1 Equipment familiarization: multimeter, breadboard, and
Contents
1. 7 107 Gray 80 8 108 White 90 9 109 Gold 5 Silver 10 None 20 Stripe 1 Stripe 2 Stripe 3 Tolerance Stripe the breadboard screw heads for example has a low resistance path to ground r If you accidentally connect power or ground to the potentiometer s center tap you can easily burn out the pot rendering it useless If in doubt have someone check your circuit before turning on the power Use Ohm s law to predict the current that will ow around the circuit if you use the power supply that you set to its midpoint in the previous exercise What current should ow if the supply is set to its minimum voltage What is the current if the supply is set to its maximum voltage www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information 8 Hands on electronics Now turn on the breadboard power measure the currents for these three voltages and compare with your predictions Make a graph of voltage vs current from these measurements Is the relationship linear How close is the slope of voltage vs current to 10 k 1 2 3 Measuring resistance Now turn off the breadboard power and disconnect your series circuit In this and the following part the pot should connect only to the meter Set the meter for resistance and m2. carbon lm metal lm or wound up wire en cased in an insulating coating with wire leads sticking out the ends Often the resistance is indicated by means of colored stripes according to the resistor color code Table 1 2 Resistors come in various sizes accord ing to their power rating The common sizes are 1 8 W 1 4 W 1 2 W 1 W and 2 W You can easily verify this linear relationship between voltage and current using the xed 10 k 10 000 ohm resistance provided between the two ends of one of the breadboard s potentiometers A potentiometer is a type of resistor that has an adjustable center tap or slider allowing electrical connections to be made not only at the two ends but also at an adjustable point along the resistive material The 10 k pot as it is called for short is located near the bottom edge of the breadboard and can be adjusted by means of a large black knob 3 Inside the breadboard s case the ends of the pot as well as the center tap connect to sockets as labeled on the breadboard s front panel By pushing wires into the sockets you can make a series circuit Fig 1 3 consisting of an adjustable power supply the 10 k pot and the multimeter con gured to measure current You can attach alligator clips to the meter leads to connect them to the wires But before doing so be sure to observe the following warnings r First turn off the breadboard power to avoid burning an
3. supply to a voltage half way between its minimum and maximum for use in the next part 1 If you wonder what we mean by within reason ask yourself what bad thing would happen if you connected the DMM common to say twenty million volts if you re interested see e g H C Ohanian Physics 2nd edition vol 2 Interlude VI Norton New York 1988 esp pp VI 8 for more information on this www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information 5 1 Equipment familiarization DMM Power Supply _ Power Supply Multimeter V V mA COM A Ground Common b a 1 F Fig 1 2 Measuring voltage a An arbitrary circuit diagram is shown as an illustration of how to use a voltmeter Note that the meter measures the voltage drop across both the resistor and capacitor which have identical voltage drops since they are connected in parallel b A drawing of the same circuit showing how the leads for a DMM should be connected when measuring voltage Notice how the meter is connected in parallel with the resistor DMM Power Supply _ Power Supply Multimeter Potentiometer Slider Center Tap Ground Common 0 011 A V mA COM A A b a Fig 1 3 Measuring curre
4. adjusts the viewing angle for greater comfort when you are seated at a workbench so we recommend that you use it 1 3 1 Probes and probe test Oscilloscopes come with probes cables that have a coaxial connector sim ilar to that used for cable TV on one end for connecting to the scope and a special tip on the other for connecting to any desired point in the circuit to be tested To increase the scope s input impedance and affect the cir cuit under test as little as possible we generally use a 10X attenuating probe which has circuitry inside that divides the signal voltage by ten Some scopes sense the nature of the probe and automatically correct for this factor of ten others such as the TDS210 need to be told by the user what attenuation setting is in use As mentioned above your scope should also have a built in calibrator circuit that puts out a standard square wave you can use to test the probe see Fig 1 4 The probe s coaxial connector slips over the ch 1 or ch 2 input jack and turns clockwise to lock into place The probe tip has a spring loaded sheath that slides back allowing you to grab the calibrator signal contact with a metal hook or grabber An attenuating scope probe can distort a signal The manufacturer there fore provides a compensation adjustment screw which needs to be tuned for minimum distortion The screw is usually located on the assembly that connects the probe to the
5. display to handle inputs of various size Note to obtain the highest measurement precision set the knob to the lowest setting for which the input does not cause over ow 1 www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information 2 Hands on electronics Table 1 1 Digital multimeter inputs Input jack Purpose Limitsa COM reference point used for all measurements V input for voltage or resistance measurements 1000 V DC 750 V AC mA input for current measurements low scale 200 mA 10 A input for current measurements high scale 10 A aFor the BK Model 2703B multimeters used in the authors labs To avoid damaging the meter be sure to read the safety warnings in its data sheet or instruction booklet 1 2 Breadboard Breadboard may seem a peculiar term Its origins go back to the days when electronics hobbyists built their circuits on wooden boards The breadboards we use represent a great step forward in convenience since they include not only sockets for plugging in components and connecting them together but also power supplies a function generator switches logic displays etc The exercises that follow were designed using the Global Specialties PB 503 Protoboard If you do not have access to a PB 503 any suitable breadboard
6. scope or occasionally on the tip assembly Display the calibrator square wave signal on the scope If the signal looks distorted i e not square carefully adjust the probe compensation using a small screwdriver If you have trouble achieving a stable display try autoset Check your other probe Make sure that both probes work are prop erly compensated and have equal calibrations Sketch the observed waveform Consult your oscilloscope user manual for more information about car rying out a probe test Note that each probe also has an alligator clip sometimes referred to as the reference lead or ground clip This connects to the shield of the coaxial cable It is useful for reducing noise when looking at high frequency www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information
7. 1 Equipment familiarization multimeter breadboard and oscilloscope In this chapter you will become acquainted with the workhorses of elec tronics testing and prototyping multimeters breadboards and oscillo scopes You will nd these to be indispensable aids both in learning about and in doing electronics Apparatus required One dual trace oscilloscope one powered breadboard one digital multi meter two 10X attenuating scope probes red and black banana leads two alligator clips 1 1 Multimeter You are probably already familiar with multimeters They allow measure ment of voltage current and resistance Just as with wristwatches and clocks in recent years digital meters commonly abbreviated to DMM for digital multimeter or DVM for digital voltmeter have superseded the ana log meters that were used for the rst century and a half or so of electrical work The multimeters we use have various input jacks that accept banana plugs and you can connect the meter to the circuit under test using two banana plug leads The input jacks are described in Table 1 1 Depending on how you con gure the meter and its leads it displays r the voltage difference between the two leads r the current owing through the meter from one lead to the other or r the resistance connected between the leads Multimeters usually have a selector knob that allows you to select what is to be measured and to set the full scale range of the
8. bs 15 15 SPDT Switches Logic Switch Bank Push Button De Bounced Switches Vertical Column Group of 25 Fig 1 1 Illustration showing many of the basic features of the PB 503 powered Protoboard with internal connections shown for clarity Note that each vertical column is broken into halves with no built in connection between the top and bottom AWG number may damage the socket so that it no longer works reliably for thin wires The PB 503 sockets are internally connected in groups of ve horizontal rows or twenty ve vertical columns see Fig 1 1 Each power supply connects to a banana jack and also to a row of sockets running along the top edge of the unit The three supplies 5 V red jack 15 V yellow jack and 15 V blue jack have a common www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information 4 Hands on electronics ground connection black jack The 15 V and 15 V supplies are actually adjustable using the knobs provided from less than 5 volts to greater than 15 volts 1 2 1 Measuring voltage Voltage is always referenced to something usually a local ground For the following exercises you will measure voltage with respect to the breadboard ground which is also the common ground for the thre
9. e position of the beam was thus a direct analog of the input voltage In the past few years analog scopes have been largely superseded by digital devices such as the TDS210 although low end analog scopes are still in common use for TV repair etc A digital scope operates on the same principle as a digital music recorder In a digital scope the input signal is sampled digitized and stored in memory The digitized signal can then be displayed on a computer screen One of your rst objectives will be to set up the scope to do some of the things for which you may already have used simpler scopes After that you can learn about multiple traces and triggering In order to have something to look at on the scope you can use your breadboard s built in function generator a device capable of producing square waves sinusoidal waves and triangular waves of adjustable amplitude and frequency But start by using the built in calibrator signal provided by the scope on a metal contact labeled probe comp or something similar often located near the lower right hand corner of the display screen www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information 10 Hands on electronics Note that a leg folds down from the bottom of the scope near the front face This
10. e power supplies To measure a voltage you will rst connect the common jack of the meter to the breadboard common i e breadboard ground Next you will connect the meter s voltage jack to the point of interest The meter will then tell you the voltage with respect to ground at this one point When connecting things it s always a good idea to use color coding to help keep track of which lead is connected to what Use a black banana plug lead to connect the common input of the meter to the ground jack of the breadboard black banana jack labeled with a or symbol Use a red banana plug lead with the V input of the meter Since the DMM is battery powered it is said to oat with respect to ground i e within reason 1 one may connect the DMM s common jack to any arbitrary voltage with respect to the breadboard ground It is therefore possible to measure the voltage drop across any circuit element by simply connecting the DMM directly across that element see Fig 1 2 Warning This is not true for most AC powered meters and oscilloscopes To practice measuring voltages measure and record the voltage between each power supply jack and ground In each case set the meter s range for the highest precision i e one setting above over ow Adjust the 15 V and 15 V supplies over their full range and record the minimum and maximum voltage for each Carefully set the 15 V
11. easure and record the resistance between the two ends of your 10 k pot Due to manufacturing tolerances you will probably nd that it is not exactly 10 k By what percentage does it differ from the nominal 10 k value Does the measured value agree more closely with the slope you previously measured than with the nominal value Explain Now connect the meter between the center tap and one end of the pot What resistance do you observe What happens to the resistance as you turn the potentiometer s knob Leavingtheknobinoneplace measureandrecordtheresistancebetween the center tap and each end Do the two measurements add up to the total you measured above They should explain why 1 3 Oscilloscope With its many switches and knobs a modern oscilloscope can easily in timidate the faint of heart yet the scope is an essential tool for electronics troubleshooting and you must become familiar with it Accordingly the rest of this laboratory session will be devoted to becoming acquainted with such an instrument and seeing some of the things it can do The oscilloscope we use is the Tektronix TDS210 illustrated in Fig 1 4 If you don t have a TDS210 any dual trace oscilloscope analog or digital can be used for these labs as long as the bandwidth is high enough ideally 30 MHz or higher While the description below may not correspond exactly to your scope with careful study of its manual you should be able to gure out how t
12. nt a Schematic diagram of series circuit consisting of power supply 10 k potentiometer and multimeter Note that the center tap of the potentiometer is left unconnected in this exercise accidentally connecting it to power or ground could lead to excessive current ow and burn out the pot b A drawing of the same circuit showing how the DMM leads should be con gured to measure current Note that the meter is connected in series with the resistor 1 2 2 Measuring current resistance and Ohm s law Current is measured by connecting a current meter an ammeter or a DMM in its current mode in series with the circuit element through which the current ows see Fig 1 3 Note carefully the differences between Fig 1 2 and Fig 1 3 www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information 6 Hands on electronics Recall that Ohm s law relates current I voltage V and resistance R according to V IR 1 1 This is not a universal law of electrical conduction so much as a statement that there exist certain materials for which current is linearly proportional to voltage 2 Materials with such a linear relationship are used to fabricate resistors objects with a known and stable resistance Usually they are little cylinders of carbon
13. o use your scope to carry out these exercises The TDS210 is not entirely as it appears In the past you may have used an oscilloscope that displayed voltage as a function of time on a www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information 9 1 Equipment familiarization TDS 210 60 MHz 1 GS s MEASURE CURSOR CH 1 CH 2 TRIGGER MENU VERTICAL CONTROLS VOLTS DIV SEC DIV HORIZONTAL CONTROLS TRIGGER LEVEL MENU OPTION BUTTONS AUTOSET CALIBRATION CONTACT POINT Trigger Info Horizontal and Vertical Info Menu Options MENU Trigger Level Menu Options Menu Options Menu Options Menu Options Volts per Division Seconds per Division Fig 1 4 Illustration of the Tektronix TDS210 digital oscilloscope The basic features to be used in this tutorial are marked Note and remember the location of the autoset button when all else fails try autoset cathode ray tube CRT While the TDS210 can perform a similar function it does not contain a CRT part of the reason it is so light and compact Until the 1990s most oscilloscopes were purely analog devices an input voltage passed through an ampli er and was applied to the de ection plates of a CRT to control the position of the electron beam Th
14. willdo providedyouhaveafunctiongeneratorandtwovariable power supplies Additional components that you will need along the way that are built into the PB 503 include a 1 k and a 10 k potentiometer a small 8 speaker two debounced push button switches several LED logic indicators and several on off switches Fig 1 1 displays many of the basic features of the PB 503 For simplic ity some PB 503 features that will be used in experiments in later chapters have been omitted While the following description is speci c to the PB 503 many other breadboards share some if not all of these features The description will thus be of some use for users of other breadboard models as well The breadboard s sockets contain spring contacts if a bare wire is pushed into a socket the contacts press against it making an electrical connec tion The PB 503 s sockets are designed for a maximum wire thickness of 22 AWG American Wire Gauge anything thicker i e with smaller www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information 3 1 Equipment familiarization 15 V 15 V 5 V Horizontal Row Group of 5 Function Generator Analog Digital Frequency Slider Amplitude Slider 10 k pot 1 k pot 8 Speaker Voltage Adjustment Kno
15. ything out if you happen to make a mistake in hooking up the circuit r Be careful to keep any exposed bits of metal from touching each other and making a short circuit Note that most of the exposed metal on 2 Of course the existence of other materials namely semiconductors for which the I V relationship is nonlinear makes electronics much more interesting and underlies the transformation of daily life brought about by electronics during the twentieth century 3 If you don t have a PB 503 breadboard nd a 10 k pot on your breadboard if it has one otherwise you will have to purchase a separate 10 k pot www cambridge org Cambridge University Press Cambridge University Press 0521815363 Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Excerpt More information 7 1 Equipment familiarization Table 1 2 Color code for nonprecision resistors 5 10 or 20 tolerance The resistance in ohms is the sum of the values in columns 1 and 2 multiplied by the value in column 3 plus or minus the tolerance in column 4 For example the color code for a 1 k resistor would be brown black red for 51 green brown black for 330 orange orange brown etc Stripe 1 2 3 4 tolerance Black 0 0 100 Brown 10 1 101 Red 20 2 102 Orange 30 3 103 Yellow 40 4 104 Green 50 5 105 Blue 60 6 106 Violet 70
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