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Gertboard User Manual

1. 17 Buttons Lestin EE E Hee Ded De ers 19 Buttons Test im Python eene tete tere rris o sete ete ae dca 19 Testing LEDS er 20 LEDS EE 21 LEEDS Testim Py thm s EES 22 Testing VO EC Q 23 MEO 24 Butled Testin Python RR 24 Open Collector Driv Gti i b eni con Ree bred qe dicen 24 Testing the Open Collector Drivers ien ecce etr erem retten etur 25 Open Collector Vest S 26 Open Collector Test 1n E EO 26 Motor T 27 Testing the Motor 28 Motor Test Im EA 29 Motor Python 30 Digital to Analogue and Analogue to Digital 32 Digital to Analogue 32 Analogue to Digital Converter 22 33 Testing the D A 33 D Acand C eee tee 35 D A an
2. 8 Figure 16 Wiring diagram to test the open collector drivers the right is small test circuit made up of two LEDs in series with 90 resistor and a 9V battery acting as power supply You may wonder why you need to connect the positive terminal of the power supply to the open collector driver via the RPWR pin The reason for this is that if the circuit happens to contain a component that has electrical inductance for example a motor or a relay when the power is turned off this inductance can cause the voltage on RLYn pin on the right of the board to quickly rise to a higher voltage than the positive terminal of the power supply dropping quickly afterwards The chip itself has an internal diode connecting the RLYn pin to RPWR this is the diode at the top of Figure 15 This allows current to flow to the top positive side of your circuit allowing the energy to dissipate and preventing damage Open Collector Test in C The ocol test is very simple First it prints out the connections required on the board and with your external circuit and power supply and then it calls setup_io to get the GPIO interface ready to use and setup gpio to set pin GPIO4 to be used as an output using the commands GPIO 4 OUT GPIO 4 as described on page 13 Then in it uses SETO and CLRO described on page 21 to set GPIO4 high then low 10 times Note the test asks which driver
3. 020 021 e e eje eje eje eje eje eje ojo eje GND 928 1 R115D6 114078115 08 116 09812101051 25 38 d or p ope Ses An 2190 qps 1 8 DAI R126 R127 5 wes 00 Bi B20UtB3 B4 RNs ole ole x eje eje 6 a 4 ie Ss e e e e e m amp Raspberry Pi Gertboard 21 Oct 2012 fal 279133 Developed by van Loo Fen Logic Ltd U8 Figure 21 The wiring diagram for the test program motor Motor Test in C The PWM is controlled by a memory map like the GPIO and SPI bus This memory map is part of the setup io function in gb common c so that is whether the PWM is used or not Further setup code is found in pwm c with an associated header file gb pwm h The function setup in gb sets the speed of PWM clock and sets the maximum value of PWM to 1024 this is the value at which the duty cycle of the PWM will be 10096 It also makes sure that the PWM is off The two routines set pwm0 and force pwmo0 set the value that controls the duty cycle for the PWM set pwmo0 sets the value first checking that it is
4. e 9 5vs Figure 28 Wiring diagram for the sketch Blink Developed by G J van Loo Fen Logic Ltd 08 Note that in this diagram we not shown the connections to the SPI pins Once you have uploaded the code you no longer need them and can remove the straps On the other hand if you want you can leave them in place and this is a good idea if you are planning on uploading some other sketches later Button Sketch Let s look at another fairly simple sketch called But ton located under File gt Examples gt Digital menu in both 0018 and 1 0 1 The comments at the beginning of the sketch read The circuit LED attached from pin 13 to ground pushbutton attached to pin 2 from 5V 10K resistor attached to pin 2 from ground Assuming that you have Blink working your LED is already wired up but what about the button As mentioned above since the ATmega chip on the Gertboard runs at 3 3V we must replace the 5V with 3 3V So they suggest using a circuit like the one below where the value read at pin 2 is logical 0 if the button is not pressed due to the 10K pull down resistor and logical 1 if the button is pressed pin 2 10 3 3V O GND Figure 29 Suggested switch circuit for use with Button sketch However the buttons on the Gertboard are used like this 44 value L pull up GND O 3 3V Raspi Figure 30 Circuit in use on the Gertboard showing
5. Ic bah RTI3D6 RT4D7RTIS mam 8 se Sa oe ojo se s 9 c20 gps lel r B20Ul B3 BARS eje U6 eee EBENE noun 015 C16 Raspberry 2012 Developed by G J van Loo Fen Logic Ltd U8 Figure 23 Wiring diagram for the test program atod Even without a multi meter or a potentiometer it is still possible to test the A D and D A by sending the output of the D A to the input of the A D The test that does this is called dad for digital analogue digital To set the Gertboard up for this test hook up all the SPI bus pins connecting GP11 though GP7 with jumpers to the pins above them and put a jumper between pins DA1 and ADO as in the diagram below 34 L E E GE L MOTB MOT B 33 F use mox R201 dde STETE STE SIS STS SS STS STS STE se 9 9 GND TINI Sicile AD M 2 20 i E Sa ore ojo u7 5 U6 e le sre sre 51551 X ojo ojo oo o e 2 C19 Es el e 53 15 C16 Raspberry Pi Gertboard 21 Oct 2012 8 M 2133 Dev
6. IN L3 3 1 1 1 5 8 n T Figure 1 and Raspberry The Gertboard is input output I O extension board for the Raspberry Pi computer It fits onto GPIO general purpose I O pins of the Raspberry Pi the double row of pins on the upper left corner via a socket on the back of the Gertboard A bit of care is required when putting the two devices together It is easy to insert just one row of pins into the socket but all of the pins need to be connected The Gertboard gets its power from those GPIO pins so you will need a power supply for the Raspberry Pi that is capable of supplying a current of at least 1A The Gertboard has collection of functional blocks the major capabilities of the board which can be connected together in a myriad of ways using header pins The functional blocks are 12x buffered I O e 3x pushbuttons e 6x open collector drivers SOV 0 5A e 18V 2A motor controller 28 pin dual in line ATmega microcontroller 2 channel 8 10 or 12 bit Digital to Analogue converter 2 channel 10 bit Analogue to Digital converter The location of these blocks on the Gertboard is shown in Figure 2 e s 8201 8212 tig TT E 82 out 83 gt 1 3 p b 0 eee te 8101 as care 3 E 7 Pi
7. common h gb spi h and gb pwm h there are a number of macros that give a more intuitive name to various parts of the arrays that have been mapped These macros are used to do everything from setting whether a GPIO is used as input or output to controlling the clock speed of the pulse width modulator 12 Page INP activates pin number for input 13 OUT GPIO n E used after above sets pin n for output 13 SET GPIO ALT n a E used after select alternate function for pin 29 GPIO PULL W set pull code 19 GPIO PULLCCLKO W select which pins pull code is applied to 19 GPIO INO R get input values 19 GPIO SETO W select which pins are set high 21 GPIO CLRO W select which pins are set low 21 Table 2 Commonly used macros their type purpose and location within this manual Table 2 shows a summary of the more commonly used macros and gives the page number on which its use is explained in more detail The T column below gives the type of the macro This shows how the macro is used E means that the command is executed as in INP GPIO 17 W means that that the command is written to assigned as in GPIO PULL 2 means that that the command is read from as in data GPIO INO The macro INP GPIO n must be called for a pin numb
8. A 4 Bi B2in Bj B4 ao mP Bana Ge Raspberry Pi Gertboard 21 Oct 2012 m Developed by G J van Loo Fen Logic Ltd Figure 34 Wiring diagram for the LEDmeter sketch Upload it the usual way and the LEDs will respond to the position of the potentiometer 49 Going Forward These examples have only just scratched the surface of the wonderful world of Arduino Check out http arduino cc en Tutorial HomePage for much much more For More Information For further information on the Raspberry Pi and its GPIO ports the datasheet for the processor can be found here http www raspberrypi org wp content uploads 2012 02 BCM2835 ARM Peripherals pdf Appendix A Schematics We have included the schematics for the Gertboard in the pages that follow They are numbered A 1 A 2 etc The page number is located in the lower left hand of each page 50 S080 MOL 8 HOLOW V HOLON 9 AVTAY v Av 13H Av 3H AVISH s JequinN en SXINOO ANG EXLNOO _ 0121 99 S080 MOL LIXINOO X pent redi EW 310H EW 31OH 310H EW 310H EW 310H SH SHIN EHIN 4 m ul 2 ANG 60SldV en XINOO 9081 4001 19
9. Developed by G J van Loo U8 The diagram in Figure 5 is created from the files that were used to design the Gertboard circuit board The blue in the diagram is generated from the silkscreen file which indicates where the white text and lines on the circuit board will be The grey in the diagram is generated from the solder mask file which roughly corresponds to where the silver conductive areas on the top of the circuit board will be We will be using this blue and grey diagram as a basis for our wiring diagrams which show you the pins that need to be connected together for each of the test programs We use these diagrams because they are much clearer than a photo of the fully assembled board Have a close look at the white text on the photo of the Gertboard in Figure 4 or the white text on your own board or the blue text in the diagram in Figure 5 These labels provide information that is required in order to connect together the various blocks of the Gertboard Almost all of the components have labels and more importantly the pins in the headers have labels It isn t necessary to be too concerned about many of the components such as resistors and capacitors labelled with and Cn where n is some number However the labels for headers integrated circuits diodes and switches are important Diodes are labelled Dn The ones that you will be interested in are D1 through D12 the LEDs light emitting diodes The LEDs are near th
10. G rtboard 7 2012 11111 11111117 ion buffered I O switches and LEDs C Atmel ATmega chip open collector driver GPIO pins motor controller C A to D and D to A converters Figure 2 Functional blocks diagram the key blocks are identified by coloured boundary marking Please note that the appearance of some components can vary This annotated photo of a populated fully assembled Gertboard shows where the functional blocks are located Some of the blocks have two areas marked For example the turquoise lines showing the Atmel ATmega chip not only surround the chip itself and the header pins next to it on the lower left but also surround two header pins near the bottom of the board in the middle These two pins are connected to the Atmel chip and provide an easy way to interface the GPIO signals from the Raspberry Pi which are in the black box with the Atmel chip There is no connection other than power and ground between the different functional blocks on the Gertboard The many headers the rows of pins sticking up from the board allow you to make these connections using straps and jumpers See Figure 11 on page 18 for an example of how these are used to connect the various blocks together Figure 3 Photograph showing straps the coloured wires above and jumpers below Straps connect two parts Gertboard together whilst jumpers conveniently connect two adjacent pins together
11. Just next to these pins are ground pins GND to provide a reference Testing the D A and A D According to the data sheet for the D A the value on the output pin Vout is given by the following formula assuming the 8 bit MCP4802 Din C Vou 256 Vout for channel 0 is DAO in 129 for channel 1 it s DAI Exe 2 ato dr 2 dm dm mo m L MOTB MOT 33 1818 21 Fuse 2A 201 212 e e eje eje 922 GND n R107 R131 nmm si 82 83 83 ee 12 E c2o T 45 17 8126 R127 u 2 r E B 820083 6 e e s gt s srs S Slc Bt B2 in B3 B4 mm o1 1019 45 id exe e 18 lo 53938888858 dos ESLIRE 199 5 558925 015 C16 Raspberry Pi Gertboard ic 21 Oct 202 EE ERE 555555 BV 5 j m a Sel 2 SS Figure 22 The wiring diagram for the dtoa test G J C4 4 Loo Fen Logic Ltd 1 ce gj 2 7 9 5 5 4 1 0 M gig elle LL 8 Develo
12. The Gertboard uses an MCP48x2 digital to analogue converter D A from Microchip The device comes in three different types 8 10 or 12 bits The one you get on your board is determined by availability of parts To see which one you have look very closely at the small chip in location U10 It should have a number 48x2 stamped on it where x is either 0 1 or 2 If x is 0 you have the 8 bit version If it s 1 you have the 10 bit version and if it s 2 you have the 12 bit one These chips are all pin compatible and are written to in the same way In particular the routine that writes to the D A 32 assumes that writes are in 12 bits so it is important that the value is selected appropriately details are below in the section Testing the D A and A D The maximum output voltage of the D A the output voltage when you send an input of all 1s is 2 04V The analogue outputs of the two channels go to pins labelled DAO for channel 0 and DA1 for channel 1 in the J29 header on the left edge of the board Just next to these pins are ground pins GND to provide a reference Analogue to Digital Converter The Gertboard uses a MCP3002 10 bit analogue to digital converter from Microchip It supports 2 channels with a sampling rate of 72k samples per second sps The maximum value 1023 is returned when the input voltage is 3 3V The analogue inputs for these two channels are ADO for channel 0 and AD1 for channel 1 in the J28 header
13. hence which ports will be set low and which LEDs will turn off So for example given the wiring above the command CLRO 0x100 will set GPIO8 pin low and thus turn off the LED for port 11 which is the port connected to GP8 In 1eds c the LEDs are always all turned off together but they don t have to be used this way 21 The test program flashes the LEDs in three patterns The patterns are specified by a collection of global arrays given values using an initializer The number in each of the arrays says which LEDs will be turned on at that point in the pattern so pattern value is submitted sequentially to produce the changing pattern switching all the LEDs off between successive pattern values Each pattern is run through twice The first pattern lights the LEDs one at a time in sequence left to right The second pattern does the same but when it reaches the rightmost LED it then reverses direction and lights them in sequence right to left The third pattern starts at the left end and at each step switches on one more LED until they are all lit up then starting at the left it switches them off one by one until they are all off Finally the test program switches off all the LEDs and then finally calls rest ore_io to clean up all the LEDs to a predictable final state LEDs Test in Python This test is available for both RPi GPIO and WiringPi for Python The only differences between the leds rg py and leds w
14. ports change the 3 led drive 3 0 ports change ports to ports rev led drive 3 0 ports changetheO toa 1 22 Testing I O Our two examples so far have only used the ports to access the pushbuttons and LEDs The next example called but 1ed for BUTton LED in C or but 1ed rg py in Python will show one of the ports serving just as an input port The idea is that one port along with its button is used to generate a signal and software then sends that signal to another port which it is used as just an input to the Raspberry Pi We read both ports in and print them on the screen gt 2 EE L MOTB 2 lis et 3132 34 55 5 51 45 8 5 15 4 5 1 Fuse 2A mS e ee ee ee ee e ep leleteteletetelelel 18191819191919191919 DiRTOSD2RIOGDSRIO D RTISD6 KTI4D7RTIS DBRTIGDSRT2 IDTORTZ2DTIRTZ D T2RT24 C8 out 21220 ojo of 616 6 lel NE 6 X1 J71 s De Sj 151 153 8 e e e 2 15 C16 Raspberry Pi Gertboard 21 Oct 2012 lal s 2133 Figure 14 The wiring diagram for test program butled which detects a button press and then displays that button state on the screen and on an LED Developed by G J van Loo Fen Logic Ltd
15. 75 of the time For example in Figure 19 above we are alternating between A low B high and A high B high the second and fourth lines of the table above When A is low the motor will receive power making it turn one way when A is high it will not receive power The end result for the 25 duty cycle shown here is that the motor will turn one way at roughly 34 speed 1 1 MOTA MOTB 0 0 Figure 20 In this example the motor will run in the opposite direction at around 25 speed If on the other hand you set MOTB low as in Figure 20 above then when A is high the motor will receive power making it turn in the other direction and when A is low the motor will not receive power The result for the 25 duty cycle is that it will turn in the other direction at about speed Testing the Motor Controller The C test program for the motor controller is called mot or In Python there are two versions motor rg py and motor wp py To set up Gertboard for this connect GP17 in J2 to the MOTB pin the MOTB pin in J5 not the one at the top of the board and GP18 to MOTA in J5 The motor leads need to be connected to the MOTA and MOTB screw terminals at the top of the board and the power supply for the motor needs to be connected to the MOT and L screw terminals This is shown in Figure 21 28 your power source goes here _ Q w 51213812 Fuse 2
16. Labels and Diagrams As you get to know the Gertboard and make connections between the various blocks you will be guided extensively by the white labels on the circuit board At this point we would like to introduce the diagram shown in Figure 5 which we will use to show you how to wire up your Gertboard for the test programs N3 J15 121 J16 D D 7 17 21111117 219 05 Had T gt Ra spberry Pi Gertboard Oct 2012 Jeveloped by LA A LA 2 ba 2 Feo clenen s4 Gertboar Figure 4 Photograph of the Gertboard 2 2 g 2 L MOTA MOTB MOT poe s r E mamahmddmd md mam dm Fi Fuse max 2 MS eje eje o P DIRT l E3 97 cn c8 85 OUlg sje ofe 51 52 E F m E Lu d Bi B20Ut B3 BR eje 616 eje C19 L SEE EE x 15 C16 Raspberry Pi Gertboard 21 Oct 2012 2 ajv Figure 5 Diagram representing bare Gertboard circuit board The blue elements correspond to the white lines and text and the gray elements correspond to the silver coloured pads Fen Logic Ltd
17. The wiring for this test is shown above Pin GPIO23 controls I O port 3 and GPIO22 controls I O port 6 so GP23 in header J2 is connected to pin B3 in header J3 and GP22 is connected to B6 Now for the interesting part The pushbutton on port 3 is going to be used here but the LED for port 3 should not be used so the output jumper for port 3 which would be placed at U3 out B3 is not installed Looking at the schematic on page A 2 it is clear that the output buffer for port 3 goes to pin 14 of buffer chip U3 This is connected to pin 1 of U3 out B3 shown as P6 in the schematic It is not obvious which header pin on the board is pin 1 but as it s connected on the circuit board to pin 14 of the chip we can guess that it s the one right above pin 14 A simple experiment shows that this is indeed the right pin so we connect this pin to the BUF6 pin at the top of the board This allows the switch to generate a signal which is then sent to port 6 A jumper is installed across U4 in B6 to allow that signal to be input from the board The value of the switch from port 3 is also read in and these two should be the same most of the time 23 Butled Test In but 1 we use GPIO to set GPIO22 GPIO23 to input PULL and GPIO PULLCLKO to set the pull up GPIO23 This is described in more detail on page 19 in the buttons test Then the GPIO values are repeatedly read in and the binary values of GPIO22 an
18. an additional 1k resistor to protect the input to BCM2835 The 1K resistor between the pushbutton and the Raspi point is to protect BCM2835 the processor on the Raspberry Pi if you accidentally set the GPIO pin connected to Raspi to output instead of input The circuit to the right of the Raspi point happens on the Raspberry Pi to use the pushbutton we set a pull up shown as a resistor in the circuit above on the pin so that the value read is logical 1 when the button is not pressed see page 19 for more info on the pull up The Gertboard buttons are connected directly to ground so they cannot be made to read logic 1 when pressed If you want to use a Gertboard button with an Arduino sketch that assumes that the button reads 1 when pressed the best approach is to modify the sketch if needed so that it will invert the value it reads from the button For the pull up we can take advantage of the pull ups in the ATmega chip To do this find the lines below in the sketch initialize the pushbutton pin as an input pinMode buttonPin INPUT and insert the following two lines after them set pullup on pushbutton pin digitalWrite buttonPin HIGH To invert the value read from the button find the line below buttonSate digitalRead buttonPin and insert a the negation operator in C as follows buttonSate digitalRead buttonPin Now upload this modified sketch as described for Blink We still need to
19. an external circuit to ground on the board thus giving the circuit power The ULN2803A can withstand up to 50V and drive 500mA on each of its ports Each driver has an integrated protection diode the uppermost diode in the circuit diagram in Figure 15 24 OUT Raspi Figure 15 Circuit diagram of each open collector driver The pin is as the name states common for all open collector drivers It is not connected to anything else on the Gertboard As with all devices the control for the open collector drivers the point can also be connected to the ATmega controller to for example drive relays or motors The open collector drivers are in the schematics on page A 3 In the Gertboard functional block diagram Figure 2 on page 6 the area containing the components for the open collector drivers are outlined in yellow The pins corresponding to Raspi in Figure 15 are RLY1 to RLY6 pins in the 14 header the pins corresponding to common are the ones marked RPWR in the headers on the right edge of the board and the pins corresponding to OUT are the RLY 1 to RLY6 pins in the headers 712 to 717 How these are then used is demonstrated by the test wiring and code examples Testing the Open Collector Drivers The C program oco1 for open collector allows the functional testing of the open collector drivers The Python version comes in two flavours ocol rg py and ocol wp py We n
20. attach Arduino digial pin 2 PD2 on the Gertboard as you can see from the table to a button say button 3 The Raspi pin in the circuit diagram above which is where we want to read the value is in the J3 header 45 MOTB uw t 5834 3 34 5 8 5 5 4 Fi Fuse mox 2A eje eje eje eje eje oje ejo eje eje ojo of 9990 ss 11306 RTI4D7RTIS out 51 2 53 126 Bi B20Ulg3 B4 6 71 20 m e eje eje eje o J71 B 2 Bj 8 15 C16 Raspberry Pi Gertboard 21 Oct 2012 pill s Figure 31 Wiring diagram for the sketch Button Developed by 0 4 van Loo Fen Logic Ltd When you have done this the first LED will be on when the third button is pressed and off when the third button is up AnalogInput Sketch Now let s try using an analogue pin Find the AnalogInput sketch under File gt Examples gt Analog This reads in a value from analogue input 0 which has already been converted by the internal A D to a value between 0 and 1023 then uses that number as a delay between turning an LED and off Thus the lower the voltage on the analogue pin the faster the LED flashes To run this example you ll need a potentiometer The one used to tes
21. between 0 and 1024 but as there are only certain points in the PWM cycle where a new value is picked up if a second value is written again quickly the first will have no effect The force_pwm0 routine takes two arguments a new value and a new mode It disables the PWM then sets the value then re enables it with the given mode setting with delays in strategic places to allow the new values to be picked up The pwm of routine simply disables the PWM The code for the mot or program is in motor c Inthe main routine first the connections that must be made on the board to run this program are printed out then call setup io to get the GPIO interface ready for use setup gpio is then called to set GPIO18 up for use as PWM output and GPIO17 up for normal output For the latter both GPIO and OUT are used see page 13 for more info To set GPIO18 first use INP GPIO 18 to activate the pin One of the alternate functions for GPIO18 is to act as the output for the this is alternative 5 Thus use the macro SET GPIO ALT 18 5 to select this alternate use of the pin See table Table 6 31 from the BCM2835 datasheet or the online version at http elinux org RPi_BCM2835_GPIOs for more 29 details about alternative functions of the GPIO pins For a summary of the alternate function of pins used on the Gertboard see Table 1 on page 11 We set the output of GPIO17 low to make sure
22. by chip U3 ports 5 to 8 by chip U4 and ports 9 to 12 by chip 05 The points in the circuit diagrams above are shown as the signals 1 to 12 on the left side of the page and the I O points are BUF1 to BUFI2 to the right of the buffer chips The input jumper locations are the blue rectangles labelled P1 P3 P5 P7 etc to the left of the buffer chips and the output jumper locations are the blue rectangles labelled P2 P4 P6 P8 etc to the right of the buffer chips The pushbutton switches S1 S2 and S3 are shown separately on the right side of the page near the middle Below the pushbuttons the pull up resistors are shown The buffered I O ports can be used with almost any of the GPIO pins they just have to be connected using straps So for example if you want to use port 1 with 17 a strap is placed between the pin in J3 and the GP17 pin in J2 Beware that the pushbuttons cannot be used with GPIOO or and in header 12 on the board as those two pins have 1800Q pull up resistor on the Raspberry Pi When the button is pressed the voltage on the input will be 16 3 3V _ eus 1 2V 10000 18000 This is not an I O voltage which can be reliably seen as low The output and input jumper locations are above and below the U3 U4 and 05 buffer chips The input jumpers need to be placed on the headers below the chips shown on the board with the in text t
23. dSVH 810199 ANG V68 EW EdZSSWV oza S080 44001 sen D 9 p MA X LLIOGT m IXZNOO dSVH AS 310H LHN 3NG HMd NOO 5080 44001 dSVH AS er JequinN en S080 gt ZNO ved gt S080 MOL ZNO ced olanal gt ZNO 024 S080 MOL sana gt ZNO 814 es 9080 ML 20184 S080 _ sana gt CER TEAK na a 9818 zg 9080 S080 _ DER TE AK ne ig 50804 8214 tid gana gt ZNO S080 44001 019 gt VZNOO 2 S080 vana gt ZNO 8d gt ZNO 9d gt ZNO JequinN V 082N Il 9 9 v AVI3H Av 3H 4 Av 3H NAEL JequinN ubru exeu peweu sjeu 030 9080 44001 5 JequinN 1ueuinooq ezi pieoque5 1 u JNQ cNOO JNQ ENOO ANG ENOO ANG ENOO ANG ENOO ANG ENOO Lor a 2 Le Lc 2 2 5 5 D D 69r 89r zor 99r sor ANG ENOO ANG ENOO ANG ENOO ANG ENOO ANG ENOOD
24. different driver say n connect the ground side of the circuit up to RLYn in the headers on the right of the board and connect GP4 in header J2 to RLYn in J4 25 Now when RLY1 in 14 is set low the circuit doesn t receive any power and thus is off When RLY1 in J4 goes high the open collector driver uses transistors to connect the ground side of the circuit to the ground on the board and since this is connected to the ground terminal on the power supply the power supply powers your circuit it is just turned off and on by the open collector driver MOTB MOT 4 S Fuse mox 2A eo 006 20 00000000 00000000005 eee eee ede m out si 41 53 8 B5 p B7 BB ans fel DAI oe 18 3v3 UD J oru PBS 18 i it i PB4 Tm St eet citis 2172 5 m eje of 9 9 6 81 858 sii i estem ERES EL 7 18 2 1 ro 9919919 fai 47 8771685 your circuit poa J3 goes here PDI am your power PDO 19 source Ped goes here 4 PC3 PC2 1 PCO C15 C16 Raspberry Pi Gertboard 21 Oct 2012 pill 3v3
25. familiar if you have been looking at the C test programs for the Gertboard 42 Uploading Sketches using the SPI Bus In order to get your sketch running on the ATmega chip on the Gertboard it has to be transferred over to the chip somehow this is called uploading the sketch There are various methods used to program ATmega chips but we are going to use the SPI bus available on GPIO pins 8 through 11 This is possible because your Arduino IDE is using the special downloader uploader avrdude that you got from projects drogon net To set this up you need to connect the GPIO pins used for the SPI bus to the 6 pin header J23 as in the diagram below Here you are simply connecting the SPI pins in the GPIO to the corresponding SPI pins in the header The arrangement of the pins in J23 is shown in the schematics on page A 6 E OD L MOTB MOT 313 23153453 5155 15 45 5 15 41 ri Fuse 2A 201 8212 3 2 n eje oje e ele eje ej IDE CENA 2 20 19 T 128 125124 isl 1 B gps cn 09 e 15 16 Raspberry Pi Gertboard 21 Oct 2012 Developed by G J van Loo Fen Logic Ltd Figure 27 The wiring diagram for uploading sketches to the ATmega microprocessor To upload your sketch to the chip in Arduino IDE choose File gt Upload Using Programmer It will take a bit of time
26. in the section on analogue to digital and digital to analogue converters D A and A D tests in C page 35 In Python we use packages to provide access to the alternative functions We mention the PC bus use GPIOO and or GPIO2 GPIO3 for rev2 RPis in Table 1 not because the bus is used in the test programs but because each of them has a 18000 pull up resistor on the Raspberry Pi and this prevents them from being used with the pushbuttons see the section on Buffered I O LEDs and Pushbuttons for more information 10 Label GB Port 11 Port RPi2 Alt function which alt Purpose GPO GPIOO GPIO2 SDA 2 I C bus GPIO3 SCL GP4 GPIO4 GPIO4 GP7 GPIO7 GPIO7 SPI_CE1_N alt 0 GP8 GPIO8 GPIO8 SPI CEO N alt 0 GP9 GPIO9 GPIO9 SPI_MISO alt 0 SPI bus GP10 GPIO10 GPIO10 SPI_MOSI alt 0 11 11 11 SPI SCLK alt 0 GP 14 GPIO14 GPIO14 TXD0 alt 0 UART GP15 GPIO15 GPIO15 RXDO alt 0 GP17 17 17 GP18 GPIO18 GPIO18 PWMO alt 5 pulse width modulation GP21 GPIO21 GPIO27 GP22 GPIO22 GPIO22 GP23 GPIO23 GPIO23 GP24 GPIO24 GPIO24 GP25 GPIO25 GPIO25 Table 1 GPIO ports corresponding to labels and alternative functions of GPIO ports GB means Gertboard RPil means Raspberry Pi rev1 RPi2 means Raspberry rev2 Schematics Whilst there are some circuit diagrams
27. is the 0 1024 PWM value to end the loop 31 with step is the incremental decremental PWM value for each successive loop printchar is the character to denote motor accelerating or decelerating The main body of the program contains four calls to Loop to demonstrate acceleration and deceleration in each of two different rotational directions with a short aesthetic pause in between each loop defined by rest 0 013 0 013s When port 17 is 0 the motor rotates in one direction When port 17 is 1 it rotates the other way As usual the main body is contained ina try except block to enable safe port reset before exit on keyboard interrupt Suggested safe tweaks to experiment with Try changing these one at a time and see what they do rest 0 013 change 0 013 to 0 and see why it s there loop 140 1024 1 change 140 to a positive number nearer 0 loop 140 1024 1 change 1024 to a lower number gt 140 loop 140 1024 1 change to another character Digital to Analogue and Analogue to Digital Converters In the Gertboard functional blocks diagram Figure 2 on page 6 the components implementing the converters are outlined in orange Both the digital to analogue converter D A and analogue to digital converter A D are 8 pin chips from Microchip although oddly they are in different sorts of packages The A D labelled U6 on the circuit board is in a dual in
28. must be set on the Raspberry Pi GPIO pins used described below page 19 so that they are read as high logical 1 when the buttons are not pressed Locating the I O Ports on the Gertboard In the functional blocks location diagram Figure 2 on page 6 the components implementing the buffered I O are outlined in red The ICs containing the buffers are U3 U4 and US near the centre of the board The LEDs are labelled D1 to D12 D1 is driven by port 1 D2 by port 2 etc The pushbutton switches the silver rectangular devices with black circles are labelled 51 to 53 51 is connected to port 1 and so on The pins corresponding to Raspi in Figure 8 and Figure 9 above are to B12 on the J3 header above and to the right of the words Raspberry Pi on the board to correspond to the Raspi points in Figure 9 and B4 to B12 correspond to the points in Figure 8 They are called Raspi because these are the ones that are usually connected to the pins in header J2 which are directly connected to the pins in J1 and which are then finally connected to the GPIO pins on the Raspberry Pi The pins corresponding to the I O point on the right of the circuit diagrams above are BUFI to BUF12 in the unlabeled single row header at the top of the Gertboard On the Gertboard schematic I O buffers on page 2 The buffer chips U3 U4 and 05 are clearly labelled It should be clear that ports 1 to 4 are handled
29. pwm c are used to control the SPI bus for reading the A D and the pulse width modulator to control the speed of the motor In the main routine for potmot first we print to the terminal the connections that need to be made on the Gertboard to run this example then we call setup io to set up the GPIO ready for use Then we call setup gpio to set the GPIO pins the way we want them In this we set up GPIO8 to GPIO11 to use the SPI bus using GPIO and SET as described in the section on the converters D A and A D tests in C page 35 GPIO17 is set up as an output using GPIO and OUT and GPIO18 is set up as a PWM using as GP IO and SET ALT as described in the section on the motor controller Motor Test in C page 29 Back in main we call setup spi and setup to get the SPI bus and PWM ready for use and get the motor ready to go Then we repeatedly read the A D and set the direction and speed of the motor depending on the value we read Lower A D values up to 511 recall that the A D chip used returns a 10 bit value so the maximum will be 1023 result in the motor B input being set high and thus the motor goes in the rotate one way as in the motor controller table Table 3 page 27 Confusingly this motor direction is called backwards in the comments of the program Higher A D values 512 to 1023 result in the motor B input being
30. setup_gpio is then called which gets GPIO pins 1 to 3 ready to be used as pushbutton inputs It does this by first using the macro INP_GPIO n where nis GPIO pin number to select these 3 pins for input Then pins are required to be pulled high the buttons work by dropping the voltage down to when the button is pressed so it needs to be high when the button is not pressed This is done by setting GPIO_PULL to 2 the code for pull up Should it ever be required the code for pull down is 1 The code for no pull is 0 this will allows this pin to be used for output after it has been used as a pushbutton input To apply this code to the desired pins set PULLCCLKO 0 03800000 This hexadecimal number has bits 23 24 and 25 set to 1 and all the rest set to 0 This means that the pull code is applied to GPIO pins 23 24 and 25 A short wait allows time for this to take effect and then PULL and GPIO PULLCLKO are set back to 0 Back in the mai n routine a loop is entered in which the button states are read using macro INO grabbing bits 23 24 and 25 using a shift and mask logical operations and if the button state is different from before it is printed out in binary up high is printed as 1 and down low is printed as 0 This loop executes until a sufficient number of button state changes have occurred After the loop unpull pins iscalled which undoes the pull
31. that the motor doesn t turn and then initialize the PWM by calling setup pwm We enable the PWM by setting the mode to PWMO_ENABLE using force_pwm0 Since 7 motor controller B input is set low when the duty cycle on the PWM motor controller A input is high enough the motor will turn the opposite way as described in the motor table on page 27 A loop now starts where the PWM is started first with a very low duty cycle because the value passed to set_pwm0 is low then gradually increasing this to the maximum which is set to 0x400 1024 in set up_pwm Then the value sent to the PWM is decreased to slow the motor down Then GPIO17 is set high so that the motor will get power on the low phase of the PWM signal The PWM is re enabled with the mode PWMO_ENABLE PWMO_REVPOLAR The reverse polarization flag flips the PWM signal so that a low value sent to the PWM results in a signal that is high most of the time rather than low most of the time That way the same code can be used to slowly ramp up the speed of the motor but in the one way direction as in the table on page 27 then slow it down again Finally the PWM is switched off and the GPIO interface is closed down Motor Tests in Python The motor rg py and motor wp py programs are rather different because the RPi GPIO package does not yet support hardware pulse width modulation PWM but WiringPi for Python does it works although it s st
32. the buffer chips are installed Straps are used to connect the following where all the pins are in header J2 and all the pins are in header J3 GP25 to GP24 to B2 GP23 to GP22 to GP21 to B5 GP18 to B6 GP17 to B7 GP11 to B8 GP10 to B9 to B10 GP8 to B11 and GP7 to B12 In other words the leftmost 12 pins are connected to the pins except that GP14 and GP15 are missed out they are already set to UART mode by Linux so it s best if they are not touched 20 If there aren t enough jumpers or straps to wire these connections all up at once don t worry Just wire up as many as possible and run the test Once it s finished the straps jumpers can be moved and the test can be run again Nothing bad will happen if you write to an unconnected pin p 2 L MOTB MOT gt 2 gt D 2 gt 21818181 85 81 81 18181518181 f Fuse mox 2 eo 0 00 0000000000000000000 R201 sls sle ae ale ole ols sls le sls SIs SF 9990 hls J28 225 1 10502 10605 1070 11506 11407 115 08 11609 1210105122011 128124 7 Bl nus 50000 1 1 0080 0804 qoe p oo P Esse x1 J71 Bs SIS 218 215 Sj re 2 HE N e 9 e e a Ew 15 C16 Raspberry Pi
33. this you can type the following from your gertboard sw directory mkdir sketchbook LEDmeter cp LEDmeter ino sketchbook LEDmeter When that is done the sketch will now be in the File Sketchbook menu on the Arduino IDE You can bring it up to inspect the code In this example we created two extra functions turn leds and turn off leds mostly to demonstrate that you can use ordinary C code including functions in sketches The pin numbers are stored in an array to make it easy to turn on or off a specific LED If you want to access LED 4 use Arduino pin 1ed pins 4 In order to do this we put a 0 into the first location of the array because there is no LED One feature of C that you may not be familiar with is the use of scat ic in the definition static int old max led 0 The keyword static means that the value of the variable should be kept the same between function calls So if we assign it a value at the end of one call to Loop the next time loop is called old max led will still have that value The initial value 0 is only assigned once before Loop is called the first time not every time 1oop is called The wiring diagram for LEDmeter is below e EE L MOTA MOTB MOT 345 H Fuse max 2A 2526 DPA L ou 12 772 B20ut B3 S eses x 919 919 eje 9
34. to compile and upload and then your sketch is running on the microcontroller Blink Sketch The Blink sketch is under the File gt Examples gt Basics menu Bring it up and upload it to the ATmega chip using the instructions above The sketch is now running but nothing is happening On most Arduino boards pin 13 the digital pin used by this sketch has an LED attached to it but not the Gertboard You have to wire up the LED yourself Looking at Table 4 above we see that digital pin 13 is labelled PB5 on the Gertboard so you need to connect PBS to one of the I O ports In the section on Buffered I O LEDs and Pushbuttons we explained that you can make an LED show the value of a signal by connecting that signal to one of the pins labelled BUF1 to BUF12 in the unlabeled single row header at the top of the Gertboard So if you connect PB5 to BUFI as below the first LED will start to blink 43 9 2 4 MOTB 181514 eer Sasi si Si sia Sika 2 4 9 9 loleleleteleleleleteleteteleleteleteletetetel ER 53 21020 R125 ep ole 07 8281 cJ fell lel 608 c B20Ut SERRET B5 86 A oea siess n ojo o e e e e amp De d J23 s e ej E x Raspberry Pi Gertboard 21 Oct 2012
35. up as described on page 19 to set GPIO11 to GP7 GPIO4 and up as outputs as described on page 13 Then we enter a loop where we read the state of the pushbuttons and light up the LED corresponding to this number after turning off the LED previously set We turn the LEDs on and off using GPIO_SETO and GPIO CLRO as described on page 21 At the time of writing there is no decoder test in Python ATmega Device The Gertboard can hold an Atmel AVR microcontroller a 28 pin ATmega device at location U8 on the lower left of the board This can be any of the following ATmega48A PA 88A PA 168A PA or 328 P in a 28 pin DIP package Usually the 168 or 328 is fitted The device has a 12MHz ceramic resonator attached to pins 9 and 10 input output pins are brought out to header J25 on the left edge of the board There is a separate 6 pin header J23 on the left side of the board that can be used to program the device The PDO PD1 pins ATmega UART TX and RX are brought out to pins placed adjacent to the Raspberry Pi UART pins so you only need to place two jumpers to connect the two devices Note that the ATmega device on the Gertboard operates at 3 3Volts That 15 in contrast to the Arduino system which runs at 5V This is the reason why the device does not have a 16MHz clock In fact at 3V3 the maximum operating frequency according to the specification is just under 12MHz Warning many of the Ardu
36. using Raspbian which is based on Debian wheezy so from now on we ll assume that you re running this The version number is given in the title bar for wheezy it s 1 0 1 First you will need to configure the IDE to work with the Gertboard Go to the Tools Board menu and choose the Gertboard option with the chip you are using there are 41 options for the ATmega168 and ATmega328 the ones most commonly used on the Gertboard Then go to the Tools Programmer menu and choose Raspberry Pi GPIO Arduino Pins on the Gertboard AII the input and output pins of the ATmega chip are brought out to header J25 on the left edge of the board They are labelled PCn PDn and PBn where is a number These labels correspond to the pinout diagrams of the ATmegal68 328 chips However in the Arduino world the pin numbers of the chips are not referred to directly Instead there is an abstract notion of digital and analogue pin numbers which is independent of the physical devices This allows code written for one Arduino board to be easily used with another Arduino board which may have a chip with a different pinout Thus in order to use your Gertboard with the Arduino IDE you need to know how the Arduino pin number relates to the labels on your Gertboard The table below shows this correspondence GB means Gertboard Arduino Pin pin Arduino Pin GB pin Arduino Pin 0 7 PD7 AO PCO 1 PD1 8 PBO Al PCI 2 PD2 9 A2
37. ANG ENOO 1 k D 2 2 2 2 5 5 D D egr zor scr 18 gsr 2 z Q JNQ cNOO L L L L k vor 5 2 N 2 JNQ cNOO JNQ cNOO Lyn ovr Spr 5 2 2 2 evt Lor 6er i z 22 o o 9 2 2 2 2 2 zer ger ser ver 9 JNQ cNOO 2 N 2 Q L 2 2 2 oer 5 JequinN en H3QV3H 202 80d NNOO XH OW 0dd LdOl 0x 19 08d Igd VI2O _ INIV ZGOd 94 9190 SS ONIV V0DO 9Qd 8d V290 ISON LL 8000 SQd vad VZOO OSIN 21 1 2 4 55 09d 090V OL MOX v Qd Z90 1LNI Edd 4 OLNI ZQd 0d EOdV vOd VGQS vVOQV D _ qxu oad 604 105 400 1 3 5 90 8n 9021 4001 _ 919 3853 94 904 S080 44001 020 S080 44001 619
38. FEN LOGIC LTD Gertboard User Manual Gert van Loo and Vanlnwegen Revision 2 0 The Gertboard is an add on GPIO expansion board for the Raspberry Pi computer It comes with a large variety of components including buttons LEDs A D and D A converters a motor controller and an Atmel AVR microcontroller There are test programs for the Gertboard written in C and Python which are freely available on the Web This manual explains both how to set up the Gertboard for various control experiments and also explains at a high level how the test code works Copyright 2012 by Fen Logic Ltd All rights reserved Contents Geri board Overview pt 5 Dia Sr aris UP 7 Power on the Gertboard 9 GPIO 10 658 ee 11 Test airicinaS auum 11 C Code 11 ibn fictas tede nes iiti 12 Code Overview 13 Downloading the SoftWare sii iet eee 13 Why Different Program Versions 14 Buffered LEDs and Pushbuttons 14 PUSH UULOUS E Ao ot Serene 15 Locating the I O Ports on the 16 Testing the Pushbutton
39. Gertboard 21 Oct 2012 lal M s 2133 Developed by G J van Loo Fen Logic Ltd 18 Figure 13 wiring diagram for LED test program LEDs Test in C The test code in leds c first calls setup io to get everything ready Then setup_gpio is called which prepares 12 GPIO pins to be used as outputs as all 12 I O ports will require controlling All of the GPIO signals except GPIO 0 1 4 14 and 15 are used To set them up for output first INP_GPIO n where is the GPIO pin number for each of the 12 pins to activate them This also sets them up for input so then call OUT GPIO n afterwards for each of the 12 pins to put them in output mode LEDs are switched on using the macro GPIO SETO the value assigned to SETO will set GPIO pin n to high if bit is set in that value When a GPIO pin is set high the I O port connected to that pin goes high and the LED for that port turns on Thus the line of code SETO 0x180 will set GPIO pins 7 and 8 high since bits 7 and 8 are set in the hexadecimal number 0x180 Given the wiring setup above ports 11 and 12 will go high because these are the ports connected to GP7 and GPS and thus the rightmost two LEDs will turn on To turn LEDs off use macro GP TO_CLRO This works in a similar way to SETO but here the bits that are high in the value assigned to GP TO_CLRO specify which GPIO ports will be set low and
40. M The Raspberry Pi has one available hardware PWM port GPIO18 We will use port 17 to control motor direction and port 18 to handle the pulsing The first part of the program imports the required modules including the Python 3 print function explained above in the section on motor rg py After initialising WiringPi port 18 is set to PWM mode with wiringpi pinMode 18 2 and port 17 is set up for normal output Then both ports are set to 0 OFF Wiring instructions are then printed out and the computer waits for user confirmation When the user is ready the program defines three functions that are used repeatedly display printchar handles the correct display of the motor acceleration deceleration indicators using the imported Python 3 print function reset ports handles the resetting of the ports on program exit This is not built into WiringPi for Python so it needs to be defined here This is particularly important in the motor program as it avoids an uncontrollable motor running situation on program exit This is an important safety consideration if you re going to run things with propellers etc loop start pwm stop pwm step printchar handles the main PWM control loop As before this is called in four different ways increasing speed then decreasing speed with motor going one way then increasing and decreasing speed with motor going the other way start pwm is the 0 1024 PWM value to start the loop with stop
41. Monitor on the toolbar of the Arduino IDE but it doesn t work on the Raspberry Pi It assumes that you are talking to an Arduino board over USB not talking to a Gertboard over GPIO The easiest way to retrieve this data is to use the minicom program You can install this easily by typing into a terminal this command sudo apt get install minicom You can use menus to configure minicom by typing minicom s Alternatively included with the Gertboard software is a file ninirc ama0 with the settings you need to read from the GPIO UART pins at 9600 baud Copy this file which was provided by Gordon Henderson to etc minicom you ll probably need to sudo this and invoke minicom by typing sudo minicom Now if you upload the sketch to the ATmega chip you should see the value from the potentiometer displayed in your minicom monitor LEDmeter Sketch This example is one that we created specifically for the Gertboard based on the AnalogInput sketch described above In the gertboard sw directory along with all the C files is one called LEDmeter ino This is an Arduino sketch that makes use of all 12 LEDs to create a bar graph 48 showing the voltage from an analogue input such as a potentiometer First you need to put this sketch in the right place You should have a directory called sket chbook in your home directory Make a subdirectory beneath that called LEDmet er and copy LEDmeter ino into that directory To do
42. P24 to B2 and GP23 to B3 The 8 lowest numbered GPIO pins are used with I O ports 5 to 12 so you need to connect GP11 to B5 GP10 to B6 GP9 to B7 GP8 to B8 GP7 to B9 GP4 to B10 GP1to and to B12 In addition since we are using I O ports 5 to 12 for output you need to install all the out jumpers for buffer chips U4 and US recall that the out jumpers are those above the chips d 4 MOTB X3 F1 Fuse max 2A 8201 8212 19 e e e e e e e e eje e e I TeTeTeTe fete yeTeTeTe Te Tee Te Tee e Te Te Te Ten GND Es eh 51 52 B 91020 gps lel B20Ul B3 s sies s Sr 990800260 6916 916 1 1 1 471 2 B3 B4 s os 816 816 x e e 21 615 C16 Raspberry Gertboard 21 Oct 2012 e 2 5 1593 Figure 26 Wiring diagram for the decoder test Developed by G J van Loo Fen Logic Ltd U8 Decoder Test in C In the main routine for decoder as always we start out by printing out to the terminal the connections that need to be made on the Gertboard Then we call setup to set up the GPIO ready for use Then we call setup_gpio to set GPIO25 to 23 for use with the pushbuttons by 40 selecting them for input and enabling a pull
43. PC2 3 PD3 10 PB2 A3 PC3 4 PD4 11 PB3 A4 PC4 5 PD5 12 PB4 A5 PC5 6 PD6 13 PB5 Table 4 The relationship between Arduino pin numbering and pins on the Gertboard In sketches digital pins are referred to with just a number For example digitalWrite 13 HIGH will set pin 13 PB5 on the Gertboard to logical 1 In the Arduino world LOW refers to logical 0 and HIGH refers to logical 1 The analogue pins are referred to as AO to A5 So to read from analogue pin 0 PCO on the Gertboard you would use the command value 1 0 A Few Sketches to Get You Going A sketch is the name that Arduino uses for a program It s the unit of code that is uploaded to and run on an Arduino board or in our case an ATmega microcontroller on a Gertboard Let s have a look at a simple one Blink which makes an LED turn on and off This is accessible from the Arduino IDE from the File gt Examples gt Basics menu When you select this a new window pops up with the Blink code There are only two functions in the code setup and loop These are required for all Arduino programs set up is executed once at the very beginning and loop is called repeatedly as long as the chip has power Note that you do not need to provide any code to call these functions this is added automatically as part of the compilation and uploading process The language used in these sketches is based on C so the syntax in programs should look
44. PI ports on the Raspberry Pi These are the alternative functions of GPIO ports 7 and 8 In order to make use of atod py dtoa py and dad py you must have SPI enabled and you must install a Python module called py spidev Instructions on how to do this are in the README txt included with the Python programs that you downloaded atod py The user chooses which channel to use on the analogue to digital converter A D then wiring instructions are printed out The function get adc channel uses spidev to read the A D It receives three bytes of data and extracts the result a number between 0 and 1023 where 0 means and 1023 means 3 3V The main loop runs 600 times with a sleep of 0 05s so the program takes about 30 seconds 600 0 05 to run During each iteration of the loop the program reads the A D and displays this reading and a number of symbols proportional to the value read which depends on the position of the 36 potentiometer It uses display char reps adc_value spaces function to achieve this Moving the potentiometer while the program is running changes both the numerical readout and the number of characters displayed Suggested tweaks to experiment with Try changing these one at a time and see what they do char change value of char from to a symbol of your choice line 30 sleep 0 05 change the 0 05 and see what happens line 56 dtoa py The dig
45. The A D value is read and if above 511 we set port 17 to 0 which sets motor direction one way Otherwise direction is set the other way Then the PWM value sent to port 18 is calculated based on the value read from the ADC This determines how fast the motor will spin After the PWM value is written to port 18 the program waits 0 05 seconds and then repeats the main loop reading the A D value again This occurs 600 times so the program runs for about 30 seconds 39 The main loop is wrapped ina try except block to enable safe resetting of the ports in the event of a CTRL C keyboard interrupt Suggested safe tweaks to experiment with e this time Decoder The decoder implemented by the decoder program takes the three pushbuttons as input and turns on one of 8 LEDs to indicate the number with the binary encoding given by the state of the buttons Switch 51 gives the most significant bit of the number 52 the middle bit and 53 the least significant bit For output the LED D5 represents the number 0 D6 represents 1 and so on so D12 represents 7 Recall that the pushbuttons are high 1 when up and low 0 when pushed so LED D12 is lit up when no buttons are pressed giving binary 111 or 7 D6 is lit up when 51 S2 are pressed giving binary 001 etc There is quite a bit of wiring for this one as we are using all but one of the I O ports GPIO25 to GPIO23 are reading the pushbuttons so you need to connect GP25 to B1 G
46. at if the output jumper is installed but the Raspi point is not driven the random behaviour will return There is a series resistor between the input buffer the left pointing triangle and the Raspi point This is to protect the BCM2835 the processor on the Raspberry Pi in case the user programs the GPIO as output but leaves the input jumper in place The BCM2835 input is a high impedance input and thus a 1K series resistor will not produce a noticeable change in behaviour when it is used as input Pushbuttons The Gertboard has three pushbuttons these are connected to ports 1 2 and 3 The circuit for these ports is shown in Figure 9 This circuit is essentially the same as that in Figure 8 with the addition of a pushbutton switch and resistor on the left side When the button is pressed the Raspi point is connected to ground through a resistor and so reads low 15 Raspi 74 244 10 1k I O Figure 9 The circuit diagram for I O ports 1 2 and 3 with pushbutton In order to use a pushbutton the input jumper must not be installed even if the intention is to use this as an input to the Raspberry Pi If it is installed the output of the lower buffer prevents the pushbutton from working properly To make clear what state each button is in the output jumper can be installed and then the LED will now show the button state LED on means button up LED off means button down To use the pushbuttons a pull up
47. d GPIO23 are printed out with GPIO23 first if they have changed since the last cycle So if 01 is displayed on the monitor we can see that GPIO23 is low and GPIO22 is high Note that the LED for port 6 labelled D6 should be off when switch 3 is pressed and on when switch 3 is up Now if the values for GPIO22 and GPIO23 are always the same 00 and 11 will only ever be printed out But occasionally we see 01 10 Note that when this occurs the first digit changes to the new value and then immediately afterwards the second digit changes But the values of both 22 and GPIO23 are read out simultaneously so why do we ever have different values on the two GPIO pins The answer is that signal from the pushbutton which is connected to GPIO23 takes a small amount of time to propagate through the buffers to get to GPIO22 Sometimes we take a reading after GPIO23 has changed but insufficient time has passed for GPIO22 to change state and follow it Butled Test in Python This program but led rg py also only works with RPi GPIO at the moment It is a very similar program to buttons but with two less buttons in use and an LED wired into the circuit which lights on button press Two GPIO ports are used One 23 is pulled HIGH for the button and the other 22 is configured as a regular input In the main while loop the program polls both ports and if there is a change increments the variable but
48. d A D tests in Python iie cte idet eg ee LUE 36 Combined Tests HU cones eee tte doe diete get iet pee 38 A D Motor Controller a tpe 38 ret rette pente dele 39 Potinottest in Python ee ae ea e p te e e ae 39 Decoder deeem nee 40 Decoder estan tme uet tdem ive tee ertet HER ELE 40 mega Device 41 Programming the A Tmeg usce eet 41 Arduino Pins onthe Gertboatd ree 42 A Few Sketches to Get You Going ace d ea te eee ded 42 Uploading Sketches using the SPI Bus eene eene entrent 43 Blink Sketch C 43 Button Sketch ette ttt esso ae ote 44 AnaloselInput Sketch eR ER e bee o t edt tesi eh ee 46 AnalogReadSerial Sketch Using Minicom eese nennen rennen nennen 47 LEDmeter Sketch o e e de e ER be ds 48 Going eedem let ive ee aet etl HEEL 50 For More gt 50 Appendix A Schematies nie pe et et secet Decet ed 50 Gertboard Overview FEE 2 m n 1 A
49. e motor off and on in either direction this is achieved by simply choosing two of the GPIO pins and installing straps between them to the MOTA and MOTB motor controller inputs Then to control the motor the pins are set high or low as in Table 3 To control the speed of the motor however pulse width modulation PWM is required This is a device that outputs a square wave that flips back and forth from on to off very rapidly as shown in Figure 17 27 11111111 LI 0 Figure 17 An example of a PWM output Here the output is on for 50 of the time so it has a duty cycle 50 With a PWM you can control the amount of time the output is high vs when it is low This is called the duty cycle and is expressed as a percentage Figure 17 above shows a 50 duty cycle the one in Figure 18 below is 25 A Lb PL 0 Figure 18 In this PWM example the duty cycle is 25 There is a PWM in the BCM2835 the Raspberry Pi processor and its output can be accessed via GPIO18 it is alternate function 5 If this is connected to one of the motor controller inputs MOTA has been used in our mot or test and the other motor controller input MOTB in our test is set to a steady high or low the speed and direction of the motor can be controlled 1 1 MOTA MOTB 0 0 Figure 19 The motor direction is set by MOTB Whilst MOTA has a duty cycle of 25 the motor receives power whenever MOTA and MOTB are different thus it receives power for
50. e top of the board on the left The labels for them are a bit crowded Each LED has a resistor next to it and thus each label Dn has an Rm next to it The LEDs are easy to find when you have the board powered up as they are a row of bright red lights See below in the section Power on the Gertboard page 9 for information on how to provide power to the Gertboard Pushbutton switches are labelled 51 52 and 53 they are located just beneath the LEDs 8 7 6 5 20 19 18 17 16 15 14 13 12 11 1 2 3 4 1 2 3 4 5 6 7 8 9 10 Figure 6 Two examples of ICs 8 pin and 20 dual inline package DIP In this package style pin 1 is always identified as the first pin anticlockwise from the package notch marking Integrated circuits also known as ICs or chips are marked Un For example the I O buffer chips are U3 U4 and 05 these are near the middle of the board while the Atmel microcontroller is U8 this is below and to the left of U3 to 05 It is important to understand IC pin numbering If the chip is orientated so that the end with the semi circle notch is to the left then pin 1 is the leftmost pin in the bottom row Pin numbers increase in an anti clockwise direction from there as shown in Figure 6 Knowing this means that the sc
51. eeded something for the driver to switch on and off so we created a little circuit consisting of two large LEDs and a resistor in series This is the small circuit to the right of the Gertboard in Figure 16 Once connected the forward voltage across each of these LEDs is a little above so we used a 9V battery as a power supply and calculated a series resistance of around about 90 to set a suitable current flow through the LEDs You can of course use any circuit you like to test this just make sure that the voltage of your power supply is appropriate for your circuit and that it is within the 50V 500mA limit of the driver To turn the circuit off and on using the open collector driver say you want to use driver 1 first check that your circuit works with the external power supply you are using Then leave the positive side of your circuit attached to the positive terminal of the power supply but in addition connect it to one of the RPWR pins in the headers on the right edge of the board they are all connected together Disconnect the ground side of the circuit from the power supply and connect it instead to RLY1 in header J12 on the right of the board Attach the ground terminal of the power supply to any GND or 1 pin on the board Now we need a signal to control the driver For the oco1 test we use GPIO4 to control the open collector you could of course use any logic signal so connect GP4 in header J2 to in J4 To test a
52. eloped by G J van Loo Fen Logic Ltd Figure 24 The wiring diagram for the dad test which allows you to test the A D and D A converters together without the aid of a multimeter or potentiometer D A and A D tests in C Since the D A and A D converters both use the SPI bus the common SPI bus code has been placed into a separate file gb spi There is also an associated header file gb spi h which contains many macros and constants needed for interacting with the SPI bus as well as the declarations for the functions in gb spi c These functions are setup spi and write dac setup spi sets the clock speed for the bus and clears status bits read adc takes an argument specifying the channel should be 0 or 1 and returns an integer with the value read from the A D converter The value returned will be between 0 and 1023 only the least significant 10 bits are set with returned when the input pin for that channel is and 1023 returned for 3 3V The write dac routine takes two arguments a channel number 0 or 1 and a value to write The value written requires some explanation The MCP48xx family of digital to analogue converters all accept a 12 bit value The MCP4822 uses all the bits the MCP4812 ignores the last two and the MCP4802 ignores the last four Since any of those chips might appear on the Gertboard depending on availability write dac is written in so that it will work with all three so
53. er n to allow this pin to be used By default its mode is set up as an input If it is required that the pin is used for an output OUT GPIO n must be called after GPIO n Python Code Overview The Python software along with the bits of this manual describing the Python programs was written by Alex Eames of Raspi TV We are very grateful to him for his help This software is written in Python 2 7 and is compatible with all current revisions of the Raspberry Pi computer and Gertboard It requires sudo user privileges to use the SPI and GPIO ports The Python code relies on several packages to access the various functions of the Gertboard To use the GPIO ports you need to have either RPi GPIO or WiringPi for Python installed or both To use the digital to analogue and analogue to digital converters which use the SPI bus you need to install a module called py spidev Instructions for how to do this are included with the Python programs Downloading the Software To obtain the Python Gertboard software with a browser or on a computer other than your Raspberry Pi visit http raspi tv downloads To get it directly on your internet connected Raspberry Pi first change directory to where you want the programs installed then from the command line type wget http raspi tv download GB Python zip This should download the small file GB Python zip Then type 13 unzip GB_Python zip cd GB_Python 15 The 15 li
54. he triangle is pointing The rectangles are resistors the black triangle and line with arrows coming out is an LED and the hollow circles are header pins In order to make the port function as an input to the Raspberry Pi you install the input jumper shown in the diagram as a staple shape labelled input then the data flows from the I O point to the Raspi point To make the port function as an output the output jumper must be installed then the data flows from the Raspi point to the I O point If both jumpers are installed it won t harm the board but the port won t do anything sensible In both the input and output mode the LED will indicate what the logic level is on the pin The LED will be on when the level is high and it will be off when the level is low There is a third option for using this port if neither the input nor output jumper is placed the I O pin can be used as a simple logic detector The I O pin can be connected to some other logic point i e one that 15 either at OV or 3 3V and the LED will show if the connect point is high or low The resistor on the right side of Figure 8 is a pull up If it were not there the LED would turn off and on with the smallest of electronic changes for example when the board is simply touched Turning the LED on when it is not being driven prevents this seemingly random behaviour and also serves as an indicator that your Gertboard is receiving power properly Note th
55. hematics in Appendix A can always be related to the pins on the ICs on the Gertboard Headers the rows of pins sticking up from the board will be a frequently used component on the Gertboard They are labelled Jn For example there is a collection of headers along the left edge of the board They allow you to access the three chips on the left side of the board J28 on top for the analogue to digital chip J29 below that for the digital to analogue chip and J25 below that for the Atmel microcontroller It is a bit difficult to see the boundary between these headers on a fully assembled board it s much clearer on the blue and grey diagram in Figure 5 On the Gertboard circuit board each header with more than two pins has pin 1 marked with a square around it and a dot next to it The dot is most useful on the assembled board but these dots don t appear in the blue and grey diagram so you can use the squares to find pin 1 there Not everything labelled Jn is a collection of pins J1 at the bottom of the board is the location of the socket that connects the Gertboard to the Raspberry Pi J19 at the top of the board right of centre is a block of screw terminals that allow you to easily connect wires from a power supply and a motor Power on the Gertboard Power pins are marked with their voltage e g 5V or 3V3 this means 3 3V 5V power supply comes onto the board from the Raspberry Pi and if you need this voltage it can be accessed fr
56. hey are separated from the chip they go with by four small resistors and the output jumpers need to be placed on the headers above the chips with the out text If viewed closely it is clearer on the blue and grey diagram it is possible to see that each row of 8 header pins above and below the buffer chips is divided up into 4 pairs of pins The pairs on U3 are labelled B1 to B4 the ones U4 are B5 to B8 and the ones on U5 are B9 to B12 The pins are for port 1 B2 for port 2 etc To use port as an input but not when using the pushbutton if is 1 2 or 3 a jumper is installed over the pair of pins in Bn in the row marked in below the appropriate buffer chip To use port as an output a jumper is installed over the pair of pins in in the row marked out above the appropriate buffer chip out s v R127 RA Du e ojo ofo J71 ba die 5 218 2555555555005 666619 x BIO jn B 45 95 10 R12 Figure 10 Example of port configuration where ports 1 to 3 are set to be outputs and ports 10 and 11 are set to be inputs As a concrete example in Figure 10 ports 1 2 and 3 are configured for output because of the jumpers across B2 and on the out side of chip U3 Ports 10 and 11 are configured for input because
57. hilst the image above is clear it isn t very good at showing exactly how the straps and jumpers are placed o 2 L MOTB MOT 3V3 5 5 5 8 5 8 5 8 8 5 8 5 Fuse 2 5 5 3 5555455 5555585 lel R201 iki ere T s J28 213 a ehhh 47128124 8 2120 gps U7 R126 R12 oo B3 B4R10 25060006655 5515 518 5155 5 423 e e e e a ES Raspberry Pi Gertboard 21 Oct 2012 2 06 9 s Developed by G J van Loo Fen Logic Ltd Figure 12 Wiring diagram for buttons test This type of diagram is much more effective at showing the connections that need to be made so from now on we will use these diagrams to show wiring arrangements 18 In the diagram in Figure 12 black circles show which pins are being connected and black lines between two pins indicate that jumpers if they are adjacent or straps if they are further apart are used to connect them Buttons Test in C The code specific to the buttons testis buttons c In the main routine the connections required for this test are firstly printed to the terminal a text description of the wiring diagram above When the user verifies that the connections are correct setup_io described on page 12 is called to get everything ready
58. ill probably be called something like Application Library for Gertboard From there you can download the file containing the C code it will have a name like gertboard sw 20120725 zip As you can tell by the file extension zip this is a zip file which means that it is a compressed collection of different files all packed together into a single file 11 retrieve the original software put the file where you want your Gertboard software to end up on your Raspberry Pi computer then extract the files by typing the following in one of the terminal windows on your RPi substituting the name of the actual file you have downloaded for the file name we are using in this example unzip gertboard_sw_20120725 zip A new directory gertboard sw will be created Change to this directory by typing cd gertboard sw and list the contents 1 5 You will see a set of C files and a makefile C files are software files but they need to be compiled to run on the processor on your system In the case of Raspberry Pi this is ARM11 The makefile tells the computer how to compile the code so all you need to do it type make all This compiles the C code into executable programs To run a program for example the program leds which tests the LEDs type sudo leds The sudo is there because accessing the GPIO ports requires special privileges and so you need to make an extra effort by typing sudo to execute it The before 1eds mea
59. ill undocumented Thus motor rg py the RPi GPIO version uses software PWM which is found in the function motor If you try both programs you ll probably get smoother results with motor wp py the WiringPi for Python version Both versions use the Python 3 print function which is imported like this from _ future import print function Without this function it would be difficult to prevent line breaks and spaces in the on screen output It means that all print statements need to be written as print instead of just print because they are now function calls and not statements motor rg py software PWM After importing the required modules we define which ports to use 18 and 17 how many times to run each loop Reps PWM cycle time Hertz frequency for motor loop time period F req Then the ports are set up as outputs and set to OFF 0 Next the function run motor Reps pulse width port num time period is defined This controls the GPIO port switching on and off for precise periods of time The port port numis switched on for time pulse width then switched off for time time period and all of that is repeated Reps times 400 in this case The main loop in run motor is inside try except block This is an important safety precaution to ensure the motor is switched off on keyboard interrupt This is even more important with hardware PWM in the other version The run motor function is called many
60. ino example sketches programs mention 5V as part of the circuit Because we are running at 3 3V you must use 3 3V instead of 5V wherever the latter is mentioned If you use 5V you risk damaging the chip The ATmega device and the headers connected to it are in the schematics on page A 6 Programming the ATmega Programming the ATmega microcontroller is straightforward once you have all the infrastructure set up but it requires a fair bit of software to be installed on your Raspberry Pi We are very grateful to Gordon Henderson of Drogon Systems for working out what needed to be done and providing the customized software Using his system you can use the Arduino IDE Integrated Development Environment on the Raspberry Pi to develop and upload code for the ATmega chip on the Gertboard the software needed along with instructions is available at https projects drogon net raspberry pi gertboard For the rest of this section we assume that you have downloaded and successfully installed and configured the Arduino IDE as described at Gordon s website and we proceed from there To get going with the ATmega chip start up the Arduino IDE This should be easy if the installation of the Arduino package was successful you will have a new item Arduino IDE in your start menu under Electronics The exact version of the IDE you get with depends on the operating system you are using The vast majority of Raspberry Pi users are
61. it simply sends to the D A the value it was given If Gertboard is fitted with the MCP4802 it can only handle values between 0 and 255 but these must be in bits 4 through 11 assuming the least significant bit is bit 0 of the bit string it is sent Thus if the desired number to be sent to the D A is between and 255 it must be multiplied by 16 which effectively shifts the information 4 bits to the left before sending this valueto write dac dtoa To test the D A the dt oa program first asks which channel to use and prints out the connections needed to make on Gertboard to run the program Then it calls setup io to get the GPIO ready to 35 use then calls setup gpio to choose which pins to use and how to use them In setup gpio as usual GPIO n where n is the pin number is used to activate the pins This also sets them up to be used as inputs They should however be used as an SPI bus which is one of the alternative functions for these pins it is alternate 0 Thus we use SET GPIO ALT n a where n is the pin number and a is the alternate number in this case to select this alternate use of the pins Then the program sends different values to the D A and asks for real verification using the multimeter that the D A converter is generating the correct output voltage atod To test the A D the at od program first asks which channel should be used and prints out the connections required Gertboard to run
62. ital to analogue converter D A is controlled by writing 2 binary bytes 16 bits in total to it via the SPI interface The program uses a Python module called spidev to handle the SPI communication We have to give spidev two base 10 numbers which it converts into 8 bit binary bytes which it sends to the D A The D A outputs a voltage according to the value given to it An input of 0 gives OV 255 gives 2 048V and it s linear in between so 128 should give 1 02V The pre determined values we send to the D A are stored in two list variables num list holds the first byte different for each channel common holds the second byte of data same for each channel The user chooses the channel and then the main loop takes the first number from each list and combines bytel with byte2 Then it sends them to the D A which immediately outputs the desired voltage until enter is pressed It iterates through all five values setting the D A and waiting for a key press Both channels are reset to zero at the end of the program Suggested tweaks to experiment with e None this time If you change the numbers in the lists you will break the program the voltage output will no longer agree with the numbers that the test program prints out If you want to see how they are derived you can look in the dad py program in the write function dad py This program uses spidev to control the A D and the D A using both of the SPI ports
63. line package whilst the A D U10 is surface mounted Each supports 2 channels Both use the SPI bus to communicate with the Raspberry Pi The SPI pins on the two chips are connected to the pins labelled SCLK MOSI MISO CSnA and CSnB in the header just above J2 on the board thus in the functional blocks diagram these pins are also outlined in orange SCLK is the clock MOSI Master Output Slave Input is the output from the RPi and MISO Master Input Slave Output is the input to the RPi CSnA is the chip select for the A D and CSnB is the chip select signal for the D A the n in the signal name means that the signal is negative thus the chip is only selected when the pin is low Both A D and D A chips have a 10K pull up resistor on their chip select pins so the devices will not be accessed if the chip select pins are not connected The SPI pins are conveniently located just above GP7 to GP11 in header J2 because one of the alternate functions of these pins is to drive the SPI signals For example the ALTO alternative 0 function of GPIO9 is SPIO MISO which is why the pin labelled MISO is just about the pin labelled Thus to use the A D and D A simply put jumpers connecting pins GP7 to GP11 to the SPI pins directly about them although technically you only need CSnA for the A D and CSnB for the D A In the schematics the D A and A D converters are on the upper left of page A 6 Digital to Analogue Converter
64. ns that the program leds isin the current directory Each functional block has at least one test program that goes with it Each test program is compiled from two or more C files The file gb common c which has an associated header file gb common h contains code used by all of the functional blocks on the board Each test has a C file that contains code specific to that test thus you will find the main function here Some of the tests use a special interface for example the SPI bus and these tests have an additional C file that provides code specific to that interface these files are gb spi c for the SPI bus and gb for the pulse width modulator In each of the sections about the individual functional blocks the code specific to the tests for that block is explained Since all of the tests share the code in gb common c an overview of that code will be given here In order to use the Gertboard via the GPIO the test code first needs to call setup io This function allocates various arrays and then calls to associate the arrays with the devices that it wants to control such as the GPIO SPI bus PWM pulse width modulator etc The result of this is that it writes to these arrays control the devices or sends data to them and reads from these arrays get status bits or data from the devices At the end of a test program restore io should be called which undoes the memory map and frees the allocated memory Macros
65. of the jumpers across B10 and B11 on the in side of U5 Figure 10 also demonstrates why we use diagrams instead of photos to show you how to wire up your Gertboard The input jumper on B10 is almost impossible to see because it is shorter than the others In the test programs the required connections are printed out before the tests are started The input and output jumpers are referred to in the following way U3 out B1 means that there is a jumper across the B1 pins on the out side of the U3 buffer chip So the 5 jumpers in the picture above would be referred to as U3 out B1 U3 out B2 U3 out B3 U5 in B10 and U5 in B11 Testing the Pushbuttons There are test programs for the buttons in both C and Python The C version is called buttons and the Python version is called but tons rg py Torun these tests the Gertboard must be set up as in the photo in Figure 11 The wiring diagram in Figure 12 shows the same thing more clearly There are straps connecting pins B2 and in header J3 to pins GP25 GP24 and GP23 in header J2 respectively Thus GPIO25 will read the leftmost pushbutton GPIO24 will read the middle one and 17 23 will read the rightmost pushbutton The jumpers on the out area of U3 out B1 U3 out B2 U3 out B3 are optional if they are installed the leftmost 3 LEDs will light up to indicate the state of the switches Figure 11 Photo showing connections for the buttons test W
66. om the lower pin marked 5V on header J24 on the lower right hand corner of the board Ground is marked with GND or a 4 symbol The supply voltage the voltage that acts as high or logical 1 on the board is 3 3V This is generated from the 5V power pin in the J1 header by the components in the lower right corner of the board To send the 3 3V power supply to the components on the Gertboard you need to install a jumper over the top two pins of the header J7 It is near the lower right corner of the board see the photo and diagram in Figure 7 The open collector and motor controllers can handle higher voltages and have points to attach external power supplies Figure 7 Power jumper installed in header J7 photo on left diagram on right The diagram on the right of Figure 7 above is our first example of a wiring diagram based on the blue and grey circuit board diagram These diagrams indicate pins via black circles around the locations of pins on the board and show connections as black lines between the circles The diagram does not indicate directly whether the two pins should be joined by straps wires or jumpers Generally if the two pins are right next to each other use a jumper and if they are further apart use a strap GPIO Pins The header J2 to the right of the text Raspberry Pi Gertboard on the board provides access to all the pins the GPIO header There 26 pins in J1 the socket which connects the Gertboa
67. on the Raspberry Pi First the wiring instructions are printed out on the screen Then the main loops one for each direction iterate from 0 to 256 and back again in increments of 32 This value is sent to the D A using dac write DAC value and the appropriate voltage appears on the ouput pin DA1 This voltage goes by a jumper to ADO an input of the A D and the adc adc channel function is called to read this voltage using the A D returning a number between 0 and 1023 Both numbers are then printed out along with a bar chart using the character representing the A DC Suggested safe tweaks to experiment with e Change the 32 in both loops for DAC value range 0 257 32 and for DAC value in range 224 1 32 37 Change the 41 adc_string 0 04d Changethe3inprint 55 855 s 0 03d Remove the jumper between ADO and DAI and see what happens Combined Tests This section shows some examples of using more than one functional block at a time A D and Motor Controller In the potmot for potentiometer motor test we use a potentiometer connected to the analogue to digital converter A D to get an input value and this value is used to control the speed and direction of the motor It is set up so that at one extreme the motor is going at top speed in one direction as you move the wiper towards the middle it slows at the middle the motor stops and as you continue to move the wiper al
68. ong the motor speeds up again but in the other direction To wire up the Gertboard for this example you combine the wiring for the A D and motor tests Jumpers connect GP8 to GP11 to the pins directly above them to allow us to control the SPI bus using GPIOS to GPIO11 You must attach your potentiometer to the ADO input GPIO17 controls the motor B input and GPIO18 controls the motor A input using the pulse width modulator PWM Thus GP17 must be connected via a strap to MOTB and GP18 must be connected to MOTA The motor and its power source must be connected to the screw terminals in J19 at the top of the board See the wiring diagram below your power source goes here uz o o o 2 1 13 1 000 000000000000000000000 201 8212 3 27 drr rrr Je eje eje oje eje oje 1084 9 kolak 128124 sO 8506 dei sp se eps qs i R127 GND E Bi B20Ut B3 6 eje ojo LLL 1 a e 3 Raspberry Pi Gertboard 21 Oct 2012 9 3 3 Figure 25 Wiring diagram for the potmot test Developed by G J van Loo Fen Logic Ltd 38 Potmot Test The main routine for this is potmot c Functions from gb_spi c and gb
69. or schematics in the main body of the manual for some of the functional blocks of the board they are simplifications of the actual circuits While these simplified diagrams and the explanations in the text will be good enough for most uses of the Gertboard there will occasionally be questions that can only answered by knowing exactly what is on the board Thus we have attached the full schematics at the end of this manual as Appendix A These pages are in landscape format The page numbers A 1 2 etc are in the lower left corner of the pages if you hold them so that the writing is the right way up Test Programs Overview There are test programs for the Gertboard written in C and in Python C provides the most direct access to the Gertboard functionality but it is not a language that is very accessible to the beginner programmer Several packages have been written to allow Python code to access the Raspberry Pi GPIO pins and alternative functions of these pins such as Serial Peripheral Interface SPI bus and pulse width modulation PWM Using these packages you can access most of the functionality of the Gertboard with Python At the time of writing the only major functional block that to our knowledge cannot be programmed with Python is the Atmel microcontroller C Code Overview To download the Gertboard C software go to http www element14 com and search for Gertboard using the box at the top of the screen The link you want w
70. ou need the potentiometer attached to analogue input 0 as for the AnalogInput sketch In addition you need to connect the ATmega chip s UART pins to the Raspberry Pi Digital pin 0 PDO on the Gertboard is RX receive and digital pin 1 PD1 on the Gertboard is TX transmit These signals are also brought out to the pins labelled MCTX and MCRX just above the GP15 and GP14 pins in header J2 on the Gertboard Thus you can use two jumpers to attach the ATmega s TX to GP15 and RX to GP14 as shown in Figure 33 47 Fuse max 2A mon Bi e e 9 ES C15 C16 Raspberry Pi Gertboard 21 Oct 2012 8 a sll Developed by G J van Loo Fen Logic Ltd Figure 33 Wiring diagram for the sketch AnalogReadSerial GPIO14 and 5 are the pins that the Raspberry Pi uses for the UART serial port If you refer back to the table of alternate functions Table 1 page 11 you will see that GPIO14 is listed as TX and GPIO15 as RX This is not a mistake This swapping is necessary the data that is transmitted by the ATmega is received by the Raspberry Pi and vice versa Now how to we get the Raspberry Pi to read and show us the data that the ATmega is sending out on the serial port There is a button labelled Serial
71. p py programs are the ways the GPIO ports are driven and cleaned up and the Raspberry Pi board revision checker In the programs first the Raspberry Pi board revision is checked and based on the result the correct ports for the LEDs are defined in a list called ports Since we need to go both forwards and backwards we then make a copy of the list name it ports rev and reverse it Then we set up the ports for output by iterating through the list ports After that we define the main engine of this script the function led drive which requires three arguments reps multiple direction reps defines how many times to run the process 1 or 3 in this demo 2 multiple defines whether or not to switch an led off before switching on the next one 1 leave it on i e multiple LEDs lit 3 direction defines whether to use the forward or reverse ports list ports for forwards ports rev for reverse There are eight calls to the 1 function so we ve saved a lot of program lines by reusing the same code multiple times the calls to the 1 drive function are enclosed ina t ry except block This ensures that if you exit via CTRL C the GPIO ports will be reset or cleaned up This avoids false warnings the next time you want to use them that the ports are already in use by another program Suggested tweaks to experiment with Try changing these one at a time and see what they do led drive 3 0
72. ped by To test the D A a multi meter is required The C test program for this is dt oa The Python version is dtoa py To set up Gertboard for this test jumpers are placed on the pins GP11 GP10 GP9 and GP7 connecting them to the SPI bus pins above them Attach the multi meter as follows the black lead needs to be connected to ground You can use any of the pins marked with L or GND for this 33 The red lead needs to be connected to DAO to test the D A channel 0 which is shown below or DAI for channel 1 Switch the multimeter on and set it to measure voltages from 0 to around 5V All this is shown in Figure 22 The test program for the A D is called at od the Python version is atod py To run this test a voltage source on the analogue input is required This is most easily provided by a potentiometer a variable resistor The two ends of the potentiometer are connected one side to high 3 3V which you can access from any pin labelled 3V3 and the other to low GND 1 and the middle wiper part to ADO for channel 0 as shown below or AD1 for channel 1 To use the SPI bus jumpers should be installed on the pins GP11 GP10 GP9 and GP8 connecting them to the SPI bus pins above them This is shown in Figure 23 MOTA MOTB MOT Fuse max 2 R201 R212 5 eje 919 916 ele 919 919 2 o GND
73. rd to the Raspberry but only 17 pins in J2 3 of the pins in J1 are power 3 3V and 5V and ground and 6 are DNC do not connect The labels on these pins GPO GP1 GP4 GP7 etc may initially seem a little arbitrary as there are some obvious gaps and the numbers do not correspond with the pin numbers on the GPIO header J1 These labels are important however they correspond with the signal names used by the BCM2835 the processor on the Raspberry Pi RPi Signal on the 2835 datasheet corresponds to the pin labelled on header 72 At least this was true of the first version of the Raspberry Pi 17 Starting in September 2012 revision 2 Raspberry Pis rev2 were starting to be shipped On the rev2 RPis some of the GPIO pins have been changed The GPIO port that used to be controlled by GPIO21 is now controlled by GPIO27 and the ports that used to be controlled by GPIOO and are now controlled by GPIO2 and GPIO3 The rest have remained the same The first three columns of Table 1 below summarize the current situation Some of the GPIO pins have an alternate function that is made use of in some of the test programs These are also shown in Table 1 in the last two columns The ports that have nothing in the Alt function column are only used as general purpose input output in the code In the C test programs we use macros to gain access to the alternative functions of the GPIO ports This is explained
74. read and if pressed a 1 is stored in a list variable called status_list If not pressed a 0 is stored Then the status_list values are all checked against the previous_status If there s a change this line if current_status previous_status executes a small section of the program that displays the new values on the screen increments the value of the iterator button press and the loop starts again from the top Now it s one button press closer to the end point of 19 The while loop is enclosed in t ry block try lt while block gt except KeyboardInterrupt This enables the program to reset the ports if CTRL C is pressed to terminate the program early If the program ends normally after 19 button presses the ports will be reset anyway If we hadn t included the try except block a keyboard interrupt ctrl c would close the program but leave the ports open This would give errors if you tried to use the ports again Suggested tweaks to experiment with Try changing these one at a time and see what they do e while button_press lt 20 change the 20 to some other number button press 1 change the 1 to some other number Testing the LEDs The test program for the LEDs is called leds The Python versions are 1eds rg py and leds wp py To set up the Gertboard to run this test see the wiring diagram in Figure 13 Every port is connected up as an output so all the out jumpers those above
75. rograms at time of writing buttons rg py buttons program using RPi GPIO leds rg py leds program using RPi GPIO leds wp py leds program using WiringPi butled rg py button and LED program using RPi GPIO motor rg py motor program using software PWM and RPi GPIO motor wp py motor program using hardware PWM and WiringPi ocol rg py relay switching program using RPi GPIO ocol wp py relay switching program using WiringPi atod py test for analogue to digital converter using SPI with spidev dtoa py test for digital to analogue converter using SPI with spidev dad test for both D A and A D using SPI with spidev potmot py test using A D and motor using WiringPi and spidev Buffered I O LEDs and Pushbuttons There are 12 pins which can be used as input or output ports Each can be set to behave either as an input or an output using a jumper Note that the terms input and output here are always with respect to the Raspberry Pi in input mode the pin inputs data to the RPi in output mode it acts as 14 output from the RPi It is important to keep this in mind as the Gertboard is set up an output from the Gertboard is an input to the Raspberry Pi and so the input jumper must be installed Raspi 3 3V input 74xx244 Figure 8 The circuit diagram for I O ports 4 12 The triangle symbols in the diagram above represent buffers they propagate logical values low and high in the direction t
76. set low and the motor goes in the rotate opposite way direction This is called forwards in the comments of the program Simple arithmetic is used to translate A D values near 511 to slow motor speeds and A D values near the endpoints of the range 0 and 1023 to fast motor speeds by varying the value sent to the PWM Potmot test in Python This program potmot wp py uses spidev to control the A D and WiringPi for Python to control the motor with the hardware PWM Essentially potmot is a simplified combination of the atod py and motor wp py programs It is simplified in that there is no on screen display of the A D reading or motor direction The potentiometer position read by the ADC determines motor direction and speed PWM value as follows middle value 511 results in no movement 1023 results in max speed one way 0 results in max speed the other way First the program imports the required modules spidev and wiringpi then sets up GPIO ports 17 and 18 as digital output and PWM output respectively Then two functions are defined get adc reads the voltage at the potentiometer using the A D reset ports ensures we can safely exit the program with the ports switched off Then the initial values of variables are set and the wiring instructions are printed out on the screen The program then waits for user input before proceeding Once the user hits enter the SPI port is opened to read the potentiometer voltage using the A D
77. should be tested but it only uses this information to print out the connections that need to be made Otherwise it ignores your response Open Collector Test in Python The two open collector programs ocol wp py and ocol rp py are identical apart from the GPIO system used In the programs the function which channel handles the user channel selection Once a suitable input is obtained correct wiring instructions are displayed Once enter is pressed to confirm the wiring is done the program switches the chosen open collector port on and off 26 ten times with 0 4 second delay between each change At the end or CTRL C keyboard interrupt the GPIO ports are reset Suggested safe tweaks to experiment with Try changing these one at a time and see what they do e vary the 0 4in sleep 0 4 changethe 10in for i in range 10 e see what happens if you try to tell it you want to use driver 7 when using the program e change the error message displayed when choosing the wrong port number to an alternative one of your choice Motor Controller The Gertboard has a ROHM BD6222HFP motor controller The motor controller is for brushed DC motors and can handle a maximum voltage of 18V and max current of 2A The controller has two input pins A and B labelled MOTA and MOTB on the board The pins can be driven high or low and the motor responds according to the table below The speed of the motor can be controlled b
78. sts all the files in the directory Most of them end in py and are Python programs The file README t xt contains amongst other info instructions on how to install the packages you need to run the Python programs Once you have the necessary packages installed you can run the programs For example if want to run the program 1eds rg py which tests the LEDs using the RPi GPIO package see below type sudo python leds rg py Why Different Program Versions There are two General Purpose Input Output GPIO packages for Python RPi GPIO and WiringPi for Python The programs that come in two versions like leds rg py and leds wp py are using these different packages It is desirable to have the both these packages because neither of them yet offers a fully finished set of capabilities but most of the capabilities are covered between them RPi GPIO s weakness is the lack of hardware PWM pulse width modulation used with the motor program WiringPi s weakness is the lack of pull up facility required to use the buttons If you want to use the full functionality of the board you will need to install both For some of the programs for example leds and 1 no special features are used and you can use either package The programs using the RPi GPIO package are the ones called ilename rg py whilst the ones using the WiringPi for Python package are the ones called ilename wp py Here is a list of all the Python test p
79. t the A D will work fine here The comments for AnalogInput say to connect the potentiometer so that the wiper is on analogue pin 0 PCO on the Gertboard and the outer pins are connected to 5 and ground Remember you must use 3 3V instead of 5V as we re running the chip at 3 3V here The diagram below shows how to connect up the Gertboard to make this sketch work after it is uploaded 46 Fuse max 2A D BHHHBHHH 1 11407 115 i 24 el E BED 99129029 9 di 423 e e 9 2 ES CI5 C16 Raspberry Pi Gertboard 21 Oct 2012 02 Figure 32 Wiring diagram for the AnalogInput sketch Developed by G J van Loo Fen Logic Ltd AnalogReadSerial Sketch Using Minicom Some of the Arduino sketches involve reading or writing data via the serial port or UART An example is AnalogReadSerial which is in File gt Examples gt Basics This sketch sets the baud rate to 9600 then repeatedly reads in a value from analogue pin and prints this value to the serial port also called The value read in is between 0 and 1023 0 means that the input pin is at OV and 1023 means that it is at the supply voltage 3 3V for the Gertboard To set up your Gertboard for this sketch y
80. the program Then it calls setup io to get the GPIO ready then calls setup gpio to choose which pins will be used and how they will be used The setup gpio used works the same way as the one in dt oa except for activating GPIO8 instead of GPIO7 Then at od repeatedly reads the 10 bit value from the A D converter and prints out the value on the terminal both as an absolute number and as a bar graph the value read is divided by 16 and the quotient is represented as a string of characters One thing to be aware of is that even if the potentiometer is not moved exactly the same result may not appear on successive reads With 10 bits of accuracy it is very sensitive and even the smallest changes such as house current running in nearby wires can affect the value read dad To test both the D A and A D at the same time the dad test sends 17 different digital values to the D A 0 to 255 in even jumps then back down to 0 The resulting values are then read in from the A D Both the original digital values sent and the values read back are printed out as is a bar graph representing the value read back divided by 16 as in at od The bar graph printed out should be a triangle shape the lines will start out very short then get longer and longer as larger digital values are read back then will get shorter again D A and A D tests in Python The analogue to digital and digital to analogue converters are connected to the S
81. times from the 1oop function Each loop 400 30 repetitions is just one step up or down in motor speed 400 repetitions at 2000 Hertz represents just 0 2 seconds Then we define the run_loop function run_loop startloop endloop step port_num printchar The arguments start 1 and endloop are the time for the switched port to be ON at the start and end of the loop step is the size of the increment for each successive loop port__num is the port we re switching 17 or 18 printchar is the acceleration deceleration indication character or The run 1 function handles the repeated calls to the run_motor function causing it to run its 400 cycles for each set of values defined After the functions are defined wiring instructions are printed out and the computer waits for a key press of enter to confirm the user is ready Then 1oop function is called four times to drive the motor speed from 596 to 9596 and back again in each direction After this both ports are set to OFF False and then reset Suggested safe tweaks to experiment with Try changing these one at a time and see what they do run loop 5 95 1 18 change to something else run loop 5 95 1 18 change 5 to a higher number lt 95 e run loop 5 95 1 18 change 95 to a lower number but still greater than what you changed the 5 to motor wp py hardware PW
82. ton press and displays the new values on the screen The strap from U3 out B3 pin to BUF6 in the top header connects the LED to the button causing it to light and the other input port 22 to go HIGH when the button is pressed The values are displayed on the screen as with the buttons program Now if the values for GPIO22 and GPIO23 are always the same 00 and 117 will only ever be printed out But occasionally we see 01 10 Note that when this occurs the second digit changes to the new value and then immediately afterwards the first digit changes This is opposite of the behaviour of the C program where the first digit sometimes changes before the second Why is it acting differently In the Python code the values are read in by this line of code status list str GPIO input 23 str GPIO input 22 This causes GPIO23 to be read before GPIO22 If the button is pressed or released between these two reads GPIO23 will still have the old value but the new value will be read from GPIO22 The new value won t be read from GPIO23 until the next time through the whi1e loop Open Collector Driver The Gertboard uses six ports of a ULN2803a to provide open collector drivers These are used to turn off and on devices especially those that are powered by an external power supply and need a different voltage or higher current than that available on the Gertboard Basically an open collector connects the ground side of
83. up on the pins then call restore common c to clean up Buttons Test in Python This program buttons rg py is only available using the RPi GPIO package at the moment because the pull up facility in WiringPi for Python is not yet available The buttons cannot be used without this facility First the program imports the RPi GPIO module it needs to handle GPIO control Then the command GPIO setmode GPIO BCM sets up the BCM numbering scheme for the pins The result of this is that the pin numbers in the Python code are the numbers that the BCM2835 the Raspberry Pi processor uses to refer to the pins Otherwise the numbers in the Python code will refer to the pin numbers in the J1 header which is the same as their placement in the P1 header on the RPi The next two lines set up ports 23 25 with pull up for i in range 23 26 GPIO setup i GPIO IN pull up down GPIO PUD UP 19 Note that because the way Python for loops work the end point of the loop must be set to one beyond the last item in the range that you want to cover So in order to set port 25 the end point of the loop command must be set to 26 Next the wiring instructions appear on the screen Once the user confirms that the wiring is ok the initial values for variables button_press and previous_status are set Next a while loop runs until 19 button presses releases have occurred For each iteration of this loop the status of each button is
84. y applying a pulse width modulated PWM signal to either the A or B pin A B Motor action 0 0 no movement 0 1 rotate one way 1 0 rotate opposite way from above 1 1 no movement Table 3 Truth table showing the behaviour of the motor controller under different logic combinations The motor controller IC has internal temperature protection Current protection is provided by a fuse on the Gertboard The motor controller is in the schematics on page A 4 On the Gertboard functional block diagram Figure 2 on page 6 the area containing the components for the motor controller are outlined in purple The motor controller and screw terminals are near the top of the board and there are two pins for the control signals in J5 a small header just above GP4 and in header J2 The MOTA and MOTB pins J5 are the inputs to the motor controller these are digital signals low and high The screw terminals at the top of the board labelled MOTA and MOTB are the outputs of the motor controller they actually provide the power to the motor The motor will probably need more power a higher voltage or current than that provided by the Gertboard The screw terminals at the top labelled MOT and 1 allow the connection of an external power supply to provide this the motor controller directs this power to the MOTA and MOTB screw terminals modulating it according to the MOTA and MOTB inputs in J5 If you just want to turn th

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