Elenco 130-in-1 Electronics Playground User Manual

Copyright © 2012, 2009 by Elenco®Electronics, Inc. All rights reserved. REV-A Revised 2012 753039

No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.

ELECTRONIC

PLAYGROUND

TM

and LEARNING CENTER

MODEL EP-130

ELENCO

®

Wheeling, IL, USA

Important: If you encounter any problems with this kit, DO NOT RETURN TO RETAILER. Call toll-free [phone]

or e-mail us at: [e-mail]. Customer Service • 150 Carpenter Ave. • Wheeling, IL 60090 U.S.A.

WARNING: Always check your wiring before
turning on a circuit. Never leave a circuit
unattended while the batteries are installed.
Never connect additional batteries or any
other power sources to your circuits.

WARNING:
CHOKING HAZARD - Small parts.

!

Not for children under 3 years.

Conforms to all applicable U.S. government
requirements.

Batteries:

• Do not short circuit the battery
terminals.

• Never throw batteries in a fire or
attempt to open its outer casing.

•

Use only 1.5V “AA” type, alkaline
batteries (not included).

• Insert batteries with correct polarity.

• Do not mix alkaline, standard (carbon­zinc), or rechargeable (nickel­cadmium) batteries.

TABLE OF CONTENTS

Before We Begin Page 4
Installing the Batteries 4
Making Wire Connections 5
Components 5
Building Your First Project 9
Troubleshooting 10
Helpful Suggestions 10

I. PLAYGROUND OF ELECTRONIC CIRCUITS 11

1. Woodpecker 12

2. Police Siren 13

3. Metronome 14

4. Grandfather Clock 15

5. Harp 16

6. Tweeting Bird 17

7. Meowing Cat 18

8. Callin’ Fish 19

9. Strobe Light 20

10. Sound Effects for Horror Movies 21

11. Machine Gun Oscillator 22

12. Motorcycle Mania 23

13. Vision Test 24

14. Patrol Car Siren 25

II. BASIC ELECTRONICS CIRCUITS

A MAJOR CHANGE 27

15. Dimming the Light 28

16. Flip Flopping 29

17. Capacitor Discharge Flash 30

18. Transistor Action 31

19. Series and Parallel Capacitors 32

20. Transistor Switching 33

21. Series and Parallel Resistors 34

22. Amplify the Sound 35

26

• Non-rechargeable batteries should not
be recharged. Rechargeable batteries
should only be charged under adult
supervision, and should not be
recharged while in the product.

• Do not mix old and new batteries.

• Remove batteries when they are used
up.

• Batteries are harmful if swallowed, so
keep away from small children.

III. LED DISPLAY CIRCUITS 36

23. LED Display Basics 37
Digital Display Circuit for the Seven-Segment LED

24.

38

25. LED Display with CdS and Transistor 39
Switching the LED Display Using Transistor Control

26.

40

IV. WELCOME TO DIGITAL CIRCUITS 41

27. “Flip-Flop” Transistor Circuit

42

28. “Toggle Flip-Flop” Transistor 43

29. “AND” Diode Transistor Logic with LED Display 44

30. “OR” DTL Circuit with Display 45

31. “NAND” DTL Circuit with Display 46

32. “NOR” Transistor Circuit with Display 47

33. “Exclusive OR” DTL Circuit 48

V. MORE FUN WITH DIGITAL CIRCUITS 49

34. “BUFFER” GATE using TTL 50

35. “INVERTER” GATE using TTL 51

36. “AND” GATE using TTL 52

37. “OR” GATE using TTL 53

38. “R-S Flip-Flop” using TTL 54

39. “Triple-Input AND” Gate using TTL 55

40. “AND” Enable Circuit using TTL 56

41. “NAND” Enable Circuit using TTL 57

42. “NOR” Enable Circuit using TTL 58

43. “NAND” Gate Making a Toggle Flip-Flop 59

44. “Exclusive OR” GATE using TTL 60

45. “OR” Enable Circuit using TTL 61

46. Line Selector using TTL 62

47. Data Selector using TTL 63

-3-

VI. MEET TRANSISTOR-TRANSISTOR LOGIC

64

48. Blinking LEDs 65

49. Machiny Sound 66

50. Astable Multivibrator Using TTL 67

51. Tone Generator 68

52. Monster Mouth 69

53. Dark Shooting 70

54. A One-Shot TTL 71

55. Transistor Timer Using TTL 72

56. LED Buzzin’ 73

57. Another LED Buzzin’ 74

58. Set/Reset Buzzer 75

59. Another Set/Reset Buzzer 76

VII. OSCILLATOR APPLICATION CIRCUITS

77

60. Ode to the Pencil Lead Organ 78

61. Double-Transistor Oscillator 79

62. Decimal Point Strobe Light 80

63. “The Early Bird Gets the Worm” 81

64. Adjustable R-C Oscillator 82

65. Heat-Sensitive Oscillator 83

66. Pulse Alarm 84

67. Pushing & Pulling Oscillator 85

68. Slow Shut-off Oscillator 86

69. Electronic Organ Detector 87

VIII. MEET THE OPERATIONAL AMPLIFIER 88

70. Operational Amplifier Comparator 89

71. Changing Input Voltage 90

72. Non-inverting Dual Supply Op Amp 91

73. Inverting Dual Supply Op Amp 92

74. Non-inverting Amplifier 93

75. Dual-Supply Differential Amplifier 94

76. Miller Integrating Circuit 95

77. Stable-Current Source 96

78. Operational Amplifier Blinking LED 97

79. LED Flasher 98

80. Double LED Blinker 99

81. Single Flash Light 100

82. Introducing the Schmitt Trigger 101

83. Initials on LED Display 102

84. Logic Testing Circuit 103

85. Voice-Controlled LED 104

86. Buzzin’ with the Op Amp 105

87. Sweep Oscillator 106

88. Falling Bomb 107

89. Alert Siren 108

90. Crisis Siren 109

91. Op Amp Metronome 110

92. Burglar Buzzer 111

93. LED Initials 112

94. Wake Up Siren 113

95. Voice Activated LED 114

96. Logic Tester 115

IX. MORE FUN WITH OPERATIONAL AMPLIFIERS

116

97. Voice Power Meter 117

98. Reset Circuit 118

99. RC Delay Timer 119

100. Listen To Alternating Current 120

101. Pulse Frequency Multiplier 121

102.

White Noise Maker

122

103. Light-Controlled Sound 123

104. DC-DC Converter 124

105. Super Sound Alarm 125

106. Op Amp Three-Input “AND” Gate 126

107. Timer 127

108. Cooking Timer 128

X. RADIO AND COMMUNICATION CIRCUITS 129

109. Operational Amplifier AM Radio 130

110. AM Code Transmitter 131

111. AM Radio Station 132

112. Crystal Set Radio 133

113. Two-Transistor Radio 134

114. Morse Code Oscillator With Tone Control 135

XI. TEST AND MEASUREMENT CIRCUITS 136

115. Water Level Warning 137

116. Water Level Alarm 138

117. Audio Signal Hunter 139

118. RF Signal Tracer 140

119. Square Wave Oscillator 141

120. Sawtooth Oscillator 142

121. Audio Continuity Tester 143

122. Audio Rain Detector 144

123. Audio Metal Detector 145

124. Water Level Buzzer 146

125. Pule Tone Generator 147

126. Resistance Tester 148

127.

Transistor Tester

149

128. Sine Wave Oscillator 150

129. Sine Wave Oscillator With Low Distortion 151

130. Twin-T Oscillator 152

INDEX 153

PARTS LIST 155

DEFINITION OF TERMS 156

IDENTIFYING RESISTOR VALUES 159

IDENTIFYING CAPACITOR VALUES 159

METRIC UNITS AND CONVERSIONS 159

BEFORE YOU START THE FUN!

Welcome to the thrilling world of electronics! Now that

®

you have your Elenco

EP-130 Electronic Playground
Kit, you can learn about electronics while doing 130
fun experiments. In this kit we have included
everything you will need to start off on this electronics
adventure, well except the batteries that is ☺.

As you go through this manual and do the
experiments, you will notice that we have arranged
the experiments, as well as information, into a logical
progression. We will start off with easy circuits and
then work toward the more intricate ones. Take your
time and be sure to have some fun!

Each electronic component in the kit is connected to
springs, so you can do all the circuit assembly without
having to solder. To build a working project, all you
have to do is connect the wires to the terminals as
shown in each wiring sequence. There is no danger
when doing these projects because you are using low
voltage batteries, not the standard AC voltages.

Our simple instructions will show you how to operate
the circuit for each experiment. A

schematic

diagram
is also included, to help you learn how the circuit
works. A

schematic

is simply a blueprint that shows
how different parts are wired together. An image or
symbols for each of the components in your kit are
printed next to each piece.

As you will notice we refer to a

Volt / Ohm Meter

(VOM) for making measurements. A VOM or
multimeter is a instrument that measures voltage,
current (amperes or amps), and resistance (ohms-Ω).
You will learn more about these in the upcoming
pages. If you really want to learn about electronic
circuits, it is vital that that you learn how to measure
circuit values - for only then will you really understand
electronic circuitry.

You do not have to have or use a VOM to do the
experiments but you will find that it helps to better
grasp how the circuits work. The VOM is a good
investment if you plan to stay interested in electricity
and electronics.

INSTALLATION OF BATTERIES

This kit requires six (6) “AA” batteries. To install the
batteries to the back of your kit make sure to install
them in the corresponding compartments. Put the +
end and the – end correctly into the kit, the + end for
the battery is the side that has the metal cap.

Remember:

battery in your kit. Even if they are “leak-proof”, they
still have the potential to leak damaging chemicals.

Never leave a dying battery or dead

-4-

+

–

+

–

–

–

+

–

–

+

–

+

–

–

+

+

+

+

+

–

+

–

+

–

-5-

Provided in your kit are spring terminals and pre-cut
wires, make the wires snap together for your use in
the numerous projects. To join a wire to a spring
terminal, just directly bend the spring over to one side
and then install the wire into the opening.

When you have to join to two or three wires into a
single spring terminal, be sure that the first wire does
not come loose when you attach the second and third
wires. The simplest way to do this is to place the
spring onto the opposing side where you have
connected the first wire.

Only insert the exposed or shiny part of the wire into
the spring terminal. The electrical connection will not
be made if the plastic part of the wire is inserted into
the terminal. Removing the wire from the spring
terminals is simply just bending each terminal and
then pulling the wires out of it.

If the exposed metal ends of some of the wires break
off due to great use, you should just simply remove
3/8” if the insulation from the wire of the broken end
and then simply twist the strands together. To remove
the installation you can use either a wire-stripper tool
or a simple penknife. Be extremely careful when doing
this because penknives are remarkably sharp.

WIRING CONNECTIONS

This kit has more than 30 distinct components. If this
happens to be your first time with electronics don’t fret
over not knowing the difference between a resistor or
a transistor, because the general purpose of each
component will be described. The following
explanations will help you comprehend what each
component does and you will also gain more
knowledge of each component as you do each
experiment. There is also a parts list in the back of
this manual, that way you can compare the parts in
your kit with those recorded in the back.

Resistors: Why is the water pipe that goes to the
kitchen faucet in your house smaller than the one
from the water company? And why is the pipe smaller
than the main water line that disburses the water to
your entire town? Because you don’t need a lot of
water. The pipe size controls the water flow to what
you really need. Electricity works in the same manner,
except that the wires have a minimal resistance that
they would have to be particularly thin to limit the
electricity flow. They would be solid enough to handle
and break effortlessly. However, the flow of water
through a large pipe could be restricted to by filling a
part of the pipe with rocks (a

COMPONENTS

fine screen would keep rocks from falling over), which
would prolong the flow of water but not stop it
completely. Like rocks are for water, resistors work in
a similar way. They regulate how much electric current
flows. The resistance, is expressed in ohms (Ω,
named in honor of George Ohm), kilohms (kΩ, 1,000
ohms) or megohms (MΩ, 1,000,000 ohms) is a
determination of how much resistor resists the flow of
electricity. The water through a pipe can be increased
by an increase in water pressure or the removal of
rocks. In a similar way you can increase the electric
current in a circuit by increasing the voltage or by the
use of a lower value resistor (this will be shown in a
moment). Below the symbol for the resistor is shown.

Resistor Color Code: The method for marking the
value of resistance on a part is by using colored
bands on each resistor. The representation of the first
ring is the digit of the value of the resistor. The second
ring is a representation of the second digit of the
resistors value. The third ring means that you to which
power of ten to multiply by, ( or the amount of zeros
to add). The fourth and final ring is a representation
of the construction tolerance. A majority of resistors
have a gold band that represents 5% tolerance.
Simply this means that the resistor value is
guaranteed to be 5% of the valued marked. See the
color chart on page 159.

Variable Resistor (Control): The variable resistor is
simply a control and this is required in many electric
circuits. The variable resistor can be used as a light
dimmer, volume control, and in many other circuits
when you are wanting to change resistance easily
and quickly. A normal resistor is shown, this contains
an additional arm contact that moves along the
resistive material and can tap off the resistance
desired.

Capacitors: Capacitors move alternating current
(AC) signals while prohibiting direct current (DC)
signals to pass. They store electricity and can function
as filters to smooth out signals that pulsate.
Capacitors that are small are traditionally used in
high-frequency applications such as radios,
transmitters, or oscillators. Larger capacitors
ordinarily reserve electricity or act as filters. The

capacitance

capacitor is expressed in a unit known as
extremely large amount of electricity defines the farad.
Most of the value of capacitors is predetermined in
millionths-of-a-farad or microfarads.

Electrolytic

capacitors. They are marked with an “–”. There is only
one-way to connect them to the circuit, the + and the
– wires must always go into the correct terminals.

Disc

- Unlike the electrolytic above, these capacitors

have no polarity and can be connected in either way.

Tuning Capacitor: Ever wonder what that knob that
changes the stations on your radio is? It’s a tuning
capacitor. When the knob is rotated, the capacitance
is changed. This alters the frequency of the circuit,
letting through only one frequency and blocking out
the rest.

(capacity for storing electricity) of a

farad

. An

- Electrolytic are the four largest

Disc Electrolytic

-6-

Diodes: Are like one-way streets. They allow the

current to flow in only one direction. There are three
of these in your kit. Your kit contains one silicon diode
(marked Si) as well as two germanium diodes (marked
Ge).

Transistors: Three transistors can be found in your
kit. The part that makes each transistor work is a tiny
chip, which is made of either germanium or silicon.
There are a total of three connections points on each
transistor. They are B, which stands for base, C, which
stands for collector, and E, which stands for emitter.
Mainly transistors are used to amplify weak signals.
Transistors can also be used as switches to connect
or disconnect other components as well as oscillators
to permit signals to flow in pulses.

LEDs (Light Emitting Diodes): These are special
diodes because they give off light whenever electricity
passes through them. (The current can only pass
through in one direction—similar to “regular” diodes).

LED Digital Display: Seven Light Emitting Diodes
are arranged to create an outline that can show most
letters of the English alphabet and all the numbers.
An additional LED is added to represent a decimal
point.

The “8” LED display is mounted on a board and to
prevent burning out the display with excess current,
permanent resistors have been wired in.

Integrated Circuit: The transistor was invented in
the 1940’s and after that the next big break through
in electronics was in the 1960’s with the invention
integrated circuit or the ICs. The advantage of this that
the equivalent of hundreds or even thousands of
transistors, diodes and even resistors can be placed
into one small package.

Two types of ICs are used in this kit. They are the
quad two-input NAND and the dual-operational
amplifier, and you will have the chance to learn more
about these in a bit.

Simple ICs will help you to understand enough to
grasp the basic theories of more advanced ICs.

Cadmium Sulfide (CdS) Cell: This is what is known
as a semiconductor, which practically resists
electricity while it conducts. The resistance changes
by the amount of light that is shined upon it.

Note: Provided is a light shield to use with the CdS
cells, to use just simply place the shield over the cell,
this helps to prevent light from leaving the cell.

-7-

PNP

NPN

Antenna: This cylindrical component with a coil of

fine wire wrapped around it is a radio antenna. If
you’re wondering what the dark colored rod is, it’s
actually mostly powdered iron. It’s also known as a
“Ferrite Core”, which is efficient for antennas, and
used in almost all transistor radios.

Transformer: Did you know that if you were to wrap
two wires from different circuits around different ends
of an iron bar, and if you were to add current in the
first circuit, it will magnetically create current in the
second circuit? That’s exactly what a transformer is!
Transformers are used to isolate parts of a circuit, to
keep them from interfering with each other.

created by variations of vibrations and then travel
across the room. When you hear a sound it is actually
your ears feeling the pressure from the air vibrations.
To operate a speaker a high current and a low voltage
are needed, so the transformer will also be used with
the speaker. (A transformer can convert a high­voltage/low current to a low-voltage/high current).

Similar to the speaker, is the earphone. It is movable
and more sensitive than the speaker, otherwise they
are the same. The earphone you will be using is
efficient as well as lightweight and can be used
without taking away too much electrical energy from
the circuit. Sound wise you will be using the earphone
for weak sounds and for louder sounds the speaker
will be used.

If the iron bar in a transformer were allowed to rotate,
it would become a motor. However, if a magnet within
a coil is rotating then an electrical current is made;
this is called a generator. Those two ideas may not
seem important but they are the foundation of the
present society. Pretty much all of the electricity used
in this world is generated by huge generators, which
are propelled by water pressure or steam. Wires
transport energy to homes and businesses where it
will be used. Motors are used to convert the electricity
back into mechanical form so that it can be used to
drive machinery and appliances.

Speaker: Did you know that electral energy is
converted into sound through a speaker? By using the
energy from an AC electrical signal it creates
mechanical vibration. Sound waves, which are

Batteries: The battery holders that are used in this
kit are constructed to hold six (6) “AA” batteries. These
batteries will be the supplier of all the power used in
your experiments. When you connect the wires to the
batteries make sure that you only connect the
batteries to terminals noted. Terminals 119 and 120
provide 3 volts while terminals 119 and 121 provide

4.5 volts. Be aware that parts can be damaged
(burned out) if you connect too much voltage (you can
get up to 9 volts from the connections to the batteries)
Be sure to make battery connections the right way.

Caution: Make sure your wiring uses the correct
polarity (the “+” and “-” sides of the component)! Some
parts can be permanently damaged if you reverse
polarity.

-9-

Switch: You know what a switch is – you use

switches every day. When you slide (or flip) to the
proper position, the circuit will be completed, allowing
current to flow through. In the other position a break
is made, causing the circuit to be “off”. The switch that
we will be using is a double-pole, double-throw switch.
You will learn about that later on.

Key: The key is a simple switch—you press it and
electricity is allowed to flow through the circuit. When
you release it, the circuit is not complete because a
break is caused in the circuit’s path. The key will be
used in most circuits often times in signaling circuits
(you can send Morse code this way as well as other
things).

Terminals:

Two terminals will be used in some
projects (terminals 13 and 14). They will be used to
make connections to external devices such as an
earphone, antenna or earth ground connection,
special sensor circuits and so forth.

Wires: Wires will be used to make connections to the
terminals.

Your parts and spring terminals are mounted on the
colorful platform. You can see how the wires are
connected to the parts and their terminals if you look
under the platform.

YOUR FIRST PROJECT

A simple wiring sequence is listed for each project.
Connect the wires with appropriate length between
each grouping of terminals listed. When doing the
experiment use the shortest wire that possibly gets
the job done. New groupings will be separated by a
comma, connect the terminals in each group.

As an example, here is the project 1 wiring sequence:

1-29, 2-30, 3-104-106, 4-28-124, 5-41-105, 27-88,
75-87-103-40, 115-42-119, 76-116, 121-22.
Connect a wire between 1 and 29, another wire

between 2 and 30, another between 3 and 104 and
then another wire between 104 and 106. Continue
until all connections are made.

Caution: The last connection in each wiring
sequence is an important power wire; this is
deliberate. It is important that you make this
connection your LAST connection. Damage can occur
if one part of the circuit is completed before another.
Therefore follow the wiring sequence exactly.

TROUBLESHOOTING

You should have no problem with the projects working
properly if you follow the wiring instructions. However,
if you do encounter a problem you can try and fix it by
using the following troubleshooting steps. These steps
are comparable to those steps that electronic
technicians use to troubleshoot complex electronic
equipment.

1. Are the batteries being used new? If they are not,
this may be your problem because the batteries
could be too weak to power the project.

2. Is the project assembled properly? Check all the
wiring connections to make sure that you have all
the terminals wired correctly. Sometimes having
someone else look at it helps to find the problem.

3. Are you following the schematic diagram and the
explanation of the circuit? As your understanding
and knowledge expands of electronics, you will be
able to troubleshoot by following only a schematic,
and once you add the description of the circuit you
will be able to figure out your own problems.

4. If you have VOM, try taking some measurements
of the voltage and current. You might be surprised
just how handy a VOM really is.

5. Try building project 24 (Digital Display Circuit for
the Seven-Segment LED). This is a very simple
circuit that lights part of the LED display using only
2 wires.

®

Contact Elenco

if you still need help.

SUGGESTIONS TO HELP

Keep a Notebook

As you’re about to find out, you are going to learn
many things about electronics by using this kit. As you
learn, many of the things you discover in the easy
projects will be built upon in later projects. We suggest
using a notebook to help you organize the data you
will be collecting.

This notebook does not have to be like the one you
use in school. Think of it more as a fun notebook, that
way you can look back on the all the projects you have
done once you finish.

Wiring Sequence Marking

When you are wiring a project, especially those with
lots of connections, you will find it helpful to mark off
each terminal number as you connect the wires to it.
Use a pencil and make light marks so that you can go
back multiple times and re-read the sequence.

Collecting Components

You should start to make your own collection of
electronic parts and therefore have your own scrap
box of electronic parts. You can build your own circuits
in or on top of a framework, box or container. You
could use your circuit as a Science Fair project at
school and even make a major research project from
it.

-11-

I. PLAYGROUND OF ELECTRONIC CIRCUITS

EXPERIMENT #1: WOODPECKER

For your first experiment you are going to make a
circuit that that sounds like a woodpecker chirping.
Follow the wiring sequence carefully and observe the
drawings. Don’t forget to make all the proper
connections and have fun!

The simple circuit shown here does not have a key
or a switch, but you can easily add one. Replace
connection 124-28 with connections 124-137 and
138-28 to connect the key. Or, you can hook the
switch up by replacing 124-28 with connections 124­131 and 132-28. Now you can easily turn off and on
the circuit. Go outside and see if you can attract birds
with it.

Want a different sound? Try varied combinations of
capacitance and resistance in place of the 100μF
capacitor and the 1kΩ resistor. To change the 100μF
capacitor to 470µF, disconnect terminal 116 and
transfer to terminal 118. Then, reconnect the wire
from 115 to connect to 117. Your “bird” might sound
like a cricket, or a bear!

Also, you can try using the 3V power supply.
Disconnect terminal 119 and connect it to terminal

123. Now your bird might sound like an English
sparrow. Feel free to experiment. Just don’t replace
the 47kΩ resistor with anything below 10kΩ,
because it might damage the transistor.

Notes:

Schematic

Wiring Sequence:

o 1-29
o 2-30
o 3-104-106
o 4-28-124
o 5-41-105
o 27-88
o 75-87-103-40
o 115-42-119
o 76-116
o 121-122

-12-

-13-

Here is the first siren you are going to do – don’t be
shocked if this experiment becomes the most famous
circuit in this kit.

This siren sounds like a real siren on a police car!
After the wiring is competed press the key. The tone
you eventually hear gets higher after pressing the
key. When you release the key, the tone gets lower
and then fades out.

Try some of these modifications:

1. If you change the 10μF capacitor to a 100μF or a
470μF it will give a very long delay for both turn
off and turn on.

2. Change the circuit to remove the delays by
temporarily disconnecting the 10μF capacitor.

3. Change out the 0.02μF capacitor to a 0.01μF
capacitor, and then to a 0.05μF capacitor.

Notes:

EXPERIMENT #2: POLICE SIREN

Wiring Sequence:

o 1-29
o 2-30
o 3-103-109
o 4-119-137
o 5-47-110
o 46-104-90
o 114-48-120
o 85-138
o 86-89-113

Schematic

EXPERIMENT #3: METRONOME

Learning to play a musical instrument? Then you
might find this experiment helpful. This is an
electronic version of the metronome, used by musical
students and musical geniuses alike, worldwide.

If you press the key, you hear a repeating sound from
the speaker. Turn the control knob to the right and
you’ll hear the sound “get faster” as the time between
sounds shortens.

Try swapping out the 4.7kΩ resistor with different
one. Also, you might want to try a different capacitor
in place of the 100μF capacitor too see what effect it
will have. Are you still keeping notes?

If you would like to hear the difference that a stronger
capacitor makes, try connecting the 470μF capacitor
to the batteries. Connect terminal 117 to 119 and
terminal 118 to terminal 120. You might need to
adjust the control to maintain the same pulse rate.

Notes:

Schematic

Wiring Sequence:

o 1-29
o 2-30
o 3-104-116
o 4-28-138
o 5-41-103
o 27-80
o 40-115-79
o 42-119
o 120-137

-15-

Does your home lack a grandfather clock? Well not
any longer, with this experiment you will make your
own electronic grandfather clock.

This circuit will produce clicks at approximately one­second intervals. The sound and timing together
might remind you of an old grandfather clock. If you
would like for it to go faster or slower then you can
change out the 100kΩ resistor.

The steady ticking can put animals (and people) into
a sleepy state of mind. If you have ever traveled on a
train, you remember how sleepy you get from
hearing the clicking sound of the wheels.

Ever scare a clock out of ticking? Shout directly into
the speaker. You can briefly stop the clock! The
speaker acts like a microphone as well. The sound
of your voice vibrates the speaker and disturbs the
electrical balance of the circuit, briefly.

Notes:

EXPERIMENT #4: GRANDFATHER CLOCK

Wiring Sequence:

o 1-29
o 2-30
o 3-104-116
o 4-90-120
o 5-41-103
o 40-72
o 42-119
o 71-89-115

Schematic

EXPERIMENT #5: HARP

Have you ever wanted to make music just by waving
your hand? Well that is just what you are going to be
doing. How does this magic work? Well, the tones
change based upon the amount of light that gets to
the CdS cell. With a bright light the tone is higher but,
if you cover the CdS with your hand, the sound gets
lower.

Since the early days of vacuum-tube circuitry, this
method of creating musical sound has been used.
Leon Theremin was the inventor of this type of
instrument, thus the instrument has been named the
Theremin in his honor.

After the wiring has been completed press the key
and then wave your hand over the CdS cell. You will
soon be able to play music with this magical
electronic instrument after just a bit of practice. Use
your CdS cell light shield and use it to experiment for
more light control. Most importantly HAVE FUN!

Notes:

Schematic

Wiring Sequence:

o 1-29
o 2-30
o 3-16-41-109
o 4-120
o 5-106-110
o 15-87
o 40-105-88
o 42-137
o 119-138

-16-

In this experiment you are going to make a circuit
that that sounds like the mockingbird.

Follow the wiring sequence and observe the
drawings. Don’t forget to make all the proper
connections and have fun!

To finish the circuit below, slide the switch to the A
position to turn on the power. No sound will come
from the speakers yet. When you press the key you
will hear a sound quite like a bird chirping from the
speaker. When you release the key, you will still be
able to hear the chirping sound but eventually it will
slow down and stop. The first transistor “Q1” is
dropped off from the battery when the key is
released. Transistor “Q2” still produces the bird sound
until the controlling current from transistor “Q1” stops.

Try using a different value capacitor instead of the
10μF and the 100μF capacitors. These capacitors
control the amount of electricity reaching the
transistors. Listen for the difference. Make sure to
start keeping notes on your experiments.

Notes:

EXPERIMENT #6: TWEETING BIRD

Wiring Sequence:

o 1-29
o 2-30
o 3-106-110
o 4-41-131-138
o 5-44-109
o 40-114-91-75
o 42-85
o 43-105-86-77
o 119-45-115-113-92
o 76-137
o 78-116
o 120-132

Schematic

EXPERIMENT #7: MEOWING CAT

Are you bothered by mice, do you not have a
mousetrap? You should try this next experiment to
help you instead—see if the sound of this cat can
keep the pests out of your life.

Just follow the drawing below and the wiring
sequence. To start the experiment switch the set to
B. Press down on the key and release it immediately.
You will hear the meow from the cat coming from the
speaker. If you adjust the control knob while the cat’s
meow is fading away, what effect on the circuit
operation does it have? Now set the switch to A and
try it once more. Now it sounds as if the cat is
begging for a dish of milk in a low, long sounding
tone.

To produce a variety of sounds try experimenting
with this circuit. Whatever you do just don’t change
the value of the 0.05μF capacitor to more than 10μF
or reduce the value of the 10kΩ resistor— or else the
transistor could get damaged.

Notes:

Schematic

Wiring Sequence:

o 1-29
o 2-30
o 3-41-109
o 4-72-82-132-114
o 5-106-110
o 27-40-105
o 115-113-42-119
o 71-138
o 81-28
o 116-131
o 120-137

-19-

Did you know that many marine animals
communicate to each other using sound? I bet you
have heard that dolphins and whales use sound for
communication, but what you probably don’t know is
that they are not the only ones. Due to research we
are able to find out that some fish are attracted to
certain sounds. Making this circuit, will allow you do
to some research of your own.

Once you make the last connection you are turning
on the power. You should be able to hear pulses of
sound coming from the speaker. The sound changes
by turning the control. This circuit is a type of audio
oscillator circuit, which you will learn more about later
in this book.

If you have a fish tank at home or at school you
should place your kit near the glass to see if the fish
are attracted to the sound. Are they?

If you like to fish, you should try this out while fishing.
What you need to do is attach another speaker to
terminals 1 and 2 using long lengths of insulated
wire. Wrap the speaker carefully in a waterproof
plastic bag or place it in a tightly sealed jar. Make
sure that no water is able to reach the speaker. Lower
the speaker into the water, cast your fishing line, and
see if you catch anything.

Notes:

EXPERIMENT #8: CALLIN’ FISH

Wiring Sequence:

o 1-29
o 2-30
o 3-93-100-110
o 4-120
o 5-41-109
o 27-94
o 28-40-99
o 42-119

Schematic

EXPERIMENT #9: STROBE LIGHT

In this experiment you will be creating an oscillator
circuit that doesn’t make sound using a speaker or
an earphone. Instead the circuit will produce light
with an LED. This will give you an idea of how larger
strobe lights work. When you press the key, watch
LED 1. At certain intervals the light turns on and off.
With the 50kΩ control you can control the rate of
blinking.

Try substituting a capacitor with a lower value for the
100μF capacitor to see how an oscillator works.
Make a prediction about what you think will happen?
Were you correct?

Schematic

Notes:

Wiring Sequence:

o 3-115
o 4-27-138
o 5-31
o 28-80
o 33-47
o 79-116-112-46
o 111-48-121
o 119-137

-21-

The sounds that you will hear from this circuit will
remind you of the music you hear in horror movies.
Once you wire the project, use your special light
shield and your hand to change the light amount that
shines onto the CdS cell. This changes the pitch of
the music.

The pitch of a sound is determined is by the sound
wave’s frequency, which is the number of cycles of
electromagnetic energy per second. The amount of
light on the CdS cell determines the resistance of the
cell. The more resistance you have the slower the
frequency of the musical sound waves. The oscillator
circuit produces the basic sound wave.

Frequency modulation, or FM, is when the frequency
of an oscillator is controlled by part of the circuit. An
FM radio signal is similar to this but at higher
frequencies.

Notes:

EXPERIMENT #10: SOUND EFFECTS FOR HORROR MOVIES

Wiring Sequence:

o 1-29
o 2-30
o 3-47-106
o 4-74-45-42-119
o 5-103-105
o 15-86
o 16-46-104
o 40-113-80
o 41-112-78
o 44-114-83-76
o 120-48-81-79-75-77
o 73-85-84

Schematic

EXPERIMENT #11: MACHINE GUN OSCILLATOR

This circuit is what engineers refer to as a “pulse
oscillator”. It will make machine gun like sounds.

There are many different ways to make oscillators. In
this kit, you will build several of them and later on,
you will be told on how they work. In the meantime,
we will just tell you what an oscillator is.

An oscillator is a circuit that goes from high to low
output on its own, or in other words, it turns itself on
and off. A pulse oscillator is controlled from pulses,
like the pulses made from a capacitor charging and
discharging. The oscillator in this kit turns off and on
slowly. However, some oscillators turn off and on
many thousands of times per second. Slower
oscillators can often be seen controlling blinking
lights, such as turn signals in a car or truck. “Fast”
oscillators are used to produce sound. The fastest
oscillators produce radio frequency signals known as
“RF signals”. The RF signal oscillators turn on and
off millions of times per second!

The amount of times an oscillator turns off and on
each second is called the frequency of the oscillator.
Frequency is measured in units called hertz (Hz).
The frequency of this oscillator is about 1 to 12Hz.
The frequency of a radio signal oscillator would be
measured in either MHz (megahertz, meaning a
million hertz) or kHz (kilohertz, meaning a thousand
hertz).

Once you finish wiring, press the key to start the
oscillator. The 50kΩ resistor is the control; you can
swap it out with other resistors to change the sound
from a few pulses per second to a dozen or so per
second. Also, you can change the frequency of this
oscillator circuit by swapping out other capacitors in
place of the 10μF. Remember to observe the correct
polarity!

Notes:

Schematic

Wiring Sequence:

o 1-29
o 2-30
o 3-110-114
o 4-27-138
o 5-41-109
o 28-82
o 40-113-81
o 42-119
o 121-122
o 124-137

-23-

Have you ever tried to steer a bicycle or a motorcycle
with just four fingers? This would be dangerous on a
real motorcycle but on electronic version it is a lot of
fun!

To do this project, connect the components following
the wiring sequence. Next grasp the metal exposed
ends of the two long wires (connected to terminals
110 and 81) in between your index finger and thumb
of your left and right hands. Now vary your
grip/pressure and listen as the sound changes in the
speaker. Due to the grip you use the sound changes.

You can create different sounds by controlling the
light that into the CdS cell. If you have a strong light
on the CdS cell you can control the entire operation
by putting more pressure on the wires within your
hands. Make a shadow over the CdS cell with your
hand and see what happens.

By holding the ends of the wires, you are making
yourself an extension of the circuit- thus a human
resistor. When you change your grip the resistance
changes in the projects current. The sound from the
circuit will make a real motorcycle noise and with
practice you can do it real well. By doing this you can
make the motorcycle idle as well as race.

Experiment with different values for the 0.1μF and

0.05μF capacitors, but make sure you don’t use
values above 10μF or you may damage the
transistor.

Notes:

EXPERIMENT #12: MOTORCYCLE MANIA

Wiring Sequence:

o 1-29
o 2-30
o 3-16-105-109
o 4-120
o 5-41-106
o 15-82
o 40-110-WIRE
o 42-119
o 81-WIRE

Schematic

WIRE

EXPERIMENT #13: VISION TEST

This circuit produces short pulses. After you close
the key, the LED display shows 1 for a second and
then turns off, even when you keep pressing the key.

You could create a game with this circuit. Display a
number or a letter on the LED display and then have
the players tell you what number it is. You change
numbers or letters on the display by just changing
the wiring to the display. Connect the terminals to
form the letters or numbers to terminal 71 (in the
place of the 21 and 23 terminals). Connections for
the number 3 would be 17-21-22-23-20-71.

You can try different values of capacitors to see their
effects. Don’t use a capacitor with a value higher than
10μF or the excessive current can damage the
transistor.

Notes:

Schematic

Wiring Sequence:

o 21-23-71
o 25-124-137
o 40-73
o 41-72
o 82-83-42-119
o 74-81-111
o 84-112-138
o 121-122

-24-

-25-

With this experiment you may want to be careful not
to confuse your neighbors. This experiment sounds
as like a loud siren just like the real sirens on police
cars and ambulances. The tone is initially high but as
you close the key the tone gets lower. You are able
to control the tone just as the police and ambulance
drivers do.

The oscillator circuit being used is the same type
used in many other experiments in this kit. Press the
key and another capacitor is added to the circuit to
slow the action of the oscillator circuit.

Notes:

EXPERIMENT #14: PATROL CAR SIREN

Wiring Sequence:

o 1-29
o 2-30
o 3-104-106-110
o 4-85-120
o 5-41-109
o 40-137-105-86
o 103-138
o 42-119

Schematic

II. BASIC ELECTRONICS CIRCUITS

-26-

-27-

Until now, in addition to the wiring sequences you have
had drawings to help guide you in the wiring connections.
The rest of the projects will have just the schematic
diagram without the circuit drawings.

A schematic diagram is like a road map but it is used for
electronic circuits. It shows you how different parts connect
together and how electricity flows through a circuit.
Electronics engineers and technicians use schematics to
help guide them through circuits.

You don’t need to build your circuits from the schematic
diagrams by themselves. We have added the number of
terminals to where you will be making the wiring
connections on each schematic, to help you out - a line
between numbers on the schematic means that you
should connect a wire between those terminals in your kit.
Every part in your kit has a schematic symbol all of its
own. At the beginning of this manual you will find a picture
of each part with its schematic symbol as well as a short
description.

As you will start to notice, the schematics have some lines
that cross each other and that there is a dot at the crossing
point. This means that the two wires which are
represented by the lines, are to be connected at the point
where the dot is located (you will find the terminal number
next to the dot). If there is not a dot where the lines cross,
this means that the wires do not connect (you won’t see a
terminal number if the wires don’t cross).

Lines Are Connected / Lines Not Connected

The schematic diagrams will look confusing at first but
they are simple once you have some practice using them.
Don’t get discouraged if you get confused at first. You will
be constructing circuits in no time by just looking at the
schematic diagrams.

To be able to read schematic diagrams is important for
anyone getting into the field of electronics. Many
electronics books and magazines display intricate circuits
only in schematic form. A schematic is also shorter and
more accurate way to show a circuit rather than a written
form.

A MAJOR CHANGE

EXPERIMENT #15: LIGHT DIMMER

Ever thought you could use a capacitor to dim a
light? Try this project. After you finish the wiring, set
the switch to A. Then the LED segments will light up
slowly and show an L. Once the LED reaches its
brightest point it will stay on. Move the switch to B
and watch as the L fades away.

Look at the schematic. When the switch is on, the
current flows from the battery to the 100μF capacitor
to charge. Once the capacitor reaches full charge,
electricity flows to the transistor base and turns it on
gradually, which turns the LED on. Eventually the
capacitor will be completely charged and then the
current flows continuingly to the base of the transistor
and the LED stays on.

When the switch is turned off and you remove the
battery from the circuit, then the capacitor starts to
discharge through the transistor and the LED. The L
dims until the discharge of the 100μF is finished.

If you want a slower dimmer circuit, all you have to
do is replace the 100μF capacitor with the 470μF
capacitor. Replace connections 25-116-124 with
connections 25-118-124. Be patient because the
LED does eventually come on.

Hint: the 10μF capacitor charges when you close the
key.

Notes:

Go back to project 2 (the police siren) and see if you
can figure out why the siren goes from high to low as
you press and then release the key.

Schematic

Wiring Sequence:

o 18-19-20-48
o 25-116-124
o 46-115-90
o 119-47-131
o 89-132
o 121-122

-29-

How about we take a break? This circuit is for
entertainment. The numbers 1 and 2 will flash on the
display in the circuit. This might remind you of some
neon signs that have eye-catching advertisements
on them.

A “flip-flop” circuit controls the LED display in this
experiment. In later projects you will be learning more
about flip-flop circuits. Try a different value for the
capacitors to see the effects on the operation speed.
Try and rewire the LED display to flash numbers
other than 1 and 2. Try placing higher values in place
of the 22kΩ and 4.7kΩ resistors. Do not use lower
values for any of the resistors or else you could
damage the transistors.

Notes:

EXPERIMENT #16: FLIP FLOPPING

Wiring Sequence:

o 17-19-20-22-41-116-82
o 21-42-45-119
o 23-44-118-84
o 79-81-83-85-25-124
o 80-117-40
o 86-115-43
o 121-122

Schematic

EXPERIMENT #17: CAPACITOR DISCHARGE FLASH

In this circuit single pulses of high voltage electric
energy are generated by suddenly discharging a
charged capacitor through a transformer. Automobile
ignition systems use a similar capacitor-discharge
reaction.

The operation of this circuit is simple but the
concepts involved are important to helping you
understand more complicated circuits. If you have
access to an oscilloscope, you can scientifically
measure the energy that is discharged through the
transformer.

The 470μF capacitor stores up energy as the
batteries supply millions of electrons to the
capacitors negative electrode. Meanwhile the
batteries draw the same number of electrons from
the capacitors positive electrode so that the positive
electrode is lacking electrons. The current must pass
through the 4.7kΩ resistor, so it requires at least 12
seconds for the capacitor to receive the full 9V
charge from the batteries.

The amount of charge a capacitor can store depends
on its capacitance value and the voltage applied
across it. This represents the amount of electrons
displaced in the electrode.
The amount of electrons in a capacitor’s electrode is
measured in coulombs. The quantity of one coulomb
is 6,280,000,000,000,000,000 electrons (6.25 x

18

10

).

when the charge held by the capacitor is released
into the transformer.

Notes:

The charge in either electrode of the capacitor is
determined by multiplying the capacitance (C) by the
voltage across the capacitor (E). (Q = C x E). The
470µF (470 x 10

-6

F) capacitor at 9V is calculated as

follows:

Q = C x E = 470 x 10

-6

x 9 = 4.23 x 10-3coulombs

or:

470 x 0.000001 x 9 = 4.23 x 10

-3

coulombs

(265,564,400,000,000 electrons)

Pressing the key causes the above number of
electrons to pass through the transformer winding in
a very short time and induces a high voltage in the
secondary winding. Thus causing the LED to flash.

An oscilloscope is an electronics measurement
instrument used by engineers and technicians. If you
have access to one, connect it (with help from
someone who knows how to use it) to terminal 3 and
terminal 5 of the transformer to indicate the presence
of 90V or more. The indicated voltage is produced

Schematic

Wiring Sequence:

o 1-138
o 2-118-124
o 3-31
o 5-33
o 79-119
o 80-117-137
o 121-122

-30-

-31-

There are three connections made on a transistor;
one of these (the base) controls the current between
the other two connections. The important rule to
remember for transistors is: a transistor is turned on
when a certain voltage is applied to the base. A
positive voltage turns on an NPN type transistor. A
negative voltage turns on a PNP type transistor.

In this project the LED display shows which transistor
is on by lighting either the top or the bottom half. This
demonstrates how a positive voltage controls an
NPN transistor and the PNP transistor is controlled
by a negative voltage.

After the connections are made the NPN transistor
will be turned on because the positive voltage
through the 1kΩ resistor is applied to the base. This
turns on the upper half of the LED display.
Simultaneously the PNP is off because current
cannot flow to its base. (The current flows from the
PNP emitter to the NPN transistor base; however,
this flow from the PNP base is blocked by the diode.)

The NPN is turned off if you press the key, because
current is diverted away from its base. The PNP is
turned on simultaneously because now current can
flow from its base through the 4.7kΩ resistor. As a
result, the upper LED segments turn off and the
lower segments turn on.

Notes:

EXPERIMENT #18: TRANSISTOR ACTION

Wiring Sequence:

o 18-17-21-48
o 19-20-23-41
o 25-124-138
o 40-80-77
o 75-78-47-42-119
o 76-46-126
o 79-137-125
o 121-122

Schematic

EXPERIMENT #19: SERIES AND PARALLEL CAPACITORS

Some of the handiest items in your kit are the
capacitors. They store electricity, smooth out pulsing
electricity into a steady flow and let some electric
current flow while blocking other current. This circuit
allows you to compare the effects of capacitors
connected in both series and parallel.

Once you have finished wiring this project, set the
switch to B. Next connect terminals 13 and 14. You
will hear a sound coming from the speaker. In this
case, electricity is flowing through the 0.01μF
capacitor (refer to the schematic to help understand
this). Press the key now. What happens?

You will hear a lower-pitched sound coming from the
speaker, because the 0.05μF capacitor has been
added in parallel to the first capacitor. Current now
flows through both capacitors at the same time,
through two channels that are separate. What do you
think happens to the total capacitance when you
connect two capacitors in parallel?

You may have guessed wrong. When connected in
parallel, two capacitors make the total capacitance
increase. The tone is lower because the increased
capacitance causes it to be.

smallest capacitor in the series connection. The
higher-pitch sound is caused by the lower
capacitance.

Notes:

Now release the key and then move the switch from
B to A. While the switch is set to A, do not press the
key. Now what do you hear?

You now hear a high-pitched sound coming from the
speaker. This is due to the 0.05μF and 0.01μF
capacitors are now connected in series – the flow of
the current goes directly from one to the other. The
total of the capacitance in the circuit is less than the

Schematic

Wiring Sequence:

o 1-29
o 2-30
o 3-91-110-132
o 4-121
o 5-41-109
o 13-42
o 14-119
o 40-92-101-137
o 102-106-133
o 105-131-138
o 13-14 (POWER)

-32-

In this experiment you study the switching action of
transistors in turning an LED on. You will be using
two different transistors - one of the two PNP types
and the NPN type included in your kit. PNP and the
NPN refers to the arrangement of the semiconductor
materials inside the transistors.

The NPN transistor at the bottom of the schematic
stays on due to the 47kΩ resistor supplying voltage
to its base. Making the connection through the 22kΩ
resistor causes the PNP transistor at the top of the
schematic to turn on.

The resistance of the 22kΩ is approximately half of
that of the 47kΩ resistor, so the current supplied to
the base of the PNP transistor is about twice that of
the NPN. Therefore the PNP is turned on “greater”
than the NPN.

Connect the circuit and then press the key: 1 is
displayed. To increase the base current for the NPN
transistor, you have to decrease the value of the
47kΩ resistor connected to the base – terminal 46.
To do this simply disconnect between 87 and 88 and
then replace them with connections to another
resistor. For example, change connection 87-42 to
83-42 and connection 46-88 to 84-46, to change the
47kΩ to a 10kΩ resistor. Every time that you lower
the resistor value more current is then supplied to the
base of the transistor, and the LED display lights a
little brighter when you press the key. If you decrease
the resistance below 1kΩ the transistor may burn
out.

Next, change the resistors to 10kΩ and then press
the key. Use terminals 83 and 84 and terminals 81
and 82. With the transistors both fully on the
brightness should not change much. If change does
occur check your batteries.

Notes:

EXPERIMENT #20: TRANSISTOR SWITCHING

Wiring Sequence:

o 21-23-41
o 25-47
o 40-85
o 87-42-119
o 46-88
o 124-48-137
o 86-138
o 121-122

Schematic

EXPERIMENT #21: SERIES AND PARALLEL RESISTORS

In this project, you will discover what happens when
you connect resistors in series and in parallel. You
will see the LED-1 on the panel flash on and off when
you finish wiring.

See what happens to the LED on side A and then on
side B when you slide the switch. There is no change
at all. The schematic shows that two 10kΩ resistors
are connected in series to side A of the switch, and
one 22kΩ resistor is connected to side B. The
resistors connected in series on side A are equal to
the sum of each resistor’s value – so 20kΩ is the total
resistance of the resistors. This is about the same as
22kΩ resistance in side B. So the LED shows no
change when you move the switch.

The LED becomes brighter when you press the key.
By looking at the schematic, you will see that resistor
R1 (470kΩ) is connected to the LED in series. The
resistor controls the flow of current to the LED. The
total resistance decreases when you press the key,
R1 and resistor R2 (100Ω) are connected in parallel.
The LED becomes brighter because of the amount of
current flowing to it increases, when the amount of
resistance decreases.

together, and then divide the product by the sum of
values. In this case, the total resistance is:

470 x 100

(470 + 100)

= 82Ω

Connect now terminals 13-14. As shown in the
schematic, this connects the 22kΩ resistor in parallel
with the two 10kΩ resistors. Is there any change in
the LED? The flashes on and off of the LED are at
shorter intervals because the resistance connected
to the slide switch decreases. Try to calculate the new
resistance value. The new value is about 10.5kΩ.

This circuit is known as a multivibrator. A multivibrator
is an oscillator that uses components that direct
current back to each other. From the schematic you
can see that the 10μF and the 100μF capacitors
discharge through the transistors. This multivaibrator
circuit controls the oscillations to create the flash
through the LED at certain intervals.
You can now see that resistors and capacitors have
opposite effects when they are connected in series
or parallel. Be careful - it is easy to get confused
about which one increases or decreases in strength.

Calculating the total resistance for resistors connected
in parallel is not as easy as when resistors are
connected in series. You must multiply the values

Schematic

Notes:

Wiring Sequence:

o 31-41-114
o 79-116-44
o 40-115-85-81
o 43-113-87
o 32-71
o 72-138
o 82-84
o 13-83-131
o 14-86-133
o 33-80-88-137-132-121
o 45-42-119

-34-

A two-transistor amplifier is used in this circuit. In an
amplifier, a small signal is used to produce or control
a large signal. This circuit is similar to an early model
transistor hearing aid amplifier.

Your kit’s speaker can change sound pressure into a
weak voltage. The transformer increases the voltage,
and which is then applied to the NPN transistor
through the 3.3μF capacitor.

Now it is time to talk about the transformer. The
transformer has a copper wire wound hundred of
turns. We call this a coil. A transformer has two coils
separated by an iron plate.

A magnetic field is created when electricity flows
through a coil. The reverse is also true - if a coil is
subjected to a change in its magnetic field strength,
electricity flows through it. The magnetic field created
depends on the number of windings in the coil, so
when electricity flows through the first coil (the
primary coil), the voltage at the second coil (the
secondary coil) will be different if the number of
windings is different. Induction is the creation of an
electric charge using a magnetic field. Now go back
to project 17 and think of how a large voltage is
induced at the secondary side when 9V is applied to
the primary side of the transformer.

Notes:

EXPERIMENT #22: AMPLIFY THE SOUND

Wiring Sequence:

o 1-29
o 2-30
o 3-112
o 5-124-48-116-102-78-13-EARPHONE
o 93-109-40
o 41-94-77-14-EARPHONE
o 42-72
o 91-100-101-111-46
o 75-92-99-110-47
o 71-76-115-119
o 121-122

Schematic

III. LED DISPLAY CIRCUITS

-36-

By using the LED display you will see the effect of
electrical signals. An LED is similar to a normal diode
except when current flows through it, it emits light.
One example of the LED display is a power indicator
on your DVD player or your radio that tells you the
power is on.

A seven-segment LED display can show the
numbers 0 through 9 for reading information on a
calculator. Seven is the minimum number of
segments (separate lines that can be each lighted)
that are necessary to clearly distinguish all ten digits.
Two conditions that you must always observe for the
proper LED operation are:

1. Polarity correctness (+ and – LED connections)

2. Proper current flow

LEDs can burn out due to reverse polarity if the
voltage is more than about 4 volts, or if the current is
not limited to a safe value. When the polarity is
reversed the LED will not light.

Series resistors (permanently wired to your kit) are
used with the LED display to keep the current flow at
a proper level. Current flows through these resistors
and the LED to terminal 25, providing a
comparatively constant voltage (approx. 1.7 volts) to
the LED. To make the current flow through the LED
display we need voltages above this value. The
series resistors set how much current flows from the
batteries through the LED.

Now it is time for you to learn about the common­cathode seven-segment LED digital display. Seven
LED display segments use one contract point –
terminal 25 – as a common negative electrode in a
common- cathode.

To allow current to flow through an LED must have
both (+) and (–) connections. The anode is the
positive side and the cathode is the negative side. In
this kit the LED display is a common cathode type.
You connect any anode segment terminals as
required, to the battery’s positive side and connect
the common cathode segment terminal (terminal 25)
to the negative side of the battery.

LEDs operate tremendously fast. An LED can turn
off and on hundreds of times per each second; so
fast that you won’t even see it blink. There is no warm
up time or large amount of heat produced unlike an
incandescent lamp.

Do the following experiment to experience how fast
the LED operates.

1. Do not close the key but hook up the circuit.

2. Decrease the light in the room to a low level so
that you are able to see the LED light emission
easily.

3. Close the key but only for less than a second.

You will notice that the display goes quickly off and
on. Hold the platform steady but glance quickly at the
LED as you quickly tap the key. It will appear that the
display goes on and off. What occurs in the
persistence of the human eye is much longer than
the LED’s time but without the use of special
instruments this gets the point across.

Notes:

EXPERIMENT #23: LED DISPLAY BASICS

Wiring Sequence:

o 17-18-19-20-21-22-23-24-138
o 25-120
o 119-137

Schematic

EXPERIMENT #24: DIGITAL DISPLAY CIRCUIT FOR THE SEVEN-SEGMENT LED

Wire the circuit as shown to connect the 3V supply
to the LED segments and the decimal point (Dp).
What numbers and letters do you see displayed?

In this experiment you can make some voltage
measurements using a Voltage/Ohm Meter (VOM) if
you have one. Connect the VOM as directed by its
instructions. Skip these measurements if you do not
have a VOM.

With this low battery voltage, you can reverse the
polarity of the circuit by reversing the connections to
the battery. (Changes to make are: change 25-120
and 119-WIRE, 25-119 and 120-WIRE.) Record your
results. After you note your results, reconnect the
battery with the correct polarity. Measure the LED
voltages between terminal 25 and each separate
terminal (17 through 24) using a VOM if you have
one. Change the battery connections to 25-124, 121­122, and 119-WIRE to temporarily change the 9V
supply. Next, make the same measurements. What
amount is the LED voltage increased by, from using
this three-time increase from the battery? (A normal
increase is 0.25V)

Notes:

Next, try measuring the voltage in each resistor
attached to one of the LED segments. All of the
resistors are 360Ω. The LED current is in milliamps
(one-thousandths of an ampere) is calculated by
dividing the voltage by 360Ω. The LED segment
currents are approximately ____ milliamperes (mA)
with the 3V supply (3mA typically), and ____ mA with
the 9V supply.

Make a chart of the connections required to display
0 through 9 on the display in the space below.

Schematic

Wiring Sequence:

o 25-120
o 119-WIRE

or

o 25-120
o 119-(17, 18, 19, 20, 21, 22, or 23)

In this project you will see how to turn on an LED by
using a transistor and a CdS cell.

Think of the CdS cell as a resistor that changes its
resistance based upon the amount of light that falls
upon it. In the dark the resistance is very high,
around 5 megohms (MΩ, 5 million ohms); in bright
sunlight, it can decrease to about 100Ω or less.

To test this easily; just set your VOM to the resistance
function and then connect it to the CdS cell. Now hold
you hand over the CdS cell and note its resistance.
Read the resistance again once you have moved
your hand.

For a switch you can use the NPN transistor. This
transistor turns on when sufficient positive voltage is
applied to its base. Positive voltage leads from the
positive terminal of the battery, then to the CdS cell,
to the control, and then finally to the 10kΩ resistor.
The amount of voltage applied to the transistor’s
base is determined by the total resistance value of
the CdS, the control, and the 10kΩ resistor. The
amount of light striking the cell and the control setting
change the base voltage - making it either high or
low enough to turn on the transistor. Using your
voltmeter on the control, try to change the control
position while casting a shadow over the CdS to
verify the voltage change. When light changes over
the CdS, adjust the control so that the transistor turns
on and off.

Under bright light the circuit displays a 1. You can
connect the wires to display any number you desire.
1 might be considered to be a binary digit, showing
logic “high” (H or ON), as indication of the presence
of a bright light on the CdS cell. Can you rewire this
circuit to display another character to indicate this
condition?

Notes:

EXPERIMENT #25: LED DISPLAY WITH CdS AND TRANSISTOR

Wiring Sequence:

o 15-21-23-119
o 16-28
o 25-47
o 124-26-48
o 27-82
o 46-81
o 121-122

Schematic

EXPERIMENT #26: SWITCHING THE LED DISPLAY USING TRANSISTOR CONTROL

This project shows how to control the LED display
through the use of transistors.

This circuit is similar to the one in Project 18
(Transistor Action). The differences between these
two are the position of the switch as well as the value
of the resistor. In this project we use the base circuit
of the NPN transistor as a switch, in order to control
the cathode of the LED. Project 18 controlled the
LED from the anode (positive side).

The transistors in this circuit act as switches. The
PNP transistor is always on, allowing the current to
flow from the collector to the emitter, because a
sufficient amount of the negative voltage is applied
to its base through one of the 10kΩ resistors. When
you press the key the NPN transistor turns on,
thereby applying sufficient positive voltage to its
base, through the use of another 10kΩ resistor.
When you close the key, then current can flow from
the PNP’s emitter to its collector.

Here are some important basic principles for you to
remember:

Notes:

• When negative voltage is applied to its base, a
PNP transistor turns on; the current flows from
the collector to the emitter.

• When positive voltage is applied to its base, a
NPN transistor turns on; the current flows from
the emitter to the collector.

Current can now flow through the NPN transistor,
thus current can now travel a complete path - from
the negative batteries side, to the NPN transistor, to
the common cathode terminal of the display, to the
PNP transistor, to the positive side of the batteries –
thus lighting the display.

Turning on the LED with either of the transistors may
not see important to you now. But, to people who
design computer circuits that are complicated, it is
an easy way to control the circuits.

Have you noticed that transistors switch on and off
as fast as you press the key? These quick switching
allows operations to be performed quickly by
computers. Transistors are many times faster than
hand operated switches or relays. Later you will see
how to delay this fast switching by using other
components.

Schematic

Wiring Sequence:

o 21-23-41
o 25-47
o 40-82
o 119-42-137
o 46-84
o 124-48-81
o 83-138
o 121-122

-41-

IV. WELCOME TO DIGITAL CIRCUITS

EXPERIMENT #27: “FLIP-FLOP” TRANSISTOR CIRCUIT

What is a flip-flop? It is a kind of circuit that changes
back and forth between two states (on and off) at
specific intervals. It flips into one state and flops into
another and so on.

Two transistors, two capacitors and four resistors are
used by the flip-flop to turn on and off the LED. Each
of the transistors are always in the opposing state of
each other; when transistor Q1 is on, transistor Q2
is off; when Q2 is on then Q1 is off. The change from
on to off or off to on, happens quickly (in
microseconds). Note the effect on the flashing rate
of the LED when adjusting the control.
To see how this circuit works, look at the schematic.
Remember when voltage is applied to the base of a
transistor, it turns on. On the negative side of the
batteries you have the two PNP transistor connected
through resistors. You may think that both transistors
would always be on however, there are two
capacitors connected to the bases that aid the cause
of the flip-flop action.

In order to explain the circuit, you should assume that
transistor Q1 is off. The 100μF capacitor will be
charging and discharging through its base, so we
can say that Q2 is on. Transistor Q2 is kept on after
the 100μF capacitor has discharged due to the 47kΩ
resistor and the control. Now the 10μF capacitor has
received a charge and is discharging through the

4.7kΩ resistor, the battery and the Q2. (Remember
that current can flow through the collector to the
emitter when transistor Q2 when it is on.) As long as
the charge on the 10μF is high enough the Q1
transistor remains off.

Transistor Q1 turns on when the charge drops to a
specific point, the negative voltage from the 47kΩ
resistor. Once Q1 turns on, and 100μF quickly starts
charging and transistor Q2 turns off. With the Q2 off,
its collector voltage rises toward the 9V of the battery
supply and thus the LED turns off. The Q1 turns on
fully through the fast charging of the 10μF. This flip
occurs very fast.

The circuit will eventually flop back to the original
state to repeat the above action due to the 100μF
discharging through the Q2 transformer.

Look back at the previous projects and try to locate
where you have used this sort of circuit.

Notes:

Schematic

Wiring Sequence:

o 21-23-41-84
o 75-81-87-25-27-124
o 28-79-82
o 40-115-80
o 45-42-119
o 43-88-83
o 44-116-76
o 121-122

-43-

Now it is time to step into the world of digital circuits
and learn some basics. A circuit that acts as a switch
to turn different components off and on is a digital
circuit. In this section you will be dealing with diode­transistor logic (DTL) circuits- these are circuits that
use diodes and transistors to turn the power on and
off.

It doesn’t usually matter how much voltage is applied
to a digital circuit; what matters is whether the circuit
is off (no voltage present) or on (presence of
voltage). When a circuit is off we describe it as logic
low or use the number 0. When a circuit is turned on
we say logic high or use the number 1.

A switch that turns circuits on and off is a toggle
switch. In this experiment we will use the flip-flop
circuit to work as a toggle switch. In this project,
unlike others that you will be doing later, the circuit
does not change until you tell it to.

Once you have completed the wiring, set the switch
to A. The lower part of the LED lights up. Press the
key now. The upper section lights up while the lower
section shuts down. Every time you press the key the
LED sections will change, thus a flip and a flop.

When a transistor is on and the other transistor is off,
it will stay either on or off until you tell it to change.
We can easily say that a flip-flop circuit remembers.
Once you put a circuit into a certain setting, it will stay
that way until you tell it to change. Controlled by a
single toggle signal, flip-flops can remember many
things. This is also why computers can remember so
many things.

Notes:

EXPERIMENT #28: “TOGGLE FLIP-FLOP” TRANSISTOR

Wiring Sequence:

o 84-108-44-17
o 81-106-41-20
o 25-124-137
o 40-107-83
o 42-110-72
o 45-130
o 43-105-82
o 71-75-111-131-129
o 76-109-112-138
o 119-132
o 121-122

Schematic

EXPERIMENT #29: “AND” DIODE TRANSISTOR LOGIC WITH LED DISPLAY

In this circuit you will first learn about the AND circuit.
When all the connections to its terminals are logic
high (receiving voltage), the AND circuit produces a
high output.

Make the connections in this circuit based upon the
wiring sequence below. After that make the
connection to terminals 119 and 124 using terminals
A (126) and B (128) in different combinations to
complete the circuit and to learn how an AND circuit
works.

Terminal 124 provides logic high (voltage) while
terminal 119 provides logic low (no voltage) in this
circuit. H is only shown on the LED after you have
connected terminal A and terminal B to terminal 124
(high terminal). If you make the connection of either
terminal A or B or both to terminal 119 (low terminal)
the LED will display nothing. For the combined output
(the LED) to read H (high), both A and B have to be
high.

The PNP transistor stays off when either or both of
the inputs are low (terminals 126 and/or terminal 128
are connected to terminal 119), and when positive
voltage is applied to the PNP transistor base through
the diode(s). The NPN transistor is also off because
the PNP transistor does not complete the circuit, and
no current is supplied to the NPN transistor base.
Also remaining off is the LED due to the fact that the
common cathode terminal is not connected to the
negative power supply.

The base of the PNP transistor turns on when both
of the inputs are high and when both diodes supply
negative voltage to the base of the PNP transistor. In
addition, the NPN transistor turns on and then the
current flows to the display to light the LED.

Symbol AB is used to represent an AND function that
mathematicians use. On the bottom right of this
schematic is the schematic symbol for the AND
circuit.

Notes:

Wiring Sequence:

o 22-23-21-18-19-72
o 25-47
o 81-40-125-127
o 41-83
o 42-129
o 46-84-85
o 86-82-48-124
o 71-130-119
o 121-122
o 126-(to 119 “HIGH” or 124 “LOW”)
o 128-(to 119 “HIGH” or 124 “LOW”)

Schematic

-44-

-45-

This next circuit is a logic OR circuit. Are you able to
guess how this circuit may work? Remember that the
AND circuit produces high logic only when inputs A
and B are both high. In the OR circuit logic high is
produced when A or B receives a logic high input.

By connecting either terminal A or B to terminal 119
(logic high terminal) the display will show H. Try
connecting each of the terminals to terminal 119;
then to terminal 124. What occurs? When connected
to H the output is high when either A or B is
connected. A+B is the symbol for this logic function.

We won’t explain the entire operation for you here
because this circuit is similar to project #29.
Compare these two projects (29 and 32); then make
notes of their similarities and their differences. On the
schematics diagram see if you can follow the circuit.

Notes:

EXPERIMENT #30: “OR” DTL CIRCUIT WITH DISPLAY

Schematic

Wiring Sequence:

o 71-41
o 72-19-18-21-22-23
o 79-25-48-124
o 81-47
o 83-127-125
o 84-80-46
o 85-42-119
o 86-82-40
o 121-122
o 126-(to 119 “HIGH” or 124 “LOW”)
o 128-(to 119 “HIGH” or 124 “LOW”)

EXPERIMENT #31: “NAND” DTL CIRCUIT WITH DISPLAY

You will not be able to find the word NAND in your
dictionary (unless it is a computer or electronic
dictionary). This term means inverted or Non-AND
function. It creates output conditions that are the
opposite of the AND circuits output conditions. When
both inputs A and B are high the NAND output is low.
If either or both of the inputs are low then the output
is high. The symbol for logic looks like the AND
symbol but with a small circle at the output. AB is the
representation of the function.

The NPN transistor stays off when either or both
terminals A and B are connected to terminal 124
(logic low terminal), and negative current flows
through the diode(s). The LED remains off. Both
diodes allow positive voltage to flow through them
when both of the inputs are connected to terminal
119 (logic high terminal). The NPN transistor is
turned on by positive voltage, thus the current flows
to light the L on the LED.

Notes:

Wiring Sequence:

o 81-20-19-18-119
o 25-47
o 82-46-128-126
o 48-130
o 121-122
o 124-129
o 125-(to 124 “LOW” or 119 “HIGH”)
o 127-(to 124 “LOW” or 119 “HIGH”)

Schematic

-46-

-47-

It is easy to determine what the NOR (inverted OR)
circuit does now that you have built and learned
about the NAND (inverted AND) circuit. When either
terminal A or B is connected to terminal H (119) the
display shows L. When low inputs are received by
terminals both A and B then the circuit output is high.
In the OR circuit this is the opposite. The schematic
shows the logic symbol for the NOR circuit. A + B is
the writing for the function. The OR is symbolized by
the + and the bar over the symbol signifies that the
circuit is inverted.

The current path for the LED is complete when you
connect either A or B (or both) to terminal H, turning
the NPN transistor on. The transistor and the LED go
off when you connect both A and B to L.

Notes:

EXPERIMENT #32: “NOR” TRANSISTOR CIRCUIT WITH DISPLAY

Wiring Sequence:

o 18-19-20-119
o 25-47
o 46-82-84
o 48-124
o 81-(to 119 “HIGH” or 124 “LOW”)
o 83-(to 119 “HIGH” or 124 “LOW”)
o 121-122

Schematic

EXPERIMENT #33: “EXCLUSIVE OR” DTL CIRCUIT

If you don’t know what an exclusive OR means, don’t
worry. An exclusive OR (abbreviated XOR) circuit
provides a high output only when one or the other of
its inputs are high.

You can see that an XOR circuit produces a low
output, only if both of the inputs are the same (high
or low). If the inputs are different (either high and low
or low and high) it results in the output being high.
This circuit is handy to let us know if we have two
inputs that are the same or if the inputs are different.

Before completing this circuit, be sure you have the
switch set to B. Once you have finished connecting
the wiring, connect terminals 13 and 14 to turn the
power on. Now watch LED 1. Press the key to
produce a high input. Is there any change in the LED
1? To make both inputs low release the switch. To
make the input through the switch high, set the
switch to A. What does LED 1 do?

Press the key while leaving the switch at A to make
both the inputs high. Now you can see that in an
XOR circuit, you need two high inputs to produce a
low output.

Notes:

If desired, you can build an XNOR circuit (exclusive
NOR). We will not build one here, however, you might
be able to figure how to do it. Hint: It is almost
identical to the NOR circuit followed by additional
wiring in order to reverse the circuit. Make sure that
you keep track of your experiments in your notebook,
particularly if you make an XNOR circuit.

Schematic

Wiring Sequence:

o 13-45-132-137
o 14-119
o 44-31-75
o 76-84-82-33-121
o 81-40-138
o 41-130
o 48-42-128
o 43-47
o 46-80
o 79-129-125
o 83-126-127-131

-48-

-49-

V. MORE FUN WITH DIGITAL CIRCUITS

EXPERIMENT #34: “BUFFER” GATE USING TTL

Have you ever wondered what happens once you
start adding digital circuits together, using the output
of one as the input of another? You’ll find out when
you build this project.

A quad two-input NAND gate IC, is one of the
integrated circuits contained in your kit. Some of
these words will probably be a confusing at first. IC
is short for integrated circuit. Something that contains
many transistors, diodes, and resistors in one small
package is an integrated circuit. This NAND gate
uses TTL, short for Transistor-Transistor-Logic,
because it is mostly constructed using transistors.

Quad means four. There are four separate NAND
gate circuits, in this IC each receiving two inputs. Two
input terminals are for Each NAND gate.

As you build this project make sure to consult to the
schematic. This circuit takes the output from one
NAND gate, and uses it for both inputs to the second
(both inputs for the two NANDs are always the same
here). What do you think happens if the input to the
first NAND is 1, after learning about NANDs? If the
first input is 0? Attempt to figure it out before building
this project.

1 is the input when the switch is set to A, and 0 is the
input when the switch is at B. When the input to the
first NAND is 1, its output is 0. But the 0 output of the
first NAND is the input to the second. The 0 input to
the second makes its output become 1, lighting the
LED.

Notes:

Set the switch to B before completing the wiring. To
turn the power on, connect terminals 13 and 14.
What happens to LED 1? Set the switch to A. LED 1
lights up.

Schematic

Wiring Sequence:

o 13-49-131
o 14-119
o 31-55
o 33-56-57-59-60-62-133-121
o 50-51-132
o 52-53-54
o 13-14 (POWER)

-50-

-51-

A circuit that has an output that is the opposite of its
input is called an inverter. If the output is 0, (low) then
the input is 1 (high). If the output is 1, then the input
is 0.

Before completing this project set the switch to A.
Next, connect terminals 13 and 14. You’ll observe
that both LED 1 and LED 2 are off. Since the input is
1, the output has to be 0. When you set the switch to
B, you will see both LEDs come on, indicating the
input is 0.

You can see from the schematic that we use two of
the four NAND gates in the IC. With the switch at A,
both inputs to the two NANDs are 1. This means the
outputs of both NANDS are 0 (and the LEDs go out).
When the switch is set to B, the LEDs come back on
because we no longer have all inputs at 1.

One extraordinary thing to think about is how big the
RTL and DTL circuits were in earlier projects. Four
of those circuits, Believe it or not, have been shrunk
down to fit inside this tiny IC.

ICs can be very complex. Large-scale integration
(LSI) is the process of putting several circuits inside
just one IC. The microprocessors running computers
and cell phones are very complex ICs.

Notes:

EXPERIMENT #35: “INVERTER” GATE USING TTL

Wiring Sequence:

o 13-49-50-131
o 14-119
o 31-52
o 36-33-56-57-59-60-62-133-121
o 34-55
o 51-53-54-132
o 13-14 (POWER)

Schematic

EXPERIMENT #36: “AND” GATE USING TTL

By using your kit’s NAND gates, are you able to
figure out how to make an AND gate? To find out let’s
experiment!

As you build this circuit, leave the switch at B.
connect terminals 13 and 14 to turn the power on
once you have finished. Now press the key. What
happens to LED 1? Now while pressing the key, set
the switch to A. Are there any changes in LED 1?

As you can observe by setting the switch to A and
then pressing the key, makes the inputs 1, causing
the overall output to be 1. Are you able to flow the 1
input through the circuit until you reach a 1 output?
Give it a try, but don’t peek at the answer.

Here is how it works – each 1 input goes into the first
NAND gate. Thus causing the output of the NAND to
be 0. This 0 output is used for both inputs to the
second NAND. The LED lights when the 0 inputs to
the second NAND cause its output to be 1. AND gate
is formed from two NAND gates.

Notes:

Schematic

Wiring Sequence:

o 13-49-131-137
o 14-119
o 31-55
o 72-56-57-59-60-62-33-133-121
o 50-71-138
o 51-132
o 52-53-54
o 13-14 (POWER)

-52-

-53-

One of the cool things about the quad two-input
NAND IC is that to make up other logic circuits all we
have to do is combine the four NAND gates. In our
last two projects you have been shown how you are
able to use NANDs to make up some other logic
circuits. In this project you will be shown how to make
up an OR gate from the NAND gates.

Can you trace what happens from each input to the
eventual output from just looking at the schematic?
(Of course you can, just try it.)

Keep the switch set to B, as you work on this project.
Connect terminals 13 and 14 when you’ve finished.
Now press the key. What happens to LED 1? Set the
switch to A and release the key. What happens to
LED 1 now? Press the key again while keeping the
switch at A and press the key again. Are there any
changes in LED 1?

You see that this circuit acts like other OR gates
you’ve experimented with. The output to the LED is
1 if at least one or the other of the inputs is 1. Have
you tried tracing what happens from input to output
yet? The explanation is in the next paragraph.

Say you press the key with the switch set to B. This
enters 1 as both inputs of the NAND, thus causing
the NAND’s output to become 0. This 0 output is one
of the inputs to the NAND gate controlling the LED.
Since a NAND’s output is 0 only if all inputs are 1,
then the 0 input causes the NAND’s output to go to
1, and LED 1 lights!

Notes:

EXPERIMENT #37: “OR” GATE USING TTL

Wiring Sequence:

o 13-49-131-137
o 14-119
o 31-58
o 72-59-60-62-33-133-121
o 50-51-71-138
o 52-56
o 53-54-132
o 55-57
o 13-14 (POWER)

Schematic

EXPERIMENT #38: “R-S FLIP-FLOP” USING TTL

R-S does not mean Radio Shack®flip-flop. As we
mentioned earlier circuits that flip-flop alternate
between two states. Those who use flip-flop circuits
most often are engineers, and they use flip-flop
circuits to switch between low (0) and high (1)
outputs. We say a circuit is at set status (S) when the
output is high or on. We use the word rest (R) when
a circuit is off.

Once you have completed the wiring, to turn the
power on turn the switch to A. LED 1 or LED 2 will
light up. Touch terminals 13 and 14 in turn with the
long wire connected to terminal 26. What occurs to
LED 1 and LED 2?

The R-S flip-flop is set when the LED 2 lights. The R­S flip flop is in reset when the LED 1 lights. Set or
reset the flip-flop, then remove the long wire from the
circuit and see what it does.

Now you can observe one of the primary
characteristics of the R-S flip flop. Once you have the
circuit either set or reset, the circuit stays in the
specific state until an input signal causes it to
change. This means that R-S flip flop can remember
things. Advanced computers use similar circuits to
remember things.

Notes:

Wiring Sequence:

o 77-75-49-31-34-131
o 33-53-52
o 36-55-51
o 50-76-13 (SET)
o 54-78-14 (RESET)
o 121-62-60-59-57-56-LONG WIRE
o 119-132

Schematic

-54-

-55-

We have been using digital circuits that have two
inputs, but that doesn’t mean that we can’t have
more than the two inputs. Here is a TTL AND gate
which has three inputs. Use the schematic to try and
figure out how to have three inputs result in an output
of 1.

We are going to do things a bit differently this time ­terminals 13 and 14 create P as an input signal.
When you connect the two terminals they create a 1
input, and disconnecting them creates a 0.
Connecting terminals 119 and 137 “turns on” this
project.

This circuit is called a gate because it is a circuit that
has more than one input and only one output. The
output of the gate is not energized until the inputs
meet the certain requirements. We will be using this
handy component in more digital circuits through
other projects.

A gate circuit that is used to keep two portions of a
circuit separated from each other is called a buffer.
Next, look at the schematic and see if you can figure
out the connections needed for the switch, the key,
and terminals 13 and 14 that will result in an output
of 1. Try to figure it out on your own and then read on
to see if you were correct.

The circuit works this way: connected to the one
NAND are both the key and the switch. When each
provides an input of 1, then the NAND has an output
of 0. This 0 creates the input of another NAND,
causing the output to become 1.

This output of 1 then goes on to another NAND gate
(can you find it on the schematic?). There it makes
up one input in addition to the input from terminals
13 and 14 that created the other. Once these inputs
are both 1, then the NAND’s output goes to 0. This
output is used with both of the inputs of the last
NAND, thus causing it to become 1 and for the LED
to light.

Doesn’t it seem simple? Well, believe it or not but,
even complex computers operate through the use of
the same principles we are using in these circuits.

Notes:

EXPERIMENT #39: “TRIPLE-INPUT AND” GATE USING TTL

Wiring Sequence:

o 13-49-131-137-119
o 14-73-57
o 31-61
o 74-71-62-33-121-133
o 50-72-138
o 51-132
o 52-53-54
o 55-56
o 58-59-60

Schematic

EXPERIMENT #40: “AND” ENABLE CIRCUIT USING TTL

Setting the switch to B blocks the channel from the
LED 1 to the LED 2 However, when you set the
switch to A, you will find that LED lights and turns off
at the same time as LED 1. The two NAND gates
produce an AND gate.

In this circuit the LED 1 is known as the data input.
The output is the LED 2. Frequently these terms are
used with enable circuits. They will show up from time
to time when we talk about digital circuitry.

As you may have suspected by now, we can use
digital circuits to perform enable functions. Are you
able to figure out how? Make sure to keep the notes
of your findings especially if you are able to figure out
how to use an OR gate in an enable circuit.

Wiring Sequence:

o 13-49-42-45-131
o 14-119
o 71-50-31-44-114
o 86-82-80-72-56-57-59-60-62-33-36-121-133
o 34-55
o 40-113-85
o 41-116-79
o 43-115-81
o 51-132
o 52-53-54
o 13-14 (POWER)

Notes:

Schematic

-56-

-57-

NAND gates are able to act as electronic
guardsmen. If you don’t want a signal to be placed
into input of a circuit, a NAND will make sure that it
doesn’t happen.

In the schematic, one thing that you recognize right
away is the multivibrator. By watching the LED you
can see the multivibrator. You will also realize that the
multivibrator provides one of the inputs to the NAND
gate. With the use of the schematic can you figure
out what occurs when the switch is set to A? B? Are
you able to figure out what occurs when LEDs 1 and
2 do with the switch set to A and then set to B? Make
sure you that you make notes and then compare
them with what you learn.

Set the switch to B, before completing the circuit.
Once you have finished the wiring connect terminals
13 and 14 and then look at LEDs 1 and 2. You will
notice that LED 1 will “blink” in order to indicate the
output of the multivibrator. Look now at the LED 2.
You will find that it is lighting continuously, thus
indicating that something is preventing the LED
signal at 1 from reaching the second LED. Set the
switch to A and then look at LED 1. What is
occurring? Is it the same occurrence that was
happening to both LED 1 and LED 2?

As you can see, LED 1 and LED 2 are taking turns
going on and off. This is because we make one of the

two inputs to the NAND equivalent to 1 once the
switch is set to A. The multivibrator sends 0 and then
signals to the other NAND input. When the output for
the mulitivibrator is 1, then the LED 1 lights but only
because both input signals to the NAND are 1, then
the NAND output is 1 and the LED 2 lights. Now try
to figure out what occurs when the switch is set to B
– why does the LED 2 always light. Hint: B switch
supplies an output of 0.

Now were you able to figure all of that out before you
built the circuit? We sure hope so ☺

Notes:

EXPERIMENT #41: “NAND” ENABLE CIRCUIT USING TTL

Wiring Sequence:

o 13-49-53-54-42-45-131
o 14-119
o 71-50-31-44-114
o 86-82-80-72-56-57-59-60-62-33-36-121-133
o 34-52
o 40-113-85
o 41-116-79
o 43-115-81
o 51-132
o 13-14 (POWER)

Schematic

EXPERIMENT #42: “NOR” GATE USING TTL

Try to mark 0 and 1 inputs on the schematic and see
if this circuit comes up at either a 0 or 1 output. Give
it try and don’t peak at the answer.

As you are constructing this circuit, make sure to
have the switch set to B. Once you have completed
the wiring, connect to terminals 13 and 14. Now
press the key. Are there any changes in LED 1? Now
release the key and place the switch to A. Now what
occurs on LED 1? Leave the switch at A and then
press the key. Is anything different occurring?

This project acts just like the other NOR gates we
have built. The NANDs mark with an A and B both
have an input of 1. Therefore they both have an
output of 0 when the input is 1. Their outputs are
used as inputs to the NAND labeled C. The output of
NAND C is 1 as long as one or both of inputs are 0.
This output is used for the inputs of the next NAND
causing it to have an output of 0. Therefore the LED
1 does not light.

A NOR gate only has an output of 1 when both inputs
are 0. This occurs when the switch is set to B and the
key is not pressed.

Notes:

Wiring Sequence:

o 13-49-131-137
o 14-119
o 31-55
o 72-33-62-133-121
o 50-58
o 51-61
o 52-53-54
o 56-57-71-138
o 59-60-132
o 13-14 (POWER)

Schematic

-58-

-59-

If you are thinking that the NAND gate is a truly
versatile circuit, well then your right! This experiment
is a toggle flip-flop circuit made by using four NAND
gates.

When you have finished building this circuit, connect
terminals 13 and 14 in order to turn the power on.
Slowly press the key several times. You will notice
that each time the key is pressed the LED 1 turns on.
Now it is time to put on your thinking cap and try to
trace what occurs from the key input to LED 1. Two
out of the four NANDs function as a R-S flip-flop. See
if you can figure out what the other NANDs are
doing.

This circuit is known as inverter because it takes the
inputs and reverses them.

Notes:

EXPERIMENT #43: “NAND” GATE MAKING A TOGGLE FLIP-FLOP

Wiring Sequence:

o 13-75-85-81-49-31-42
o 14-119
o 33-57-61-87
o 40-88
o 41-74-77
o 46-102-86
o 47-53-50-76
o 78-62-48-112-116-137-121
o 51-55-60
o 52-56
o 73-54-115
o 58-59
o 82-101-111-138
o 13-14 (POWER)

Schematic

EXPERIMENT #44: “EXCLUSIVE OR” GATE USING TTL

Since we have made up some digital circuits by
combining NAND gates, it makes sense that we
make XOR gates too. This circuit will show you how.
Before you complete this circuit set the switch to B.
Connect the terminals 13 and 14, once you have
finished the wiring. Does anything happen to LED 1
when you press the key? Release the key now and
set the switch to A. What occurs with the LED 1?
Now press the key while leaving the switch at A.
What happens with the LED 1 now?

As long as the inputs are different, output is 1. The
output of the XOR gate is 0, as long as both of the
inputs are the same - either 0 or 1.

Its thinking cap time again. Follow each 0 or 1 input
throughout the circuit until they reach the output. It
will help if you mark 0 or 1 on the input and the output
of each NAND gate on the schematic.

Wiring Sequence:

Notes:

o 13-49-131-137
o 14-119
o 31-61
o 72-62-33-133-121
o 71-50-53-138
o 57-51-132
o 54-52-56
o 55-59
o 58-60
o 13-14 (POWER)

Schematic

-60-

-61-

Have you figured out how to make an enable circuit
using an OR gate? Well, if the answer is yes, then
this is your chance to compare you design to our OR
enable circuit.

As done in projects 35 and 36, the multivibrator
provides the input to the OR gate in this circuit. You
can observe the output of the OR gate when you
view LED 1—it flashes on and off corresponding to
the output of the multivibrator. Can you tell what
occurs when the multivibrator’s input is applied to the
OR gate by viewing the schematic? Give it a try
before building the project.

Before completing this circuit, set the switch to A.
Connect terminals 13 and 14 to turn the power on
once you have finished the wiring. What does LED 1
do? What does LED 2 do? Set the switch to B. What
occurs to LED 1 and LED 2 now?

We can simplify the circuit by stating that setting the
switch to A blocks the flow of the data from LED 1 to
LED 2. We call this inhibit status. An enable status
occurs when the switch is at B; then data can flow
from LED 1 to LED 2.

Notes:

EXPERIMENT #45: “OR” ENABLE CIRCUIT USING TTL

Wiring Sequence:

o 13-49-42-45-131
o 14-119
o 71-50-51-31-44-114
o 86-82-80-72-59-60-62-33-36-121-133
o 34-58
o 40-113-85
o 41-116-79
o 43-115-81
o 52-56
o 53-54-132
o 55-57
o 13-14 (POWER)

Schematic

EXPERIMENT #46: LINE SELECTOR USING TTL

It isn’t hard to think of some situations where we
might want to send input data to two or more different
outputs. This experiment shows how we can use a
network of NAND gates to help do that.

This circuit uses three NAND gates and a
multivibrator. Build the circuit, connecting terminals
13 and 14 last. If the switch is set to A then LEDs 1
and 2 will be blinking; if the switch is set to B then
LEDs 1 and 3 will be blinking.

Setting the switch to A or B controls the inputs to the
two NANDs that light LED 2 and LED 3 as shown in
the schematic. When the switch is A then the NAND
is controlling LED 2 gets one steady input of 1. The
other input is supplied by the output of the
multivibrator. As the multivaibrator’s output switches
from 0 to 1, NAND controlling the LED 2 switches it
output from 1 to 0.

When you have the switch set to B, the opposite
happens. According to the input from the multivibrator
LED 3 can go on and off because the NAND
controlling the LED 3 gets a steady input of 1.

Notes:

Wiring Sequence:

o 13-49-34-37-42-45-131
o 14-119
o 71-57-54-31-44-114
o 86-82-80-72-59-60-62-33-121-133
o 36-55
o 39-58
o 40-113-85
o 41-116-79
o 43-115-81
o 50-51-53-132
o 52-56
o 13-14 (POWER)

Schematic

-62-

-63-

The last experiment you did let you explore how data
could be sent to two or more different outputs. You
can probably think of situations where we might want
to or need to do the opposite - which is sending data
from two different sources of output. This circuit
shows you how.

You see two different input sources when you view
the schematic. The multivibrator circuit provides one
of the input signals to LED 2; can you guess what the
other signal is provided by?
YOU! You provide the input signal by pressing and
relieving the key. The LED 1 is controlled by the
action of the key.

Before completing this project set the switch to A.
Once you have connected terminals 13 and 14 to
switch on the power LED 2 blinks. Keep your eye on
both LED 1 and LED 3. Has anything happened yet?
See what happens to LED 1 and LED 3 when you
press the key. At the same time as LED 1, LED 3
goes on and off. Set the switch to B. Now LED 3 turns
on and off according to the blinking of LED 2. To
determine the output of LED 3, you can use either of
the two sources as the input.

Put on your thinking cap, and try following the inputs
from the multivibrator, to the key, to the setting of the
switch, to the LED. By each of the terminals of the
NANDs, mark either a 1 or 0 to observe the different
high and low inputs.

Computers use a more complex version of these
circuits. As you probably guessed, the switching from
one input channel to another is usually done
electronically.

Notes:

EXPERIMENT #47: DATA SELECTOR USING TTL

Wiring Sequence:

o 13-49-42-45-131-137
o 14-119
o 73-50-31-138
o 86-82-74-72-80-62-33-36-39-121-133
o 71-57-34-44-114
o 37-61
o 40-113-85
o 41-116-79
o 51-53-54-132
o 43-115-81
o 52-59
o 55-56
o 58-60
o 13-14 (POWER)

Schematic

VI. MEET TRANSISTOR-TRANSISTOR LOGIC

-64-

-65-

Connect terminals 13 and 14 to turn on the power
and finish the wiring sequence for this circuit. You’ll
notice that both LED 1 and LED 2 alternate going on
and off. By substituting different values for the 100μF
capacitor you can change the speed of the blinking.

In place of transistor multivibrators, TTL
multivibrators are becoming widely used today. Think
of some reasons why? Make notes on any reasons
you think TTL multivibrators would work better than
regular transistor multivibrators.

TTL multivibrators use much less space than
transistor multivibrators. TTL ICs also exert less
current than comparative transistor arrangements.

Notes:

EXPERIMENT #48: BLINKING LEDS

Wiring Sequence:

o 13-49-31-34
o 14-119
o 33-60-59-58
o 36-61
o 50-51-77-115
o 52-53-54-78-75
o 55-57-56-76-116
o 62-121
o 13-14 (POWER)

Schematic

EXPERIMENT #49: MACHINY SOUND

Listen to the sound this project makes. Take your
time and check your work because there are a lot of
wiring steps. Once you’ve finished, set the switch to
position A. What are you hearing? From looking at
the schematic, can you explain how the circuit
produces this sound?

This circuit has two multivibrators, one with PNP
transistors, and one built with NAND gates. You have
used both types before, but not together in the same
circuit. The NAND gate multivibrator affects the
operation of the transistor multivibrator, which sends
its output through the NPN transistor to the audio
amplifier. You hear the resulting sound from the
speaker.

By substituting a different value for the 470μF
capacitor, you can change the sound this circuit
makes. See what happens when you try different
values for the 10kΩ resistor and the 0.05μF
capacitor.

Notes:

Wiring Sequence:

o 1-29
o 2-30
o 3-48
o 5-50-51-53-54-72-80-62-121
o 40-109-85
o 41-106-79
o 42-45-47-131-115-49
o 43-105-81
o 44-110-83-71
o 46-84
o 57-56-77-117
o 58-59-60-75-78
o 61-73-76-118
o 74-82-86-116
o 119-132

Schematic

-66-

-67-

Multivibrator circuits can be created from NAND
gates. This experiment is an example of an astable
multivibrator – are you able guess what astable
means? Generate a guess, and complete this project
to see if you were right.

To turn the circuit on, connect terminals 13 and 14.
LED 1 begins to flash. Astable means the
multivibrator’s output keeps switching back and forth
between 0 and 1. So far most of the multivibrators
that you have built do the same things.

You shouldn’t trouble figuring out how this particular
circuit works. The 100μF capacitor is the key. In
place of the 100μF capacitor, try using other
electrolytic capacitors and see what result they have
on LED 1 (Be sure to apply the correct polarity.)

By now can see why NAND gate ICs are so useful.
Quad two-input NAND ICs, like the one in this set,
are among the most widely used electronic
components in the world, because there are so many
different types of circuits that they can be used in.

Notes:

EXPERIMENT #50: ASTABLE MULTIVIBRATOR USING TTL

Schematic

Wiring Sequence:

o 13-49-31
o 14-119
o 33-58
o 50-51-77-115
o 54-53-52-75-78
o 55-56-57-76-116
o 59-60-62-121
o 13-14 (POWER)

EXPERIMENT #51: TONE GENERATOR USING TTL

We’ve been constructing tones with audio oscillators
for so long that it might seem as if there’s no other
way to produce tones from electronic circuits.
Multivibrators made from NAND gates do the job just
as well.

Connect the earphone to terminals 13 and 14 and
set the switch to A to turn on the power once you
finish wiring this circuit. A tone produced from the
multivibrator will be what you hear. Change the value
of the capacitors from 0.1μF to 0.5μF. What effect
does this have on the sound?

Try using different capacitors within this experiment.
Don’t try using any of the electrolytic capacitors,
(terminals 111-118). To vary the tone, try to arrange
the circuit so you can switch different value
capacitors in and out of this circuit.

Notes:

Schematic

Wiring Sequence:

o 49-131
o 50-51-77-109
o 52-53-54-60-59-75-78
o 55-57-56-76-110
o 62-121
o 119-132
o 58-13-EARPHONE
o 61-14-EARPHONE

-68-

-69-

Do you know of someone who is a big mouth? (Or,
have you ever been accused of being one?) This
experiment lets you and your friends see who’s got
the most ear-splitting voice.

How does this work? When you yell, you create
sound waves, which are actually variations in air
pressure. These air pressure variations create
pressure on the crystalline structure in the earphone.
In a crystal structure, pressure creates voltage
through a process called piezoelectricity. The voltage
produced by the earphone is applied to a two­transistor circuit, which amplifies it. You can use the
control to adjust the amount of the signal from the
earphone that is amplified. Two NAND gates in
series control the lighting of LED 1.

Set the switch position A and set the control to
position 5. Watch LED 1 as you yell into the
earphone; it probably lights. To make it more difficult
to light LED 1, try turning the control counter­clockwise. (Try adjusting it just a tiny bit each time.)
See how far you can lower the control to reduce the
strength of the amplifier and still light the LED.

Notes:

EXPERIMENT #52: MONSTER MOUTH

Wiring Sequence:

o 27-79
o 28-110
o 124-131-31-49
o 33-55
o 41-43-100-81
o 42-72
o 44-109-99-83
o 45-88-78
o 46-80
o 47-115-51-50
o 52-53-54
o 77-71-123
o 119-132
o 40-87-13-EARPHONE
o

121-26-48-116-62-60-59-57-56-84-82-14-EARPHONE

Schematic

EXPERIMENT #53: DARK SHOOTING

Think you have good night vision? This experiment is
a game that lets you find out how well you can see in
the dark. In a completely dark room, it tests your aim!

Once you have completed this project, put it in as
dark of a room as possible. Slide the switch to
position A and modify the control in a counter­clockwise direction until LED 1 and LED 3 light. Now
it is time to test your ability.

For this game your “gun” is a typical flashlight. With
a beam of light you use your flashlight to “shoot” the
kit. If your aim is correct, you’ll hit the CdS cell to light
LED 2 and turn off LED 1 and LED 3. Then turn off
your flashlight and wait until LED 2 goes off before
you try your next shot.

Start off trying to hit the CdS cell from around five
feet or so. You aim will improve as you increase your
distance. Once you get really good, you can try
hitting the CdS cell simply by switching your flashlight
on and off rather than using a continuous stream of
light.

You may have to modify the control knob very
carefully to have LED 2 come on when light strikes
the CdS cell. For the best results, use a sharply
focused flashlight (not a fluorescent lamp or other
light) and be sure you have the kit in a completely
dark room. Once you’ve found the best setting, keep
it there so you can use it again. Don’t change it until
you want to stop using the “shot in the dark” game.
Have fun and good luck ☺

Notes:

Wiring Sequence:

o 15-34-49-50-51-37-42-131
o 16-28
o 48-121-26-88-74-62-60-59-57-56-33
o 27-81
o 31-41
o 32-54-85
o 35-45
o 73-44
o 39-55-116
o 40-115-87
o 43-86
o 46-82
o 47-53
o 119-132

Schematic

-70-

-71-

What does “one-shot” mean to you?

Turn the switch to A, and see what happens to LED
1 when you press the key once at a time. Try holding
the key down for different periods while watching
LED 1. Does LED 1 stay on the same length of time
or does it change?

Regardless of the length of the input, you see that a
one-shot multivibrator has an output for a certain
length of time. (It “fires one shot.”) This means that it
can be applied in many circuits as a timer. This circuit
is also called a monostable multivibrator.

Notes:

EXPERIMENT #54: A ONE-SHOT TTL

Wiring Sequence:

o 81-75-49-53-31-131
o 33-58
o 50-55
o 51-82-83-109
o 52-56-57-115
o 54-77-116
o 59-60-62-78-84-138-121
o 76-110-137
o 119-132

Schematic

EXPERIMENT #55: TRANSISTOR TIMER USING TTL

This is another type of one-shot circuit; in this project
you hear the effects of the multivibrator. From the
schematic you can see that this experiment uses a
combination of simple components and digital
electronics. Once you press the key, the 100μF
capacitor is charged and lets the NPN translator in
the left corner of the schematic operate. You can
observe that the collector of this transistor serves as
both inputs for the first NAND gate.

The digital portion in the middle controls the PNP
transistor on the right side of the schematic. To turn
the power on, set the switch to A. You hear a sound
from the speaker when the output of the first NAND
is 1, and the multivibrator is enabled.

This sound will continue until the 100μF capacitor
discharges, preventing the first transistor from
operating. When the output of the first NAND
becomes 0, the multivibrator shuts off. With the
component values as shown in the schematic, the
sound will last for about 10 seconds. Try substituting
the 22kΩ with the 47kΩ or the 100kΩ resistor and see
what occurs.

Part B: press the key and release it. When the sound
stops, remove the wire between springs 52 and 54.
What happens? Can you explain why?

Notes:

Wiring Sequence:

o 1-29
o 2-30
o 3-41
o 5-59-60-62-48-116-121
o 40-82
o 79-49-42-131-138
o 46-86
o 47-50-51-80
o 52-54
o 53-77-111
o 55-57-56-75-78
o 58-76-81-112
o 85-115-137
o 119-132

Schematic

-72-

-73-

This is another circuit that uses both transistor and
NAND type multivibrators. As you hear a sound
through the earphone you see LED 1 light up.

Build the circuit, connect the earphone to terminals
13 and 14, and set the switch to position A. Each
time the LED lights up you’ll hear a pulse in the
earphone. Do you know why?

Trace the output from the NAND multivibrator to the
transistor multivibrator, assuming the output of the
NAND multivibrator is 0. Do you think the NAND
multivibrator affects the operation of the transistor
multivibrator? If you respond yes, how is it affected?

Try using other electrolytic capacitors in place of the
100

μ

F capacitor in the NAND multivibrator to see
what effects they have on the circuit. Next, try
changing the ceramic capacitors in the transistor
multivibrator to other ceramic ones.

By connecting the NPN transistor, the output
transformer, and maybe a resistor or two you can use
the speaker instead of the earphone.

Notes:

EXPERIMENT #56: LED BUZZIN’

Wiring Sequence:

o 31-55-56-57-76-116
o 33-59-60-62-72-80-121
o 40-109-85
o 131-45-42-49
o 43-105-81
o 50-51-77-115
o 52-53-54-75-78
o 58-82-86
o 119-132
o 110-44-71-13-EARPHONE
o 106-41-79-14-EARPHONE

Schematic

EXPERIMENT #57: ANOTHER LED BUZZIN’

Carefully compare the schematic for this experiment
with the schematic for the last experiment. While they
are similar in many ways, but there’s a critical
difference. Can you find what it is? Can you tell how
the operation will be different?

Attach the earphone to Terminals 13 and 14 and set
the switch to position A. You will hear nothing in the
earphone but you should find that LED 1 lights up.
You will hear a sound in the earphone once LED 1
turns off.

Try to decipher why this happens. Examine the
schematic and when you think you have the answer,
read on to check your guess.

When the output of the NAND multivibrator is 0, the
voltage at the junction of springs 42-58-33 is low. This
allows current to flow through LED 1, but the
transistor multivibrator won’t work because there is
no voltage to its left transistor. When the output of the
NAND multivibrator is 1, the voltage at the springs
42-58-33 junction is high. This prevents current from
flowing through LED 1, but the transistor multivibrator
now works because there is voltage to its left
transistor, and this multivibrator controls the
earphone sound.

Notes:

Wiring Sequence:

o 131-45-31-49
o 116-76-56-57-55
o 40-109-85
o 42-58-33
o 43-105-81
o 50-51-77-115
o 52-53-54-75-78
o 72-59-60-62-80-82-86-121
o 119-132
o 44-110-71-13-EARPHONE
o 41-106-79-14-EARPHONE

Schematic

-74-

-75-

Does anything look familiar about the schematic for
this project? This circuit uses an R-S flip-flop circuit
made from NAND gates, comparable to the circuit in
experiment 38 (R-S Flip-Flop using TTL).

Once you have finished building this project, set the
switch to position A and press the key. A sound
should result from the earphone. Try pressing the key
multiple times. This should not alter the sound in your
earphone. Now move the switch to position B and
push the key one more time. What occurs now?

Circuits like this are used in alarms. Since intruders
usually can’t figure out how to make them stop, they
are extremely useful.

Notes:

EXPERIMENT #58: SET/RESET BUZZER

Wiring Sequence:

o 13-77-75-49-45
o 14-119
o 40-109-85
o 41-106-79
o 42-55-51
o 43-105-81
o 50-78-131
o 52-53
o 54-76-133
o 132-138
o 44-110-71-EARPHONE
o 121-137-62-60-59-57-56-80-82-86-72-EARPHONE
o 13-14 (POWER)

Schematic

EXPERIMENT #59: ANOTHER SET/RESET BUZZER

Here’s a variant of the last project. This time we use
an R-S flip-flop made with transistors and a NAND
multivibrator.

You will hear a sound in the earphone when you set
the switch to B and press the key. No matter how
many times you press the key you can still hear the
sound. The sound will stop when you set the switch
to A and press the key.

Compare the operation of this experiment with the
last one. What makes them independent from each
other? Are you able to think of some situations where
one circuit might be better suited than the other? Be
sure to make some notes about what you are
learning.

Wiring Sequence:

o 13-49-42-45-138
o 14-119
o 81-32-41
o 33-59-60-62-36-121
o 44-35-51-84
o 40-133-83
o 82-43-131
o 50-77-109
o 54-53-52-75-78
o 132-137
o 110-76-57-56-55-EARPHONE
o 58-EARPHONE
o 13-14 (POWER)

Notes:

Schematic

-76-

-77-

VII. OSCILLATOR APPLICATION CIRCUITS

EXPERIMENT #60: ODE TO THE PENCIL LEAD ORGAN

This experiment is an oscillator that is controlled in
an abnormal way: with a pencil mark! You have
caught a glimpse in other oscillator projects how
changing the circuit’s resistance can change the
sound that is produced. Resistors, such as the ones
in your kit, are made of a form of carbon, and so are
pencils (we still call them “lead” pencils, even though
they are now made with carbon, not lead). By
causing the current to flow through different amounts
of pencil lead, we can vary the resistance and
consequently, the tone of the sound coming from the
speaker.

Make a very heavy pencil mark on a sheet of paper
(a sharp #2 pencil works best) once you complete
the wiring. The mark needs to be approximately half
inch wide and 5 inches long.

Set the switch to position A to turn on the power, and
hold one of the probe wires on one end of the mark.
Move the other probe back and forth from one end
of the mark to the other end of the mark. As you
move the probe you’ll hear the pitch rise and fall.
After a little practice you should be able to play a tune
with this organ.

Notes:

Schematic

Wiring Sequence:

o 1-29
o 2-30
o 3-105-109
o 4-80-131
o 5-47-110
o 92-48-120
o 119-132
o 46-106-91-PROBES
o 79-PROBES

-78-

-79-

Now you will build an oscillator using two transistors
connected directly to each other. As you have
witnessed, there are many ways to make an
oscillator. This way is easier compared to some.

After finishing the wiring, press the key. You hear a
beep sound coming from the speaker. Now rotate the
control. How does it change the sound?
The two transistors collaborate with each other and
act as a single transistor. The NPN transistor
amplifies the signal from the 22kΩ resistor and sends
it to the PNP transistor, to obtain a larger output.

The frequency of the oscillation is determined by the
capacitor. The project starts with the 0.01μF
capacitor in the circuit but you can experiment with
alternate value capacitors. The control alters the
voltage leading to the base of the NPN transistors. It
alters the tonal quality as well as the frequency. You
should be sure to record your results like a
professional scientist, so you can repeat the
experiment later. If you alternate capacitor values, be
sure to observe the polarity (+ and –) of the
electrolytic capacitors.

Notes:

EXPERIMENT #61: DOUBLE-TRANSISTOR OSCILLATOR

Wiring Sequence:

o 1-29
o 2-30
o 3-48-138
o 5-101-44
o 26-45-76
o 27-85
o 28-124-137
o 46-102-86
o 47-43
o 75-119
o 121-122

Schematic

EXPERIMENT #62: DECIMAL POINT STROBE LIGHT

This circuit is an oscillator with a slow frequency, and
you can see the LED lighting and turning off. The off
time is longer than the on time, so you observe short
pulses of light with long periods between them. The
wiring sequence below will make the decimal point
light, however you can light any part of the LED
display.

This type of circuit is known as a sawtooth wave
oscillator, because the electrical waveform of the
signal looks like a sawtooth pattern between two
voltage values. The signal alters as the LED lights
and turns off. Shorter pulses are generated when the
output from the emitter of the PNP transistor supplies
the base current to the NPN transistor (as in this
circuit).

Try experimenting by altering the value of the 3.3μF
capacitor to 10μF. You can also differ the 1kΩ resistor
and alter the 470kΩ resistor to 220kΩ. The rate of
charge and discharge of the capacitor controls the
frequency of this oscillator. Changing its value or the
values of the resistors that supply current to the
capacitor alters the frequency.

Notes:

Schematic

Wiring Sequence:

o 47-40-25-89
o 41-46
o 42-76
o 90-112-48-120
o 75-94-111
o 93-119-24

-80- -81-

r

a

s

.

t

g

.

e

d

e

.

EXPERIMENT #63: “THE EARLY BIRD GETS THE WORM”

c

:

29

09

37

110

88-28

0

108

38

This is the electronic bird circuit that you built fo
Project 6 (The Woodpecker), but now it has
photoelectric control of the transistor base. Thi
circuit is activated by light, so you can use it as an
early bird wake up alarm

To make the sound of the bird, press the key. You can
modify the control so that the right amount of ligh
will set off the bird and wake you up in the mornin
– not too early and not too late

From the original electronic bird, we have changed
only a few component values, and rearranged th
circuit schematic. See if you can find the changes an
rearrange the circuit so that it looks like Project 6. Us
the space provided to redraw the schematic

tes:

chemati

Wiring Sequence

-

-30

-107-1

-27-1

-41-

-

76-87-106-4

-42-115

75-116

5-

20-1

-81-

s

g

e

h

.

u

e

ild th

B.

4

e

y

?

d

see

ccurs.

e

w

e

t

.

:

EXPERIMENT #64: ADJUSTABLE R-C

OSC

OR

:

9-30

0

38

9

88

2

1

1

133

137

c

ILLAT

The “R-C” in this experiment’s name represent
resistance-capacitance. You have seen how varyin
resistance and capacitance can affect the pulsing
action of an oscillator. This experiment lets us se
the effects when we can alter the strengths of bot
resistors and capacitors

ew the schematic. You can see the switch lets yo
choose between two different capacitors. Connecting
terminals 13 and 14 adds another resistor to th

ircuit.

u

e circuit and set the switch to position

ress the key, and leave terminals 13 and 1
unconnected. What kind of sound comes from th
speaker? Now set the switch to A and press the ke
another time. Is there any difference in the sound

ow attach terminals 13 and 14 and press the key.
Try both settings of the switch with terminals 13 an
14 attached and

what o

Which combination gives you the highest tone? Th
lowest? What does this show you about ho
capacitors and resistors affect each other? Tak
meticulous notes about the effects of the differen
value capacitors and resistors

otes

Schemati

Wiring Sequence

-2

3-47-11
4-87-89-1

-101-105-10

-

4-90-46-13

48-12

02-13

-

-

-82-

s

s

a

P

e

e

.

s

ill h

EXPERIMENT #65: HEAT-SENSITIVE OSCILLATO

R

9-30-101-103

9

48

you know that a transistor alters it
characteristics according to the temperature? This
experiment will show you how temperature affect
transistor action.

View the schematic. The NPN transistor acts as
pulse oscillator. The 22k

resistor and the PN
transistor control the voltage applied to its base. Th
transistor’s base current and collector current vary
with the temperature.

Build this experiment and you will hear a sound from
the speaker. Modify the 50kΩcontrol so that th
sound is low or a series of pulses

Hold the PNP transistor between your fingers to
warm it up. As the transistor temperature increase
you w

ear the tone become higher.

tes:

chematic

iring Sequence:

-2

4-26-41-11

-47-104
7-81

-28-

40-82

-85

46-102-86

-83-

o

e

ill

lli

ill

e

e

e

r

ill

o

e

e

e

ff.

l

t

ΩΩΩ

2

μ

EXPERIMENT #66: PULSE ALARM

30-103-109

138

5

111-8

89

90

124

c

Now you will let one oscillator control another t
create an alarm. Here we have a multivibrator-typ
osc

ator contro

ng a pulse osc

ator. The puls
oscillator produces frequency in the audible rang
(the range that our ears can hear, about 20 to 20k
Hertz). The multivibrator circuit on the left side of th
schematic should look familiar. The multivibrato
commands the pulse osc

ator by allowing current t

low to the transistor base.

Build the experiment and press the key to hear th
alarm sound coming from the speaker. You hear th
alarm resonate turning on and off as the puls
oscillator turns on and o

This intermittent sounding alarm is more beneficia
than a continuous tone, because it is more
noticeable. You can experiment with this experimen

resistors, and the 0.0

capacitor.

Notes:

Wiring Sequence:

1-29
2-

-42-45-

-47-110
40-113-87
41-112-7

-

5
44-114-73­46-104­76-86-88-74-48­119-137
121-122

Schemati

-84-

d

t

e

r

e

d

EXPERIMENT #67: PUSHING & PULLING OSCILLATO

R

9

30

101-41

82

84

In this experiment you will make a push/pull, square
wave oscillator. This oscillator is known a push/pull

ecause it uses two transistors that are connecte
to each other. They take turns maneuvering so tha
while one transistor is “pushing,” the other is “pulling.
This type of oscillator is called a square wave
oscillator because the electrical waveform of th

gnal has a square shape.

Slide the switch to position A to turn on the powe
after wiring the circuit. We will be using square wav

ignals in later projects therefore, note the soun

rom the speaker.

tes:

chematic

Wiring Sequence:

-2

-

-83-

4-131

-81-102-44

-

45-42-119

-

20-132

-

ge

.

ill

h

0

μ

.

ill

t

.

n

ill

a

o

l

t

s

Thi

.

t

bili

s

e

.

g

EXPERIMENT #68: SLOW SHUT-OFF

OSC

OR

:

29

110

118-13

ILLAT

You have seen how a capacitor’s charge/dischar
cycle can be used to delay certain circuit operations

ow let’s slow the osc

a 47

F capacitor

ress and release the key. The circuit osc

ator action in this project wit

ates, bu
slowly shuts down as the capacitor charges up
When the capacitor is fully charged, no current ca

low to the oscillator, and it is off. When you press the
key, it instantly discharges the capacitor, and the
osc

ator resumes working.

On its positive (+) and negative (–) electrodes,
discharged capacitor has an equal number of
electronics. Electrical charge is stored in a capacitor
by drawing electrons from the positive electrode (t
actually make it positive) and adding an equa
number of electrons to the negative electrode (to
make it negative). Charging current or displacemen
current is the current that flows to charge the
capacitor. The same amount of current must flow in
the opposite direction when the capacitor i

scharging.

s current is known as discharge

current or displacement current

tes:

With the voltmeter function if you have a VOM, use i
to measure the charge on the capacitor. The

splacement current can be measured with the

current function.

s electrical-storage a

ty makes capacitor
useful in many different ways. However, this storag
ability can be dangerous in very high voltage circuits
due to possible shock if you are not careful with it
You need to discharge capacitors before touchin
them if they use voltages above 50V.

Schematic

Wiring Sequence

-

-30

-85-105-109

-120

-41­0-106-86

-

17-138-119

7

-86-

r

a

).

e

s

1

μ

d

05

μ

e

ill

.

ff.

y

3

μ

u

l

n

0

μ

r

s

.

EXPERIMENT #69: ELECTRONIC ORGAN

OSC

OR

:

29

06

9

109

0

86-111-80

113-82

112-8

6

38

88

ILLAT

This circuit has a multivibrator connected to a pulse
type oscillator. Rather than turning the oscillato
completely on and off, the multivibrator provides
tremolo effect (a wavering tone

After you build the circuit, use the control to vary th
base current supplied to the NPN transistor. Thi
changes the charge/discharge rate of the 0.

.

capacitors, as well the frequency of the puls

osc

ator

an

The key works to turn the whole circuit on and o
You can substitute it with the slide switch. B
changing the 10μ and 3.

capacitor values, yo

can change the tonal range.

Try using the switch or the key to add additiona
components to the circuit (like an extra capacitor i
parallel with the 1

or 3.3μF), so you can alte
from one tonal range to another, quickly. These
changes will make a more complete organ from thi
experiment. Be sure to make notes on what you do

Notes:

Wiring Sequence

-

-30

-47-1

4-74-45-42-11

-105­7-46-11

-

41-114-78

-

-

7-7
77-75-81-79-48-1
73-85-

20-137

chematic

-87-

88-

VIII. MEET THE OPERATIONAL AMPLIFIE

R

-

c

r

r

e

r

,

n

s

s

ge

r

t

.

s

l

e

a

.

o

s

C

LED, b

e

.

EXPERIMENT #70: OPERATIONAL AMPLIFIER

CO

:

67-82-33-70-121

2

8

6

2

4

133

1

MPARATOR

For this section you will need some basi
understanding about the operational amplifie

ntegrated circuit. First, we can use separate powe
sources or we can use one power source for both th
circuit and the IC.

The operational amplifier (often called “op amp” fo
short) can be operated as a non-inverting amplifier
an inverting amplifier, or a differential amplifier. A
non-inverting amplifier reproduces an input signal as
an output signal without any alteration in polarity. A
inverting amplifier does the reverse: its output ha
the reverse polarity of its input. The differential
amplifier has an output that is the contrast between
the strengths of the two input signals.

omparing two voltages and telling you which one i
stronger than the other is the job of a comparator. We
call the controlled voltage the reference volta
because we use it as a reference for measuring othe
voltages. The voltage that is compared is the inpu
voltage

The reference voltage in this experiment is about

3.7V. It is connected to terminal 68 of one of the op
amp integrated circuit. Input voltage is connected to
terminal 69 of the same IC. The LED will light if thi
input voltage is higher than the reference voltage,
and the LED stays off if it is lower. The operationa
amplifier acts as an inverting amplifier for th
reference voltage to keep the LED turned off, or as
non-inverting amplifier to light the LED

tes:

Build the experiment and then set the switch t
position A. This supplies an input of 6V. The LED lights
because the input voltage is higher than the reference
voltage. Now slide the switch to position B. Thi
supplies an input voltage of 1.5V. The comparator I

oes not turn on the

ecause the input voltag

is now lower than the reference voltage

Schematic

Wiring Sequence

1-

3-12
8-83-7

9-81-7
75-13
77-119-12

-

123-13

-89-

.

e

high

e

LEDs i

light

ff,

t

V.

t

e

e

V

t

.

r

Ω

/ 100k

Ω

.

Ω

e

e

w

Ω

/

s

.

o

k

Ω

k

Ω

l,

Ω

he

Ω

/ 32k

Ω

,

.

t

e

e

V

es:

EXPERIMENT #71: CHANGING INPUT VOLTAG

E

:

1

132-84-133

124

After you finish the wiring, set the switch to position B

LEDs 1 and 2 indicate the output voltage of th
operational amplifier IC. An LED lights if it is

onnected to 1.5V or
onnect the two

er. In this experiment, w

n series, so they only
when connected with about 3V. When they are o
the output voltage of the operational amplifier mus

e less than 3

ew the schematic diagram. With the switch a

position B, the 1.5V battery voltage is connected to

resistors, with the positive terminal of th

operational amplifier connected between th

resistors divide the 1.5
supply voltage in half. This signifies the positive inpu
terminal receives an input voltage of only 0.75V

To total the output voltage of the operational amplifie
you multiply its input voltage by the amplification
factor (R1/R2) + 1. So, the output voltage is 0.75V x

+ 1) = 2.4V

resistors from the circuit, so the amplifier’s positiv
input terminal receives the full 1.5V input voltage.
Using the above equation, you can see that th
output voltage of the operational amplifier is no

1.5V x ((220k

100kΩ +1) = 4.8V. Because the
voltage supplied to them is more than 3V, the LED
light dimly

11.8V. However, the actual output voltage will b
limited by the available battery voltage, which is 1.5
+ 3.0V + 3.0V = 7.5V.

Not

Let’s alter the amplification factor. Slide the switch t
position B again and press the key. This adds the
47

resistor to the 100

resistor in paralle

Now t

+1) = 5.9V

enough to light the LEDs brightly

Now slide the switch to position A again (to connec

.5V to the amplifier’s positive (+) input terminal), and
press the key. The LEDs light brightly. Calculating th
output voltage gives 1.5V x ((220k/ 32k

Schematic

+1) =

iring Sequence

31-67-92
32-34

1-89-88-70-36-12
3-122
8-90-91-138

-

3-131-120
7-137

-

-90-

ill

e

s

.

g

,

w

r

s

e

-

l

t

s

g

d

n

Ω

/ 1k

Ω

EXPERIMENT #72: NON-INVERTING DUAL SUPPLY OP AM

P

29

907-69

131

E

n this experiment, you w

make a microphon
amplifier, using the operational amplifier (op amp) a
a non-inverting amplifier with two power sources. The
earphone acts as a microphone

Begin by sliding the switch to position B and finishin
the wiring for the circuit. When your wiring is ready

et the switch to position A to turn on the power. No

rotate the control fully clockwise, and lightly tap you

microphone” – the earphone. The tapping sound i
heard through the speaker.
The earphone is a better microphone if you remov
the end that you put in your ear, by turning it counter

lockwise to unscrew it. To adjust the volume, turn

the control.

s you can observe in the schematic, the operationa
amplifier uses two power sources: 4.5V for the circui
and 9V for the IC. The signal from the earphone i

onnected to the operational amplifier’s non-invertin
input through the control. The input is amplified, an
the output is applied to the transformer. The gai
through the amplifier is about 100, determined by the

= 100).

tes:

chematic

iring Sequence:

-

-30

-67-

-

8-89-75

70-134

21-135
22-132
24-119-26-76-5-14-EARPHONE

-13-EARPHON

-

u

ill

.

e

o

e

g

a

a

t

s

r

EXPERIMENT #73: INVERTING DUAL SUPPLY OP AM

P

:

92-30

90

9-131-89-76

5

34

35

32

E

c

This is another two-power source microphone
amplifier, but this one is an inverting amplifier. Yo
w

use the earphone as a microphone again

Slide the switch to position B and construct th
circuit. Once you finish the wiring, slide the switch t
position A to turn the power on, adjust the control
clockwise, and speak into the “microphone” – th
earphone. This project works just like the precedin

.

IC 2 is an inverting amplifier and IC 1 is used as
buffer between the earphone and IC2, and has
gain of 1. IC2 is an inverting amplifier, with the inpu
applied through its negative (–) terminal, not the
positive (+) one as in our last project. IC2’s gain is
about 100, as determined by:
R1/R2 = 100k/1k=100.

If you increase R1 or decrease R2, the gain become
larger. See what occurs to the gain when you alte
the value of R2 to 470.

otes:

Wiring Sequence

-2

-64-

27-6

-67-7

70-1

21-1
22-1
24-119-26-66-5-14-EARPHON

28-13-EARPHONE

chemati

-92-

y

h

ill

ke

a

.

e

e

e

like Proj

s

e

e

00

k

Ω

t

.

d

t

s

u

y

EXPERIMENT #74: NON-INVERTING AMPLIFIER

:

9

0

6

2

114

31

5

113

1

4

32

E

E

In Projects 72 and 73 (“Non-inverting Dual Suppl
Op Amp,” and “Inverting Dual Supply Op Amp,”
respectively), we used the operational amplifier wit
two power sources. In this experiment, we w

ma
a single-power source, non-inverting microphone
amplifier. Again, the earphone works as
microphone

lide the switch to position B and assemble the

ircuit. When you competed the wiring, slide th

witch to position A to turn on the power, alternat
the control clockwise, and speak into th
microphone. The experiment works just

ect

72 and 73, but you’ll notice something different.

The contrast comes from the gain of this microphon
amplifier. It is still determined by R1 and R2, but now
it’s much bigger. Can you observe why? Yes, we us
the 1

resistor in place of the 1kresistor from
the last two experiments. Try changing R2 to 1
and the gain drops to the level of the las
experiments

n this experiment, two power sources are connecte
in series to operate the dual operational amplifier a
9V. But the operational amplifier can work at half thi
voltage, at 4.5V. See what occurs when yo
disconnect the operational amplifier from batter
terminal 122 and connect it to terminal 119.

tes:

Wiring Sequence

-2

2-3

-11
27-11
71-

1-63-1
7-90-11

-68­4-82-69-11
19-12
22-1
21-26-70-83-72-5-14-EARPHON

28-13-EARPHON

chematic

-

.

a

e

.

e

A

d

d

l

e

e

d

e

d

,

s

s

r

s

s

e

e

.

a

s

e

EXPERIMENT #75: DUAL-SUPPLY DIFFERENTIAL AMPLIFIER

9-30

93

132

This is the last in the series of microphone amplifiers
Now you will use the operational amplifier as
differential amplifier. It is a two-power source typ
amplifier, and this time we use the speaker as a
microphone

Slide the switch to position B and construct the

ircuit. When you finish the wiring, apply th

arphone to your ear, slide the switch to position
to turn on the power, and tap the speaker lightly with
your finger.

In this circuit the operational amplifier is configure
to amplify the difference between its positive (+) an
negative (–) inputs, so we call it a differentia
amplifier. The speaker is connected to th
transformer, which is then connected to th
amplifier’s inputs, so the speaker signal will be
amplified.

In a speaker, an electrical signal flows through a coil
and creates a magnetic field; the magnetic fiel

hanges as the electrical signal changes. Th
magnetic field is used to move a small magnet, an
this movement creates variations in air pressure
which travel to your ears and are interpreted a

ound.

his circuit is simplified by using the speaker as

microphone. To use the earphone as in previou

xperiments, you would have to make a far mor
omplex circuit.

tes:

This circuit uses the speaker as a microphone. In thi
arrangement, your voice creates variations in ai
pressure, which move the magnet inside the
speaker. The moving magnet’s magnetic field create
an electrical signal across both ends of a coil. Thi
small signal is applied to the primary of th
transformer, which then results in larger signal at th
secondary side of the transformer

Schematic

Wiring Sequence:

-2

3-110

-68­3-131
9-81-109

70-134

21-135

­24-119-82-13-EARPHONE
4-67-14-EARPHONE

-94-

LED

ligh

n

light i

,

’ll b

LED

hil

g

t

f

0

μ

e

g

d

ff.

LEDs

y

h

EXPERIMENT #76: MILLER INTEGRATING CIRCUI

T

c

:

122-137

116-133

32

9

121

138

ou know that an

t on. You can also
you
w

e able to observe the

e you hold down the key.

promptly

ts when you tur

t up gradually. In this project

s slowly get brighter

This circuit arrangement is called a Miller integratin

ircuit. The output of the circuit increases as its inpu
rises. The integrating circuit increases the value o
the 10

F capacitor above its actual value. When

you press the key, the LEDs become brighter and th

apacitor charges slowly through resistor R. Settin
the switch to position B discharges the capacitor, an
the LEDs turn o

Before completing the project, set the switch to
position B, to discharge the capacitor. Set the switch
to position B and hold the key down to watch

, 2, and 3 become brighter. In about 5 seconds the
will reach maximum brightness. Now set the switc
to B to discharge the capacitor, then hold down the

ey to do the experiment again.

tes:

Wiring Sequence

-63-

32-34

-37

-72

71-67-

-90-115-1

-124-11

70-

-

chemati

-

96-

t

a

Thi

t

e

,

f

e

Q1

y

t

Thi

LED

d

e

w

s

u

e

t

t

ed.

EXPERIMENT #77: STABLE-

CU

SOURCE

131-122

119-124

133

RRENT

In this experiment, we will make a constant curren
circuit, using an operational amplifier and
transistor.
even when the input voltage is changed, becaus
more energy is used up in the circuit.

View the schematic. When the current is modified
the voltage across R1 is also modified. The output o
the operational amplifier changes corresponding to
the feedback signal from R1. This output from th
amplifier controls the base voltage of transistor
allowing it to maintain the continual current.

First set the switch to position A, and press the ke
while monitoring LED 1. When the key is pressed i
gets dimmer.
LED 2 are in the circuit when the key is closed. Th
total current through the circuit is the same, but no
it is split between LED 1 and LED 2, so LED 1 get

mmer.

Set the switch to position B with the key off. Do yo
notice any changes in LED brightness from position
A to position B? Setting the switch to B modifies th
supply voltage from 9V to 6V. However, the curren
remains constant again, so the LED brightness is no

ffect

s circuit maintains a constant curren

s occurs because both

1 an

otes:

Schematic

Wiring Sequence:

1-132-137

-35-47

4-138

-67

48-68-75

-

-

6-70-121

-

-

blinking LED ci

it

n

s

e

e

D

t

.

e

g

Ω

e

n

ild

blink

h

EXPERIMENT #78: OPERATIONAL AMPLIFIER BLINKING LE

D

94

89

132

ow you’re going to make a

rcu
using an operational amplifier. In this experiment, a
LED continuously lights and turns off slowly.

Slide the switch to position B and connect the wire
for this circuit. When you finish connecting th

roject, slide the switch to position A to turn on th

ower. After a couple seconds, you’ll see the LE

tart to blink. Watch carefully and you should be able
to observe that it’s on and off periods are abou
equal

The operational amplifier works as an astable
multivibrator at low frequency. You can alter th

eriod of oscillation (the LED blinking rate) by usin
different values for R and C. See what happens to
the blinking rate when you make the value of R

ne last thing - the operational amplifier has high
input resistance at its inputs - so there is very littl
current flowing into its inputs. This means you ca
operate it to bu

accurate

ers and timers wit

longer intervals.

tes:

Wiring Sequence:

1-31-63-131

-67-90-

93-68-113

-82-84-

-70-114-121

19-124

-

chematic

7-

98-

g

u

ild thi

e

.

d

LED

blinki

.

r

f

n

h

EXPERIMENT #79: LED FLASHE

R

8

6

5

84

6

Begin by sliding the switch to position B and wirin
the circuit. This LED flasher uses two diodes. As yo

u

s experiment, be sure to connect thes

diodes in the correct direction

When you finish assembling the experiment, turn on
the power by sliding the switch to position A, an
press the key. The

starts

ng immediately
Even if you don’t press the key, this LED flashe
starts flashing shortly after you turn on the power; i
you press the key, it begins blinking right away.

This LED flasher uses an operational amplifier as a
astable multivibrator, but its flashing time is muc
shorter because of the two diodes.

tes:

iring Sequence:

1-31-63-131-13

-67-88-90-7

-115-137-128-12

-87-82-

-70-116-121

75-127

-12
19-124
22-132

Schematic

-

LED

9

D

s

e

liding th

o

t

.

g

Ω

EXPERIMENT #80: DOUBLE LED BLINKER

3

69

134-131

e

circuits in experiments 78 and 7

(“Operational Amplifier Blinking LED” and “LE

lasher”) each use one LED, but the circuit in thi
project uses two LEDs that take turns lighting. Slid
the switch to position B and assemble the circuit.

en, turn the power on by s

e switch t
position A and wait for a few seconds. The LEDs ligh
and turn off in rotation.

The operational amplifier works as an astable
multivibrator. When the output is low, LED 2 lights;
when it is high, LED 1 lights

You can alter the speed of the blinking by usin
different values for R and C. See how the speed of
the pulses alters when you alter the value of R to

tes:

Wiring Sequence:

1-36-67-90-94

33-70-135

4-63-132

-68-11

-89-

82-114-124-119

-

chematic

-99-

l

h

.

o

D

s

ff.

f

0

μ

e

.

:

EXPERIMENT #81: SINGLE FLASH LIGH

T

:

131-138

0

93

9

5-137-129

6

132

You’ve built many circuits using the operationa
amplifier, but there are lots of other ways to use this
handy IC. One of them is the single flas
multivibrator. With this multivibrator, you can make
the LED stay on for a preset amount of time when
the key is pressed - a single flash light

lide the switch to position B and construct the
circuit. Turn the power on by sliding the switch t
position A. The LED lights, but quickly turns off. Now,
press the key and observe what happens. The LE
lights and stays on for 2 to 3 seconds and then turn
o

By using different values for C You can change the
amount of time the LED is on. Change the value o

from 1

F to 100μF and see what occurs to th

LED. It stays on longer

otes

Wiring Sequence

-63-94-

-67-114

-68-11

-82-89-

70-134

1-86-130-124-11

-11

113-11
121-135

-

Schematic

-100-