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Practically there Measuring current and voltage Now that we’ve looked at the theory behind current and voltage measurement, let’s go on and build a few circuits to put it into practice. Figure 3.10 shows the breadboard layout of the circuit of Figure 3.6, where a single resistor is connected in series with a multi-meter and a battery. With this circuit we can actually prove Ohm’s law. The procedure is as follows: 1) set the meter’s range switch to a current range — the highest one, say, 10 A, 2) insert a resistor (of say 1k5) into the breadboard, and connect the battery leads, 3) touch the multi-meter leads to the points indicated. You will probably see the pointer of the multi-meter move (but only just) as you complete step 3. The range you have set the multi-meter to is too high — the current is obviously a lot smaller than this range, so turn down the range switch (to, say, the range nearest to 250 mA) and do step 3 again. This time the pointer should move just a bit further, but still not enough to allow an accurate reading. Turn down the range switch again, this time to, say, the 25 mA range and repeat step 3. Now you should get an adequate reading, which should be 6 mA give or take small experimental errors. Is this right? Let’s compare it to the expression of Ohm’s law: 65
Starting electronics Figure 3.10 A breadboard layout for the circuit of Figure 3.6: the meter is in series with the resistor; only the meter itself makes the circuit complete If we insert known values of voltage and resistance into this we obtain: Not bad, eh? We’ve proved Ohm’s law! You can try this again using different values of resistor if you wish, but don’t use any resistors lower than about 500 Ω as you won’t get an accurate reading, because the battery can’t supply currents of more than just a few mA. Even if it could the resistor would overheat due to the current flowing through it. In all cases where the battery is able to supply the current demanded by the resistor, the expression for Ohm’s law will hold true. 66
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Starting Electronics i
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Starting Electronics Keith Brindley
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Contents Contents Preface vi 1. The
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The very first steps 1 The very fir
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The very first steps potential rewa
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The very first steps Photo 1.2 tool
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The very first steps that electrici
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The very first steps Going back to
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The very first steps tially exist.
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The very first steps by a scientist
Page 22 and 23: The very first steps Hint: Ohm’s
Page 24 and 25: The very first steps Electronic com
Page 26 and 27: The very first steps Larger values
Page 28 and 29: The very first steps Time out That
Page 30 and 31: On the boards 2 On the boards In th
Page 32 and 33: On the boards If you are following
Page 34 and 35: On the boards Hint: The theoretical
Page 36 and 37: On the boards Photo 2.2 Inside brea
Page 38 and 39: On the boards Down the edges of the
Page 40 and 41: On the boards Hint: The multi-meter
Page 42 and 43: On the boards of leads should be su
Page 44 and 45: On the boards it gets older and sta
Page 46 and 47: On the boards Hint: The bands group
Page 48 and 49: On the boards In practice, you migh
Page 50 and 51: On the boards called just ohmmeter)
Page 52 and 53: On the boards ends. We say resistor
Page 54 and 55: On the boards we would get: and thi
Page 56 and 57: On the boards Figure 2.9 A comparat
Page 58 and 59: Measuring current and voltage 3 Mea
Page 60 and 61: Measuring current and voltage forme
Page 62 and 63: Measuring current and voltage Netwo
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Page 68 and 69: Measuring current and voltage Figur
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Page 84 and 85: Capacitors 4 Capacitors You need a
Page 86 and 87: Capacitors Capacitors We’re going
Page 88 and 89: Capacitors In our experiments in th
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Page 94 and 95: Capacitors Time (seconds) 5 10 15 2
Page 96 and 97: Capacitors In a capacitor circuit l
Page 98 and 99: Capacitors Figure 4.11 An experimen
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Page 102 and 103: Capacitors plates of the capacitor
Page 104 and 105: Capacitors where ε is the permitti
Page 106 and 107: ICs oscillators and filters 5 ICs,
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Page 114 and 115: ICs oscillators and filters (a) (b)
Page 116 and 117: ICs oscillators and filters Ouch, t
Page 118 and 119: ICs oscillators and filters output
Page 120 and 121: ICs oscillators and filters Value o
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ICs oscillators and filters voltage
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ICs oscillators and filters Value o
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ICs oscillators and filters Figure
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ICs oscillators and filters simple
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Diodes I 6 Diodes I We’re going t
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Diodes I Photo 6.1 A horizontal pre
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Diodes I Now, with a resistance of
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Diodes I here. We needn’t know an
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Diodes I Figure 6.9 The breadboard
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Diodes I but we never said it was a
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Diodes I Current (mA) Voltage (V) 0
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Diodes I voltages, reverse currents
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Diodes I battery voltage of 9 V sim
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Diodes I Figure 6.17 The circuit, w
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Diodes I Figure 6.19 My results fro
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Diodes II 7 Diodes II In the last c
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Diodes II the same experiment we di
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Diodes II We need to draw diode cha
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Diodes II Generally, diodes don’t
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Diodes II Diode voltage (VD) Resist
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Diodes II Diode circuits We’re no
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Diodes II Figure 7.9 Waveforms show
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Diodes II Filter tips Although we
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Diodes II We’ve already seen a de
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Diodes II as that from a 230 V a.c.
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Diodes II Figure 7.19 The same circ
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Transistors 8 Transistors In previo
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Transistors Figure 8.1 How to recog
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Transistors Black meter lead Red me
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Transistors Well, as mentioned earl
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Transistors Figure 8.8 A breadboard
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Transistors In effect, the transist
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Transistors Figure 8.10 transistors
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Transistors Hint: Yes, that’s rig
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Transistors These two operational m
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Analogue integrated circuits 9 Anal
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Analogue integrated circuits circui
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Analogue integrated circuits Figure
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Building on blocs Analogue integrat
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Analogue integrated circuits As the
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Analogue integrated circuits circui
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Analogue integrated circuits an app
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Digital integrated circuits I 10 Di
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Digital integrated circuits I Logic
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Digital integrated circuits I If we
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Digital integrated circuits I Figur
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Digital integrated circuits I It’
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Digital integrated circuits I The t
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Digital integrated circuits I Trans
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Digital integrated circuits I going
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Digital integrated circuits I OR an
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Digital integrated circuits I For t
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Digital integrated circuits II 11 D
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Digital integrated circuits II A se
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Shutting the ’stable gate Digital
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Digital integrated circuits II gate
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Digital integrated circuits II In o
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Digital integrated circuits II Figu
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Digital integrated circuits II Swit
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Digital integrated circuits II The
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Open the black box Digital integrat
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Digital integrated circuits II Ther
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Glossary Glossary 180 ° out-of-pha
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Glossary bode plots method of showi
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Glossary decibels logarithmic units
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Glossary integrated circuit a semic
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Glossary peak voltage the voltage m
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Glossary squarewave a signal which
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Glossary Components used Resistors
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Glossary Index A ampere, 9 AND gate
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