in this text Normally open means any sensor which when in its normal required active state when monitoring an entry exit point has its contacts in an open condition see Fig 4a Devices that work in this context of normally open include pressure pads which require for example someone to tread on them in order to trigger the alarm system Normally closed means any sensor which when in its normal required active state when monitoring an entry exit point has its contacts in a closed condition see Fig 4b Everyday Practical Electronics April 2002 Devices that work in this context of normally closed include magnetically operated switches secured either side of two adjacent sections on a door and its frame The proximity of the magnet when the door is closed keeps
222. s even advised once to discon nect the earth from one of the appliance s 3 pin mains plugs Have a look at Fig 2 which illustrates a mains earth loop between two circuits instruments hi fi components etc This topic is also one that we re covering in our current educational series Teach In 2002 Making Sense of the Real World Noise and shielding are important aspects of using sensors as our series shows as signals and test measurements can be adversely affect ed by unwanted noise The resistor labelled Rg represents the resistance of the earth wire of a test lead e g an oscilloscope probe or an audio cable if Circuit 1 and Circuit 2 are hi fi separates or some other interconnection between the circuits This lead links the earths of the two circuits together The two circuits are connected to mains earth via their mains leads and thus they are linked POWER SUPPLY WITH GROUNDED OV RAIL V SUPPLY OV CONNECTED INTERNALLY TO GROUND O via the mains wiring so completing the loop The loop will act like the secondary of a transformer and pick up magnetic interfer ence such as mains hum and may also act like an antenna picking up radio frequency interference r f 1 as well That interfer ence causes a current J to flow in the ground loop which in turn causes an addi tional voltage drop equivalent to the value of IRo across the resistance Rg of the ground connection between the equip
223. sers will have to use the code sequences as TASM lacks a macro translator as do all EPE programers Ed An example of how the code would be used by an assembler that Everyday Practical Electronics April 2002 does not recognise macros is shown in Listing 7c Hopefully INTPROG7 can be used as a model answer for well structured inter rupt driven programs MULTIPLE INTERRUPTS As mentioned earlier more than one interrupt source can be enabled simulta neously To illustrate this INTPROG8 is an alternative version of INTPROGS that uses timer interrupts and so has both the INTF and TOIF interrupts enabled The heart of this program is shown in Listing 8 The ISR checks for each interrupt and also allows for both interrupts to have occurred A critical section is used to pre vent COUNT from being changed by the ISR while it is being read and possibly reset by the main loop Proof that both interrupts work correctly is that the l e d is caused to flash because the TMRO interrupt increments COUNT and that it is caused to stop when the RBO interrupt is triggered by touching the wire link from RBO to pin 15 It is suggested that you Experiment 3 with INTPROGS Observant readers will spot one other change from INTPROGS At the beginning of the critical section the test for COUNT SPEED is changed from repeat XORWF COUNT W BTFSS STATUS Z to SUBWF COUNT W BTFSS STATUS C LISTING 7a Macros DEFINE B
224. st programs because there are eight levels available and programs rarely nest CALLs anything like this deep However if you do blow the Stack there is no STATUS or other warning to let you know you ve done it not that it matters much because your program will really go bananas then CONCLUSION The author hopes that all this hasn t put you off experimenting with interrupts The reverse in fact armed with this informa tion he hopes that many people will now feel more confident to have a go themselves What he does hope to have done how ever is to have convinced you that inter rupts and poor software do not mix very well and to have encouraged the use of good software design and implementation techniques If so then a successful outcome to experimentation is much more likely OBTAINING SOFTWARE The demonstration software for this article is available from the EPE Editorial EPE BINDERS L Za ur Tal se office on 3 5 inch for which a nominal handling charge applies or free from the EPE web site See this month s Shoptalk page for more details PCLATH An article on the correct use of the bank and block switching command PCLATH is scheduled for a forthcoming issue It is of special relevance to using tables that are longer than 256 jumps and to using PICI6F87x program locations above 2K Understanding PCLATH is as much an imperative as are Interrupts if you wish to expand your PIC progr
225. student The fifth button has a similar func tion but displays any graph in a separate window Again if the stu dent makes any changes to the default values the contents of the window will change accordingly Obviously the calculations and graphs are not applicable to all pages but where available they are included on printouts Conclusion It is not possible to give details of the full range of topics cov ered by Electronic and Computing Principles V7 1 because it is too vast There are over a thousand pages available in the current version Full details are available from EPTsoft and at their web site It is relevant to a number of examination courses that cover basic electronics and or computing The program is well thought out and seems to be completely stable in use Electronic and Computing Principles remains easy to use despite the huge number of pages available in version V7 1 You will not spend hours learning to use this program before you can actually start learning from it It has to be pointed out that it is not an electronics course but a number of pages devoted to electronics and related topics When used in educational establishments there will be a tutor to guide students through the material It would presumably be possible to learn a great deal by going through the pages in each topic However for those studying at home it would probably be better to use the program in conjunction with a suitable course book By th
226. t or by measur ing the voltage directly using a multitester If doing this take great care to avoid short circuiting the terminals Note that a fully charged battery will have a terminal voltage a little higher than the stated value 2 6V approximately for the nominal 2 4V variety This circuit is not suitable for phones that use a higher voltage than 3 6V Also it has not been tested on batteries other than the nickel metal hydride NiMH and nick el cadmium NiCAD type 286 If you decide to devise some means of attaching the unit to the top of your back pack to maximise the amount of light reaching it remember that as described it is not weatherproof It would therefore be necessary to waterproof it yourself or pack it in a dry place when it rains Remember also that the solar cells and meter used will not withstand too much abuse such as dropping them on the ground TO THE EDGE The unit is built in a plastic box with two solar panels an edge type meter and a light emitting diode l e d mounted on top The meter monitors the current provided by the solar panels and helps the user to align the unit for maximum illumination Inside the box there is a circuit panel and two sets of AA size cells in holders One comprises three re chargeable cells and the other three of the throwaway alkaline variety The re chargeable cells provide a reserve of energy collected by the solar panels which may then be used to
227. t runs OK till an interrupt occurs which will cause the low byte to wrap and high byte to increment while it is in the middle of copying that value CRITICAL SECTIONS It turns out that this is a very common problem Most programs have sequences of code where they are manipulating sev eral related variables together such that if they get interrupted during the sequence the variables will be left in a half updated or inconsistent state Everyday Practical Electronics April 2002 Software engineers call these code sequences critical sections What is needed is some mechanism to ensure that these critical sections are not interrupted but allowed to complete safely The PIC hap pily provides a suitable mechanism We ve already met it it s called the GIE The three instructions following MAIN in INTPROG6 which copy ISRCL and ISRCH are a critical section If the pro gram is interrupted during this sequence then as we ve just analysed above things can go wrong And if they can go wrong by Murphy s Law they will We need to prevent the program from being interrupted during this sequence So we protect it by disabling interrupts before it and re enabling them after it MAIN BCF INTCON GIE _ disable Interrupts MOVE ISRCL W copy ISR low byte counter MOVWE COUNTL MOVE ISRCH W copy ISR high byte counter BSF INTCON GIE _ enable Interrupts MOVWE COUNTH Now the ISR cannot be run during the copy
228. t sufficient charge into the bat tery to make a short call A typical time needed to do this is one hour Next check that with bright light reaching the solar panels the phone bat tery charges up to say the 50 per cent level in a few hours A DUMMY AA CELL SHOWING THE METAL STRIP TERMINALS CONNECTED TOGETHER TO SOCKET SK2 METAL STRIP CUT AND A SMALL SECTION REMOVED SOLDERED JOINTS Fig 3 How two dummy cells may be used to make the con nections to socket SK2 sometimes the cells are used side by side Test the amount of charge by replacing the battery in the phone Do not be deceived by the display This will probably give a read ing on the high side and take some time to settle down to the correct value OVER THE TOP If the solar panels receive full sunlight for 20 hours approximately with nothing plugged into either output the re charge able cells could be overcharged assuming they start from flat This would damage them over a period of time To prevent such problems set switch S1 to the low position after this time However if the unit is used to operate a cassette player every so often or if a mobile phone battery is being charged the switch should be left set to high With a reasonable amount of use overcharging is not likely to occur Avoid overcharging the mobile phone battery by leaving it in place for no longer than necessary Before the phone battery
229. t that we cannot provide data or answer queries on articles or projects that are more than five years old Letters requiring a personal reply must be accompanied by a stamped self addressed envelope or a self addressed envelope and international reply coupons All reasonable precautions are taken to ensure that the advice and data given to readers is reliable We cannot however guarantee it and we cannot accept legal responsibility for it COMPONENT SUPPLIES We do not supply electronic components or kits for building the projects featured these can be supplied by advertisers see Shoptalk We advise readers to check that all parts are still available before commencing any project in a back dated issue ADVERTISEMENTS Although the proprietors and staff of EVERYDAY PRACTICAL ELECTRONICS take reasonable precautions to protect the interests of readers by ensuring as far as practicable that advertisements are bona fide the maga zine and its Publishers cannot give any under takings in respect of statements or claims made by advertisers whether these advertise ments are printed as part of the magazine or in inserts The Publishers regret that under no circum stances will the magazine accept liability for non receipt of goods ordered or for late delivery or for faults in manufacture TRANSMITTERS BUGS TELEPHONE EQUIPMENT We advise readers that certain items of radio transmitting and telephone equipment which may be advertis
230. tended Memory Use Practically Speaking Ingenuity Unlimited e New Technology Update Circuit Surgery Net Work The Internet Page JULY 01 PROJECTS Stereo Surround Sound Amplifier e PIC to Printer Interface Perpetual Projects 1 Solar Powered Power Supply and Voltage Regulator e MSF Signal Repeater and Indicator FEATURES e The World of PLCs Ingenuity Unlimited Circuit Surgery New Technology Update Net Work The Internet Page 270 DID YOU MISS THESE PROJECTS e Digitimer Lead Acid Battery Charger Compact Shortwave Loop Aerial Perpetual Projects 2 L E D Flasher Double Door Buzzer FEATURES e Controlling Power Generation Ingenuity Unlimited Interface Circuit Surgery e New Technology Update Net Work The Internet Page SEPT 01 PROJECTS e Water Monitor L E D Super Torches Synchronous Clock Driver Perpetual Projects 3 Loop Burglar Alarm Touch Switch Door Light Solar Powered Rain Alarm FEATURES e Controlling Flight Ingenuity Unlimited e Practically Speaking Circuit Surgery 6 New Technology Update Net Work The Internet Page OCT 01 Photostats onl PROJECTS e PIC Toolkit Mk3 Camcorder Power Supply 2 Valve SW Receiver Perpetual Projects 4 Gate Sentinel Bird Scarer In Out Register FEATURES e Traffic Control Ingenuity Unlimited 6 New Technology Update Circuit Surgery Interface 6 Net Work The Internet Page
231. the PIN code to return to SELECT MODE MODE SUMMARY The following is the summary of the modes and their keyed identities It is sug gested that you photocopy it and secure the details to the front panel of your enclosed alarm Set alarm on Set main PIN code Set access time out Set access zone Set active zones Set bell time Set zone logic Show zone logic Set 2nd PIN code Set 2nd time out Set passive mode CHOICE OF SENSORS It is believed that this design can be used with any type of intruder sensor currently available The choice is entirely yours as to which type you use for which zone Many companies sell intruder alarm products and they or their catalogues should be consult ed for advice on the sensors available The choice of case and back up battery is also yours For the latter a sealed lead acid type rated at 12V and say 5Ah is sug gested If you are using the anti tamper option it recommended that a microswitch is installed in the case and the bell housing causing an alarm condition if either enclo sure 19 entered without authority The system can be used to monitor just one zone Each zone used can be connect ed by using 2 core cable available specifi cally for alarm use If anti tamper detec tion is required 4 core alarm cable should be used the entry sensor itself wired to one pair the anti tamper connections made by the other and connected separately to the system s
232. the fact that its input and output are in phase stray feedback to long input wiring could cause severe instability A screened cable must be used to connect SK1 to the circuit board if this cable is more than a few centimetres long TUNE SWITCH Switch S1 is a 6 way 2 pole rotary switch but in this circuit only one pole is used Consequently there are no connec tions to seven tags of this switch Modern switches of this type invariably have an adjustable end stop and in this application the end stop should obviously be set for 6 way operation The circuit board is bolted in place on the base panel of the case If a metal case is used it is essential to use spacers of at least 6mm in length over the mounting bolts between the case and the board This will keep the connections on the underside of the board well clear of the metal case Even if a plastic case is used it is still necessary to use spacers washers or a cou ple of extra nuts to provide at least a small stand off between the case and the board Most makes of stripboard are quite brittle and there is otherwise a risk of the board buckling and cracking as it is bolted in place Details of the hard wiring are also includ ed in Fig 4 and this is largely straightfor ward The polarity of l e d D1 is unimpor tant in this case If it is connected the wrong way round the on and off states will be swapped but this is of no consequence and the unit will still work per
233. the popular repro grammable EEPROM PICs P16C84 16F84 as well as the P54 and P71 families Order code NE36 UNDERSTANDING PC SPECIFICATIONS R A Penfold Revised Edition If you require a microcomputer for business applica tions or a high quality home computer an IBM PC or compatible is often the obvious choice They are com petitively priced and are backed up by an enormous range of applications programs hardware add ons etc The main difficulty for the uninitiated is deciding on the specification that will best suit his or her needs PCs range from simple systems of limited capabilities up to complex systems that can happily run applications that would have been considered beyond the abilities of a microcomputer not so long ago It would be very easy to choose a PC system that is inadequate to run your applications efficiently or one which goes beyond your needs and consequently represents poor value for money This book explains PC specifications in detail and the subjects covered include the following Differences between types of PC XT AT 80386 etc Maths co processors Input devices keyboards mice and digitis ers Memory including both expanded EMS and extended RAM RAM disks and disk caches Floppy disk drive formats and compatibility Hard disk drives including interleave factors and access times Display adaptors including all standard PC types CGA Hercules Super VGA etc Contains everything you ne
234. the switch contacts closed When the door is opened the con tacts open and so the alarm is triggered When ordering components for your alarm system it is important to understand these descriptions in relation to this design Such terms have been known to create con siderable confusion in the past Hence our defining them now ZONE CIRCUIT LOGIC In Fig 4 sensors are inserted into resis tor networks as shown In Fig 4a with the sensor in a normally open condition the voltage at the junction of the 100k and 47k resistors is OV and monitored as such by the PIC 12V 1k C B NORMALLY OPEN SENSORS ARE WIRED IN PARALLEL OV A NORMALLY OPEN WHEN IN USE ALARM TRIGGERED WHEN CONTACTS CLOSE E G DOOR ENTRY PRESSURE PAD B NORMALLY CLOSED WHEN IN USE ALARM TRIGGERED WHEN CONTACTS OPEN E G MAGNETICALLY CLOSED REED SWITCH Fig 4 Zone intrusion sensor logic options If a zone is intruded the sensor s con tacts close and the voltage across the com ponent series becomes the voltage at the output of diode D4 about 0 7V below that present at the battery nominally 12V The voltage actually fed to the PIC is that set by the potential divider values and will vary depending on the voltage across the divider Providing the input voltage is above 0 7Vpp SV x 0 7 3 5V the PIC will recognise it as logic 1 The battery voltage can probably drop to as low as 10V and the PIC should still receive an input voltage recog
235. ther pages there are slider controls to provide variable volt ages analogue voltmeters and graphs to show voltage changes and so on There is good use of graphics and even some simple animations such as the one that shows how a raster image is pro duced see Fig 7 Overall the user interface is very consistent and it is usually pretty obvious in operation Coverage The range of topics covered goes well beyond basic electronics and there are plenty of pages covering mathematics and comput ing The Logic and Micro s section includes some coverage of the PIC microcontrollers Examples are based on the PICI6F84 and PIC16C71 chips These chips are not the most up to date in the range but nevertheless remain a good starting point I My x pa m N f a jaa e Ee AP T O 79 iF in l ay Dal L Fana I Maai lt Min Baa 4 etla paari nr LES i Taima m Ge bir Fil tk pane ier fi L N iiid P 18 hy j N G alp 0 E eop lt 108 DH N C b S Y pmd s T KB f i VO b 5 Barv K bre i L i A Fig 6 The calculated figures have changed to suit the change in the value of resistor R2 2 J 9 Soman Phosphor Triad Compainr Moning Serman Bererez e lI aan Fig 7 Some of the pages use simple animations as in this example that shows how a raster image is built up It is not possible to simulate programs but the relevant registers can be loaded with values and then an instruction can be r
236. ti turn trimpots which have better resolution and are easier to adjust accurately than bog standard pre sets It should not be difficult to modify the layout to accept vertical trimpots but six of these components will substantially boost the cost of the project Ordinary miniature preset potentiometers will suffice and are used on the prototype but they must be adjusted very carefully In order to fit into the layout easily capacitors C2 and C4 should be types that have 5mm 0 2 inch lead spacing It is preferable to use a high quality component O Z Z PX K T GTH m DOD gt BB 6 O0 e oo eo oondc0 eooc00 000800000000 0 O BB AAIOO 0000000000000 0 OMe 00 6 e M0028e00000 AA ZIO00008 8 00QM008 00000080000000080000 0 2 YIQO000000000000000000000000000000 Y Xl 0 00QM000000000000000000000000 0 0 W 10 QQ 0C0O0O0Oee eo0oQMQedoodog VIG 06 0000 00080 ee0M000e400M0e40ee000 V UlOo O00 000e0OMee000MHe000eOM0e0e0 00 ei TIOO 0000000 6 QUe QQ 0 QU 06 000000 e o00000JT SIOO000000000000000000000000000000 OQ159 RIOQO000008000000000800000000000000 R QlIO 000000000000800000000000000000 Q PlIOO00 000000008 00000084000008 e0 00 61H 010 00 0000000000000000000000000000 0 0 NIOO0 0000000080 0000000080000008008000IN MIOQ000008 0000000080 00000000808800000 M LIe oe 0000006000 0000000 0000000000000 koooo0oo0oo000000000000000000000000000JK O O O O O o O O O O X 00e 00000o0JW
237. tic clip at the top of the battery ensured that it was held securely in the unit However in some cases a rubber band may be needed FULL SCALE READING The value of shunt resistor Rl may be modified if necessary so that the meter reads near to full scale deflection in full sunlight To increase the reading increase the value of R1 and vice versa If it is necessary to make a change tem porarily de solder the solar panel positive wire from the meter terminal This is because even a small current could damage the meter TESTING Allow the nickel metal hydride cells to charge for a few hours in bright light longer under cloudy conditions Next make up a connecting lead for the cassette player This will be easy if it has a 3V input socket Failing this you could use dummy bat teries Their real purpose is to take up unoccupied space in battery chargers so the terminals are connected end to end To use them for the present purpose the metal strip which forms this connection will need to be cut through and a small sec tion removed Connecting wires may then be soldered to the cut ends see Fig 3 Attach the correct type of plug on the other end observing the polarity Connect the cassette player up and check that it works correctly Allow the phone battery to run down by leaving the phone switched on until it cuts out not by con necting an artificial load to it Now check that the backup sup ply can pu
238. tic field on current in a thin sheet of gold when he noticed that a small voltage was generated at the edges of the sheet when the magnetic field was per pendicular to the foil This effect occurs in all conductors but is strong in silicon and other semiconductors Panel 6 1 gives an explanation of magnetic field and Panel 6 2 explains the Hall Effect As we can see from Panel 6 2 the volt age across a wafer of silicon is proportion al to the product of the current flowing through the wafer and the applied magnet ic field Commercial Hall Effect devices can operate with magnetic fields from about 0 1mT to 1T tesla A strong perma nent magnet has a field of about tesla The tesla T is the SI unit of magnetic flux density and is related to gauss the equivalent CGS unit symbol G by multi plying the value in mT by 10 i e 1OmT 100 gauss 1G 10 T There are three types of Hall effect device linear unipolar and bipolar The linear device has an output voltage propor tional to the magnetic flux density and is used in applications where the magnetic flux density is to be measured e g for an electronic compass or for measuring cur rent without contact Unipolar and bipolar sensors provide digital outputs For example a sensor may be off in the absence of a magnetic field and on when a field over a certain level is OUTPUT VOLTAGE MAGNETIC FIELD B millitesla mT Fig 6 13 Output graph for
239. timers flip flops dividers and decoder cir cuits Some practical circuits are used to illustrate the use of TTL devices in the real world 64 pages 142 pages Order code BP332 5 45 HOW TO USE OP AMPS E A Parr This book has been written as a designers guide covering many operational amplifiers serving both as a source book of circuits and a reference book for design calculations The approach has been made as non math ematical as possible Order code BP88 4 49 CIRCUIT SOURCE BOOK 2 R A Penfold This book will help you to create and experiment with your own electronic designs by combining and using the vari ous standard building blocks circuits provided Where applicable advice on how to alter the circuit parameters is provided The circuits covered are mainly concerned with signal generation power supplies and digital electronics The topics covered in this book include 555 oscillators sinewave oscillators function generators CMOS oscilla tors voltage controlled oscillators radio frequency oscillators 555 monostables CMOS monostables TTL 298 160 pages monostables precision long timers power supply and regulator circuits negative supply generators and voltage boosters digital dividers decoders etc counters and dis play drivers D A and A D converters opto isolators flip flops noise generators tone decoders etc 192 pages Over 170 circuits are provided which it is hoped
240. tor R3 Of course you could omit the l e d to save power but care would then be needed to switch back to normal as soon as possible LOCK ON Normally a cassette player will have its input voltage limited by the nickel metal hydride cells It therefore remains more or less constant whatever the intensity of light reaching the solar panels Should a fault develop whereby B1 becomes disconnected due to say one of the cells dislodging from its holder or to a 288 COMPONENTS Resistors ee R1 195 see text S Z 5 R2 R3 100Q 2off TALK R4 33Q fora page 2 4V phone battery or 10Q fora 3 6V battery All 0 25W 5 carbon film Semiconductors D1 D4 1N4001 50V 1A diode 2off D2 1N5817 Schottky diode D3 3mm red l e d D5 3V9 0 5W Zener diode Miscellaneous X1 X2 3V 80mA nominal solar panels see text 2 off ME1 1004A f s d edge panel meter 1750 ohms coil resistance see text soldered joint failing the locking effect is removed The supply will then rise to that of the solar panels less the forward voltage drop of diodes D1 and D4 This will exceed 6V off load under bright conditions Since the solar panels cannot supply more than 80mA to 100mA this will prob ably be insufficient to operate a cassette player The effect will be that the on load voltage will fall below the operating value and it will simply stop working However this cannot be guaranteed
241. tored Each mode will now be discussed in detail MODE 0 activate alarm system When Mode 0 is entered the software first checks that all zones have the open or closed status as set in Mode 6 assess zone logic If they do not a 2 line message is displayed of which the following is an example in which zone 6 is not in the required con dition e g a door open when it should be closed The allocated entry exit zone may remain open at this time since that is the route that will be taken by the user once the alarm has been set on This message will continue to be dis played until the zone has been returned to its required condition or the blank key pressed to exit this mode and return to a display of ALL OFF If the blank key is not used when the incorrect zone status has been remedied the alarm on procedure will resume and a 2 line message shown such as where the countdown starts at the seconds value previously set for the entry exit delay and proceeds to count down to zero The buzzer sounds during this period The countdown may be terminated and a return made to ALL OFF if the blank key is pressed Otherwise when zero is reached the system will be placed into the full alarm monitoring condition watching those zones set through Mode 4 An exit from and closure of the allocat ed entry exit zone must be made within the allotted entry exit time Failure to do so will cause an al
242. tors for this pur pose How such a signal may be generated from an instrumentation amplifier is shown in Fig 6 9 The two resistors with equal value R5 provide the guard signal via the unity gain buffer The exact value for RS is not too critical about 10kQ would be suit able The other resistor values and general operation were discussed last month YET MORE TO WORRY ABOUT Sensor systems are also prone to a vari ety of forms of interference based noise and errors other than electrically magneti cally coupled signals including mechani cal and electrochemical effects Movement and vibration of sensor cables can create electric current through the tri boelectric effect charges created due to friction between a conductor and an insula tor Low noise cables are available for situ ations where this may be a particular problem Making sure that cables are well supported and not subject to vibration or large temperature fluctuations helps reduce this effect for any cable Movement can also generate unwanted signals through the piezoelectric effect recently discussed in relation to sensors Part 4 Feb 02 which occurs when mechanical stress is applied to insulators and may also occur in the terminals used to connect input signals Unwanted signals due to movement and mechanical stress are sometimes called microphonic effects because if the signal is listened to the movement of for example a cable will be audible
243. troduction to the of electronic subject Nearly 40 Tutorials cover virtually every aspect of PIC programming in an components A high quality selection of over 200 JPG images This selection of high resolution photos can be Whilst the CD ROM can be used on its own the physical demonstration provided by used to enhance the PiCtutor Development Kit plus the ability to program and test your own projects and PIC16x84s really reinforces the lessons learned The hardware will also be an presentations or to help with training bira invaluable development and programming tool for future work and educational material They are The Virtual PIC Two levels of PICtutor hardware are available Standard and Deluxe The Standard royalty free for use in commercial or personal printed projects and can also be used royalty free in books battery holder all switches for both PIC ports plus I c d and 4 digit 7 segment l e d catalogues magazine articles as well displays It allows users to program and control all functions and both ports of the as worldwide web pages subject to PIC All hardware is supplied fully built and tested and includes a PIC16F84 ain see licence for full etails Also contains a FREE 30 day PiCtutor CD ROM HARDWARE evaluation of Paint Shop Pro 6 Hobbyist Student 000000e 45 inc VAT Standard Development Kit 47 inc VAT Paint Shop Pro image editing tips Institutional Schools HE FE Industry
244. ty of attaching the code and an explanation In the code to reduce cycle time when dividing smaller numbers two bytes are still used for the dividend the program may not always know how big the numbers are My piece of code simply checks the dividend s upper byte to see if it is zero or not If it is the upper and lower bytes are swapped and the count reduced by eight This saves eight redundant Rotations Through Carry Then the code snippet checks for leading zeros Once again if any of these are shifted round and the bit count reduced without the unnecessary comparison part of the algorithm executing Part of Peter Hemsley s original divide movfw divisL iorwf divisH w skpnz goto divO Division by zero movlw 16 16 bit division movwf bitcnt clrf remdrH Clear remainder clrf remdrL My piece of code movfw dividH btfss STATUS Z test high byte for any set bits goto leadoff movfw dividL high byte of dividend empty movwf dividH swap the two bytes clrf dividL movlw 8 make the count just 8 movwf bitcnt this would cut down the number of iterations to 8 leadoff btfsc dividH 7 now remove the leading Zeros goto dvloop clre rlf dividL rlf dividH decf bitcnt goto leadoff Peter s code again dvloop clrc Set quotient bit to 0 rlf dividL Shift left dividend and quotient rlf dividH Msb into carry rlf remdrL and then into partial remainder rlf remdrH etc Gerard Galvin via email Thanks Gerard
245. ubject in the ftp TK3 folder downloaded a copy of the Sybera product and am now able to run TK3 under XP successfully I followed the notes written by Peter Shew for which he and the other contributors is to be much thanked Many thanks for your Herculean efforts with all the various PIC projects I find them all very absorbing and I am looking forward to reading all about interrupt programming Colin Birtwistle Swanley Kent Thanks Colin for the Drive information Ill look into adding it to TK3 for general release With XP now so firmly on the scene and I ve yet to hear any good reports about it it s useful to know that there is a fix to using TK3 with it Why on earth have Microsoft made it so hard to communicate with the outside world via printer ports In this respect machines of 20 years ago were better suited having such things as user ports Everyday Practical Electronics April 2002 CAPACITANCE METER Dear EPE The Capacitance Meter in Nov 01 was inter esting but to say that it allows any capacitor type to have its true value readily measured and dis played is totally inaccurate and could be very misleading In fact as an electrolytic capacitor ages and starts to dry out its capacitance value becomes much more frequency dependant A worn capacitor may be perfectly OK smoothing a 100Hz ripple in a linear regulator but the same capacitor fitted to a switch mode power supply working at a switching fre
246. ucted materials and devices Computer control gives these robots and androids two types of artificial intelligence an expert sys tem and a neural network A lifelike android hand can be built and programmed to function doing repetitive tasks A fully animated robot or android can also be built and pro grammed to perform a wide variety of functions The contents include an Overview of State of the Art Robots Robotic Locomotion Motors and Power Controllers All Types of Sensors Tilt Bump Road and Wall Detection Light Speech and Sound Recognition Robotic Intelligence Expert Type Using a Single Board Computer Programmed in BASIC Robotic Intelligence Neutral Type Using Simple Neural Networks Insect Intelligence Making a Lifelike Android Hand A Computer Controlled Robotic Insect Programmed in BASIC Telepresence Robots With Actual Arcade and Virtual Reality Applications A Computer Controlled Robotic Arm Animated Robots and Androids Real World Robotic Applications Order code MGH1 14 99 224 pages 19 99 296 DIRECT BOOK SERVICE NOTE ALL PRICES INCLUDE UK POSTAGE The books listed have been selected by Everyday Practical Electronics editorial staff as being of special interest to everyone involved in elec tronics and computing They are supplied by mail order to your door Full ordering details are given on the last book page For a further selection of books see the next two issues of EPE BASIC RADIO PRI
247. uestions fault finding virtual laboratories and investigations worksheets Hobbyist Student sse e lt lt x x e e in cuent 45 inc VAT Institutional Schools HE FE Industry 000000005 99 plus VAT Institutional 10 user Network Licence 0 55 199 plus VAT Institutional Site Licence 0c cece eee eee eee 499 plus VAT UK and EU customers add VAT at 17 5 to plus VAT prices ELECTRONICS IN CONTROL Two colourful animated courses for students on one CD ROM These cover Key Stage 3 and GCSE syllabuses Key Stage 3 A pictorial look at the Electronics section featuring animations and video clips Provides an ideal introduction or revision guide including multi choice questions with feedback GCSE Aimed at the Electronics in many Design amp Technology courses it covers many sections of GCSE Electronics Provides an ideal revision guide with Homework Questions on each chapter Worked answers with an access code are provided on a special website Single User 29 inc VAT Multiple User 39 plus VAT Student copies available only with a multiple user copy 6 plus VAT UK and EU customers add VAT at 17 5 to plus VAT prices MODULAR CIRCUIT DESIGN Contains a range of tried and tested analogue and digital circuit modules together with the knowledge to use and interface them Thus allowing anyone with a basic understanding of circuit symbols to design and build their own
248. umably responsible children to let them selves into the house by use of a coded keypad or similar technique and could we help After weighing up the various pros and cons it was decided to include a second keypad with this con troller which would be largely indepen dent of the main sys tem but which would allow a PIN code to be keyed in and acti vate line RBS and Darlington transistor TR4 As said earlier transistor can com requests at office or apartment premis es for example The PIN code required for keypad S2 is initially set via keypad S1 as part of the main system In operation though keying the correct PIN into S2 directly activates TR4 A count down is started at that instant and TR4 remains on for a period which can be pre viously set as required via the main system During this time the buzzer on line REO TR1 is also activated At the end of the preset period the buzzer and TR4 are turned off again This secondary control is not tied into the main zone sensing system If the sec ondary entry time out period is not met for example the main alarm system is not triggered However secondary entry could be made to tie in with the main system as well by treating this entry zone as an alarm zone with its own separate sensor This would require therefore David Mynatt s children to enter their own PIN on keypad S2 installed in a porch outside the main entry door for example This could cause
249. un The page for the DECF f d instruction is shown in Fig 8 The values in the registers show the changes produced by running the instruction so that the student can see the exact effect of each instruction In addi tion to the pages covering the instruction set others cover topics such as the clock oscillator PIC architecture and the Status register Tools For The Job The small toolbar just below the menu bar provides some use ful functions Starting with the button on the extreme left this is Mi iA ENS TLE IWE OEGE bil Chernin i Derema prir T Ac a ORe maia dme 0 he i aier jaf ja j Bere io ioed beck in easier T Fig 8 PIC instructions can be tried by loading values into the registers executing the instruction and noting the changes operated in order to print the current page on the default printer The relevant topic notes are also printed and these are explanato ry notes that can be brought up for any page by operating the third button in the toolbar The notes appear in a second window that can be removed by left clicking on a passive part of the screen Operating the second button in the toolbar copies the current page to the Windows clipboard From here it can be pasted into other programs such as a DTP type so that it can be formatted prior to printing Where appropriate the fourth button can be used to show any calculations in a separate window The calculations will reflect any changes made by the
250. vels of hum in their hi fi systems due to earth loops The ground loop will pick up magnetic interference probably mains hum and may also act like an antenna picking up radio frequency interference Large loops will make the problem worse Ground loops are a particular problem when two or more 249 mains powered systems such as lab instru ments and sensor circuits are separately earthed and connected together The interference causes a current I to flow in the ground loop which in turn causes an additional voltage drop I Rg across the resistance Rg of the ground connection between the equipment or sub circuits The best solution to ground loops is to avoid them by using a single grounding point Fig 6 5b Use of differential signals use of screening and use of very low resis tance ground connections between circuits reducing Rg also help to minimise ground loop problems SIGNAL GUARDING Signal guarding is concerned with get ting the most out of screened cable connec tions particularly when connecting very low level signals from high impedance sources to high precision circuits In such cases effects such as leakage currents in the cables and cable capacitance can cause significant errors SIGNAL OUTER SHIELD CHASSIS GROUND SIGNAL RETURNS Fig 6 6 Triaxial connector use with tri axial cables for guarded connection Example of a triaxial connector TRIAXIAL CABLE Fig 6 7 Guarded signa
251. ver since such switches generally do not have 360 degrees rotation a three pole four way rotary switch is used instead A standard break before make rotary switch is not really suitable here since it would cause power to be lost momentarily across the leads of the motor during rota tion and this would adversely affect torque especially if the motor is vertically mounted Therefore a make before break rotary switch is used This makes a new contact before it breaks the previous one Electrolytic capacitor Cl picks up the momentary surge in power when the switch makes If no holding torque is required the cir cuit may be switched off once the stepper motor has been turned to its desired posi tion Detent torque the remaining torque Everyday Practical Electronics April 2002 when the stepper motor is switched off is typically one tenth of holding torque Red l e d D9 indicates the state of On Off switch S3 MOTOR LEAD IDENTIFICATION In reality there appears to be no standard colour coding for identifying the leads of a four phase unipolar stepper motor The author tested six four phase unipolar step per motors of which only two had the same colour coding for the leads every wire was brown Such motors sometimes have five leads sometimes six sometimes even eight leads there being four windings or phas es in all Fortunately the task of lead identification is not too difficult Current only flows i
252. via preset VR1 Keypad s The main control of the system is accessed via a standard 16 key alphanu meric data entry keypad S1 through which a unique 4 digit alphanumeric per sonal identity PIN code has to be keyed There are 28560 permutations 134 1 The status of the keypad s pushbutton keys is monitored via port pins RC4 RC7 used in output mode and RBO RB3 used in input mode Port B s internal light pull ups are activated in the software and addi tional biasing resistors for RBO RB3 are not needed Facilities for the use of an optional sec ond 16 key keypad S2 are provided for reasons discussed later Four of its pins share pins RC4 RC7 with keypad S1 The others are monitored by pins RD4 RD7 used in input mode with logic high bias ing provided by resistors R3 to R6 Prototype PIC Controlled Intruder Alarm showing control board main function selecting keypad and I c d dis play but excluding entry sensors and alarm sounders etc 260 Everyday Practical Electronics April 2002 PANEL 1 PIC Controlled Intruder Alarm Features Monitors between one and eight entry exit points zones of a building or room Allows monitoring to be totally or partially suspended when required by the legitimate guardians users of the premises Indicates audibly e g bell and or visibly e g strobe when one or more zones have been entered without authority Turns off activated bell after a pres
253. vide tips which passed through the slot to make contact with the battery terminals The correct spacing for the prototype battery terminals 5mm was obtained by attaching the switch bodies together and these were in turn mounted on a small aluminium bracket Thin flexible wires were tightly twisted on to the pivot end of the arms soldering could possibly damage them The other ends of the wires were soldered to one of the switch terminals in each case to provide take off points Connections from here were made to the wires which passed through a hole in the box A cable tie was used to provide some strain relief to the wire and prevent the connections becoming dislodged if it was pulled in service A 2 5mm mono jack plug was then sol dered to the other end Take care to observe the polarity so that the positive Lever arm microswitches used for bat tery contacts in the prototype battery holder unit Interior of the battery holder showing the aluminium microswitch mounting angle bracket Everyday Practical Electronics April 2002 The mobile phone battery mounted on the battery holder contact box between the locating pegs 289 terminal of the battery leads to the pin connection of the plug Also take care not to cause a short circuit inside the plug since this would damage the phone bat tery when this was in position Check that the battery terminals make proper con tact In the prototype the plas
254. will be useful to all those involved in circuit design and applica tion be they professionals students or hobbyists Order code BP322 5 45 Project Building amp Testing ELECTRONIC PROJECTS FOR EXPERIMENTERS R A Penfold Many electronic hobbyists who have been pursuing their hobby for a number of years seem to suffer from the dreaded seen it all before syndrome This book is fairly and squarely aimed at sufferers of this complaint plus any other electronics enthusiasts who yearn to try some thing a bit different No doubt many of the projects fea tured here have practical applications but they are all worth a try for their interest value alone The subjects covered include Magnetic field detector Basic Hall effect compass Hall effect audio isolator Voice scrambler descrambler Bat detector Bat style echo loca tion Noise cancelling LED stroboscope Infra red torch Electronic breeze detector Class D power amplifier Strain gauge amplifier Super hearing aid 138 pages Order code BP371 5 45 ELECTRONIC PROJECT BUILDING FOR BEGINNERS R A Penfold This book is for complete beginners to electronic project building It provides a complete introduction to the practi cal side of this fascinating hobby including the following topics Component identification and buying the right parts resistor colour codes capacitor value markings etc advice on buying the right tools for the job soldering making
255. wiring inside the case The protection Zener diode D5 has not been included on the tagboard see Fig 2 pe RECHARGEABLE VY e r A A a Everyday Practical Electronics April 2002 SOLAR PANELS NORMAL BACKUP BACKUP ON Fig 2 Tagboard component layout and interwiring details to off board components The solar panels used in the prototype work well However others may be just as suitable A single nominal 6V unit provid ing around 80mA should be satisfactory or a combination of individual solar cells con nected in series or in parallel to provide a similar output PREPARING THE PANELS Drill holes in the case for the solar panel wires also for mounting the meter l e d clip switches output sockets battery hold ers and circuit panel Note that miniature toggle switches were used in the prototype unit but it would be better to use slide switches if there is a chance that these could be operated unintentionally Attach the circuit panel and all other parts If using the specified solar panels cut the connecting leads to a suitable length One of these has a stripe and in this case it denotes the negative OV one Secure the solar panels using adhesive fixing pads Refer to Fig 2 and complete the internal wiring using light duty stranded connect ing wire Sleeve the soldered joint which connects the solar panels in series When wiring the sockets make the pin centre connecti
256. xt p c b supports 4 off connecting wire solder etc Alarm fittings Intruder sensors bell strobe buzzer types as required to suit application 2 way or 4 way alarm cable see text Everyday Practical Electronics April 2002 control logic is inverted if the transistors are not used If the buzzer is to be used TR1 must be installed The 1 e d s and their ballast resistors can also be omitted as you see fit although they do offer a useful monitoring facility if you need to troubleshoot the circuit at any time Whilst it is not necessary to fit link wires between unrequired zone terminal track pairs it is preferable to retain all zone OV biassing via resistor module RM1 This will help to provide electrical stability to the PIC s unused inputs If Panic mode detection via RB4 is not needed wire this pin to the OV line to keep it stable It is suggested that the keypad s should be connected via ribbon cable and suitable 9 pin connectors to match their terminal pins and those on the board A rear view of the keypad pinouts is shown in Fig 6 9 8 7 6 5 4 3 2 1 REAR VIEW PIN 9 CONNECT TO OV Fig 6 Rear view of keypad connec tions plus keypad legends It is recognised that if the second key pad is also used the cost of running 9 way ribbon cable from the unit across several metres to a door could be considerable An alternative is to use two lengths of standard 4 way alarm system cable to m
257. y has to be on the outside and connected to earth or OV Interference screening and grounding are important topics and you can read more in Part 6 of Teach In 2002 Even then we 300 have not covered every aspect of these mat ters so if anyone has any further questions please let us know IMB Transceiver Supply Surprise Mr George Jacob writes from Mid Glamorgan in Wales I have a query about a Yaesu FT290 RII 2 metre transceiver I purchased recently It came minus the Nickel Cadmium rechargeable batteries or a charger I purchased new NiCads 9 x 2500mAh C cells but I cannot buy d suitable charger to charge all of the cells as they are no longer made The approved charger provides 13 05V d c at l65mA One type I have been offered is rated at 13 5V at 700mA I wondered if this would work Can you also explain more about mA I can t usually help with commercial equipment problems but I didn t want to see you fry an expensive new battery pack so here goes I guessed that the battery pack is probably a separate removable unit like a video camera pack which must be recharged externally so it then boiled down to how intelligent the battery pack was if at all and what to suggest for a suitable external charger To answer your other queries first We mentioned in last month s Circuit Surgery that batteries have a capacity measured in ampere hours Ah or milliampere hours mAh it is an i

EPE 2002

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