Copyright © 2009 by Elenco® Electronics, Inc. All rights reserved. 753039No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.

ELECTRONICPLAYGROUNDTM

and LEARNING CENTER

MODEL EP-130

Elenco® Electronics, Inc.Wheeling, IL, USA

99 Washington Street Melrose, MA 02176 Phone 781-665-1400Toll Free 1-800-517-8431

Visit us at www.TestEquipmentDepot.com

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

I. ENTERTAINMENT CIRCUITS 11

1. Electronic Woodpecker 12 2. The Chirping Bird 13 3. Electronic Cat 144. Sonic Fish Caller 155. Machine Gun Pulse Oscillator 166. Electronic Motorcycle 177. Two-tone Patrol Car Siren 188. Electronic Siren 199. Electronic Metronome 2010. Electronic Grandfather Clock 2111. Light-controlled Electronic Harp 2212. Horror Movie Sound Effects 2313. Strobe Light 2414. Rapid LED Display Switching

(persistence of vision test) 25

II. BASIC SEMICONDUCTOR & COMPONENTS CIRCUITS 26

A BIG CHANGE 2715. Capacitor Discharge/High Voltage Generator 28 16. Capacitors in Series & Parallel 29 17. Resistors in Series & Parallel 30 18. Light Dimmer 31 19. Transistor Switcher 32 20. Transistor Circuit Action 33 21. Sound Amplifier 34 22. Flip-flop Multivibrator with LED Display 35

III. LED DIGITAL DISPLAY CIRCUITS 36

23. Seven-segment LED Digital Display Circuit 37 24. Basic LED Display 38 25. Transistor Control Switching of the LED Display 39 26. Transistor, CDS Cell, and LED Display Circuit 40

IV. A TOUR THROUGH DIGITAL CIRCUITS 41

27. Diode-Transistor Logic AND with LED Display 42 28. DTL OR Circuit with LED Display 43 29. DTL NAND Circuit with LED Display 44 30. DTL Exclusive OR Circuit 45 31. Transistor NOR Circuit with LED Display 46 32. Transistor Flip-Flop Circuit 47 33. Transistor Toggle Flip-Flop 48

V. MORE ADVENTURES WITH DIGITAL CIRCUITS 49

34. Transistor-Transistor Logic Buffer Gate 50 35. TTL Inverter Gate 51 36. TTL AND Gate 5237. TTL OR Gate 5338. TTL Exclusive OR Gate 5439. TTL NOR Gate 5540. TTL Three-Input AND Gate 5641. TTL AND Enable Circuit 5742. TTL OR Enable Circuit 5843. TTL NAND Enable Circuit 5944. TTL R-S Flip-Flop 6045. Toggle Flip-Flop Circuit Made from NAND Gate 6146. TTL Line Selector 6247. TTL Data Selector 63

Important: If you encounter any problems with this kit, DO NOT RETURN TO RETAILER. Call toll-free (800) 533-2441or e-mail us at: help@elenco.com. Customer Service • 150 Carpenter Ave. • Wheeling, IL 60090 U.S.A.

• Do not short circuit the batteryterminals.

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

• Use only 1.5V “AA” type, alkalinebatteries (not included).

• Insert batteries with correct polarity.

• Do not mix alkaline, standard (carbon-zinc), or rechargeable (nickel-cadmium) batteries.

• Non-rechargeable batteries should notbe recharged. Rechargeable batteriesshould only be charged under adultsupervision, and should not berecharged while in the product.

• Do not mix old and new batteries.

• Remove batteries when they are usedup.

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

WARNING: Always check your wiring beforeturning on a circuit. Never leave a circuitunattended while the batteries are installed.Never connect additional batteries or anyother power sources to your circuits.

WARNING:CHOKING HAZARD - Small parts.Not for children under 3 years.

Conforms to all applicable U.S. governmentrequirements.

Batteries:

!

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VI. THE WORLD OF TRANSISTOR-TRANSISTOR LOGIC 64

48. TTL Astable Multivibrator 6549. TTL Tone Generator 6650. Winking LEDs 6751. A One-Shot TTL 6852. Transistor Timer with TTL 6953. Buzzin’ LED 7054. Son of Buzzin’ LED 7155. Set / Reset Buzzer 1 7256. Set / Reset Buzzer 2 7357. Sound Machine 7458. Big Mouth 7559. Shot in the Dark 76

VII. APPLICATION CIRCUITS BASED ON THE OSCILLATOR 77

60. Variable R-C Oscillator 7861. Oscillator with Turn-off Delay 7962. Temperature-Sensitive Audio Oscillator 8063. Two-Transistor, Directly-Connected Oscillator 8164. Push / Pull Square Wave Oscillator 8265. Pencil Lead Organ 8366. LED Strobe Light 8467. Electronic Organ 8568. Daylight Early Bird 8669. Intermittent Alarm Detector 87

VIII. BASIC OPERATIONAL AMPLIFIER CIRCUITS 88

70. Comparator 8971. Basic Increase in DC Voltage 9072. Constant-Current Source 9173. Integrating Circuit 9274. Schmitt Trigger Circuit 9375. Non-inverting Two Power Supply Amplifier 9476. Inverting Two Power Supply Amplifier 9577. Non-inverting Single Power Supply Amplifier 9678. Two Power Supply Differential Amplifier 9779. Tone Mixing Amplifier 9880. Power Amplifier Using Operational Amplifier 9981. Voltage Controlled Oscillator Circuit 10082. Operational Amplifier Buzzer 10183. Burglar Alarm 10284. Hand-Operated Sweep Oscillator 10385. Falling Bomb Squad 10486. Emergency Siren 10587. First Aid Siren 10688. Musical Tempo Generator 10789. Operational Amplifier Winking LED 10890. LED Flashing Light 10991. Two LED Winker 11092. One Shot Light 111

93. LED Initials 11294. Wake Up Siren 11395. Voice Activated LED 11496. Logic Tester 115

IX. MORE ADVENTURES WITH OPERATIONAL AMPLIFIERS 116

97. Alternating Current Sound 11798. Light Control Sound Circuit 11899. Sound Alarm Circuit 119100. Study Timer 120101. Kitchen Timer 121102. Three-Input AND Gate Using Operational Amplifier 122103. Voice Level Meter 123104. Power-on Reset Circuit 124105. Delayed Timer 125106. Pulse Frequency Doubler 126107. White Noise Generator 127108. DC-DC Converter with Operational Amplifier 128

X. COMMUNICATION CIRCUITS 129

109. Code Practice Oscillator with Tone Control 130110. Crystal Set Radio (Simple-Diode Radio) 131111. Two-Transistor Radio 132112. Wireless Code Transmitter 133113. AM Radio Station 134114. Operational Amplifier Radio 135

XI. TESTING AND MEASURING CIRCUITS 136

115. Aural Continuity Tester 137116. Conductivity Tester 138117. Transistor Checker 139118. Sinewave Audio Oscillator 140119. Low Distortion Sinewave Oscillator 141120. Twin-T Audio Oscillator 142121. Pulse Oscillator Tone Generator 143122. Audio Signal Tracer 144123. Radio Frequency Signal Tracer 145124. Square Wave Audio Oscillator 146125. Sawtooth Wave Oscillator 147126. Rain Detector 148127. Water Level Buzzer with Operational Amplifier 149128. Metal Detector 150129. Water Level Alarm 151130. Three-Step Water Level Indicator 152

INDEX 153

PARTS LIST 155

DEFINITION OF TERMS 156

IDENTIFYING RESISTOR VALUES 159

IDENTIFYING CAPACITOR VALUES 159

METRIC UNITS AND CONVERSIONS 159

Welcome to the exciting world of electronics! TheElenco® EP-130 Electronic Playground Kit may beyour first experience in electronics. This manualdescribes 130 different experiments you can performwith your kit. We have included everything that youneed for all of the experiments (except the batteries).

As you read this manual and complete theexperiments, you will notice that we’ve organized theprojects and information in a logical sequence. We’llhave you start with simple circuits and work towardmore complex ones. Take your time and have fun.

You can assemble all of the projects withoutsoldering because each component is connected tospring terminals. A wiring sequence is included witheach project, so all you have to do to build a workingproject is connect wires between the terminals listedin the wiring sequence. We have provided plenty ofpre-cut, insulated wire. All of the projects arepowered by low voltage batteries, so there is none ofthe danger associated with using standard ACvoltages.

Simple, clearly-written instructions help you operateand experiment with each project. A diagram called aschematic is included with later projects. Aschematic is an electronics blueprint that shows howvarious components are wired together. Eachcomponent has its own schematic symbol. Thesymbols for the various components in your lab kitare printed next to each component.

You’ll notice that we often refer to a Volt / Ohm Meter(VOM) for making measurements. A VOM, ormultimeter, is a device that measures voltage,current (amperes or amps), and resistance (ohms -Ω). We will tell you more about these later. If you aregoing to understand electronic circuits, it is importantthat you learn to measure circuit values - for onlythen can you really begin to understand electroniccircuitry.

So, we recommend that you invest in a VOM with asensitivity reading of 20,000 ohms-per-volt or more.Ohms-per-volt is a rating for the sensitivity of thedevice (the higher the rating, the more sensitive themeter).

You don’t have to use a VOM to build theexperiments, but you’ll find it will help you to betterunderstand how the circuits work. A VOM is a basictest instrument and it is an excellent investment -you’ll always want and need one as long as you stayinterested in electricity and electronics.

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BEFORE WE BEGIN

Your kit requires six (6) “AA” batteries. Install thebatteries in the compartment at the back of your kit.Be sure to install them correctly according to the (+)and (–) markings inside the compartment. The (+)end of a battery is the one with the small metal cap.

Note: Whenever you are not using your kit, removethe batteries. Never leave weak or dead batteries inyour kit - they can leak damaging chemicals, even ifthey are “leak-proof” type batteries. This is a goodhabit to get into for all battery-operated products.

INSTALLING THE BATTERIES

+

––

+

–

+

+

––

+

–

+

+

––

+

–

+

+

––

+

–

+

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The spring terminals and the pre-cut wires suppliedwith your lab kit make it a snap to wire together thevarious projects. To connect a wire to a springterminal, simply bend the spring over to one side andinsert the wire into the opening.

Sometimes you need to connect two or three wires toa single spring terminal, so be sure the first wiredoesn’t come loose when you add the second andthird wires. The easiest way to do this is to push thespring on the side opposite side where youconnected the first wire.

Be sure that you only insert the exposed, shiny partof the wire into the spring terminal. If the plasticinsulation part of the wire is inserted into theterminal, electrical contact is not made. To removethe wire from the spring terminals, simply bend eachterminal and pull the wires from it.

After a lot of use, the exposed metal ends of some ofthe wires might break off. If this happens, remove3/8” of insulation from the broken end and twist thestrands together. You can remove the insulation witha wire-stripper tool or a penknife. Be very carefuldoing this, as a penknife is very sharp.

MAKING WIRING CONNECTIONS

Your kit has more that 30 separate components. Ifthis is your first experience with electronics, youprobably don’t know the difference between aresistor and a transistor. If so, don’t worry - thegeneral purpose fo each component will beexplained. The explanations help you understandwhat each component does, and you will understandmore about each component as you build theprojects.

There is a parts list near the back of this manual. Youmight want to compare the parts in your kit withthose in the list.

Resistors: Why is the water pipe that goes to yourkitchen faucet smaller than the one that comes toyour house from the water company? And why is itmuch smaller than the main water line that supplieswater to your entire town? Because you don’t needso much water. The pipe size limits the water flow towhat you actually need. Electricity works in a similarmanner, except that wires have so little resistancethat they would have to be very, very thin to limit the

COMPONENTS

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flow of electricity. They would be hard to handle andbreak easily. But the water flow through a large pipecould also be limited by filling a section of the pipewith rocks (a thin screen would keep the rocks fromfalling over), which would slow the flow of water butnot stop it. Resistors are like rocks for electricity, theycontrol how much electric current flows. Theresistance, expressed in ohms (Ω, named afterGeorge Ohm), kilohms (kΩ, 1,000 ohms), ormegohms (MΩ, 1,000,000 ohms) is a measure ofhow much a resistor resists the flow of electricity. Toincrease the water flow through a pipe you canincrease the water pressure or use less rocks. Toincrease the electric current in a circuit you canincrease the voltage or use a lower value resistor(this will be demonstrated in a moment). The symbolfor the resistor is shown below.

Resistor Color Code: The colored bands on theresistors are the method for marking the value ofresistance on the part. The first ring represents thefirst digit of the resistor’s value. The second ringrepresents the second digit of the resistor’s value.The third ring tells you the power of ten to multiply by,(or the number of zeros to add). The final and fourthring represents the construction tolerance. Mostresistors have a gold band for a 5% tolerance. Thismeans the value of the resistor is guaranteed to bewithin 5% of the value marked. See color code charton page 159.

Control (variable resistor): Many electronic circuitsrequire a variable resistor, and that is just what thecontrol is. You can use it as a light dimmer, a volumecontrol, and in many other circuits where you’d like tobe able to change resistance easily and quickly.This is a normal resistor with an additional armcontact that can move along the resistive materialand tap off the desired resistance.

Capacitors: Capacitors can pass alternating current(AC) signals while blocking direct current (DC)signals. They can also store electricity or act as filtersto smooth out pulsating signals. Very smallcapacitors are usually used in high-frequencyapplications such as radios, transmitters, andoscillators. Very large capacitors normally storeelectricity or act as filters.

The capacitance (electricity storage capacity) of acapacitor is expressed in a unit called a farad. Thefarad is an extremely large amount of electricity, sothe value for most capacitors is given in millionths-of-a-farad (microfarads).

Electrolytic - The four largest capacitors areelectrolytics. They are marked with a “–”. You mustconnect them into the circuit only one way - the (+)and (–) wires must always go to the correctterminals.

Disc - These capacitors have no polarity and can beconnected either way.

Tuning Capacitor: The tuning capacitor is used withthe antenna to select radio frequencies. As yourotate the knob, you change the capacitance. Thischanges the frequency these circuits work best with.The tuning capacitor lets through only one frequencyand blocks out the rest.

Diodes: There are three diodes in your kit. Diodeshave many uses in electronics, but they have onesimple characteristic - they allow electricity to flowthrough them in only one direction. Your kit has onesilicon diode (marked Si) and two germanium diodes

Disc Electrolytic

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(marked Ge); they each have their own uses as we’llexplain later.

Transistors: Your lab kit has three transistors. Theworking part of each transistor is a tiny chip (made ofeither germanium or silicon). Each transistor hasthree connection points: B (base), C (collector), andE (emitter). Transistors are used to amplify weaksignals. They are also used as switches to connect ordisconnect other components and as oscillators toallow signals to flow in pulses.

LEDs (Light Emitting Diodes): LED stands for LightEmitting Diode. These little parts are special diodesthat give off light when electricity flows through them.(Current can pass through only in one direction - justlike “regular” diodes).

LED Digital Display: To make the display, sevenLEDs are arranged to form an outline that can showall the numbers and most of the letters in ouralphabet. An eighth LED is added for the decimalpoint.

The LED display is mounted on a little board withresistors permanently wired to it. (The resistors arethere to help prevent you from burning out thedisplay with excess current).

Integrated Circuit: As you might already know, afterthe transistor was invented in the middle 1940’s, thenext big breakthrough in electronics was theintegrated circuit in the early 1960’s. The greatadvantage of ICs (as we call them) is that theequivalent of hundreds or even thousands oftransistors, diodes, and resistors can be put into asmall package.

There are two types of ICs used in this kit - the quadtwo-input NAND and the dual-operational amplifier.You will learn more about these later.

Our simple ICs will help you learn enough to begin tounderstand the basic principles of the moreadvanced ICs.

Cadmium Sulfide (CdS) Cell: This is asemiconductor - that is, it conducts electricity, butpartially resists it. The resistance of this devicechanges with the amount of light that shines on it. (Itis similar to your kit’s control - to vary the resistanceof the control, you rotate the knob; to vary theresistance of the CdS cell, you permit more or lesslight to shine on the front of the cell.)

Note: We’ve provided a special light shield to usewith the CdS cell. When you place this over the cell,it helps block light from the cell.

PNP NPN

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Antenna: The radio antenna is the cylindricalcomponent with a coil of fine wire wrapped around it.The dark colored rod is made mostly of powderediron. Ferrite cores (rods made from powdered ironand other oxides) make efficient antennas for almostall transistor radios.

Transformer: If you wrap two wires from differentcircuits around different ends of an iron bar then acurrent flowing through the wire from the first circuitwill magnetically create a current in the wire from thesecond circuit! If the second coil has twice as manyturns (more magnetic linkage) as the first coil thenthe second coil will have twice the voltage but halfthe current as the first coil. A device like this is calleda transformer.

The magnetic field created in an iron bar by anelectric current in the coil around it can be harnessedif the bar is allowed to rotate - it is a motor. It couldbe used to drive the wheels of a car, for example. Thereverse is also true, if a magnet within a coil isrotating then an electric current is created in the coil- a generator. These two statements may not seemimportant to you at first but they are actually thefoundation of our present society. Nearly all of theelectricity used in our world is produced at enormousgenerators driven by steam or water pressure. Wiresare used to efficiently transport this energy to homesand businesses where it is used. Motors convert theelectricity back into mechanical form to drivemachinery and appliances.

Speaker: A speaker converts electrical energy intosound. It does this by using the energy of an ACelectrical signal to create mechanical vibrations.These vibrations create variations in air pressure,called sound waves, which travel across the room.You “hear” sound when your ears feel these airpressure variations. You need high current and lowvoltage to operate a speaker, so we will always usethe transformer with the speaker. (Remember that atransformer converts high-voltage/low-current to low-voltage/high-current).

The earphone is similar to the speaker, except that itis more sensitive (and moveable). It is an efficient,lightweight earphone that can be connected withoutdrawing too much electrical energy from the circuit.For very weak sounds, the earphone is best; forstronger sounds, you will use the speaker.

Batteries: The battery holders are designed to holdsix (6) “AA” batteries. Batteries supply the power for allthe experiments in your kit. When connecting wires tothe batteries, be sure you connect only to the terminalsnoted. Terminals 119 and 120 provide 3 volts. Terminals119 and 121 provide 4.5 volts. You need to be awarethat connecting too much voltage (you can get up to 9volts from these battery connections) can damagesome parts (they can be burned out). So, be sure tomake the right battery connections.

Caution: When you connect wires to the batteries,you must be sure to use the correct polarity: (+) and(–) sides of the battery. With some parts and circuits,components can be permanently damaged if youreverse the polarity.

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Switch: You know what a switch is - you use it toconnect or disconnect electrical circuits. When youslide the switch to the correct position, the circuit iscomplete, allowing electricity to flow through it. Inanother position, the switch causes a break in thecircuit’s path, so that the circuit is not complete andelectricity cannot flow through it. The switch we’reusing is a double-pole, double-throw switch; thismeans it can connect one pair of terminals to eitherof two other pair of terminals. You will learn how thisworks later on.

Key: The Key is a very simple switch - press it andthe circuit allows electricity to flow through it.Release it and there is a break in the circuit’s path,so the circuit is not complete. You will use the key inmany circuits, most often in the signaling circuits (tosend Morse code, and so on).

Terminals: You will use the two terminals (13 and 14)in some projects to make connections to externaldevices, such as the earphone, an antenna or earthground connection, special sensor circuits, and so on.

Wires: You will use the wires to make connectionsbetween terminals.The parts and spring terminals are mounted onto aplatform. If you look underneath it you can see howwires are used to connect the parts and theirterminals.

BUILDING YOUR FIRST PROJECTThere is a simple wiring sequence listing for eachproject. You should connect appropriate length wiresbetween the terminals listed in each grouping.Always use the shortest wire that will do the job.When you come to a new grouping (separated by acomma), connect the terminals in that group.

Here’s an example:

Project 1 has the following wire sequence listing:

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

You should connect a wire between 1 and 29,another between 2 and 30, another between 3 and104, and then another between 104 and 106. So, youcontinue until all connections are made.

Caution: In each wiring sequence, we’vedeliberately left an important power wire connectionas the last connection. It is important that you makethis last connection LAST. With some circuits, if youcomplete one part of the electronic circuit beforeanother, a transistor or another part can bedamaged. So, follow the wiring sequence exactly.

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HELPFUL SUGGESTIONSKeeping a Notebook

You’re going to find out a lot about electronics as youplay around with this kit. Much of what you discoverabout electronics in early projects will be useful inlater projects. We strongly suggest that you keep anotebook to help you collect and organize all of thisinformation.

Your notebook doesn’t have to be like the ones youkeep at school. Think of it as your diary - you’ll havefun looking at it after you finish connecting all 130projects.

Marking the Wiring Sequence

As you wire up a project (especially the ones withlots of connections) you might find it helpful to markthrough each terminal number as you connect a wireto that terminal. Mark lightly with a pencil so that youwill be able to build a circuit many times and still beable to read all of the wiring sequence.

Collecting Components

It would be a good idea for you to start collectingdifferent electronic parts and make your ownelectronic parts scrap box. You can build circuitsinside or on a convenient chassis, box, or container.You might turn it in as a Science Fair project atschool and make a major research project out of it.

TROUBLESHOOTINGIf you assemble each project according to its wiringsequence, you should have no problem getting theprojects to work properly. But if you do have aproblem, you can usually find and correct it by usingthe following troubleshooting steps. These steps aresimilar to those used by electronics technicians whotroubleshoot complex electronic equipment.

1. Are the batteries fresh? If not, they may be tooweak to power the project.

2. Have you assembled the project properly? Ifeverything else checks out okay, check all thewiring connections to be sure you have wired allthe terminals correctly. Sometimes it’s a good ideato have someone else take a look at it too.

3. How about following the schematic diagram andcircuit explanation? As you progress in yourknowledge and understanding of electronics, youshould be able to do some troubleshooting only byfollowing a schematic; and if you add the circuitdescription, you should be able to figure outproblems for yourself.

4. If you have a VOM, try some voltage and currentmeasurements - very soon you’ll find out just howhandy a VOM can be to an electronics technician!

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I. ENTERTAINMENT CIRCUITS

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Have you ever heard a red-headed woodpeckerchirping? Here is an electronic bird that sounds alittle like a red-headed woodpecker. If you have oneof these birds around your house, it might come tovisit this electronic relative!

This is a fairly simple circuit. Follow the wiringsequence below and the drawings we’ve provided.Make all the connections and have some fun withthis project.

The basic circuit we’ve shown here does not have aswitch or key, but you can add one very easily.Simply replace wire connection 124-28 withconnections 124-137 and 138-28 in order toconnect the key. To use the switch, replaceconnection 124-28 with connections 124-131 and132-28. When you press the key or slide the switch,the circuit path for the electrical current is completeand you hear the woodpecker. The key provides amore convenient control for carrying the kit outsideas you try to attract birds with your bird caller.

Try different combinations of resistance andcapacitance in place of the 1kΩ resistor and the100μF capacitor. To change the 100μF capacitanceto 470μF, disconnect the wire at terminal 116 andreconnect it to terminal 118. Then, transfer the wireattached to terminal 115 to terminal 117. Now your“bird” might sound more like a cricket or a bear!

You can also try the 3V power supply (V is theabbreviation for volt or volts - the basic unit ofmeasure of electric energy). Disconnect the wirefrom terminal 119 and connect it to terminal 123.Now the “bird” will sound more like an Englishsparrow.

When experimenting with this circuit, you canchange almost anything without causing damage.However, do not decrease the 47kΩ resistor tobelow 10kΩ or the transistor might be damaged.

EXPERIMENT #1: ELECTRONIC WOODPECKER

Wiring Sequence:

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

Schematic

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Here’s a circuit that imitates more of our featheredfriends - you could say it mocks the mockingbird!

Complete the circuit as shown below and slide theswitch to position A to turn on the power. You won’thear any sound from the speaker yet. Press the keyand you’ll hear a chirping sound from the speaker.Release the key - you’ll still hear the chirping sound,but then it will slow down and stop. You can see thatwhen the key is released, the first transistor “Q1” iscut off from the battery. The second transistor “Q2”can still produce the chirping sound, until transistor“Q1” stops controlling it through its base.

Try a different value capacitor in place of the 10μFand the 100μF capacitors and hear what happens.These capacitors control the amount of electricityreaching the transistors through connections to thetransistor bases. Remember to keep notes on yourexperimentation.

Notes:

EXPERIMENT #2: THE CHIRPING BIRD

Wiring Sequence:

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

Schematic

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Bothered by mice? And you don’t have amousetrap? Try this instead - see if the sound of theelectronic feline can keep those pests away.

Follow the wiring sequence and drawing, and startthe experiment with the switch set to B. Press thekey and release it immediately. You’ll hear the “cat’smeow” from the speaker. Adjust the control knobwhile the meow is dying away - what effect does ithave on the circuit’s operation? Set the switch to Aand try again. Now the sound is lower and lastslonger as if the cat is begging for a dish of milk.

You can experiment with this circuit to produce avariety of other sounds. But don’t change the valueof the 0.05μF capacitor to more than 10μF orreduce the value of the 10kΩ resistor - otherwise,the transistor might be damaged.

Notes:

EXPERIMENT #3: ELECTRONIC CAT

Wiring Sequence:

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

Schematic

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Did you know that some marine animalscommunicate with each other by sound? You’veprobably heard that whales and porpoisescommunicate by sound, but they’re not the onlyones. Research indicates that some fish areattracted by certain sounds. This circuit will let youdo some research of your own.

When you make the last connection, you’re actuallyturning on the power. You should hear sound pulsesfrom the speaker. Change the sound by turning thecontrol. This circuit is a variation of the audiooscillator circuit. (You’ll learn more about audiooscillators later on in this manual).

How well does this work in attracting fish? If youhave an aquarium at home or at your school, placeyour kit near the aquarium glass and see if fish areattracted to the sound.

Or, you can actually try it out while fishing. Getanother speaker and attach it to terminals 1 and 2using long lengths of insulated wire. Carefully wrapthe speaker in a waterproof plastic bag or seal itinside a jar. Be sure no water can reach the speaker.Now, lower it into the water. Then, cast a line into thewater and wait for the results.

If you don’t have much luck with this project, tryaltering a few parts values for a different pulsesound. Try a different value for the 0.1μF capacitor

or the 0.05μF capacitor. Be sure to keep notes ofyour results - and good fishing! Who knows, youmight find the type of signal that attracts a whale!

Notes:

EXPERIMENT #4: SONIC FISH CALLER

Wiring Sequence:

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

Schematic

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In this you’ll build a circuit that engineers call a“pulse oscillator”. It makes sounds like a machinegun. (Engineers have all kinds of technical words todescribe their circuit and ideas - you might as wellget used to them now and soon you’ll be talking justlike an electronics engineer.)

There are many ways to make oscillators. You willbuild several of them in this kit. Later on, you will betold how they work. For now, we’ll simply tell youwhat an oscillator is.

An oscillator is a circuit that turns itself on and off (orgoes from high to low output). A pulse oscillator iscontrolled by pulses such as those made by acapacitor charging and discharging. This oscillatorturns on and off slowly, but some oscillators turn onand off many thousands of times per second. “Slow”oscillators are often used to control blinking lights(like the turn signal in a car or truck). Fasteroscillators are used to produce sounds. “Super” fastoscillators produce radio frequency signals (RFsignals). These RF signal oscillators turn on and offmillions of times per second.

The number of times an oscillator turns on and offeach second is called the frequency of the oscillatorand is measured in units called hertz (Hz). Thisoscillator has a frequency of about 1 to 12Hz. Thefrequency of a radio frequency signal oscillator wouldbe measured in kHz, (kilohertz, meaning a thousandhertz) or MHz (megahertz, meaning a million hertz).

When you finish wiring, press the key to start theoscillator. Adjust the control (50kΩ variable resistor)to change the sound coming from the speaker froma few pulses per second to a dozen or so persecond. You can also change the frequency of thisoscillator by trying other capacitors in place of the10μF capacitor. Be sure to observe the (+) and (–)connections (polarity) on the capacitors markedwith a (+) sign.

Notes:

EXPERIMENT #5: MACHINE GUN PULSE OSCILLATOR

Wiring Sequence:

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

Schematic

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Ever try steering a motorcycle (OK, maybe abicycle) with just four fingers? That’s dangerous ona real motorcycle, but it’s a lot of fun in thiselectronic version.

To use this project, connect the componentsaccording to the wiring sequence. Then grasp theexposed metal ends of each of the two long wires(connected to terminals 110 and 81) between yourthumb and the index finger of each hand. Now varythe pressure (your “grip”) and listen to the soundfrom the speaker. The sound changes as youchange your grip on each wire.

You can also get different sounds by controlling theamount of light that falls on the CdS cell. With astrong light on the CdS cell, you can control theoperation entirely by exerting more pressure on thewires in your hand. Use your hand to make ashadow over the CdS cell and see what happens.

When you hold the ends of the wires, you makeyourself another part of the circuit - a resistor.Changing your grip changes the resistance to thecurrent in the project. With some practice you will beable to make this circuit sound like a real motorcycleon the go. You can make it idle as well as race.

You can experiment with different values for the0.1μF and 0.05μF capacitors, but don’t use valuesabove 10μF or the transistor might be damaged.

Notes:

EXPERIMENT #6: ELECTRONIC MOTORCYCLE

Wiring Sequence:

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

Schematic

WIRE

-18-

Here is a loud siren that is so much like the realsirens on some police cars and ambulances, thatyou may have to be careful not to confuse yourneighbors. The initial tone is high, but when youclose the key, the tone lowers. You can control thetone the same way police and ambulance driversdo.

This is the same type of oscillator circuit used inmany other projects. When you press the key,another capacitor is added to the circuit to slowdown the oscillator action.

Notes:

EXPERIMENT #7: TWO-TONE PATROL CAR SIREN

Wiring Sequence:

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

Schematic

-19-

Here’s another siren - don’t be surprised if thisbecomes the most popular circuit in this entire kit.

This circuit sounds even more like a real siren on apolice car! After completing the wiring, press thekey. You’ll hear a tone gradually getting higher.Release the key, and the tone becomes lower andthen fades out.

Here are some of the modifications you might wantto try:

1. Change the 10μF capacitor to a 100μF or 470μF.This gives a very long delay for both turn on andturn off.

2. Change the circuit to eliminate the delays bytemporarily disconnecting the 10μF capacitor.Simply disconnect one of the wires from terminal113 or terminal 114. (Sounds dead incomparison doesn’t it!)

3. Change the 0.02μF capacitor to a 0.01μF andthen to a 0.05μF.

Notes:

EXPERIMENT #8: ELECTRONIC SIREN

Wiring Sequence:

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

Schematic

-20-

Here’s a circuit you might find useful if you’relearning to play a musical instrument. This is anelectronic version of the metronome used by musicstudents everywhere.

Press the key. You’ll hear a sound from the speakerat fixed intervals. Now, turn the control knob to theright and you’ll hear the sound “speed up” as theintervals between sounds shorten.

Try a different resistor in place of the 4.7kΩ resistor.(This resistor is in series with the control. That is,they are connected end to end so that the currentruns through both components.) Also, try a differentcapacitor in place of the 100μF capacitor and seewhat effect this has on circuit operation. Rememberto keep track of the results in your notes.

Try connecting the 470μF capacitor to the batteriesto hear the difference a stronger capacitor makes.Connect terminal 117 to terminal 119 and terminal118 to terminal 120. You might have to adjust thecontrol also to maintain the same pulse rate.

Notes:

EXPERIMENT #9: ELECTRONIC METRONOME

Wiring Sequence:

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

Schematic

-21-

Do you want to perk up the ears of some of yourelders? Anyone who has lived in a house with agrandfather clock will think you have one when theyhear this project.

The circuit produces clicks at approximately onesecond intervals. The timing and sound together willremind you of an old grandfather clock. You canchange the 100kΩ resistor to obtain faster or slowerpulse rates.

The steady monotonous ticking can put animals(and people) into a restful state of mind. If you havetraveled on a train, you know how sleepy you get asyou hear the click, click, click of the wheels.

Now, want to scare this “clock” to stop? Yell into thespeaker. How about that? You can momentarily stopthe clock! The speaker acts as a microphone. Thesound of your voice vibrates in the speaker andupsets the electrical balance of the circuitmomentarily.

Notes:

EXPERIMENT #10: ELECTRONIC GRANDFATHER CLOCK

Wiring Sequence:

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

Schematic

-22-

You are going to play musical tunes by waving yourhand over the board without touching it! Magic?Incredible? The tones change with the amount oflight that reaches the CdS cell. Under a bright light,the tone is high. As you block the light with yourhand, the tone lowers.

This method of creating musical sound has beenused since the early days of vacuum-tube circuitry.The first instrument of this type was invented by aman named Leon Theremin, so the instrument wasnamed Theremin in his honor.

When you complete the wiring, press the key andwave your hand over the CdS cell. With a littlepractice, you will be able to play tunes with thismagical electronic musical instrument. Experimentwith the CdS cell light shield for more light control.Have fun!

Notes:

EXPERIMENT #11: LIGHT-CONTROLLED ELECTRONIC HARP

Wiring Sequence:

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

Schematic

-23-

The sound that this circuit produces will remind youof the scary music you hear in horror movies. Afterwiring the project, use your special light shield andyour hand to change the amount of light that falls onthe CdS cell. The music changes in pitch.

The pitch of a sound is determined by the frequencyof the sound wave - the number of cycles ofelectromagnetic energy per second. The amount oflight of the CdS cell determines the resistance valueof the cell. More resistance from the cell slows downthe frequency of the music sound waves. The basic“music” is produced by the oscillator circuit.

When a circuit controls the frequency of anoscillator, we call it FM or frequency modulation. AnFM radio signal is something like this, but at muchhigher frequencies.

Notes:

EXPERIMENT #12: HORROR MOVIE SOUND EFFECTS

Wiring Sequence:

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

Schematic

-24-

Here’s an oscillator circuit that doesn’t use thespeaker or earphone - you don’t hear its output.Instead, you see the output from an LED. This givesyou an idea of how large strobe lights work. Pressthe key and watch LED 1. It turns on and off atcertain intervals. You can control the blinking ratewith the 50kΩ control.

This lets you “see” how an oscillator works. Trysubstituting a lower value capacitor for the 100μFcapacitor. What do you think will happen? Were youright?

Notes:

EXPERIMENT #13: STROBE LIGHT

Wiring Sequence:

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

Schematic

-25-

This is a control circuit that produces short pulses.When you close the key, the LED display shows 1for an instant and then goes off, even if you keeppressing the key.

You can make up a game with this circuit. Display anumber or letter on the LED, and have the playerstell you what number is on the display. You can havedifferent numbers or letters displayed by the LED bychanging the wiring of the LED. Connect theappropriate terminals to form letters or numbers toterminal 71 (in place of terminals 21 and 23). Theconnections for the number 3 would be: 17-21-22-23-20-71.

You might want to try different values of capacitorsand see their effects, but don’t use a capacitor valuehigher than 10μF or the transistor might bedamaged by excessive current.

Notes:

EXPERIMENT #14: RAPID LED DISPLAY SWITCHING (PERSISTENCE OF VISION TEST)

Wiring Sequence:

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

Schematic

-26-

II. BASIC SEMICONDUCTOR ANDCOMPONENTS CIRCUITS

-27-

Until now, you have had drawings of your kit, in additionto the wiring sequences, to guide you in making wiringconnections. The rest of the projects in this manual willhave a schematic diagram in place of the kit drawing.

A schematic diagram is a road map for electronic circuits.It shows how different parts are connected together andlets you follow the flow of electricity through the circuit.Highly skilled electronics technicians and engineers canbuild entire circuits with nothing more than schematicdiagrams to guide them.

We won’t ask you to build circuits from schematicdiagrams alone. To help you, we’ve added the number ofthe terminal where you will make each wiring connectionon the schematics. A line between numbers 32 and 64 onthe schematic means you should connect a wire betweenthose two terminals on your kit. Each part in your kit hasits own schematic symbol. You’ll find a picture of eachpart, along with its schematic symbol and a briefdescription at the beginning of this manual.

You’ll notice on the schematics that some lines crosseach other and there’s a dot at the point where theycross. This means that the two wires represented by thelines are connected at the point indicated by the dot.(You’ll usually find a terminal number beside the dot.) Iftwo lines cross without a dot, that means the wires aren’tconnected. (You also won’t see a terminal number nearthe area where they cross.)

Lines Are Connected / Lines Not Connected

At first, schematic diagrams might look confusing, butthey are actually quite simple once you get some practiceusing them. Don’t be discouraged if you get confused bythem at first. Before long, you will be building circuits justby looking at their schematic diagrams.

The ability to read schematic diagrams is important inelectronics. Many electronics magazines and books giveinteresting circuits only in schematic form. A schematic isalso a shorter and more accurate way to describe orshow a circuit than a written description.

A BIG CHANGE

This circuit shows how single pulses of high voltageelectric energy are generated when a chargedcapacitor is suddenly discharged through atransformer. (Capacitor-discharge automobileignition systems use this same type of reaction.)

The operation of this circuit is simple, but theconcepts involved are important to understandingmore complicated circuits. If you have aVoltage/Ohm meter, you can scientifically measurethe energy that is discharged through thetransformer.

The 470μF capacitor stores up energy when thebatteries supply millions of electrons to thecapacitor’s negative electrode. At the same time, thebatteries draw the same number of electrons fromthe capacitor’s positive electrode so that the positiveelectrode is deficient in electrons. Since the currentmust pass through the 4.7kΩ resistor, it requires atleast 12 seconds for the capacitor to receive the 9Vcharge from the batteries.

The amount of charge in a capacitor can beindicated by the “voltage across” the capacitor (thevoltage supplied by a battery or other power source)or, more accurately, by the quantity of electronsdisplaced in one of the capacitor’s electrodes.

The quantity of electrons in an electrode of acapacitor is measured in coulombs. One coulomb isa quantity of 6,280,000,000,000,000,000 electrons(6.25 x 1018).

To determine the charge in either electrode of thecapacitor (Q), multiply the capacitance (C) by thevoltage across the capacitor (E). (Q = C x E). For the470μF (470 x 10-6F) capacitor at 9V, this iscalculated as follows:

Q = C x E = 470 x 10-6 x 9 = 4.23 x 10-3 coulombs

or:

470 x 0.000001 x 9 = 4.23 x 10-3 coulombs(265,564,400,000,000 electrons)

When you press the key, the above number ofelectrons pass through the transformer winding avery short time and induce a high voltage in thesecondary winding. This causes the LED to flash.

If you have a VOM, connect it as directed to terminal3 and terminal 5 of the transformer to indicate thepresence of 90V or more. The indicated voltage isheld by the capacitor and is released when thetransformer is brought into the circuit.

Notes:

-28-

EXPERIMENT #15: CAPACITOR DISCHARGE / HIGH VOLTAGE GENERATOR

Wiring Sequence:

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

Schematic

-29-

The capacitors are some of the handiest items inyour kit. They can store electricity, smooth outpulsing electricity into a steady flow and let someelectric current flow while blocking other current.This lets you hear the effects of capacitorsconnected in series and parallel.

When you finish wiring this project, set the switch toB. Then, connect terminals 13 and 14. You’ll hear asound from the speaker. In this case, electricity isflowing through the 0.01μF capacitor (refer to theschematic while we talk about this). Now press thekey. What happens?

You hear a lower-pitched sound from the speaker.This is because the 0.05μF capacitor has beenadded in parallel to the first capacitor. That is, thecurrent flows through both capacitors at the sametime, through two separate channels. What do youthink happens to the total capacitance when youconnect two capacitors in parallel?

You might have guessed wrong. When twocapacitors are connected in parallel, the totalcapacitance increases. The increased capacitancecauses the tone to be lower.

Now release the key and move the switch from B toA, but do not press the key while the switch is set toA. (The transistor can be damaged.) What do youhear?

You hear a high-pitched sound from the speaker.This is because the 0.05μF and 0.01μF capacitorsare not connected in series - current flows from onedirectly to another. The total capacitance in thecircuit is now less than the smallest capacitormaking up the series connection. This lowercapacitance allows the more high-pitched sound.

Notes:

EXPERIMENT #16: CAPACITORS IN SERIES AND PARALLEL

Wiring Sequence:

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

Schematic

-30-

In this project, you will see what happens when youconnect resistors in series and in parallel. When youfinish wiring, you can see LED-1 on the panel flashon and off.

Slide the switch and see what happens to the LEDon side A and then on side B. It shows no change atall. The schematic shows you that two 10kΩresistors are connected in series to side A of theswitch, and one 22kΩ resistor is connected to sideB. The total resistance of the resistors connected inseries on side A is equal to the sum of eachresistor’s value - 20kΩ. This is about the same asthe 22kΩ resistance in side B. That’s why the LEDshows no change, even when you move the switch.

Press the key and you see the LED becomebrighter. Look at the schematic and you’ll see thatresistor 1 - R1 (470Ω) is connected to the LED inseries. This resistor controls the flow of current tothe LED. When you press the key, R1 and resistor 2- R2 (100Ω) are connected in parallel, and the totalresistance decreases. The LED becomes brighterbecause the current flowing to it increases when theamount of resistance decreases.

Calculating the total resistance in a parallelconnection is not as easy as calculating resistance

in a series connection. You must multiply the valuestogether, then divide the product by the sum of thevalues. In this case, the total resistance is:

Now, connect terminals 13-14. As shown in theschematic, this connects the 22kΩ resistor inparallel with the two 10kΩ resistors. Any change inthe LED? It flashes on and off at shorter intervalsbecause the resistance connected to the slideswitch decreases. Try calculating the new resistancevalue. It’s about 10.5kΩ.

This circuit is called a multivibrator. A multivibrator isan oscillator that uses components that directcurrent back to each other. In the schematic you cansee that the 10μF and the 100μF capacitorsdischarge through the transistors. This multivibratorcircuit controls oscillations to make the LED flash atcertain intervals.

You can see now that resistors and capacitors haveopposite effects when connected in series or inparallel. Be careful - it’s easy to get confused aboutwhich one increases or decreases in strength.

Notes:

EXPERIMENT #17: RESISTORS IN SERIES AND PARALLEL

Wiring Sequence:

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

Schematic

470 x 100

(470 + 100)= 82Ω

-31-

In this project, you use a capacitor’s charging anddischarging to dim a light (an LED in this case).When you finish the wiring, set the switch to A. TheLED segments slowly light up, displaying an L. In afew seconds, the LED reaches its brightest pointand stays on. Now move the switch to B, and the Lgradually fades away.

Take a look at the schematic. With the switch on,current flows from the battery to charge the 100μFcapacitor. As the capacitor approaches full charge,more and more electricity flows to the base of thetransistor, gradually turning it on (and therebyturning the LED on). When the capacitor iscompletely charged, the current continues to flow tothe transistor base, and the LED stays on.

When you turn the switch off, you remove thebattery from the circuit and the capacitor begins thedischarge through the transistor and the LED. The Lgradually dims until the 100μF fully discharged.

If you want a slower dimmer circuit, replace the100μF capacitor with the 470μF capacitor. Simplyreplace connections 25-116-124 with connections25-118-124, and replace connections 46-115-124,and replace connections 45-115-90 with 46-117-90.You’ll have to be patient, but the LED comes oneventually.

Now go back to project 8 (Electronic Siren) and seeif you can figure out why the siren sound goes fromhigh to low as you press and release the key.

Hint: when you close the key the 10μF capacitorbegins to charge.

Notes:

EXPERIMENT #18: LIGHT DIMMER

Wiring Sequence:

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

Schematic

-32-

This is designed to help you study the switchingaction of the transistors in turning on the LED. Youwill use two different transistors – the NPN type andone of two PNP types included in your kit. NPN andPNP refer to the arrangement of the semiconductormaterials that make up the transistors.

The 47kΩ resistor supplies a base voltage so thatthe NPN transistor at the bottom of the schematicstays on. The PNP transistor at the top of theschematic turns on when you close the switch andmake the connection through the 22kΩ resistor.

Because the 22kΩ resistance is about half that ofthe 47kΩ resistor, the current supplied to the baseof the PNP transistor is about twice as much as thatof the NPN. The PNP is therefore “more” on than theNPN.

Hook up the circuit and press the key: 1 is displayed.To increase the base current of the NPN transistor,decrease the value of the 47kΩ resistor connectedto the base – terminal 46. Simply disconnectterminals 87 and 88, and replace them withconnections to another resistor. For example,change connections 87-42 and 46-88, to 83-42 and84-46 to change the 47kΩ resistor to a 10kΩresistor. Each time you use a lower value resistor,more current is supplied to the base of thetransistor, and the LED display lights a little brighterwhen you use the key. Don’t decrease theresistance below 1kΩ, or the transistor might burnout.

Now change the resistors to 10kΩ and press thekey. Use terminals 81 and 82, and terminals 83 and84. The brightness should not change much withtransistors both fully on. If much change does occur,check the batteries. They might be weak.

Notes:

EXPERIMENT #19: TRANSISTOR SWITCHER

Wiring Sequence:

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

Schematic

-33-

A transistor has three connections; one of these (thebase) is used to control the current between theother two connections. Remember this importantrule for transistors: a transistor turns on when acertain voltage is applied to its base. Positivevoltage turns on an NPN type transistor. Negativevoltage turns on a PNP type transistor.

In this project, the LED display shows whichtransistor is on by lighting either its top or its bottomhalf. This will demonstrate how positive voltagepowers an NPN transistor and negative voltagepowers a PNP transistor.

After you make the connections, the NPN transistoris on because positive voltage is applied to its basethrough the 1kΩ resistor. This turns on the upperhalf of the LED. At the same time, the PNP is offbecause no current can flow to its base. (Currentflows from the PNP emitter to the base of the NPNtransistor, but this flow is blocked from the PNPbase by the diode.)

When you press the key, the NPN is turned offbecause negative voltage is applied to its basethrough the diode. The PNP is turned on at thesame time because the current now flows throughthe 4.7kΩ resistor. This lights the lower segments ofthe LED.

Notes:

EXPERIMENT #20: TRANSISTOR CIRCUIT ACTION

Wiring Sequence:

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

Schematic

-34-

This circuit is a strong two-transistor amplifier. Anamplifier uses a small signal to control or produce alarge signal. This amplifier is similar to an earlymodel transistor hearing aid amplifier. The speakeracts as a dynamic microphone.

Using your VOM on this amplifier to measure circuitvoltages will help you learn how transistors work.The measured voltages will help you determinecurrent measurements and the way this circuitworks.

Your kit’s speaker can change sound pressure intoweak voltages. The transformer increases thevoltage somewhat. This voltage is then applied tothe NPN transistor through the 3.3μF capacitor.

The amplifier voltage at the output of the NPNtransistor is coupled into the PNP transistor throughthe 0.1μF capacitor. It is further amplified by thePNP, and is coupled to the earphone through the100μF capacitor.

It’s about time to talk about the transformer. Thetransformer has a copper wire wound hundreds ofturns. We call it a coil. A transformer has two coilsseparated by a plate.

When electricity flows through a coil, it creates amagnetic field. The reverse is also true – if a coil issubjected to a change in its magnetic field strength,electricity flows through it. So, when electricity flowsthrough the first (or primary as we often call it) coilof a transformer, the magnetic field created by thenumber of windings of each coil is different, so thevoltage of the electricity for each coil is alsodifferent.

This establishment of an electric charge using amagnetic field is called induction. Go back to Project15 (Capacitor Discharge / High Voltage Generator)and recall how large voltage is induced at thesecondary side when 9V is applied by the primaryside of the transformer.

Notes:

EXPERIMENT #21: SOUND AMPLIFIER

Wiring Sequence:

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

Schematic

-35-

How about some rest? Here’s another circuit forentertainment. This circuit flashes the numbers 1and 2 on the display. You might be reminded ofsome neon signs with flashing, eye-catchingadvertisements on them.

A circuit called a flip-flop controls the LED display inthis project. You will learn more about flip-flopcircuits in later projects. For the moment, try adifferent value for the capacitors to see their effectson the speed of operation. See if you can rewire theLED to display numbers other than 1 and 2. You cantry different, higher values in place of the 2kΩ and4.7kΩ resistors. Do not use lower values for any ofthe resistors or you might damage the transistors.

Notes:

EXPERIMENT #22: FLIP-FLOP MULTIVIBRATOR WITH LED DISPLAY

Wiring Sequence:

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

Schematic

-36-

III. LED DIGITAL DISPLAY CIRCUITS

-37-

In this section, we perform some basic circuitexperiments with the LED display to learn how tobetter use this component. We’ll be using the LEDdisplay in all four of these projects.

The LED display allows you to see the effect ofelectrical signals. It is similar to a normal diode but itemits light when current flows through it. One exampleof an LED display is a power indicator on your radio orDVD player that tells you the power is on.

Similar seven-segment LED displays show thenumbers 0 through 9 for reading the output of acomputer or a calculator. Seven is the minimumnumber of segments (separate lines that can beindividually lighted) necessary to clearly display allten digits. You must always observe two conditionsfor proper LED operation:

1. Correct polarity (+ and – LED connections)

2. Proper amount of current flow

Reverse polarity can burn out the LED unless thevoltage is below about 4 volts, or the current islimited to a safe value. The LED will not light whenthe polarity is reversed.

To keep the current flow at a proper level, we useseries resistors (permanently wired to your kit) withthe LED. These resistors supply a relatively constantvoltage (around 1.7 volts) to the LED through theterminal 25. We need voltages above this value tomake current flow through the LED display. Theseries resistors determine how much current flowsfrom the batteries to the diodes.

Complete the wiring as shown to connect the 3Vsupply with the LED segments and the decimalpoint (Dp). What numbers and letters can youdisplay?

At this low battery voltage, you can reverse thepolarity of the circuit by reversing the connections tothe battery. (Change 25-120 and 119-WIRE, 25-119and 120-WIRE.) Record your results on the right.After noting the results, reconnect the battery withthe correct polarity. Use your VOM to measure theLED voltages between terminal 25 and eachseparate terminal (17 through 24). Temporarilychange to the 9V supply by changing the batteryconnections to: 25-124, 121-122, and 119-WIRE.Then, make the same measurements. With thisthree-time increase in voltage supplied from thebattery, the LED voltages only increased by whatamount? (A typical increase is 0.25V.)

Now try measuring the voltage in each resistorattached to an LED segment. The resistors are all360Ω. LED current in milliamps (one-thousandths ofan ampere) is calculated by dividing the voltages by360Ω. LED segment currents are about ____milliamperes (mA) with the 3V supply (3mAtypically), and ____ mA with the 9V supply.

In the space below make a chart of connectionsrequired to display 0 through 9 on the display.

Notes:

EXPERIMENT #23: SEVEN-SEGMENT LED DIGITAL DISPLAY CIRCUIT

Wiring Sequence:

o 25-120o 119-WIRE

or

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

Schematic

-38-

Now you will learn about a common-cathode,seven-segment, LED digital display. Common-cathode means that the seven LED displaysegments use one contact point – terminal 25 – asa common negative electrode.

The LED must have (+) and (–) connections so thatcurrent can flow through it. The positive side iscalled the anode, and the negative side is called thecathode. Because the seven-segment displayconsists of seven LEDs (not counting the decimalpoint), there should be 14 connection points in total– seven anodes and seven cathodes.

However, we can make either anodes or cathodescommon, making the number of terminals only eight– one whole anode terminal for each of the evensegments and one terminals to act as a commoncathode (or seven cathode terminals and onecommon anode).

The LED display in this kit is a common cathodetype. You connect the common cathode segmentterminal (terminal 25) to the negative side of thebattery, and any anode segment terminals asrequired, to the positive side of the battery.

LEDs operate extremely fast. An LED can turn onand off hundreds of times each second; so fast youcan’t see it blink. Unlike an incandescent lamp, thereis no warm up time, and no great amount of heat isproduced.

Perform the following experiment to see how fast theLED operates.

1. Hook up the circuit but do not close the key.

2. Decrease the surrounding the room light to avery low level so you can see any LED lightemission easily.

3. Close the key for only a fraction of a second.

Notice that the display goes quickly on and off. Nowhold the platform steady but glance quickly acrossthe LED display as you briefly tap the key. Thedisplay should appear to go abruptly on and off.Actually, the persistence of the human eye is muchlonger than the LED’s on time, but without specialinstruments this gets the point across.

Notes:

EXPERIMENT #24: BASIC LED DISPLAY

Wiring Sequence:

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

Schematic

-39-

Now we’re getting down into the field of electronics.The explanations from now on will become a bitmore difficult, and more interesting! This projectshows how to control the LED display withtransistors.

This circuit is very much like the one in Project 20(Transistor Circuit Action). The only differences arethe position of the switch and the value of theresistor. This project uses the base circuit of theNPN transistor as a switch, to control the cathode ofthe LED. In project 20 we controlled the LED fromthe anode (positive side).

Both transistors in this project act as switches. ThePNP transistor is always on, allowing current to flowfrom collector to emitter, because a sufficientamount of negative voltage is applied to its basethrough one of the 10kΩ resistors. The NPNtransistor turns on when you close the key, therebyapplying sufficient positive voltage to its base,through another 10kΩ resistor. So, the current canflow from emitter to collector only when you closethe key.

The following basic principles are important for youto remember:

• A PNP transistor turns on when negative voltageis applied to its base; the current flows fromcollector to emitter.

• An NPN transistor turns on when positivevoltage is applied to its base, the current flowsfrom emitter to collector.

Now that the current can flow through the NPNtransistor, it can travel a complete path – from thenegative side of the batteries, to the NPN transistor,to the common cathode terminal of the display, to band c anode terminals of the display, to the PNPtransistor, to the positive side of the batteries – thusthe display lights.

Turning on the LED with either transistor might notseem important now. But to people who designcomplicated computer circuits, it is a handy way tocontrol circuits.

Have you noticed that the transistors switch on andoff as fast as you press the key? This speedyswitching allows computers to perform operationsvery quickly. Transistors are many times faster thanrelays or hand operated switches. Later we willshow you how to delay this fast switching by usingother components.

Notes:

EXPERIMENT #25: TRANSISTOR CONTROL SWITCHING OF THE LED DISPLAY

Wiring Sequence:

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

Schematic

-40-

This project shows you how to turn on the LEDusing a transistor and a CdS cell.

Think of the CdS cell as a resistor that changes itsresistance with the amount of light that falls on it. Indarkness the resistance is very high, around 5megohms (MΩ, 5 million ohms); in bright sunlight, itincreases to about 100Ω, or less.

You can test this easily; set your VOM to theresistance function and connect it to the CdS cell.Hold your hand over the CdS cell and note theresistance. Now remove your hand, and read theresistance again.

You can use the NPN transistor as a switch. As wesaw in the last project, it turns on when sufficientpositive voltage is applied to its base. The positivevoltage leads from the positive terminal of thebattery, to the CdS cell, to the control, to the 10kΩresistor.

The amount of voltage applied to the base isdetermined by the total resistance value of the CdS,the control, and the 10kΩ resistor. The amount oflight striking the cell and the setting of the controlchange the base voltage – making it low or makingit high enough to turn on the transistor. Use yourvoltmeter on the control and try changing the controlposition while casting a shadow over the CdS toverify this voltage change. Adjust the control so thatthe transistor turns on and off when the lightchanges over the CdS.

This circuit displays 1 under bright light. Of course,you can connect the wires to display any numberyou desire. We might consider 1 to be a binary digit,showing logic “high” (H or ON), to indicate thepresence of a bright light on the CdS cell. Can yourewire the circuit to display another character toindicate this condition?

Notes:

EXPERIMENT #26: TRANSISTOR, CdS CELL AND LED DISPLAY CIRCUIT

Wiring Sequence:

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

Schematic

-41-

IV. A TOUR THROUGH DIGITAL CIRCUITS

-42-

Now let’s step into the world of digital circuits andlearn some basics. First, a digital circuit is a circuitthat acts as a switch to turn different components onand off. This section deals with diode-transistor logic(DTL) circuits – circuits that use diodes andtransistors in switching power on and off.

It usually doesn’t matter how much voltage isapplied to a digital circuit; what matters is whetherthe circuit is on (voltage is present) or off (voltage isnot present). When the circuit is on, we describe itas logic high, or use the number 1 to describe thecircuit. When the circuit is off, we say logic low, oruse a number 0.

First, you will learn about the AND circuit. The ANDcircuit produces output when all the connections toits terminals are logic high (receive voltage).

Connect this circuit according to the wiringsequence below. Then, connect terminals A (126)and B (128) to terminals 119 and 124 in differentcombination to complete the circuit and learn howan AND circuit works.

In this circuit, terminal 124 provides logic high(voltage) and terminal 119 provides logic low (novoltage). The LED shows H only when you connectterminal A and terminal B to terminal 124 (the highterminal). If you connect terminal A or B, or both, toterminal 119 (low terminal), the LED shows nothing.Both A and B must be high for their combined output(the LED) to read H (high).

When either or both inputs are low (that is, terminal126 and/or terminal 128 is connected to terminal119), positive voltage is applied to the PNPtransistor base through the diode(s) and the PNPtransistor stays off. Because the PNP transistordoes not complete the circuit, no current is suppliedto the base of the NPN transistor and it is also off.The common cathode terminal is not connected tothe negative power supply and the LED remains off.

When both inputs are high, both diodes supplynegative voltage to the base of the PNP transistor,so it turns on. The NPN transistor also turns on, andthe current flows to the readout to light the LED.

Mathematicians use the symbol AB to represent anAND function. On the bottom right of the schematicyou can see the schematic symbol for the ANDcircuit.

Notes:

EXPERIMENT #27: DIODE-TRANSISTOR LOGIC “AND” WITH LED DISPLAY

Wiring Sequence:

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

Schematic

-43-

This next logic circuit is a logic OR circuit. Can youguess how this circuit works? Remember the ANDcircuit produces logic high when both A and B inputsare high. The OR circuit produces logic high when Aor B receives a logic high input.

The display shows H when you connect eitherterminal A or B to terminal 119 (our logic highterminal). Try connecting both terminals to terminal119; then, to terminal 124. What happens? Theoutput is high when either A or B is connected to H.This logic function is symbolized as A + B.

This circuit is similar to the previous project, so wewon’t explain the whole operation for you here.Compare the two projects and make notes of theirsimilarities and differences. See if you follow thecircuit on the schematics diagram.

Notes:

EXPERIMENT #28: DTL “OR” CIRCUIT WITH LED DISPLAY

Schematic

Wiring Sequence:

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

-44-

No, you cannot find the word NAND in yourdictionary (unless it is an electronics or computerdictionary). This is a newly coined term that meansan inverted, or a Non-AND function. It producesoutput conditions that are the opposite of the ANDcircuit’s output conditions. The NAND output is lowwhen both inputs A and B are high. And the outputis high if either or both of the inputs are low. Thelogic symbol looks like the AND symbol, but with asmall circle at the output. The function isrepresented AB.

When either or both terminals, A and B areconnected to terminal 124 (the logic low terminal),negative current flows through the diode(s) and theNPN transistor stays off. The LED remains off. Whenboth inputs are connected to terminal 119 (the logichigh terminal), both diodes allow positive voltage toflow through them. This positive voltage turns theNPN transistor on, so that current flows to light L onthe LED.

Notes:

EXPERIMENT #29: DTL “NAND” CIRCUIT WITH LED DISPLAY

Wiring Sequence:

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

Schematic

-45-

Don’t worry if you don’t know what exclusive ORmeans. An exclusive OR (abbreviated XOR) circuitprovides a high output only when one or the other ofits inputs is high.

So, you can see that an XOR circuit produces a lowoutput if both inputs are the same (high or low). Ifthe inputs are different (high and low, or low andhigh), then the output is high. This is a handy circuitto let us know if we have two inputs that are thesame or that are different.

Before you complete this circuit, be sure the switchis set to B. When you finish the wiring, connectterminals 13 and 14 to turn on the power. WatchLED 1. Now press the key to produce a high input.Is there any change in LED 1? Release the key tomake both inputs low. Now set the switch to A andmake the input traveling through the switch high.What does LED 1 do now?

Leave the switch at A and press the key to makeboth inputs high. You can see that in an XOR circuit,two high inputs produce a low output.

You can also build an XNOR circuit (exclusiveNOR). We won’t build one here, but you might beable to figure out how to do it. Hint: It’s the samething as a NOR circuit followed by additional wiringto reverse the circuit. Be sure to keep track of yourexperiments in your notebook, especially if youmake an XNOR circuit.

Notes:

EXPERIMENT #30: DTL “EXCLUSIVE OR” CIRCUIT

Wiring Sequence:

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

Schematic

-46-

Now that you’ve built and learned about the NAND(inverted AND) circuit, it’s easy to determine whatthe NOR (inverted OR) circuit does. The displayshows L when either terminal A or B is connected toterminal H (119). The circuit output is high onlywhen both A and B receive low inputs. This is theopposite of the OR circuit. The logic symbol for theNOR circuit is shown with the schematic. Thefunction is written as A + B. The + symbolizes theOR circuit and the bar over the symbol indicates thecircuit is inverted.

When you connect either A or B (or both) to terminalH, the NPN transistor turns on, completing thecurrent path for the LED. When you connect both Aand B to L, the transistor turns off and LED goes off.

Notes:

EXPERIMENT #31: TRANSISTOR “NOR” CIRCUIT WITH LED DISPLAY

Wiring Sequence:

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

Schematic

-47-

What is a flip-flop? It is a kind of circuit that changesback and forth between two states (on and off) atcertain intervals. It flips into one state, and thenflops to another, and so on.

This flip-flop uses two transistors, two capacitors,and four resistors to turn the LED on and off. Eachtransistor is always in the opposite state of theother; when transistor Q1 is on, transistor Q2 is off;when Q2 is on, Q1 is off. This change from on to off(and off to on) happens very fast (in microseconds).Adjust the control and note its effect on the flashingrate of the LED.

Look at the schematic to see how this circuit works.Remember that a transistor turns on when voltageis applied to its base. The two PNP transistors’bases are connected to the negative side of thebatteries through resistors. You might think that bothtransistors would always be on, but there are twocapacitors connected to the bases that help causethe flip-flop action.

To explain the circuit, let’s assume that transistor Q1is off. Transistor Q2 is on because the 100μFcapacitor is charging and discharging through itsbase. The 4.75kΩ resistor and the control keeptransistor Q2 on after the 100μF capacitor hasdischarged. Now, the 10μF capacitor has received acharge and is discharging through the 47kΩresistor, the battery, and the Q2. (Remember, whentransistor Q2 is on, this means current can flowthrough its collector to its emitter.) Transistor Q1remains off as long as the charge on the 10μFcapacitor is high enough.

When the charge drops to a certain point, thenegative voltage from the 47kΩ resistor turns ontransistor Q1. And, when Q1 turns on, the 100μFquickly starts charging and lets transistor Q2 turnoff. With Q2 off, its collector voltage rises toward the9V of the battery supply and the LED turns off.Through the fast charging of the 10μF, the Q1 turnsfully on. This flip occurs very quickly.

After a while the 100μF discharges through the Q2transformer, and the circuit flops back to the originalstate to begin the above action again.

We have used this sort of circuit in several previousprojects. Look back and try to locate them.

Notes:

EXPERIMENT #32: TRANSISTOR “FLIP-FLOP” CIRCUIT

Schematic

Wiring Sequence:

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

-48-

A toggle switch is a switch that turns circuits on andoff. Here we use the flip-flop circuit to work as atoggle switch. In the previous project, the circuitflipped and flopped automatically. In this project, thecircuit does not change until you tell it to.

After you complete the wiring, set the switch to A.The lower segment of the LED lights. Now press thekey. The lower segment goes off and the uppersegment lights. Each time you press the key theLED segments change – flip and flop.

When one transistor is on, the other is off; it stays on(or off) until you tell it to change. So, we can say thatflip-flop circuits can remember things. When youleave a circuit in a certain condition, it stays in thatcondition until you want to change it. Many flip-flopsthat are controlled by a single toggle signal canremember many things. That is how computers canremember so many things.

Notes:

EXPERIMENT #33: TRANSISTOR “TOGGLE FLIP-FLOP”

Wiring Sequence:

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

Schematic

-49-

V. MORE ADVENTURES WITHDIGITAL CIRCUITS

-50-

Did you ever wonder what happens when you startadding digital circuits together, using the output ofone as the input of another? When you build thisproject you’ll find out.

One of the integrated circuits contained in your kit isa quad two-input NAND gate IC. You are probablynot familiar with some of these words. IC is short forintegrated circuit. An integrated circuit containsmany transistors, diodes, and resistors in one smallpackage.

Quad literally means four. In this IC there are fourseparate NAND gate circuits, each receiving twoinputs. Each NAND gate has two input terminals.We have been using only two-input logic circuits sofar, but some circuits have more than two inputs.

Finally, this circuit is called a gate, because this isyour entrance to the digital world (just a joke).Seriously, a gate is a circuit that has more than oneinput and only one output. Its output is not energizeduntil its inputs meet certain conditions. We will usethis handy component with more digital circuits inother projects.

This gate circuit is called a buffer because it is usedto keep two portions of a device isolated from eachother.

Refer to the schematic as you build this project. Wetake the output from one NAND gate, and use it forboth inputs to the second (note the two inputs forthe two NANDs are always the same). From whatyou know about NANDs, what do you think happensif the input to the first NAND is 1? If the first input is0? Try to figure it out before building this project.

Before completing the wiring, set the switch to B.Connect terminals 13 and 14 to turn the power on.What happens to LED 1? Now set the switch to A.LED 1 lights up.

As you’ve probably figured out, 1 is the input whenthe switch is set to A, and 0 is the input when theswitch is at B. When the input to the first NAND is 1,its output is 0. But the 0 output of the first NAND isthe input to the second. The 0 input to the secondmakes its output become 1, lighting the LED.

Notes:

EXPERIMENT #34: TRANSISTOR-TRANSISTOR LOGIC “BUFFER” GATE

Wiring Sequence:

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

Schematic

-51-

An inverter is a circuit that has an output that is theopposite of its input. If the input is 1 (high), the outputis 0 (low). If the input is 0, then the output is 1.

Set the switch to A before you complete this project.Then, connect terminals 13 and 14. You’ll notice thatboth LED 1 and LED 2 are off. Since the output is 0,the input must be 1. Now, set the switch to B and seeboth LEDs come on, indicating you’re inputting 0.

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

One amazing thing to think about is how large theRTL and DTL circuits were that we played with inearlier projects. Believe it or not, four of those circuitshave been shrunk down to fit inside this tiny IC.

There’s a special type of IC, a bit bigger than the ICsin your kit, which is actually a computer shrunk tominiature size. This mini-computer is called amicroprocessor. The process of putting severalcircuits inside just one IC is called large-scaleintegration (LSI). You’ll see this term often used todescribe ICs.

Notes:

EXPERIMENT #35: TTL “INVERTER” GATE

Wiring Sequence:

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

Schematic

-52-

Can you figure out how to make an AND gate usingyour kit’s NAND gates? Let’s experiment, to find outhow.

Leave the switch at B as you build this circuit. Whenyou are finished, connect terminals 13 and 14 toturn the power on. Press the key. What does LED 1do? Now set the switch to A while pressing the key.Is there any change in LED 1?

As you see, pressing the key and setting the switchto A make the inputs 1, causing the overall output tobe 1. Can you flow the 1 input through the circuituntil you reach a 1 output? Try it – and don’t peek atthe answer.

It works like this – each 1 input goes into the firstNAND gate. This causes the output of the NAND tobe 0. This 0 output is used for both inputs to thesecond NAND. The 0 inputs to the second NANDcause its output to be 1, and the LED lights. So, twoNAND gates form an AND gate.

Notes:

EXPERIMENT #36: TTL “AND” GATE

Wiring Sequence:

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

Schematic

-53-

One of the nice things about the quad two-inputNAND IC is that we can combine the four NANDgates to make up other logic circuits. Our last twoprojects have shown how we can use NANDs tomake up some other logic circuits. This project willshow how to make up an OR gate from the NANDgates.

Take a look at the schematic for this project – canyou trace what happens from each input to theeventual output? (Sure you can, just give it a try.)

As you work on this project, keep the switch set to B.When you’ve finished, connect terminals 13 and 14.Now press the key. What happens to LED 1? Releasethe key and set the switch to A. When happens toLED 1 now? Keep the switch at A and press the keyagain. Is there are any change in LED 1?

You see that this circuit indeed behaves like otherOR gates you’ve played with. If at least one or theother of the inputs is 1, the output to the LED is 1.Have you traced what happens from input to outputyet? The explanation is in the next paragraph, but nofair peeking.

Let’s say you press the key with the switch set to B.This enters 1 as both inputs of the NAND, causingthe NAND’s output to become 0. This 0 output is oneof the inputs to the NAND gate controlling the LED.Since a NAND’s output is 0 only if all inputs are 1,the 0 input causes the NAND’s output to go to 1, andLED 1 lights!

We can make up AND, NOR, XOR, and NAND gatesusing the quad two-input IC. Can you figure out howwe would connect the NANDs in the IC to makethese other logic circuits? Give your best try andtake notes – because we’re soon going to find out.

Notes:

EXPERIMENT #37: TTL “OR” GATE

Wiring Sequence:

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

Schematic

-54-

Since we’ve made up other digital circuits bycombining NAND gates, it makes sense that we canmake XOR gates as well. We can, as this circuit willshow you.

Set the switch to B before you complete this circuit.After you finish the wiring, connect terminals 13 and14. Press the key – does anything happen to LED1? Now release the key and set the switch to A.What does LED 1 do? Leave the switch at A andpress the key. What happens to LED 1 now?

The output is 1 as long as the inputs are different. Ifboth inputs are the same – either 0 or 1 – the outputof the XOR gate is 0.

Put on your thinking cap and follow each 0 or 1 inputthrough the circuit until you reach the output. Itmight help if you mark 0 or 1 on the schematic at theinput and output of each NAND gate.

Notes:

EXPERIMENT #38: TTL “EXCLUSIVE OR” GATE

Wiring Sequence:

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

Schematic

-55-

Try marking 0 and 1 inputs on the schematic asyou’ve been doing with the past few projects and seehow this circuit arrives at a 0 or a 1 output. Give it agood try, and don’t peek at the answer.

As you’re building this circuit, keep the switch set toB. When you complete the wiring, connect terminals13 and 14. Press the key. Is there any change in LED1? Release the key and set the switch to A. Whathappens to LED 1 now? Leave the switch at A andpress the key. Does anything different happen?

As you can see, this project behaves just like otherNOR gates we’ve built. Both of the NANDs markedA and B have input of 1. So, they each have anoutput of 0 when the input is 1. Their outputs areused as inputs to the NAND marked C. NAND C hasan output of 1 as long as one or both of its inputs are0. This 1 output is used for the inputs of the nextNAND causing an output of 0. Thus LED 1 does notlight.

As you can see, a NOR gate has an output of 1 onlywhen both inputs are 0 that is, when the switch is setto B and the key is not pressed.

Notes:

EXPERIMENT #39: TTL “NOR” GATE

Wiring Sequence:

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

Schematic

-56-

Although we’ve been using digital circuits that havetwo inputs, that doesn’t mean we can’t have morethan two inputs. Here’s a TTL AND gate that hasthree inputs. Try to use the schematic to figure outhow three inputs produce an output of 1.

You’ll notice that we’re doing things a bit differentlythis time – terminals 13 and 14 make P an inputsignal. Connecting the two terminals makes a 1input and disconnecting them makes a 0. You “turnon” this project by connecting terminals 119 and137.

You know how AND gates work, so we won’t go intodetail here. Can you look at the schematic andfigure out the connections for the switch, the key,and terminals 13 and 14 that will give you a 1output? Try to figure it out, and then read on to seeif you were right.

Here’s how this circuit works; the key and switch areboth connected to one NAND. When they eachprovide an input of 1, that NAND has an output of 0.This 0 makes up the input of another NAND,causing its output to become 1.

This 1 output then goes to another NAND gate (seeit on the schematic?). There it makes up one input,along with the input from terminals 13 and 14making up the other. When these inputs are both 1,the NAND’s output goes to 0. This output is used forboth inputs of the last NAND, causing it to become1, and the LED lights.

Seems simple, doesn’t it? Believe it or not, evencomplex computers operate by using the samebasic principles we’re using with the digital circuitsin this kit.

Notes:

EXPERIMENT #40: TTL “THREE-INPUT AND” GATE

Wiring Sequence:

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

Schematic

-57-

Our last project had a characteristic that could be aproblem in some situations. LEDs 1 and 2 take turnslighting and turning off. We might want both LEDs tolight and turn off together. Did you figure out how tomake the LEDs do this when you experimented withthe last project? This circuit shows you how.

If you look carefully at the schematic for this projectand the schematic for the last project, you will findthey are almost identical. The only change is theaddition of another NAND gate circuit.

As in our last project, setting the switch to B blocksthe channel from LED 1 to LED 2. But when you setthe switch to A, you’ll see LED 2 light and turn off atthe same time at LED 1. The two NAND gates makeup an AND gate (remember this circuit from Project36 (“TTL “AND” GATE’)).

In this circuit, LED 1 is called the data input. LED 2is called the output. These terms are often used withenable circuits. They will pop up from time to timewhen we talk about digital electronics.

You might suspect by now that we can use otherdigital circuits to perform enable functions. Can youfigure out how? Be sure to keep notes of ourfindings, especially if you figure out how to use anOR gate in an enable circuit. (You’ll see why in theproject.)

Notes:

EXPERIMENT #41: TTL “AND” ENABLE CIRCUIT

Wiring Sequence:

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

Schematic

-58-

Have you figured out how to make an enable circuitusing an OR gate? If so, here’s a chance to checkyour design against our OR enable circuit.

As in the last two projects, a multivibrator providesinput to the OR gate in this circuit. You can see theoutput of the OR gate when you look at LED 1 – itflashes on and off according to the output of themultivibrator. Can you tell what happens once themultivibrator’s input is applied to the OR gate bylooking at the schematic? Give it a shot beforebuilding the project.

Before you complete this circuit, set the switch to Arather than B as we have done for the last twoprojects. After you finish the wiring, connectterminals 13 and 14 to turn the power on. What doesLED 1 do? And what is LED 2 doing? Now set theswitch to B. What happens to LED 1 and LED 2now?

We simplify the circuit by saying that setting theswitch to A blocks the flow of data from LED 1 toLED 2. (This is called the inhibit status.) But whenthe switch is at B, data can flow from LED 1 to LED2. This is called the enable status.

This is the third circuit in the family of enable circuitsso we won’t show you how it works. Try to follow theoperational flow on the schematic.

Notes:

EXPERIMENT #42: TTL “OR” ENABLE CIRCUIT

Wiring Sequence:

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

Schematic

-59-

NAND gates can act as electronic sentries. If youdon’t want a signal to be input into a part of thecircuit, a NAND gate can be sure it is not.

You probably recognized one circuit in the schematicright away – the multivibrator. You can see the outputof the multivibrator by watching LED 1. You’ll alsonotice that the multivibrator provides one of theinputs to the NAND gate. Use the schematic to figureout what happens when the switch is set to A? To B?Can you figure out what LEDs 1 and 2 do with theswitch set to A and set to B? Be sure to make somenotes and compare them with what you learn.

Before you complete this circuit, set the switch to B.When you finish the wiring, connect terminals 13and 14 and look at LEDs 1 and 2. You’ll see LED 1“blink” to indicate the output of the multivibrator. Butlook at LED 2. You’ll see that it lights continuously,indicating that something is preventing the signal atLED 1 from reaching LED 2. Now set the switch to Aand observe LED 1. What is happening? Is the samething happening to both LED 1 and LED 2?

You can see that LED 1 and LED 2 take turns goingon and off. This is because we make one of the twoinputs to the NAND equal 1 when the switch is set toA. The multivibrator sends 0 and signals to the otherNAND input. When the multivibrator’s output is 1,

LED 1 lights, but because both input signals to theNAND are 1, the NAND’s output is 0, and LED 2goes out. When the multivibrator’s output is 0, theNAND’s output becomes 1, and LED 2 lights. Try tofigure out what happens when the switch is set to B– why LED 2 always lights. Hint: switch B supplies aninput of 0.

Now, did you figure all that out before building thecircuit? We hope so.

Notes:

EXPERIMENT #43: TTL “NAND” ENABLE CIRCUIT

Wiring Sequence:

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

Schematic

-60-

No, R-S does not mean Radio Shack® flip-flop. Aswe mentioned, earlier, flip-flop circuits are circuitsthat alternate between two states. Engineers oftenuse flip-flop circuits to switch between high (1) andlow (0) outputs. When the output is high, or on, wesay the circuit is at set status (S). When it is off, wesay it is at rest (R). This explains where the R-S flip-flop circuit got its name.

After you finish the wiring, turn the switch to A toturn on the power. Either LED 1 or LED 2 lights. Takethe long wire connected to terminal 56 and touchterminals 13 and 14 in turn. What happens to LED 1and LED 2?

When LED 2 lights, the R-S flip-flop is in the setstate. When LED 1 lights, the R-S Flip-flop is reset.After you set or reset the flip-flop, remove the longwire from the circuit and see what happens.

Now you can see one of the prime characteristics ofthe R-S flip-flop. Once the circuit is set or reset, thecircuit keeps that state until an input signal causes itto change. This means the R-S flip-flop canremember things. Advanced computers use circuitssimilar to this one so they can remember things aswell.

Notes:

EXPERIMENT #44: TTL “R-S FLIP-FLOP”

Wiring Sequence:

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

Schematic

-61-

If you think the NAND gate is a very versatile circuit,you’re right! Here’s a toggle flip-flop circuit madefrom four NAND gates.

Connect terminals 13 and 14 to turn the power onafter you finish building this circuit. Press the keyslowly several times. You’ll see that LED 1 turns onor off each time the key is pressed. Put on yourthinking cap and try to trace what happens from thekey input to LED 1. Two of the four NANDs functionas an R-S flip-flop. See if you can figure out what theremaining NANDs are doing.

This circuit is an inverter, because it takes inputs andreverses them.

Notes:

EXPERIMENT #45: “TOGGLE FLIP-FLOP” CIRCUIT MADE FROM “NAND” GATE

Wiring Sequence:

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

Schematic

-62-

It isn’t hard to think of situations where we mightwant to send input data to two or more differentoutputs. This project shows how we can use anetwork of NAND gates to help do just that.

You can see that we use a multivibrator and threeNAND gates in this circuit. You can leave the switchat either A or B as you build this project. When youconnect terminals 13 and 14, you’ll see that LED 1is blinking. If the switch is at A, LED 2 is blinkingalso. If the switch is at B, LED 3 blinks.

As you can see on the schematic, setting the switchto A or B controls the inputs to the two NANDs thatlight LED 2 and LED 3. With the switch at A, theNAND controlling LED 2 gets one steady input of 1.The output of the multivibrator supplies the otherinput. As the multivibrator’s output switches from 0to 1, the NAND controlling LED 2 switches its outputfrom 1 to 0.

The opposite happens when you set the switch to B.Now the NAND controlling LED 3 gets a steadyinput of 1 so that LED 3 can go on and off accordingto the input from the multivibrator.

Notes:

EXPERIMENT #46: TTL LINE SELECTOR

Wiring Sequence:

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

Schematic

-63-

Our last projects let you see how data could be sentto two or more different outputs. You can probablythink of some situations where we might want (orneed) to do the opposite – send data from two ormore different sources to output. The following circuitshows how to send data this way.

When you look at the schematic for this project,you’ll notice two different input sources. Themultivibrator circuit provides one input signal tocontrol LED 2. The other signal is provided by – canyou guess?

Yourself! You provide the input signal by pressingand relieving the key. The action of the key controlsLED 1.

Set the switch to A before you complete this project.When you connect terminals 13 and 14 to switch onthe power LED 2 blinks. Watch both LED 1 and LED 3.Is anything happening yet? Now press the key andsee what happens to LED 1 and LED 3. LED 3 goeson and off at the same time as LED 1. Now set theswitch to B. LED 3 turns on and according to theblinking of LED 2. You can use either of the twosources as the input to determine the output of LED 3.

Now put on your thinking cap and try to follow theinputs from the multivibrator, to the key, to the settingof the switch, to the LED. Mark a 1 or 0 by eachterminal of the NANDs to see the different high andlow inputs.

Computers and other highly advanced digital circuitsuse a more complex version of these circuits. As youprobably suspect, switching from one input channelto another is done electronically in most cases.

Notes:

EXPERIMENT #47: TTL DATA SELECTOR

Wiring Sequence:

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

Schematic

-64-

VI. THE WORLD OFTRANSISTOR-TRANSISTOR LOGIC

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Even multivibrator circuits can be made from NANDgates. This project is an example of an astablemultivibrator – can you guess what astable means?Make a guess, and complete this project to see ifyou were right.

Connect terminals 13 and 14 to turn the circuit on.You’ll see LED 1 begin to flash. Astable means themultivibrator’s output keeps switching back and forthbetween 0 and 1. As you remember, most of themultivibrators you’ve built so far do the same thing.

You shouldn’t have much trouble figuring out howthis particular circuit works. The 100μF capacitormakes it all possible. Try using other electrolyticcapacitors in place of the 100μF capacitors and seewhat effect they have on LED 1 (Be sure to use thecorrect polarity.)

By now you can see why NAND gate ICs are souseful. The quad two-input NAND IC in your kit isone of the most widely used electronic componentsin the world. It can be applied to many differentcircuits. (You can probably think of many more!)

Notes:

EXPERIMENT #48: TTL ASTABLE MULTIVIBRATOR

Schematic

Wiring Sequence:

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

-66-

We’ve been producing tones with audio oscillatorsfor so long that it might seem as if there’s no otherway to produce tones from electronic circuits. Not so– a multivibrator made from NAND gates does thejob nicely.

When you finish wiring this circuit, connect theearphone to terminals 13 and 14 and set the switchto A to turn on the power. You’ll hear a tone that isproduced by the multivibrator. Try changing thevalue of the capacitors from 0.1μF to 0.5μF. Whateffect does this have on the sound you hear?

You might also want to try different capacitors in thisproject. Don’t try using any of the electrolyticcapacitors, however (terminals 111-118). Try toarrange the circuit so you can switch different valuecapacitors in and out of this circuit to vary the tone.Can you think of ways to use this circuit with anyother digital circuits?

Notes:

EXPERIMENT #49: TTL TONE GENERATOR

Wiring Sequence:

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

Schematic

-67-

Complete the wiring sequence for this circuit andconnect terminals 13 and 14 to turn on the power.You’ll see both LED 1 and LED 2 take turns going onand off. You can change the speed of the blinking bysubstituting different values for the 100μF capacitor.

TTL multivibrators are becoming more widely usedtoday in place of transistor multivibrators. Can youthink of some reasons why? Write down any reasonsyou think TTL multivibrators would work better thanregular transistor multivibrators.

TTL multivibrators take up much less space thantransistor multivibrators. TTL ICs also use lesscurrent than similar transistor arrangements.

Notes:

EXPERIMENT #50: WINKING LEDS

Wiring Sequence:

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

Schematic

-68-

Does the term one-shot mean anything to you? (No,it’s not a nickname for a cowboy or a gun that holdsjust one bullet!)

After you complete the wiring for this circuit, turn theswitch to A to turn on the power. Press the key onceand see what happens to LED 1. Try holding the keydown for different periods of time. Does LED 1 stayon the same length of time or does it vary?

You see that a one-shot multivibrator has an outputfor a certain length of time regardless of the lengthof the input. (It “fires one shot.”) This means that itcan be used in many circuits as a timer. You mightalso see this circuit called a monostablemultivibrator.

Since this is a multivibrator, you might suspect thatthere’s some way to vary the time it produces anoutput. You’re right – there is a way – and we’ll letyou try to figure out what it is. (Actually, youshouldn’t have much trouble discovering whichparts you need to change. Be sure to make notesabout the effect of higher and lower componentvalues on circuit operation.)

Notes:

EXPERIMENT #51: A ONE-SHOT TTL

Wiring Sequence:

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

Schematic

-69-

Here’s another type of one-shot circuit, but in thisproject you hear the effects of the multivibrator. Youcan see from the schematic that this project uses acombination of simple components and digitalelectronics. When you press the key, the 100μFcapacitor is charged and lets the NPN translator inthe left corner of the schematic operate. You can seethat the collector of this transistor serves as bothinputs for the first NAND gate.

The digital portion of this circuit controls theoperation of the PNP transistor on the right side ofthe schematic. Set the switch to A to turn the poweron. When the output of the first NAND is 1, themultivibrator works, and you hear a sound from thespeaker.

The sound will continue until the 100μF capacitordischarges, keeping the first transistor fromoperating. The output of the first NAND becomes 0,stopping the multivibrator. The sound will last about10 seconds with the 22kΩ resistor. Try replacing the22kΩ with the 47kΩ or the 100kΩ resistor and findout what happens.

After you’ve experimented with this project a bit, trythis: press the key and release it. When the soundstops, find the wire running between terminals 52and 54. Disconnect the wire from terminal 52. Doesanything happen? If something does happen, canyou explain why?

Notes:

EXPERIMENT #52: TRANSISTOR TIMER WITH TTL

Wiring Sequence:

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

Schematic

-70-

Here’s another circuit that uses both transistor andNAND type multivibrators. It allows you to see LED1 light up at the same time you hear a soundthrough the earphone.

When you finish building this project, connect theearphone to terminals 13 and 14 and set the switchto position A. You’ll hear a pulse in the earphoneeach time the LED lights up. Do you know why thishappens?

Assume the output of the NAND multivibrator is 0,and trace that output from the NAND multivibrator tothe transistor multivibrator. Do you think theoperation of the transistor multivibrator is affectedby the NAND multivibrator? If you say yes, how is itaffected?

Try using other electrolytic capacitors in place of the100μF capacitor in the NAND multivibrator to seewhat effects they have on the circuit. Try changingthe transistor multivibrator and see how you canalter its operation.

You can use the speaker instead of the earphonewith this project by connecting the NPN transistor,the output transformer, and maybe a resistor or two.Try adding the speaker – but be sure to write downthe new circuit you design.

Notes:

EXPERIMENT #53: BUZZIN’ LED

Wiring Sequence:

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

Schematic

-71-

Carefully compare the schematic for this project withthe schematic for the last project. They are similar inmany ways, but there’s an important difference.

Do you see what it is? Better still, can you tell whateffect the difference has on the project’s operation?Try to figure it out before you build this circuit.

Connect the earphone to Terminals 13 and 14 andset the switch to position A. You should find that LED1 lights up, but you hear nothing in the earphone.When LED 1 turns off, then you hear a sound in theearphone.

Try to figure out why this happens. Study theschematic and when you think you have the answer,read on to check your guess.

When the output of the NAND multivibrator is 0,current can flow through LED 1 to light it but thetransistor multivibrator won’t work because the lefttransistor has a 1 signal applied to its emitter. Whenthe output of the NAND multivibrator is 1, LED 1won’t light but a 0 signal is applied to the emitter ofthe left transistor. The transistor multivibrator canthen work, and you can hear the sound in yourearphone.

Notes:

EXPERIMENT #54: SON OF BUZZIN’ LED

Wiring Sequence:

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

Schematic

Anything look familiar about the schematic for thisproject? This circuit uses an R-S flip-flop circuitmade from NAND gates, similar to the circuit inProject 44 (“TTL R-S Flip-Flop”).

After you finish building this project, set the switch toposition A and press the key. You should hear asound through the earphone. Try pressing the keyseveral times. This should not affect the sound inyour earphone. Now move the switch to position Band press the key one more time. What happensnow?

Circuits like this can be used in alarms. They arevery useful since intruders often can’t figure out howto make the sound stop. You might also want toexperiment using light from LEDs instead of soundto tell you that the circuit has been set or reset.

Notes:

EXPERIMENT #55: SET/RESET BUZZER 1

Wiring Sequence:

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

-72-

Schematic

Here’s another version of the last project. This timewe use a NAND multivibrator and an R-S flip-flopmade with transistors.

This circuit works like the last one. When you set theswitch to B and press the key, you hear a sound inthe earphone. You can still hear the sound no matterhow many times you press the key again. Set theswitch to A and press the key and the sound willstop.

Compare the operation of this project with theprevious one. What makes them different from eachother? Can you think of some situations where onecircuit might be better suited than the other? Be sureto make some notes about what you learn.

Notes:

EXPERIMENT #56: SET/RESET BUZZER 2

-73-

Wiring Sequence:

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

Schematic

This digital sound project makes use of a circuitwe’ve used in some earlier projects. Try to tell whichcircuit we’re talking about by looking at theschematic.

While you’re looking for that certain circuit, why notlisten to the sound this project makes? Becausethere are a lot of wiring steps, you need to take yourtime and check your work. When you’ve finished, setthe switch to position A. What do you hear? Can youexplain how looking at the schematic produces thissound?

The two PNP transistors are used to make up amultivibrator circuit. (Did you recognize this familiarcircuit?) Notice that we’re also using two NANDgates to make a multivibrator. The NAND gatemultivibrator affects the operation of the transistormultivibrator, which sends its output through theNPN transistor to the audio amplifier. The result isthe sound you hear from the speaker.

You can change the sound this circuit makes bysubstituting a different value for the 470μFcapacitor. Try different values for the 10kΩ resistorand the 0.05μF capacitor and see what happens.

Notes:

EXPERIMENT #57: SOUND MACHINE

Wiring Sequence:

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

-74-

Schematic

Do you know someone who is a big mouth? (Or,have you been accused of being one?) This projectlets you and your friends see who’s got the loudestvoice.

You can see how this project works by looking at theschematic. When you yell into the earphone, yourvoice creates electrical energy through the processof piezoelectricity, the special characteristics ofcrystalline substances. The crystal in your kit’searphone produces voltage when it is subjected tomechanical stress – such as the sound pressure ofyour voice.

The two-transistor circuit amplifies the electricalenergy from the earphone. You can use the control tochange the amount of the signal from the earphonethat is amplified. The two NAND gates in seriescontrol the lighting of LED 1. Trace 0’s and 1’s asthey change from input to output.

To use this circuit, set the switch position A and setthe control to position 5. Yell into the earphone andwatch LED 1. It probably lights. If so, try turning thecontrol counter-clockwise to make it more difficult tolight LED 1. (Try adjusting it just a tiny bit each time.)See how far you can lower the control to reduce thestrength of the amplifier and still light the LED.

Notes:

EXPERIMENT #58: BIG MOUTH

-75-

Wiring Sequence:

o 27-79o 28-110o 124-131-31-49o 33-55o 41-43-100-81o 42-72o 44-109-99-83o 45-88-78o 46-80o 47-115-51-50o 52-53-54o 77-71-123o 119-132o 40-87-13-EARPHONEo 121-26-48-116-62-60-59-57-56-84-82-14-EARPHONE

Schematic

Do you think you have good night vision? This lastproject in this section is a game that lets you find outhow well you can see in the dark. It tests your aim –in a completely dark room!

After you finish building the project, put it in as darka room as possible. Slide the switch position A andadjust the control in a counter-clockwise directionuntil LED 1 and LED 3 light. Now you’re ready to testyour skill.

Your “gun” for this game is any ordinary flashlight.You use your flashlight to “shoot” the kit with a beamof light. If you aim correctly, you’ll hit the CdS cell tolight LED 2 and turn off LED 1 and LED 3. Then turnoff your flashlight and wait until LED 2 goes offbefore you try the next shot.

First try hitting the CdS cell from about five feet orso. As your aim improves try increasing thedistance. When you are really good, you can tryhitting the CdS cell simply by switching yourflashlight on and off rather than using a continuousstream of light.

You might have to adjust the control knob verycarefully to have LED 2 come on when light strikesthe CdS cell. For the best results, be sure you havethe kit in a completely dark room and use a sharplyfocused flashlight (not a fluorescent lamp or otherlight). Once you’ve found the best setting, keep itthere so you can use it again. Don’t change it untilyou want to stop using the “shot in the dark” game.

Good luck and may you become “the fastestflashlight in the West!”

Notes:

EXPERIMENT #59: SHOT IN THE DARK

Wiring Sequence:

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

-76-

Schematic

-77-

VII. APPLICATION CIRCUITS BASEDON THE OSCILLATOR

The “R-C” in this project’s name stands forresistance-capacitance. We’ve seen how varyingresistance and capacitance can affect the pulsingaction of an oscillator. This project lets us see theeffects when we change the strengths of bothresistors and capacitors.

Look at the schematic. You can see the switchallows you to choose between two differentcapacitors. You can add a second resistor to thecircuit by connecting terminals 13 and 14.

After you build the project, set the switch to positionB. Leave terminals 13 and 14 and press the key.What kind of sound do you hear from the speaker?Now set the switch to A and press the key again. Isthere any change in the sound? Now connectterminals 13 and 14 and press the key. Try bothsettings of the switch with terminals 13 and 14connected and see what happens.

Which combination gives you the highest tone? Thelowest? What does this tell you about howcapacitors and resistors affect each other? Takecareful notes about the effects of the different valuecapacitors and resistors.

Notes:

EXPERIMENT #60: VARIABLE R-C OSCILLATOR

Wiring Sequence:

o 1-29o 2-30o 3-47-110o 4-87-89-138o 5-101-105-109o 13-88o 14-90-46-132o 48-121o 102-131o 106-133o 119-137

-78-

Schematic

We’ve seen how a capacitor’s charge/dischargecycle can be used to delay certain circuit operations.Now let’s delay the oscillator action in this projectwith a 470μF capacitor.

When you press the key, the capacitor discharges.When you release the key, the capacitor begins tocharge. The circuit continues to oscillate until thecapacitor is charged, then current stops flowing.When you close the key for the second time, itimmediately discharges the capacitor.

A discharged capacitor has an equal number ofelectronics on its positive (+) and negative (–)electrodes. A charge is stored in a capacitor bydrawing electrons from the positive electrode (toactually make it positive) and an equal number ofelectrons are added to the negative electrode (tomake it negative). The current that flows to chargethe capacitor is called charging current ordisplacement current. When the capacitor isdischarging, the same amount of current must flowin the opposite direction. This current is calleddischarge current or displacement current.

If you have a VOM, use it to measure the charge onthe capacitor with the voltmeter function. Thedisplacement current can be measured with thecurrent function.

Only the capacitor has this unique storage-action.We can use capacitors to perform many functionsusing this characteristic. However, this storage-action makes capacitors in very high voltage circuitsdangerous sources of possible shock orelectrocution. Play it safe? You should dischargecapacitors before touching them if they use voltagesabove 50V.

Notes:

EXPERIMENT #61: OSCILLATOR WITH TURN-OFF DELAY

Schematic

-79-

Wiring Sequence:

o 1-29o 2-30o 3-85-105-109o 4-120o 5-41-110o 40-106-86o 42-118-137o 117-138-119

Did you know that a transistor changes itscharacteristics according to the temperature? Thisproject will show you how temperature affectstransistor action.

Look at the schematic. The NPN transistor acts as apulse oscillator. The voltage applied to its base iscontrolled by the 22kΩ resistor and the PNPtransistor. The base current and collector current ofthe PNP transistor vary with the temperature of thetransistor.

Build this project and you will hear a sound from thespeaker. Adjust the 50kΩ control so that the soundis low or a series of pulses.

Now warm up the PNP transistor by holding itbetween your fingers. You hear the tone becomehigher as the transistor temperature increases.

Notes:

EXPERIMENT #62: TEMPERATURE-SENSITIVE AUDIO OSCILLATOR

SchematicWiring Sequence:

o 1-29o 2-30o 3-101-103o 4-26-41-119o 5-47-104o 27-81o 120-28-48o 40-82o 42-85o 46-102-86

-80-

Now we will build an oscillator using two transistorsconnected directly to each other. As you have seen,there are many ways to make an oscillator. This wayis simple compared to some.

After completing the wiring, press the key. You heara beep sound from the speaker. Now rotate thecontrol. How does it affect sound?

The two transistors cooperate with each other andact as a single transistor. The NPN transistoramplifies the signal from the 22kΩ resistor anddirects it to the PNP transistor, to obtain a greateroutput.

The capacitor determines the frequency of theoscillation. The project starts with the 0.01μFcapacitor in the circuit but you can experiment withdifferent value capacitors. The control adjusts thevoltage leading to the base of the NPN transistors. Itchanges the tonal quality as well as the frequency.You should be sure to record your results like aprofessional scientist, so you can repeat theexperiment later on. Be sure to observe the polarity(+ and –) of the electrolytic capacitors.

Notes:

EXPERIMENT #63: TWO-TRANSISTOR, DIRECTLY CONNECTED OSCILLATOR

-81-

Wiring Sequence:

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

Schematic

In this project we will make a push/pull, square waveoscillator. This oscillator is called a push/pullbecause it uses two transistors that are connectedto each other. They take turns operating so thatwhile one transistor is “pushing,” the other is“pulling.” Scientists study waveform patterns to helpunderstand electronic signals – such as the signalproduced by the current in this project. A squarewave oscillator produces waves that look likesquares.

After wiring the circuit, slide the switch to position Ato turn on the power. Note the sound from thespeaker, because we will be using square wavesignals in later projects.

This oscillator circuit works well with low DC voltagesupplies. For this reason, scientist and techniciansuse DC to AC converters and DC to DC inverterswith supply voltages of about 0.5 to 12 volts.

Another characteristic of this oscillator is that itmakes a maximum use of the transformer. Thecircuit produces the maximum power for theparticular size transformer that is used.

Notes:

EXPERIMENT #64: PUSH/PULL SQUARE WAVE OSCILLATOR

Wiring Sequence:

o 1-29o 2-30o 3-83-101-41o 4-131o 5-81-102-44o 40-82o 45-42-119o 43-84o 120-132

-82-

Schematic

This project is an oscillator that is controlled in anunusual way: with a pencil mark! You have seen inother oscillator projects how changing the circuit’sresistance can change the sound that is produced.The resistors, like the ones in your kit, are made of aform of carbon, and so is pencil lead. By causing thecurrent to flow through different amounts of pencillead, we can vary the resistance and therefore, thetone of the sound coming from the speaker.

After you complete the wiring, make a very heavypencil mark on a sheet of paper (a soft lead pencilworks best). The mark needs to be about an inchwide and 5 to 6 inches long.

Now slide the switch to position A to turn on thepower and hold one of the probes to one end of themark (or attach it with tape). Move the other probeback and forth along the mark. You hear the pitchrise and fall as you move the probe. With a littlepractice you should be able to play a tune with thisorgan.

Notes:

EXPERIMENT #65: PENCIL LEAD ORGAN

-83-

Wiring Sequence:

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

Schematic

This circuit is an oscillator with a low frequency. So,you can see the LED lighting and turning off. The offtime is longer than the on time, so you see shortpulses of light with long periods between them. Thewiring sequence below will make the decimal pointlight, but you can light any part of the LED display.

This type of circuit is called a sawtooth waveoscillator. The signal changes as the LED lights andturns off. The waveform of this signal’s frequencyshows a sawtooth pattern representing the twodifferent voltage values. When the output from theemitter of the PNP transistor supplies the basecurrent to the NPN transistor (as in this circuit),shorter pulses are generated.

Try experimenting by changing the value of the3.3μF capacitor to 10μF. You can also vary the 1kΩresistor and change the 470kΩ resistor to 220kΩ.The frequency of this oscillator is controlled by therate of charge and discharge of the capacitor. Sochanging its value or the values of the resistors thatsupply current to the capacitor changes thefrequency.

Notes:

EXPERIMENT #66: LED STROBE LIGHT

Schematic

Wiring Sequence:

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

-84-

This circuit has a multivibrator connected to a pulsetype oscillator. The multivibrator provides a tremoloeffect (a wavering tone), rather than turning theoscillator completely on and off.

After you build the project, you can use the control tovary the base current supplied to the NPN transistor.This changes the charge/discharge rate of the 0.1μFand 0.05μF capacitors, and the frequency of thepulse oscillator.

The key works to turn the entire circuit on and off.You can replace it with the slide switch. Also, you canchange the tonal range by changing the 10μF and3.3μF capacitor values.

Try using the switch or the key to add extracomponents to the circuit (like an extra capacitor inparallel with the 10μF or 3.3μF), so you can changefrom one tonal range to another, quickly. Thesechanges will make a more complete organ from thisproject. Be sure to keep notes on what you do.

Notes:

EXPERIMENT #67: ELECTRONIC ORGAN

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Wiring Sequence:

o 1-29o 2-30o 3-47-106o 4-74-45-42-119o 5-105-109o 27-46-110o 28-86o 40-111-80o 41-114-78o 43-113-82o 44-112-87-76o 77-75-81-79-48-138o 73-85-88o 120-137

Schematic

This is the electronic bird circuit that you built forProject 1 (Electronic Woodpecker), but now it has aphotoelectric control of the transistor base. Youknow how the CdS cell works. Since this electroniccomponent is activated by daylight, you can use itas an early bird wake up alarm.

Press the key to make the sound of the early bird.You can adjust the control so that the right amountof light will set off the bird and wake you up in themorning – not too early and not too late.

We have changed only a few component values,and rearranged the circuit schematic from theoriginal electronic bird. See if you can spot thechanges and rearrange the circuit so that it lookslike Project 1. Use the space below to redraw theschematic.

Notes:

EXPERIMENT #68: DAYLIGHT EARLY BIRD

Schematic Wiring Sequence:

o 1-29o 2-30o 3-107-109o 4-27-137o 5-41-110o 15-88o 16-28o 76-87-106-40o 119-42-115o 75-116o 105-108o 120-138

-86-

Now we’ll let one oscillator control another to makean effective alarm. In this project we have amultivibrator-type oscillator controlling a pulseoscillator. You should recognize the multivibratorcircuit on the left side of the schematic. The pulseoscillator’s frequency is in the audible range (20 to20K Hertz). The multivibrator controls the pulseoscillator by allowing current to flow to the transistorbase.

Build the project and press the key to hear the alarmsound coming from the speaker. You hear the alarmsound turning on and off as the pulse oscillator turnson and off.

This intermittent sounding alarm is more effectivethan a continuous tone, because it is morenoticeable. You can experiment with this project byvarying the values of the 22kΩ, 47kΩ, and 100kΩresistors, and the 0.02μF capacitor.

Notes:

EXPERIMENT #69: INTERMITTENT ALARM GENERATOR

-87-

Wiring Sequence:

o 1-29o 2-30o 3-103-109o 4-42-45-138o 5-47-110o 40-113-87o 41-112-75o 43-111-85o 44-114-73-89o 46-104-90o 76-86-88-74-48-124o 119-137o 121-122

Schematic

-88-

VIII. BASIC OPERATIONALAMPLIFIER CIRCUITS

For this section you will need some basic knowledgeabout the operational amplifier integrated circuit.First, we can use one power source for both thecircuit and the IC, or we can use separate powersources.

The operational amplifier can be used as a non-inverting amplifier, an inverting amplifier, or adifferential amplifier. A non-inverting amplifierreproduces an input signal as an output signalwithout any change in polarity. An inverting amplifierdoes the opposite: its output has the reverse polarityof its input. The differential amplifier has an outputthat is the difference between the strengths of thetwo input signals.

A comparator compares two voltages and tells youwhich one is stronger than the other. We call thecontrolled voltage the reference voltage because weuse it as a reference for measuring other voltages.The voltage that is compared is the input voltage.

The reference voltage in this project is about 3.7V. Itis connected to terminal 68 of one of the integratedcircuits. Input voltage flows to terminal 69 of thesame IC. The LED lights if this voltage is higher thanthe reference voltage, and stays off if it is lower. Inthis circuit the operational amplifier acts as aninverting amplifier for the reference voltage to keepthe LED turned off, or as a non-inverting amplifier tolight the LED.

Build the project and then set the switch to positionA. This provides an input of 6V. The LED lightsbecause the input voltage is higher than thereference voltage. Now slide the switch to position B.This provides an input voltage of 1.5V. Thecomparator IC does not let the current pass becausethe input voltage is now lower than the referencevoltage – the LED remains off.

Notes:

EXPERIMENT #70: COMPARATOR

Schematic

-89-

Wiring Sequence:

o 31-67o 84-82-33-70-121o 63-122o 68-83-78o 69-81-76o 75-132o 77-119-124o 120-133o 123-131

Now we move along to the simplest experiment onamplifying DC voltage. After you complete thewiring, set the switch to position B.

LEDs 1 and 2 indicate the output voltage of theoperational amplifier IC. An LED only lights when itis connected with about 1.5V. In this project, weconnect the two LEDs in series, so they only lightwhen connected with about 3V. Now they are off, sothe output voltage of the operational amplifier mustbe less than 3V.

Look at the schematic diagram. With the switch atposition B, a 10kΩ resistor is connected in seriesbetween each of the battery terminals and thepositive (+) input terminal of the operationalamplifier. These two 10kΩ resistors divide the 1.5Vsupply voltage in half. This means the positive inputterminal receives an input voltage of only 0.75V.

To calculate the output voltage of the operationalamplifier you multiply its input voltage by theamplification factor (R1/R2) + 1. So, the outputvoltage is 0.75V x ((220kΩ / 100kΩ) + 1) = 2.4V.

Now, slide the switch position A. This eliminates the10kΩ resistors from the circuit, so the amplifier’spositive input terminal receives the full 1.5V inputvoltage. Using the above equation, you can see thatthe output voltage of the operational amplifier is now1.5V X ((220kΩ / 100kΩ) +1) = 4.8V. The LEDs lightdimly because the voltage supplied to them is morethan 3V.

Let’s change the amplification factor. Slide theswitch to position B again and press the key. Thisadds the 47kΩ resistor to the 100kΩ resistor inparallel, making total resistance of R2 about 32kΩ.(Do you remember how to calculate the totalresistance for parallel connection from Project 17(“Resistors in Series and Parallel”)). Now the outputvoltage is 0.75V x ((220kΩ / 32kΩ) +1) = 5.9V,enough to light the LEDs.

If you slide the switch to position A again and pressthe key to connect 1.5V to the amplifier’s positive (+)input terminal, the LEDs light brightly. Try tocalculate the value of the output voltage with theswitch at position A with the key pressed.

Notes:

EXPERIMENT #71: BASIC INCREASE IN DC VOLTAGE

Wiring Sequence:

o 31-67-92o 32-34o 81-89-88-70-36-121o 63-122o 68-90-91-138o 69-132o 82-84-133o 83-131-120o 87-137o 119-124

-90-

Schematic

In this project, we will make a constant currentcircuit, using an operational amplifier and atransistor. This circuit maintains a constant currenteven when the source voltage changes, becausemore energy is used up in the circuit.

Look at the schematic. When the current changes,the voltage transmitted through R1 changes. Theoutput of the operational amplifier changesaccording to the feedback signal from R1. Thisoutput from the amplifier controls the base voltage oftransistor Q1 allowing it to maintain the constantcurrent.

Let’s get to the experiment. First set the switch toposition A, and press the key while watching LED 1.It is dimmer when the key is closed. This is becauseboth LED 1 and LED 2 are in the circuit when the keyis closed. The load – the amount of energy used bythe LEDs in this circuit – increases, but the currentremains constant. So the LED becomes dimmer.

Now, set the switch to position B with the key off. Doyou see any change in LED brightness from positionA to position B? Setting the switch to B changes thesupply voltage from 9V to 6V. But the currentremains constant again, so the LED brightness doesnot change.

Notes:

EXPERIMENT #72: CONSTANT-CURRENT SOURCE

Schematic

-91-

Wiring Sequence:

o 31-132-137o 32-35-47o 34-138o 46-67o 48-68-75o 63-131-122o 69-119-124o 76-70-121o 123-133

You know that an LED instantly lights when you turnit on. But you can also light it up gradually. In thisproject, you’ll be able to watch the LEDs slowly getbrighter while you hold down the key.

This circuit is called a Miller integrating circuit. Theoutput of this IC increases as its input increases.The integrating circuit increases the value ofcapacitor CA past the stated 100μF. When youpress the key, the capacitor charges slowly throughresistor R and the LEDs become brighter. Settingthe switch to position B discharges the capacitorand turns the LEDs off.

Set the switch to position B before completing theproject to discharge the capacitor. Set the switch toposition B and hold the key down to see LEDs 1, 2,and 3 become brighter. They reach maximumbrightness in about 5 seconds. Set the switch to B todischarge the capacitor and then hold down the keyto repeat the experiment.

Notes:

EXPERIMENT #73: INTEGRATING CIRCUIT

Schematic

Wiring Sequence:

o 31-63-122-137o 32-34o 35-37o 38-72o 71-67-116-133o 68-90-115-132o 69-124-119o 70-121o 89-138

-92-

We’re going to use the operational amplifier as aSchmitt trigger circuit and as a comparator. Theoperational amplifier produces a signal as long as itsinput voltage exceeds a certain value. Look at theschematic: can you see how it works? It shows thatthe voltage level that causes the output to turn on ishigher then the voltage level that stops the output. Itlooks like the Schmitt trigger circuit resists changingthe output state. We call such operation as“hysteresis loop.”

Now, let’s get to the experiment. First leave the keyoff. The operational amplifier works as a comparatorin this state. When you rotate the control, LEDs 1and 2 take turns lighting at some point. Note that thispoint doesn’t change whether you turn the controlclockwise or counterclockwise.

Now, press the key on, and you’ll have a Schmitttrigger circuit that produces hysteresis loops, asshown in Figure 1.

The width of hysteresis becomes narrower as theRB/RA increases. Notice how the width changeswhen using different values for RA and RB.

Notes:

EXPERIMENT #74: SCHMITT TRIGGER CIRCUIT

-93-

Wiring Sequence:

o 70-36-26-121o 27-83o 63-28-130-131o 34-33-67-90o 68-134o 84-69-138o 89-137o 119-124-135o 122-132o 31-129

Schematic

In this project, we will make a microphone amplifier,using the operational amplifier as a non-invertingamplifier with two power sources. The earphoneworks as a microphone.

Start by sliding the switch to position B andcompleting the wiring for the circuit. When you finishconnecting the wires, set the switch to position A toturn on the power, rotate the control fully clockwise,and lightly tap your microphone – the earphone. Thetapping sound comes through the speaker.

When you use the earphone as a microphone, as inthis project, it’s better to remove the end that you putin your ear. You can unscrew it by turning it counter-clockwise. Turning the control adjusts the volume.

As you can see in the schematic, the dualoperational amplifier uses two power sources: 4.5Vfor the circuit and 9V for the IC. Note that the dualoperational amplifier has two input terminals, thepositive (+) and negative (–) terminals 69 and 68.The non-inverting input is applied to the positive (+)terminal. The gain in strength of the signal throughthis amplifier is about 100 – determined with theformula R1/R2. Thus 100k/1k = a gain of 1.

Notes:

EXPERIMENT #75: NON-INVERTING TWO-POWER SUPPLY AMPLIFIER

Wiring Sequence:

o 1-29o 2-30o 3-67-90o 27-69o 63-131o 68-89-75o 70-134o 121-135o 122-132o 124-119-26-76-5-14-EARPHONEo 28-13-EARPHONE

-94-

Schematic

Here’s another two-power source microphoneamplifier, but this one is an inverting amplifier. Weuse the earphone as a microphone again.

Slide the switch to position B and assemble thecircuit. When you finish the wiring, slide the switch toposition A to turn the power on, rotate the controlclockwise, and speak into the microphone – theearphone. You will find that the project works just likeour last project.

IC 1 used as a buffer of gain 1, and IC 2 as aninverting amplifier. Input reaches this invertingamplifier through its negative (–) terminal, not thepositive (+) one as in our last project. Its gain isabout 100, as determined by: R1/R2 = 100k/1k.

The gain becomes larger if you increase R1 ordecrease R2. See what happens to the gain whenyou change the value of R2 to 470.

Notes:

EXPERIMENT #76: INVERTING TWO-POWER SUPPLY AMPLIFIER

-95-

Wiring Sequence:

o 1-29o 2-30o 3-64-90o 27-69o 63-131o 65-89-76o 68-67-75o 70-134o 121-135o 122-132o 124-119-26-66-5-14-EARPHONEo 28-13-EARPHONE

Schematic

In Projects 75 and 76 (“Non-inverting Two-PowerSupply Amplifier,” and “Inverting Two-PowerAmplifier,” respectively), we used the operationalamplifier with two power sources. In this project, wewill make a single-power source, non-invertingmicrophone amplifier. Again, the earphone works asa microphone.

Slide the switch to position B and assemble thecircuit. When you finish the wiring, slide the switch toposition A to turn on the power, rotate the controlclockwise, and speak into the microphone. Theproject works just like Projects 75 and 76, but you’llnotice something different.

The difference comes from the gain of thismicrophone amplifier. It is still determined by R1 andR2, but now it’s much larger. Can you see why? Yes,we use the 100kΩ resistor in place of the 1kΩresistor from the last two projects. Try changing R2to 1kΩ, and the gain drops to the level of the lastprojects.

In this project, two power sources are connected inseries to operate the dual operational amplifier at9V. But the operational amplifier can work at half thisvoltage, at a 4.5V. See what happens when youdisconnect the operational amplifier from batteryterminal 122 and connect it to terminal 119.

Notes:

EXPERIMENT #77: NON-INVERTING SINGLE-POWER SUPPLY AMPLIFIER

Wiring Sequence:

o 1-29o 2-30o 3-116o 27-112o 71-114o 81-63-131o 67-90-115o 89-68-113o 84-82-69-111o 119-124o 122-132o 121-26-70-83-72-5-14-EARPHONEo 28-13-EARPHONE

-96-

Schematic

This is the last in the series of microphoneamplifiers. Now we use the operational amplifier as adifferential amplifier. It is a two-power source typeamplifier, and this time we use the speaker as amicrophone.

Slide the switch to position B and assemble thecircuit. When you finish the wiring, apply theearphone to your ear, slide the switch to position Ato turn on the power, and tap the speaker lightly withyour finger. Can you hear the tapping sound from theearphone?

The dual operational amplifier works as a differentialamplifier when two inputs are applied at the sametime to its positive (+) and negative (–) terminals.The transformer plays an important role in thisamplifier circuit. Its two different outputs fromterminals 3 and 5 supply the opposite inputs forterminals 68 and 69.

You should remember that the speaker has a coiland a magnet inside. When used as a normalspeaker, electricity flows through the coil, and amagnetic field is created around the coil. Themagnet attracts or repulses the coil depending onthe magnetic field created by the coil. So the coilmoves; this movement is transferred to the conepaper attached to it and this creates the sound youhear.

Here, the speaker is used as a microphone, so theopposite takes place. When sound makes the coilmove, the distance from the magnet changes, andthe strength of the magnetic field changes so thatthe voltage appears at both ends of the coil. Thissmall voltage is applied to the primary of thetransformer, which then results in larger voltage atthe secondary side of the transformer.

So using the microphone simplifies the circuit. Inorder to use the earphone as in previous projects,we would need to make a far more complex circuit.

Notes:

EXPERIMENT #78: TWO-POWER SUPPLY DIFFERENTIAL AMPLIFIER

-97-

Wiring Sequence:

o 1-29o 2-30o 3-110o 5-68-93o 63-131o 69-81-109o 70-134o 121-135o 122-132o 124-119-82-13-EARPHONEo 94-67-14-EARPHONE

Schematic

How about building a tone mixing amplifier thatmixes two tones together? There are many differentkinds of tone mixing circuits, but the operationalamplifier is considered one of the best.

After completing the wiring, slide the switch toposition A to turn on the power. Note the tone of thesound that is produced. Now press the key to mixthis tone with another. You can change the twoseparate tones by changing the values for the two10kΩ resistors.

Thus, the tone mixing amplifier allows you to mixtwo tones together by changing resistances with noneed to change the other circuits.

Notes:

EXPERIMENT #79: TONE MIXING AMPLIFIER

Wiring Sequence:

o 1-29o 2-30o 3-49-91-119-124o 5-67-90o 50-51-85-106o 52-53-54-87-86o 55-88-105-113o 56-57-75-110o 58-59-60-76-77o 78-61-109-111o 62-70-134o 63-131o 68-82-84-89o 69-92o 81-112o 83-138o 114-137o 121-135o 122-132

-98-

Schematic

Now we’re going to produce a loud sound bycombining the operational amplifier with twotransistors. After you complete the wiring, set theswitch to position A to turn on the power. When youpress the key, you hear a loud sound from thespeaker.

The signal source for this sound is a capacitor-resistor oscillator. The operational amplifier acts asan inverting amplifier, and transistors Q2 and Q3cause the speaker to produce the sound. This circuitis called a single ended push-pull circuit (SEPP). Youhave learned about push-pull circuits. Single endedmeans the circuit has only one output. Mostamplifiers have a second output that is connected tothe negative (–) side of the battery.

Notes:

EXPERIMENT #80: POWER AMPLIFIER USING OPERATIONAL AMPLIFIER

-99-

Wiring Sequence:

o 1-29o 2-30o 3-90-67-47-44o 5-94-48-119-124o 73-81-86-87-32-113-45-131o 33-63-43o 35-46-70o 76-92-36-134o 91-88-104-40o 75-100-111-41o 74-114-42o 68-80-89o 69-93o 79-138o 82-84o 83-102-103o 85-99-101o 112-137o 121-135o 122-132

Schematic

VCO? What’s that? VCO stands for voltagecontrolled oscillator, and as the name implies, thisoscillator changes its oscillation frequencyaccording to the voltage applied to the circuit. Thecircuit produces two different output signals thathave triangular and square waves.

When you complete the wiring sequence, slide theswitch to position A to turn on the power. Turn thecontrol slowly while you listen to the sound from theearphone. When you turn the control clockwise, thesound becomes lower.

When the voltage through terminal 27 of the controlchanges, the 0.01μF capacitor’s charging /discharging time also changes, causing a change inthe frequency of the oscillator. Current that shows atriangular wave travels from terminal 67 of the firstoperational amplifier to terminal 65 of the secondamplifier which acts as a comparator. Thecomparator releases output from terminal 64 -current that shows a square wave.

Notes:

EXPERIMENT #81: VOLTAGE CONTROLLED OSCILLATOR CIRCUIT

Wiring Sequence:

o 79-63-26-131o 27-87-89o 46-91o 47-76o 86-92-109-64o 65-78o 66-80-83-85o 67-102-77o 68-90-101-75o 69-88-81o 84-70-134o 121-135o 122-132o 124-119-28-48-94-82-14-EARPHONEo 110-93-13-EARPHONE

-100-

Schematic

The dual operational amplifier works well as anoscillator. In this project, we will build an electricbuzzer that makes a continuous beep. You canchange the tone of this buzzer by rotating thecontrol.

When you complete the wiring, set the control to the12 o’clock position and press the key. You hear acontinuous beep from the speaker. Now turn thecontrol while pressing the key. The tone of the buzzerchanges.

The electronic buzzer only makes a beep, but it canbe used for many different purposes as you’ll seelater.

The oscillating circuit of this buzzer is an astablemultivibrator and works as an oscillator producingcurrent that shows a square wave. Changing thecontrol changes the tone of the sound because itchanges the frequency of the signal. The frequencyis determined by the resistance from the batteryinput (+) and the resistance from the capacitor thatis connected to the (–) battery terminal. Test to findout how the tone changes when you set the value ofthe capacitor to 0.02μF or 0.1μF.

Notes:

EXPERIMENT #82: OPERATIONAL AMPLIFIER BUZZER

-101-

Schematic

Wiring Sequence:

o 1-29o 2-30o 3-116o 5-84-70-106-121o 63-27-138o 28-81o 67-90-92-115o 91-68-105o 69-82-83-89o 119-124o 122-137

This burglar alarm makes a buzzing sound whenanyone sneaking into your house trips over a wireand breaks it off or disconnects it from a terminal.Instead of stretching out the wire, try to figure outhow to connect a switch to the door of your house,so that the alarm sounds when a burglar opens thedoor.

Start by sliding the switch to position B andassembling the circuit. When you finish the wiring,connect the terminals 13 and 14 to the long wire,and slide the switch to position A to turn on thepower. At this time, no sound comes from thespeaker.

To test the alarm, detach the wire from terminal 13.The speaker gives out a beep. This beep is thealarm that tells you a burglar is about the break intoyour house.

As you can see in the schematic, this burglar alarmuses the dual operational amplifier as an astablemultivibrator, as the electronic buzzer in the lastproject did. You can change its frequency by usingdifferent values for the 10kΩ resistor and the 0.1μFcapacitor. Note how the tone of the buzzer changeswhen you set the 10kΩ resistor to 47kΩ or switchthe 100kΩ and 220kΩ resistors with each other.

Notes:

EXPERIMENT #83: BURGLAR ALARM

Schematic

Wiring Sequence:

o 1-29o 2-30o 3-114o 5-14-83-70-110-121o 13-89-68109o 81-63-132o 67-90-92-113o 69-82-84-91o 119-124o 122-131o 13-14 (LONG WIRE)

-102-

The electronic buzzer we built in project 82 can onlymake a continuous beep, but we can make a similarcircuit that produces various siren sounds.

Now we’re going to make a siren that gives out asound with a variable pitch. When you move theswitch, this siren wails and then makes a continuoushigh-pitched noise.

Slide the switch to position B and assemble thecircuit. When you finish the wiring, turn the power onby sliding the switch to position A. You hear thespeaker give out a sudden, roaring siren sound. Thesound is low at first and becomes higher, thenchanges to a steady tone in about 3 to 4 seconds.When you press the key and release it, the capacitordischarges and starts the siren sound again.

Refer to the schematic. IC 1 works as a buffer and IC2 as an astable multivibrator. The pitch changeswhen the 100kΩ resistor increases the voltageapplied to the 10μF capacitor.

Notes:

EXPERIMENT #84: HAND OPERATED SWEEP OSCILLATOR

-103-

Wiring Sequence:

o 1-29o 2-30o 3-116o 5-84-70-106-114-137-121o 89-63-131o 64-88-92-115o 65-87-105o 66-82-83-91o 68-67-81o 90-69-113-138o 119-124o 122-132

Schematic

Here’s another siren that changes its pitch. Thesiren we built in our last project changes pitch fromlow to high, but this one changes its pitch from highto low and finally stops making any sound. When itstops, press the key and the siren sound will startagain.

Set the switch to position B and assemble thecircuit. When you complete the wiring, slide theswitch to position A to turn on the power. You hear ahigh-pitched siren sound that becomesprogressively lower. Press the key to start the soundagain.

Like the siren in our last project, this siren uses IC 1as a buffer and IC 2 as an astable multivibrator. Thecapacitor C and the resistor R change the pitch ofthe siren sound. The pitch changes slowly when youincrease the values of C and R, and it changesquickly when you decrease their values. Use the3.3μF capacitor for C and notice how the pitchchanges.

Notes:

EXPERIMENT #85: FALLING BOMB SOUND

Wiring Sequence:

o 1-29o 2-30o 3-116o 5-84-94-106-70-121o 63-113-131-138o 64-90-92-115o 65-105-89o 66-82-83-91o 68-67-81o 93-69-114-137o 119-124o 122-132

-104-

Schematic

The sirens we built in Projects 84 and 85 (“Hand-Operated Sweep Oscillator” and “Falling BombSound”, respectively) change pitch only in onedirection, but this one makes a low sound thatbecomes higher, and goes back to its original lowsound. The siren sounds only once when you pressthe key.

Assemble the circuit after setting the switch toposition B. Turn on the siren by sliding the switch toposition A. When you press the key, the siren startsover at the original low pitch. Do you hear the sirensound change pitch as you expected? IC 1 is anoscillator that produces current that forms atriangular wave, so when you press the key, itproduces a triangular wave output. Then the outputis sent to IC 2 which acts as an astable multivibrator.

In projects 84, 85, and 86, the astable multivibratorproduces the siren sound and the pitch changesaccording to the values of R and C. Find out how thepitch changes when you set C to 0.02μF and then to0.1μF.

Notes:

EXPERIMENT #86: EMERGENCY SIREN

-105-

Wiring Sequence:

o 1-29o 2-30o 3-116o 5-70-108-137-121o 80-63-132o 64-90-92-115o 65-89-107o 66-82-91o 81-67-118o 78-79-68-117o 69-119-124o 77-138o 122-131

Schematic

The sirens we built in Projects 84, 85, and 86 (Hand-Operated Sweep Oscillator”, “Falling Bomb Sound”,and “Emergency Siren”, respectively) change thepitch of their sounds smoothly between low andhigh, but this siren is a little different. It gives offalternating high and low sounds.

Slide the switch to position B and assemble thecircuit. After you finish the wiring and slide the switchto position A, the power turns on and the speakermakes the sound of a two-pitch siren.

This siren is made up of two astable multivibrators.IC 2 provides the normal beep sound that we heardin Project 82 (“Operational Amplifier Buzzer”), andIC 1 produces the signal that changes the pitch of itssound at regular intervals.

Let’s perform a small experiment now. Detach the22kΩ resistor, and you find that the siren gives outan intermittent beep instead of the two-pitch sound.Can you figure out why? Yes, IC 1 interrupts the sirensound produced by IC 2.

Notes:

EXPERIMENT #87: FIRST AID SIREN

-106-

Wiring Sequence:

o 1-29o 2-30o 3-116o 5-83-70-108-112-121o 85-63-131o 64-90-92-115o 65-107-89o 66-82-84-86-91o 81-94-88-67o 93-68-111o 69-80-87o 79-119-124o 122-132

Schematic

Here’s the operational amplifier version of theelectronic metronome from Project 9 (“ElectronicMetronome”). Slide the switch to position B, andconnect the wires carefully - this project is muchmore complicated than most of the others. Whenyou finish assembling the circuit, set the control tothe 12 o’clock position and slide the switch toposition A to turn on the power. You’ll hear a pipsound from the speaker at fixed intervals. Nowslowly rotate the control clockwise, and the beatscome faster.

Now take a look at the schematic. IC 1 and IC 2 areused as astable multivibrators, as in our last project.But you’ll notice that IC 1 uses diodes to generateshort pulses and the control is used to adjust thespeed of the pulses. The transistor turns on eachtime a pulse is generated, and produces a sound.

Notes:

EXPERIMENT #88: MUSICAL TEMPO GENERATOR

-107-

Wiring Sequence:

o 1-29o 2-30o 3-114o 5-47o 27-127o 28-77o 46-80-84o 79-70-108-116-48-121o 63-131o 89-91-113-64o 65-90-107o 86-92-66o 78-76-83-88-67o 68-115-125-128o 82-87-69o 75-126o 85-81-119-124o 122-132

Schematic

Now we’re going to make a winking LED circuitusing a dual operational amplifier. In this circuit, anLED continues to light and turn off slowly.

Slide the switch to position B and connect the wiresfor this circuit. When you finish assembling theproject, slide the switch to position A to turn on thepower. After a few seconds, you’ll see the LED startto blink. Watch carefully and you should be able tosee that its on and off periods are about equal.

The dual operational amplifier works as an astablemultivibrator of a low frequency. You can change theperiod of oscillation, that is, the LED blinking rate, byusing different values for R and C. See whathappens to the blinking rate when you change thevalue of R to 220kΩ.

One last thing - the dual operational amplifier has ahigh input impedance - resistance to input - so itloses very little input current. This means you canuse it to build accurate blinkers and timers withlonger intervals.

Notes:

EXPERIMENT #89: OPERATIONAL AMPLIFIER WINKING LED

Schematic

-108-

Wiring Sequence:

o 81-31-63-131o 33-67-90-94o 93-68-113o 69-82-84-89o 83-70-114-121o 119-124o 122-132

The winking LED in the last project stays on and offfor about the same amount of time, but we can makeit flash on for a very short time.

Start out by sliding the switch to position B andwiring the circuit. This LED flasher uses two diodes.As you build this project, be sure to connect thesediodes in the correct direction.

When you finish assembling the project, turn on thepower by sliding the switch to position A, and lightlytap the key. The LED starts blinking immediately.Even if you don’t press the key, this LED flasherstarts flashing shortly after you turn on the power; ifyou press the key, it begins blinking immediately.

Just like the LED winker in the last project, this LEDflasher uses a dual operational amplifier as anastable multivibrator, but its flashing time is muchshorter because of the two diodes.

Notes:

EXPERIMENT #90: LED FLASHING LIGHT

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Schematic

Wiring Sequence:

o 81-31-63-131-138o 33-67-88-90-76o 68-115-137-128-125o 69-87-82-84o 83-70-116-121o 75-127o 89-126o 119-124o 122-132

The LED circuits in Projects 89 and 90 (“OperationalAmplifier Winking LED” and “LED Flashing Light”,respectively) each use one LED, but the circuit inthis project uses two LEDs that take turns lighting.Slide the switch to position B and assemble thecircuit. Then, turn the power on by sliding the switchto position A and wait for a few seconds. The LEDslight and turn off alternately.

The dual operational amplifier works as an astablemultivibrator as in previous projects. When theoutput is high, LED 1 lights; when it is low, LED 2lights.

You can change the speed of the winking by usingdifferent values for R and C. See how the speed ofthe pulses change when you change the value of Rto 220kΩ.

Notes:

EXPERIMENT #91: TWO LED WINKER

Schematic

-110-

Wiring Sequence:

o 31-36-67-90-94o 33-70-135o 34-63-132o 93-68-113o 81-89-69o 82-114-124-119o 121-134o 122-131

We’ve built many circuits using the dual operationalamplifier, but there are many other ways to use thishandy IC. The one shot multivibrator is one of them.With this multivibrator, we can make the LED stay onfor a preset amount of time when the key is pressed- a one shot light.

Slide the switch to position B and build the circuit.Turn on the power by sliding the switch to position A.The LED lights, but quickly turns off. Now, press thekey and see what happens. The LED lights and stayson for 2 to 3 seconds and then turns off.

You can change the amount of time the LED is on byusing different values for C. Change the value of Cfrom 10μF to 100μF and see what happens to theLED. It stays on much longer.

Notes:

EXPERIMENT #92: ONE SHOT LIGHT

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Schematic

Wiring Sequence:

o 31-63-94-131-138o 33-67-114o 85-68-110o 69-82-89-93o 70-134o 81-86-130-124-119o 90-115o 109-137-129o 113-116o 121-135o 122-132

The digital LED display can’t display all 26 letters ofthe alphabet, but it’s possible to display many ofthem. Let’s make an LED display that alternatelyshows the initials E and P of our ELECTRONICPLAYGROUND. You can display other initials too.You can thrill your sweetheart by displaying his/herinitials!

Slide the switch to position B and build the circuit.When you complete the wiring, slide the switch toposition A to turn on the power, and you’ll see theletters E and P lighting alternately on the LEDdisplay.

IC 1 works as an astable multivibrator and displaysthe letter E. IC 2 is used as an inverter, with anoutput that is opposite to that of IC 1; it displays theletter P.

Now that you’ve successfully displayed the letters Eand P, why not try displaying other letters? It shouldbe a cinch if you take a close look at the schematic.

Notes:

EXPERIMENT #93: LED INITIALS

Schematic

-112-

Wiring Sequence:

o 22-17-18-19-63-131-81o 20-65-67-90-94o 21-64o 83-114-70-25-121o 66-69-82-84-89o 93-68-113o 119-124o 122-132

Are you a late sleeper? Even if you are, don’t worry!Because you can make this alarm siren that wakesyou up gradually as the day dawns.

First, set the switch to position B and complete thewiring. Then, set the switch to A to turn on the power.Can you hear the siren sound coming from thespeaker?

The siren sounds when you expose the CdS cell tolight. When you cast a shadow over the CdS, thesiren sound stops.

Like the electronic buzzer in Project 82 (“OperationalAmplifier Buzzer”), the alarm siren uses amultivibrator, and controls its operation with the CdS.

Turn on the power for this project when you go to bedat night, and sleep with your room dark. Then, thealarm siren will wake you up the next morning.

Notes:

EXPERIMENT #94: WAKE UP SIREN

-113-

Schematic

Wiring Sequence:

o 1-29o 2-30o 3-116o 5-83-108-70-121o 15-63-132o 16-81o 67-90-92-115o 91-68-107o 69-82-84-89o 119-124o 122-131

You can use a microphone to detect sound. Here wewill make a circuit that lights the LED when themicrophone detects sound, using the speaker as amicrophone.

Slide the switch to position B and assemble thecircuit. When you finish the wiring, turn on the powerby sliding the switch to position A. Then speak intothe microphone - the speaker - or give it a light tap.The LED flashes in response.

Look at the schematic. IC 1 acts as a microphoneamplifier - a non-inverting amplifier with a gain ofabout 100. IC 2 works as a comparator. Its positive(+) input terminal receives a reference voltage fromthe battery. The output of the microphone amplifiergoes to the comparator’s negative (–) input terminal.When this input voltage is higher than the referencevoltage, the comparator’s output level becomes lowand the LED lights.

Notes:

EXPERIMENT #95: VOICE ACTIVATED LED

Schematic

-114-

Wiring Sequence:

o 1-29o 2-30o 3-110o 5-76-74-80-70-121o 85-31-63-132o 33-64o 79-65-112o 73-86-66o 90-67-111o 89-68-115o 69-109o 75-116o 119-124o 122-131

You know that digital circuits produce high or low (Hor L) outputs (1 or 0). Now we’re going to make alogic tester that shows 1 for high level (H) and 0 forlow level (L) on the LED display.

Slide the switch to position B and assemble thecircuit. When you finish the wiring, turn on the powerby sliding the switch to position A. The number 0 ison the display because the test terminal (terminal13) is at low level when no input is applied. Connectthe test terminal to terminal 122 to apply +4.5V. Thedisplay changes to 1.

Look at the schematic. The dual operational amplifierworks as a comparator. A reference voltage of about3V is applied to its negative (–) input terminal. Whenthe input applied to its positive (+) terminal is higherthan this reference voltage, the comparator’s outputlevel becomes high, turning off the transistor Q1.Segments A, E, F, and D of the display turn off,leaving 1 on the display.

Notes:

EXPERIMENT #96: LOGIC TESTER

-115-

Wiring Sequence:

o 17-18-19-20-44o 86-79-63-21-23-45-132o 43-80-82o 67-81o 68-83-85o 119-124o 122-131o 69-89-13-CHECK POINTo 121-25-70-90-84-14-CHECK POINT

Schematic

-116-

IX. MORE ADVENTURES WITHOPERATIONAL AMPLIFIERS

The circuit in this project allows you to hearalternating current. You probably know that theelectric power running through your home is analternating current. All your appliances that receivepower from electric outlets operate on AC -including lamps. Lamps actually flicker at the rate of60 times per second, but it looks constant becauseour eyes see after images. In this project you willhear sound converted from light.

Ready to start? After building this circuit, turn on thepower to your kit by setting the switch to A. Place theCdS cell near an electric lamp. Can you hear ahissing sound coming from the earphone? This isthe sound of the alternating current. Now place theCdS cell under a fluorescent lamp, and listen for asimilar sound.

This circuit greatly amplifies the signals of light onthe CdS cell through the operational amplifier.Adjust the quantity of light on the CdS cell with yourhand. You can probably hear the volume of thehissing sound reduce and the quality of the soundimprove. See what happens when you expose theCdS to sunlight.

Notes:

EXPERIMENT #97: ALTERNATING CURRENT SOUND

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Schematic

Wiring Sequence:

o 15-88-113o 87-63-131o 76-93-68o 70-121o 69-90o 75-99-114o 122-132o 67-94-81-13-EARPHONEo 124-119-16-100-89-82-14-EARPHONE

This circuit changes the intervals between eachsound according to the amount of light falling on theCdS cell. The sound changes continuously as youadjust the light intensity.

Set the switch to position A to turn on the powerafter you complete the wiring. The speakerimmediately makes a sound. Move your hand overthe CdS to change the sound.

You can calculate the approximate value of thefrequency of the signal by using the equation 1/2 xC1 x R1. However, R1, in this project, is the CdSand is not constant. You can change the value of theoutput frequency by changing C1. In thisexperiment, the speaker is equipped with a buffer sothat the light control sound circuit is not affectedwhen the speaker emits sounds.

Notes:

EXPERIMENT #98: LIGHT CONTROL SOUND CIRCUIT

-118-

Wiring Sequence:

o 1-29o 2-30o 3-64-65o 5-86-110-119-124o 15-68-109o 16-66-67-88o 63-131o 69-87-85o 70-134o 121-135o 122-132

Schematic

This alarm gives out an alarm light and sound whenit detects your voice or any other sound. Theearphone acts as a microphone. Sounds picked upby the microphone are amplified by IC 1. Diodes Daand Db rectify the amplified signal - that is, theyconvert the sound signal from AC to DC. The signaltravels through IC 2, the comparator, and activatesthe LED and the speaker.

When you finish building the circuit, rotate thecontrol fully counter-clockwise, and set the switch toposition A. Then, rotate the control clockwise whilespeaking into the microphone, and set the control ina position where the LED light only when you speakinto the microphone. Stop speaking and you will seethe LED turn off.

Now, see what happens when you disconnect thewire between 57 and 62, and reconnect it between57 and 32. When you blow into the microphone(earphone), the LED and the speaker sounds.

Notes:

EXPERIMENT #99: SOUND ALARM CIRCUIT

-119-

Wiring Sequence:

o 75-63-28-131o 29-76o 30-47o 31-64o 46-86o 56-77-110o 58-59-60-79-78o 85-80-61-109o 66-83o 67-90-73o 68-89-71o 87-69-113o 74-111o 84-91-115-127o 112-129-128o 49-50-51-53-54-135o 114-13-EARPHONEo 122-132o 27-65o 57-26-121-130-48-116-70-92-88-62-33-72-14-EARPHONEo 119-124-134

Schematic

Here’s a timer you can use for taking timed tests orsimply for knowing when an amount of time haspassed. You can preset this timer for as much timeas you like, up to about 15 minutes. When the timeis up, it gives out a continuous buzzer sound untilyou turn off the power or press the key to reset thecircuit.

After you build this project, set the control to position2 on the dial and slide the switch to position A toturn on the power. Hold a stop-watch and start itwhen you press the key. The timer makes a buzzingsound in about 30 seconds or more.

Now set the control to each division on the dial from2 to 8, and note how long it takes the timer toproduce a sound. Setting the timer’s calibration - thetime that passes at each setting of the dial - requiresa lot of patience, but it is necessary for making sureyour timer works accurately. After you set thecalibration, make a graph showing each controlposition and the time it takes for the buzzer tosound. Now, your tester is ready for use.

Look at the schematic. The control changes thereference voltage of the comparator (IC 1). Thetimer setting is determined by the resistor R and thecapacitor C. When the voltage applied to thepositive (+) terminal of IC 1 exceeds the referencevoltage, the alarm sounds.

Since the dual operational amplifier has a high inputimpedance (input resistance), its current loss is verysmall, so you can use it to make a timer with a verylong setting. IC 2 works as an astable multivibratorthat produces the buzzer sound.

Notes:

EXPERIMENT #100: STUDY TIMER

-120-

Wiring Sequence:

o 1-29o 2-30o 3-114o 5-83-70-106-118-137-26-121o 93-63-28-132o 92-90-64-113o 65-105-91o 66-82-84-89o 67-81o 94-69-117-138o 119-124o 122-131o 27-68

Schematic

Wouldn’t you like to make a kitchen timer that youcan use for cooking meals? This timer is the sameas the test timer in the last project, except for onepoint. It gives out a buzzer sound for 1 to 2 secondsand automatically stops.

Slide the switch to position B and build the circuit.When you finish assembling the project, turn on thepower by sliding the switch to position A. Set thecontrol to position 2 on the dial, and press the key tostart the timer. After about 40 seconds, the timersounds for 1 to 2 seconds and stops. Use the graphyou made in project 100 to preset this timer.

Look at the schematic. When the preset time is up,the comparator (IC 2) sends out an output. After atime lag of 1 to 2 seconds produced by R and C, thetransistor Q1 turns on to stop the multivibrator. Thesilicon diode discharges C and restores the circuit tothe original state when the timer is restarted.

Notes:

EXPERIMENT #101: KITCHEN TIMER

-121-

Wiring Sequence:

o 1-29o 2-30o 3-114o 5-83-70-104-116-118-137-48-26-121o 27-68o 93-63-28-131o 46-85o 91-103-65-47o 92-88-64-113o 81-84-87-66o 67-82-89o 69-94-117-138-129o 86-90-115-130o 119-124o 122-132

Schematic

Who says the operational amplifier can’t be used tomake a digital circuit? Here, we use one to make anAND gate. The LED display is the output device. If itdisplays nothing, at least one of the output signals islogical 0 or low; if it displays H, they are all logical 1or high.

When you complete the wiring, turn on the power bysetting the switch to position A. The LED remainsdark. Terminals 125, 127, and 129 are the inputterminals. These terminals are connected to thenegative (–) terminal, so they do not cause the LEDto light. Terminal 14 is connected to the positive (+)terminal, so it is the logic 1 terminal. When youconnect terminals 125, 127, and 129 to terminal 14in various combinations, you see that the LED lightsand shows H only when terminals 125, 127, and129 are all connected to terminal 14 - logic 1.

Notes:

EXPERIMENT #102: THREE-INPUT “AND” GATE USING OPERATIONAL AMPLIFIER

-122-

Wiring Sequence:

o 14-85-81-63-19-18-21-22-23-132o 25-47o 46-88o 78-76-83-80-70-48-121o 67-87o 68-82-84o 86-69-126-128-130o 129-75-WIREo 127-77-WIREo 125-79-WIREo 119-124o 122-131

Schematic

In this project, we will make a voice input level meter.The brightness of the LED in this circuit changesaccording to the level of voice input that comes fromthe microphone (the earphone). Since voice levelschange very quickly, the brightness of the LEDshould also change very quickly. In order to show thehighest voice input levels, we use a circuit called apeak-level hold circuit. This allows the LED to hold acertain brightness after it reaches peak strength,rather than turning off immediately.

Set the switch to position A after completing thewiring. You will use the earphone as a microphone.Speak loudly or blow strongly into the earphone. Youcan see the LED get brighter temporarily and thengradually grow dimmer.

Look at the schematic. You can see that the signalfrom the earphone travels through the PNPtransistor and then becomes the positive (+) input forthe first operational amplifier. The output of thisoperational amplifier is stored at the 100μFcapacitor. The voltage of the capacitor lowers as itslowly discharges through the 47kΩ resistor. As thevoltage decreases, the LED grows dim. At the sametime, the voltage that lights the LED flows to thenegative (–) input of the first operational amplifier.The first operational amplifier compares this voltagewith the input signal from the earphone; when theinput signal is larger, it charges the 100μF capacitor,when the input signal is smaller, no output isproduced.

You can change the brightness of the LED bychanging resistor RA (47kΩ) or the capacitor CA(100μF).

Notes:

EXPERIMENT #103: VOICE LEVEL METER

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Wiring Sequence:

o 112-13-EARPHONEo 119-124-116-33-88-90-80-72-14-EARPHONEo 31-65-64-82o 32-71o 93-111-40o 79-94-113-41o 63-42-131o 87-66-127-115o 67-129-128o 81-68-130o 89-69-114o 70-134o 121-135o 122-132

Schematic

Do you know what a reset circuit does? It activatesother circuits and detects any power fluctuations inorder to prevent malfunctions. In this project, wechange the supply voltage to the circuit with theswitch. The power to the display portion of the circuitis on, or logic high, when the switch is set to positionA; it is off when the switch is at position B. The LEDdisplay shows 1 when the circuit has been reset.

Let’s start experimenting. First, complete the wiringand set the switch to position B. Now, with the switchset to B, the power reset circuit operates under 6V,and the three LEDs light dimly. The LED display isoff, meaning that the display circuit is not activated.

Now, set the switch to position A. You can see thethree LEDs light brightly because the supply voltagehas been changed to 9V. For a moment, the LEDdisplay still shows no change, indicating that thecircuit is being reset. After a short interval, the LEDdisplays 1 to show that the circuit has finishedresetting and now it is stabilized.

Set the switch to position B to switch the power backto 6V. You will see the 1 on the LED disappear,because now the display circuit is off.

Look at the schematic as you read the following. Theoperational amplifier acts as a comparator. Thenegative (–) terminal receives the reference voltageof about 5.4V. When the switch is at position B, thepositive (+) terminal receives about 4.1V, so thecomparator does not allow the display to light. When

you use position A to switch to the 9V supply, the100μF capacitor causes the comparator’s positive(+) terminal voltage to gradually increase to about6V. When this voltage exceeds the reference voltageof 5.4V, the LED display lights 1.When you set the switch to B, the voltage at theamplifier’s positive (+) terminal discharges throughthe diode, so the voltage is reduced immediately to4.1V.

Although this circuit seems very simple (consistingof only one operational amplifier), it is very complexand important for later use.

Notes:

EXPERIMENT #104: POWER-ON RESET CIRCUIT

-124-

Wiring Sequence:

o 21-23-67-116o 85-70-38-25-121o 31-68-74o 32-34o 35-37o 73-81-63-129-132o 86-82-69-115-130o 119-124o 122-131o 123-133

Schematic

This circuit is a delayed timer that uses anoperational amplifier and the CR time constant. Youremember that CR stands for capacitor/resistor. Atime constant is a circuit that delays an operation.

The negative (–) terminal of the operationalamplifier receives a voltage of about 4.5V throughresistors RA and RB. This is the comparator’sreference voltage. The positive (+) terminal of thecomparator is connected to capacitor C1. Thiscapacitor receives its charge through the seriesresistance of R2 and the control. The chargingspeed is slower when the resistance is large, andfaster when the resistance is small. This chargingspeed set the delay time for the timer circuit.

Now turn the control fully clockwise to position 10.Set the switch to position A to turn on the power.LED 1 lights first; LED 2 lights about 5 to 7 secondslater. This 5 to 7 second time difference is the delaytime that is set by the CR time constant.

Now, turn off the power, set the control fully counter-clockwise to position 1, and see what happenswhen you turn on the power again. LED 2 lights laterthan LED 1 again, but how many seconds later?

Notes:

EXPERIMENT #105: DELAYED TIMER

-125-

Schematic

Wiring Sequence:

o 81-31-63-27-131o 28-87o 83-33-36-70-116-135-121o 34-67o 68-82-84o 88-69-115-136o 119-124o 122-132

This is a pulse frequency multiplier with onetransistor. It is called a pulse frequency doublerbecause it doubles the frequency of the input signal.

The operational amplifier IC 728 acts as a square-wave oscillator. The output from the oscillator is anAC signal of about 500Hz.

When you complete the wiring, set the switch toposition A to turn on the power. Connect theearphone to terminals 93 and 134 and press the keyto listen to the oscillating sound of 500Hz. Note thepitch of the tone.

Now, connect the earphone to terminals 13 and 14and press the key. Listen through the earphone; thistime you hear a sound that is an octave higher thanthe previous sound. This means the frequency isdoubled to 1,000Hz.

Now let’s see how this frequency doubler works.Transistor Q1 receives signals from the operationalamplifier through its transistor base. The basevoltage changes with the oscillations. This results inthe opposite phase signals appearing at thecollector and emitter - when one signal is at a wavepeak, the other is at the bottom. The two outputsfrom transistor Q1 are applied to diodes Da and Db.The diodes pass through only the positive portion ofthe waves. These two signals combine to give us thedoubled frequency.

Notes:

EXPERIMENT #106: PULSE FREQUENCY DOUBLER

-126-

Wiring Sequence:

o 125-127-91-13-EARPHONEo 134-110-92-80-83-76-14-EARPHONEo 32-63-87-131o 33-47-107o 35-48-105o 89-36-70-121o 88-90-103-46o 81-86-67-137o 85-68-109o 69-82-84o 75-77o 78-106-128o 79-108-126o 94-104-138o 119-124-135o 122-132

Schematic

White noise is a noise that has a wide frequencyrange. The shower-like noise you hear when youtune your FM radio to an area with no station is onekind of white noise. It is a useless noise normally,but when you play electronic musical instruments,you can use white noise as a sound source.

When you finish building this circuit, set the switchto position A to turn on the power. Look at theschematic. We will use the noise that is generatedwhen you apply a reverse voltage to the base andthe emitter of transistor Q1.

IC 1 acts as an oscillator. The output of this oscillatoris rectified (remember this term from Project 99(“Sound Alarm Circuit”) by diodes D1 and D2 andflows to Q1. IC 2 amplifies the noise so that you canhear it through the earphone.

Notes:

EXPERIMENT #107: WHITE NOISE GENERATOR

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Wiring Sequence:

o 64-90-13-EARPHONEo 121-114-112-46-47-70-96-84-85-14-EARPHONEo 93-48-101o 94-111-127o 82-88-63-132-126o 76-89-65o 113-66-81-83o 77-91-67-110o 68-95-92o 69-80-87-86o 78-79o 109-128-125o 119-124o 122-131o 102-75

Schematic

Here’s a DC-DC converter circuit; it can gain 5VDCfrom 3VDC. Build the project, set the switch toposition A, and see how this circuit works.

Look at the schematic. IC 1 acts as an oscillator. Theoutput of IC 1 turns on transistor Q1. Self-inductionof the transformer coil instantly generates a highvoltage current. Diode D1 rectifies this voltage andpasses on a high DC voltage current. IC 2 is acomparator that examines the voltage increase.When the input voltage to IC 2 is more than 5V, theLED lights.

By the way, did you try rotating the control? Howdoes it affect the circuit? In this circuit the control isused as a fixed resistor of 50kΩ. Rotating the controlhas no effect. (Sorry if we had you worried).

Notes:

EXPERIMENT #108 DC-DC CONVERTER WITH OPERATIONAL AMPLIFIER

-128-

Wiring Sequence:

o 3-134o 5-47-130o 26-67-72-81o 28-69-90-92-94o 31-64o 33-76-83-86-93-91-70-106-116-48-120o 46-71-75o 89-88-63-131o 84-87-65o 85-66-115-129o 82-68-105o 119-124-135o 122-132

Schematic

-129-

X. COMMUNICATION CIRCUITS

-130-

Would you like to become an amateur radio ham?Many radio operators started out using an oscillatorwith a tone control like this one. The tone control inthis project can be very helpful because listening tothe same tone for a long time can be very tiring.Simply connect the wires for this circuit and yourcode practice oscillator is ready for use.

You can use the different tones to make up your ownspecial code, in addition to the Morse Code - thecode system with dots and dashes invented bySamuel Morse. The best way to learn the MorseCode is to find someone else who is interested inlearning the code. Set up a schedule and practiceeveryday. Make a progress chart so you can seeyour improvement. Take turns sending andreceiving, and it won’t be long until the codebecomes almost like a spoken language. Operatingthe key becomes automatic, like riding a bike ordriving a car. It takes hard work to get to this point,but you’ll be proud when you do.

If you want to practice privately, you can use theearphone. Simply disconnect the speaker andconnect the earphone to terminals 27 and 28. Withthese connections, the control acts as a volumecontrol as well as a tone control. You can replace thecontrol with a fixed resistance if you want a fixedtone and volume.

When you adjust the control for less resistance inthe circuit, more electricity flows to the 0.05μFcapacitor, so it charges faster between pulses. Thepulses are closer together, making the frequency(and the tone) higher. The opposite situation occurswhen the control is adjusted for more resistance.

After you master Morse Code, the next step is tocontact your nearest store and see what studymaterials are available for the written part of theFCC (Federal Communications Commission) exam.Good luck!

Notes:

EXPERIMENT #109: CODE PRACTICE OSCILLATOR WITH TONE CONTROL

Wiring Sequence:

o 1-29o 2-30o 3-87-105-109o 4-124o 5-41-110o 85-106-40-27o 28-88o 86-42-137o 119-138o 121-122

Schematic

-131-

No project kit is complete without a crystal radiocircuit. Most people in electronics have experimentedwith this oldest of all radio circuits. Before the days ofvacuum tubes or transistors, people used crystalcircuit sets to pick up radio signals.

The signals from a crystal radio are weak, so youmust use an earphone to pick up the sounds. Yourearphone will reproduce these sounds well becauseit is a ceramic type and requires very little current foroperation.

A good antenna and earth ground connection arenecessary for receiving distant stations, but you canhear local stations using almost anything as anantenna. A long piece of wire (like the green wire inyour kit) makes an adequate antenna in most cases.Earth ground means just that; you connect the wire tothe ground. One easy way to do this is to connect awire to a metal cold water pipe. If you can’t do that,you can drive a metal stake into the ground andconnect the wire to the stake.

Build the circuit according to the wiring sequence touse your crystal diode radio. Two antennaconnections are provided on the radio circuit in yourkit, but don’t use them both at the same time. Tryeach connection and use the one that results in thebest reception. Short antennas, 50 feet or less, workbest on terminal 95. Longer antennas work best onterminal 97.

The part of the radio circuit that includes the antennacoil and the tuning capacitor is called the tank circuit.When a coil and the tuning capacitor are connectedin parallel, the circuit resonates only at onefrequency. So the circuit picks up only the frequencythat causes the tank circuit to resonate. The tuningcapacitor changes its capacitance as you rotate it.When the capacitance changes, the resonatingfrequency for the circuit changes. Thus, you can tunein various stations by rotating the tuning capacitor.Without this selectivity, you might hear severalstations mixed together (or only a lot of noise).

The signals received by the tank circuit are high-frequency RF (radio frequency) signals. At abroadcast station, sound signals are used to controlthe amplitude (strength) of the RF signals - that is,the height of the RF wave varies as the sound varies.The diode and the 0.001μF capacitor in this circuitdetect the changes in the RF amplitude and convertit back to audio signals. This converting of amplitudemodulation into audio signals is called detection ordemodulation.

Notes:

EXPERIMENT #110: CRYSTAL SET RADIO (SIMPLE-DIODE RADIO)

Schematic

Wiring Sequence:

o 6-12-96o 7-98-126o 8-11-90-100-EARPHONEo 89-99-125-EARPHONEo 95-ANT or (97-ANT)

This is a two-transistor receiver with enough gain(amplification) to allow you to hear the signalthrough the speaker. Simple radios like this onerequire a good antenna and ground system.Connect the circuit and use terminal 74 as theground terminal. Connect the antenna to terminal 95or 97. Use the one that provides the best results.

The radio’s detector circuit uses a diode and a 22kΩresistor. Try to use the radio without the 22kΩresistor. Simply disconnect the wire from terminal85. The results are ________ (worse / improved) forweak stations and ________ (worse / improved) forstrong stations.

The basic rules of radio reception are the same asin Project 110 (“Crystal Set Radio (Simple-DiodeRadio)”). The tuning capacitor selects the radiostation frequency. The diode and 0.02μF capacitorrectify (detect) the audio signal, changing it from ACto DC. This signal is so weak that we must amplify itto be able to hear it through the speaker. TransistorQ1 amplifies the signal first, then the control adjuststhe volume, and finally Q2 amplifies the signalagain. Finally, the speaker produces the amplifiedsounds.

Notes:

EXPERIMENT #111: TWO-TRANSISTOR RADIO

-132-

Wiring Sequence:

o 1-29o 2-30o 3-44o 5-72-131o 6-12-96o 7-98-126o 8-11-74-86-88-104-115-117-42-119o 71-82-116-26o 27-113o 28-43-87o 40-112-91o 81-92-114-41o 45-118-73o 85-103-111-125o 121-122o 124-132o 95-ANT (or 97-ANT)

Schematic

This project is a simple but effective code transmitterlike the kind used by military and amateur radiooperators around the world. When you press andrelease the key, the transmitter turns on and off insequence.

You can use a common AM radio to receive the codesent out by this transmitter. Tune the radio to a weakstation. The transmitter signal mixes with the station’ssignal to produce an audio tone called a beat note.This beat note is what you hear as the code signal.Use the tuning capacitor to tune this transmitter untilyou can hear the beat note in the receiver when youpress the key.

You can receive the carrier wave (CW) signal of thistransmitter on a communications receiver, withouttuning to another station, if the communicationsreceiver has a beat frequency oscillator (BFO). TheBFO beats with your transmitter’s CW signal andproduces the tone.

This oscillator sends out an RF signal because thefrequency is very high (500,000Hz to 1,600,000Hz).When you tune to a weak AM station first and thensend a signal slightly off from the station frequency,you can hear the beat note that you produced.

Transmission and reception of CW signals is veryefficient. In fact, it is the most reliable type oftransmission for some emergencies. You might findthat you do not need an antenna, but if you do, 1, 2,or 3 feet (about 60-90 cm) of wire will probably beenough. Have fun!

Notes:

EXPERIMENT #112: WIRELESS CODE TRANSMITTER

-133-

Schematic

Wiring Sequence:

o 41-6-11-ANTo 7-89-110-137o 8-12-100o 40-90-99o 42-79o 80-109-119o 121-122o 124-138

If you ever wanted to be a disc jockey, this is yourchance. This AM radio station lets you actually sendyour voice through the air. You built an AM radiotransmitter in the last project, but it could send onlya single tone or a series of dots and dashes.

When you finish the wiring, turn on your AM radioreceiver and tune it to a weak station or silentsetting on the dial. Now, begin to talk into thespeaker while adjusting the tuning capacitor, untilyou hear your voice on the air. This transmitter canonly send signals a few feet, so place your AM radioclose to the kit.

Transistor Q1 amplifies the audio frequency signal.The amplified signal controls the amplitude of theRF oscillator signal. The tuning capacitor andantenna coil tune the RF signal to the setting onyour AM radio dial and send it through the antenna.

Transistor Q2 helps control the amplitude of the RFsignal. The NPN transistor is a part of the RFoscillator and provides the primary amplification ofthe RF signal (before the AF (audio frequency)signal modulates it).

Notes:

EXPERIMENT #113: AM RADIO STATION

-134-

Wiring Sequence:

o 1-29o 2-30o 3-111o 5-7-90-42-119o 6-12-47-ANTo 8-11-99o 40-112-94o 41-43-93-78o 77-44-131o 45-79o 89-100-46o 48-80o 121-122o 124-132

Schematic

Germanium diode radios generally do not performwell, but they can be important for emergencycommunication because they need no power source.

Usually, you can listen to a germanium radio onlythrough an earphone, but we have added anoperational amplifier to this project so that you canhear it through the speaker. We are going to make anIC radio using the dual operational amplifier as a two-power source, non-inverting amplifier. This is thesimplest way to use this IC.

Slide the switch to position B and assemble theproject. When you complete the circuit, put up theantenna, connect it to the circuit, set the control tothe 12 o’clock position, and slide the switch toposition A to turn on the power. Turn the tuningcapacitor until you hear a station. To pick up weakerstations, try using the earphone in place of thespeaker in connections to terminals 1 and 2.

Notes:

EXPERIMENT #114: OPERATIONAL AMPLIFIER RADIO

-135-

Wiring Sequence:

o 1-29o 2-30o 3-67-90o 5-8-11-76-92-26-119-124o 6-126o 7-12-ANTo 27-69o 28-109o 63-135o 68-89-75o 70-132o 91-110-125o 121-131o 122-134

Schematic

-136-

XI. TESTING AND MEASURING CIRCUITS

This circuit emits a sound if the material you arechecking conducts electricity. This is convenientwhen you are looking at wires, terminals, or otherthings and cannot look at a signal lamp or LED. Yourears detect the results of the test while your eyes arebusy.

If the circuit that you are testing conducts electricity,it will complete a voltage supply connection to astandard pulse-type oscillator that uses a sensitivePNP transistor. This tester can check almost anycomponent on the board. When testing the diodesand transistors, remember that electricity only flowsin one direction through them (unless they have beendamaged).

If you look at the schematic, you will see that theoutput from the transistor goes through thetransformer to the 0.02μF capacitor and then to thebase of the transistor. The emitter of the transistor isconnected to the TEST terminal. When somethingthat allows electricity to flow is connected to theterminal, the transistor starts to oscillate.

You can safely check almost any component with thiscontinuity checker because it carries a very lowcurrent of about 15mA or less. You may want to trymeasuring the continuity of pencil lines on paper,water, metallic surfaces, and many other things.

Notes:

EXPERIMENT #115: AURAL CONTINUITY TESTER

-137-

Schematic

Wiring Sequence:

o 1-29o 2-30o 3-103-109o 4-87-120o 5-110-41o 88-104-40o 42-116-PROBESo 115-131-PROBESo 119-132

You can find the exact value of a resistance if youuse a meter; but when you only want to knowapproximate resistance values, you can use thisconductivity tester.

This circuit converts resistance to electric currentand compares it with the comparator’s referencecurrent to tell you the approximate range ofresistance. The comparator has a reference voltageof about 0.82V.

To use this project, build the circuit and set theswitch to position A to turn on the power. Connectthe material to be tested between terminals 13 and14. If the LED lights, the resistance is less than100kΩ. If the LED does not light, the resistance isgreater than 100kΩ.

If the LED lights, connect terminals 93 and 86, andsee if the LED stays on or turns off. If it turns off, theresistance is in the range of 10Ω to 100kΩ. If it stayson, remove the wire from terminal 86 and connect itto terminal 84. If the LED turns off, the resistance isin the range of 1 to 10kΩ. If the LED still doesn’t turnoff, remove the wire from terminal 84 and connect itto terminal 76. Does the LED turn off? If it does, itmeans that the resistance is in the range of 100Ω to1kΩ. If it stays on, the resistance is less than 100Ω.

Notes:

EXPERIMENT #116: CONDUCTIVITY TESTER

Schematic

-138-

Wiring Sequence:

o 13-93-69-WIREo 14-79-70-121o 75-83-94-90-88-31-63-131o 33-67o 68-80-87o 85-89o 119-124o 122-132

You will probably test transistors more than any othercomponent. You can’t tell if a transistor is working ornot by looking at it, but this project lets you hearwhether or not it is. You can also tell if a transistor isa PNP or an NPN with this circuit.

You’ll notice that this project has three long wires -one for the emitter, one for the collector and one forthe base. The schematic shows the terminals markedfor checking PNP transistors.

To use this project, connect the long wires to thebase, collector, and emitter of the transistor you wantto test. Turn the control fully counter-clockwise. Then,press the key and turn the control clockwise. If youhear a sound from the speaker, the transistor is aworking PNP transistor. If you hear no sound at all,change connections 4-124 and 119-138 to 4-119 and124-138, and repeat the test. If you get a sound fromthe speaker this time, the transistor is a working NPNtype. If you get no sound from the speaker usingeither set of connections, the transistor is defective.

As you start to accumulate parts for other electroniccircuits, you’ll find this a handy circuit for testingunmarked transistors.

Notes:

EXPERIMENT #117: TRANSISTOR CHECKER

-139-

Schematic

Wiring Sequence:

o 1-29o 2-30o 3-105-COLLECTORo 4-124o 5-94-106-110o 26-72-137o 27-71o 28-EMITTERo 93-109-BASEo 119-138o 121-122

Now, you will learn about generating sinewavesignals. We can define a sinewave as a wave of puresingle-frequency tone. For example, a 400Hzsinewave is a wave that oscillates 400 cycles in onesecond and contains no other frequencycomponents. Non-sinewaves have harmonics -waves with frequencies that are multiples of thesingle-frequency fundamental wave. A non-sine400Hz wave can include the 400Hz wave (itsfundamental wave) along with an 800Hz wave (its2nd harmonic wave) and a 1200Hz wave (its thirdharmonic wave).

An experienced technician can test a circuit byusing a sinewave and listening to its output. Soon,you will be able to do this too. If you put in asinewave, and something else comes out, theundesired harmonic frequencies must have beengenerated somewhere in the circuit.

The part of this project that generates a 400Hzsinewave has:

• A 0.1μF capacitor connecting terminals 3 and5 of the transformer to form a tank circuit thatresonates at about 600Hz.

• A 470kΩ resistor to turn on the base of thetransistor only a small amount.

• An adjustable feedback circuit that includesthe control and the 0.05μF capacitor.

• A 100Ω resistor connected to the emitter tohelp stabilize the circuit and keep the soundfrom being distorted.

Connect the earphone to terminals 1 and 2 of thetransformer. Start with the control on maximum - 10on the dial - and slowly decrease the control settingwhile listening to the tone quality of the output.Before the oscillations stop, you will reach a pointwhere you hear only one tone. This last clear-sounding tone is the sinewave. Repeat these controladjustments until you have no trouble distinguishingbetween a sinewave and a distorted wave.

Notes:

EXPERIMENT #118: SINEWAVE AUDIO OSCILLATOR

Schematic

-140-

Wiring Sequence:

o 1-EARPHONEo 2-EARPHONEo 3-28-109o 4-94-106-124o 5-41-110o 26-40-93o 27-105o 42-71o 72-119o 121-122

In this project, you will build and study a low-distortion sinewave oscillator. Build this project afteryou have built and studied the previous projectbecause this one has no transformer; transformersare likely to cause distortion because of their non-linear characteristics.

As in the previous project, you should listen to thetone of this oscillator and adjust the control for theclearest-sounding single tone (the one with the leastdistortion). Again, start with the control nearmaximum. The frequency of operation is about300Hz, at the minimum distortion setting of thecontrol.

This circuit is called an RC phase shift oscillator andis considered a basic sinewave oscillator. Oscillationsoccur because of the positive feedback of thesignals. The resistors (R) and capacitors (C) make upthe path for the circuits to the transistor base. Everytime the signals pass the RC circuits, a slight time lagoccurs. In other words, the rise and fall of the wave(the phase) shifts slightly. That’s why we call it phaseshift. After the signal has traveled through the circuit,the phase shifts 180 degrees. When the collectorvoltage rises, this rise is fed back to the collector withthe phase shifted. When the base voltage rises, thecollector voltage falls. This repeating cycle causesthe transistor to oscillate.

When you change the control setting, the frequencychanges. This is because the degree of phase shiftchanges. The tonal quality also changes. Set thecontrol to the point where you can hear the puresttone. At this point, a clear sinewave is generated.

Notes:

EXPERIMENT #119: LOW DISTORTION SINEWAVE OSCILLATOR

-141-

Wiring Sequence:

o 124-27-48-82-80-EARPHONEo 47-105-93-77-EARPHONEo 81-109-108-28o 94-110-46o 78-138o 79-106-107o 119-137o 121-122

Schematic

Because it is very stable, the twin-T type audiooscillator is very popular for use with electronicorgans and electronic test equipment.

The oscillation frequency depends on the resistorsand capacitors in the twin-T network. The letter T isused because the schematic diagram for this circuitshows its resistors and capacitor arranged in theshape of the letter T. The term twin comes from theface that there are two T networks in parallel acrossfrom each other. The capacitors in series shift thephase of the wave; the resistors in series supplyvoltage to the transistor’s base as well as shifting thephase of the wave.

Carefully adjust the circuit to obtain pure sinewaveoutput as in the previous two projects. Adjust thecontrol very slowly over its entire range until youhear a tone in the earphone that is very low andresembles the lowest note of a large pipe organ. Thiscontrol setting should be between 7 and 10 on yourdial.

Once the oscillation has started, adjust the controlcarefully for the setting that gives the purestsounding low note near the high end of the dial.

You can experiment with this circuit in many ways.We suggest you try different values for the 10kΩ and470Ω resistors, and try using higher and lowerbattery voltages. Also, if you have a VOM, trymeasuring circuit voltages.

Notes:

EXPERIMENT #120 TWIN-T AUDIO OSCILLATOR

Schematic

-142-

Wiring Sequence:

o 72-106-116-27-124o 28-104-102o 46-103-87o 47-101-86-81-EARPHONEo 48-71o 119-115-82-EARPHONEo 85-88-105o 121-122

This project is a pulse-tone oscillator with anadjustable frequency that can obtain a wide range ofnotes. With practice, you can play tunes on it thatsound like an electronic organ.

To play a tune, adjust the control to the proper noteand press the key. Readjust the control for the nextnote and press the key again.

When you close the key the first time, the basecurrent flows around the loop formed by the battery,the 10kΩ resistor, the 50kΩ resistor, the transistorbase and emitter, and the key.

The base current causes the collector current toflow around the loop formed by the 3V supply, thelower half of the transformer winding, the transistorcollector and emitter, and the key.

The current flowing in the transformer causes acurrent to flow around the loop formed by the toptransformer winding, the 0.05μF capacitor, thetransistor base and emitter, the key, the battery andback to the transformer’s center terminal (terminal2). This current quickly (in less than 0.0001seconds) charges the 0.05μF to about 4V or so witha polarity negative on the transformer side andpositive on the transistor base lead side. Outputactivates the speaker only while the current flows inthe transformer.

The charging of the 0.05μF capacitor stops whenthe induced voltage from the top half of thetransformer winding stops. Then, the capacitorbegins to charge again. As soon as the dischargebegins, the capacitor voltage becomes higher thanthe battery voltage. The reverse polarity voltage isapplied to the base and the transistor turns off. Now,all transistor junctions act as open circuits. Thecapacitor discharges around the loop formed by thetop transformer winding, the 10kΩ resistor, and the50kΩ resistor. When you reduce the control setting,the discharge is faster, so the process is repeated ata faster rate causing a higher frequency. As soon asthe 0.05μF capacitor discharges to slightly belowthe 3V of the battery, this cycle repeats.

Notes:

EXPERIMENT #121: PULSE OSCILLATOR TONE GENERATOR

-143-

Schematic

Wiring Sequence:

o 1-29o 2-30o 3-108-110o 4-82-120o 27-40-107o 28-81o 5-41-109o 42-137o 119-138

This project is a simple transistor audio amplifierused as an audio signal tracer. You can use thisamplifier to troubleshoot transistor audio equipment.When a circuit does not work correctly, you canconnect the wires to different terminals in the circuituntil you find the stage or component that does notpass the signal along.

The 0.1μF input capacitor blocks DC so you canprobe around circuits without worrying aboutdamaging the circuit.

The amplifier circuit is a common-emitter type. Thatis, the transistor’s emitter is connected directly to theinput and the output of the earphone. Its basecurrent is the self current type. The current from thetransistor collector provides current to the base(through the 470kΩ resistor). This provides somestabilizing negative DC feedback.

You can use this amplifier to check any transistorradio or amplifier you have that needs fixing.

Notes:

EXPERIMENT #122: AUDIO SIGNAL TRACER

Schematic

-144-

Wiring Sequence:

o 46-110-94o 47-79-93-EARPHONEo 124-48-PROBESo 119-80-EARPHONEo 109-PROBESo 121-122

This project is a wide band, untuned RF signaltracer. You can use it to find sources of RF noise andinterference, and to check for antenna signals. Thiscircuit is like an untuned crystal set.

We use the 100pF capacitor for the input in thiscircuit because it blocks DC and the 60Hz powerline frequency so that the wires can touch almostanywhere without fear of electrical shock. Of course,you should never probe around high voltage onpurpose. There is an old saying, “There are OLDtechnicians and BOLD technicians, but there are noOLD BOLD technicians.”

Connect the probes between grounded objects andother metallic objects that can act as antennas. Youwill find that this circuit allows you to receive allkinds of AM signals as well as noise. For example, ifyou have citizens’ band transmitters, you can hearthese signals if the transmitter is close enough tothe signal tracer.

Some of the noise you might hear and identifyoriginates from auto ignition systems, light dimmers,fluorescent lights, or switches opening and closing.

Notes:

EXPERIMENT #123: RADIO FREQUENCY SIGNAL TRACER

-145-

Schematic

Wiring Sequence:

o 89-97-126o 90-92-100-EARPHONE-PROBESo 125-99-91-EARPHONEo 98-PROBES

You can use square waves as test signals, too.Square waves are produced by multivibratoroscillators. Remember, you used this type of circuitin previous projects. The name square wave comesfrom the pattern produced by the signal on anoscilloscope (shown below).

Build this circuit and you will hear the soundproduced by a square wave signal. You can vary thepitch and the frequency of the signal by adjusting thecontrol. This varies the current supplied to the PNPtransistor bases.

Notes:

EXPERIMENT #124: SQUARE WAVE AUDIO OSCILLATOR

Schematic

-146-

Wiring Sequence:

o 77-75-48-27-124o 28-81-83o 40-107-84o 41-106-76o 119-42-45-80-EARPHONEo 43-105-82o 78-87-108-44o 46-88o 47-79-EARPHONEo 121-122

When you connect the signal from this oscillator toan oscilloscope, it makes a pattern that looks likethe teeth of a saw (as shown below).

The shape of this wave comes from the slowcharging of the 0.1μF capacitor through the controland the 100kΩ resistor, and the capacitor’s quickdischarge through the PNP and NPN transistors.

The voltage divider - the 470Ω and 100Ω resistors -provides about 1.6 volts to the transistors. Thecurrent flowing into the 0.1μF capacitor from the 9Vsupply (through the control and the 100kΩ resistor)causes the charge of the capacitor to slowlyincrease. When the charge of the capacitor exceedsthe voltage of the voltage divider (1.6V), thetransistors turn on and provide a path for the 0.1μFcapacitor to discharge quickly. Now, the transistorsturn off again, and the capacitor begins to slowlycharge to repeat the cycle.

You can change the oscillator frequency bychanging the values of the components in the timercircuit - the control, the 100kΩ resistor and the0.1μF capacitor. Try a 47kΩ resistor or a 220kΩresistor in place of the 100kΩ resistor, and tryseveral different capacitors. If you connect one ofthe electrolytic capacitors, be sure that you use theproper polarity (+ and –).

Notes:

EXPERIMENT #125: SAWTOOTH WAVE OSCILLATOR

-147-

Schematic

Wiring Sequence:

o 73-81-27-119o 28-89o 71-74-47-40o 41-46o 42-43-90-109o 124-44-48-110-72-EARPHONEo 45-82-EARPHONEo 121-122

This circuit works as a rain detector. When theresistance between the long wires is more thanabout 250kΩ, no current is drawn from the circuit -whether the key is open or closed. When the key isclosed and water (or anything else that has aresistance of less than about 400kΩ) is connected toboth of the test wires, the speaker produces a tone.

Connect the wires to other wires or metallic plateslaid out on an insulated surface. When watercompletes the circuit by spanning the two wires orplates, the alarm turns on.

This oscillator is the basic pulse-type that we’veused several times in this kit. The 22kΩ resistorprotects the circuit against excess base current, incase the wires are shorted together. The 100kΩresistor keeps any transistor leakage current fromturning on the oscillator.

Notes:

EXPERIMENT #126: RAIN DETECTOR

Schematic

-148-

Wiring Sequence:

o 1-29o 2-30o 3-104-110o 124-4-WIREo 5-41-109o 86-89-103-40o 42-90-138o 85-WIREo 119-137o 121-122

You can use the dual operational amplifier as acomparator for detecting changes in voltage. In thisproject, we’re going to use this comparator functionto make a water buzzer that sounds when the wireends come into contact with water.

Slide the switch to position B and assemble thecircuit. When you finish connecting the wiring, slidethe switch to position A to turn on the power. Youshould hear no sound from the speaker. Now,connect the two output terminals with a wire. You willhear a sound from the speaker.

Next, touch the two output terminals with yourfingers. If the speaker makes a sound again, theelectricity is flowing through your body because thewire lead is in contact with sweat.

This project uses two dual operational amplifiers. IC1 works as a comparator. The IC’s negative (–) inputterminal has a reference voltage of about 1.6V.When a voltage exceeding 1.6V is applied to thepositive (+) input terminal, the output of thecomparator allows IC 2 to work as an astablemultivibrator.

Notes:

EXPERIMENT #127: WATER LEVEL BUZZER WITH OPERATIONAL AMPLIFIER

-149-

Wiring Sequence:

o 1-29o 2-30o 3-114o 5-83-80-94-70-110-121o 13-86-63-131o 14-93-69o 65-89-109o 66-82-84-91o 64-90-92-113o 67-81o 68-79-85o 119-124o 122-132

Schematic

This project demonstrates how a metal detectorworks. When the coil comes close to the metal, theoscillator changes the frequency; then, you knowthere is something close by that is made of metal.This type of metal detector has been used to locatelost treasures, buried pipes, hidden land mines, andso on. During war time, these have been used tosave many lives by locating mines and booby trapsset out by the enemy.

This circuit is a low distortion oscillator that drawsonly one milliamp from the 9V supply. Using lowpower allows the nearby metal to have maximumeffect on oscillation frequency.

Use a small transistor radio tuned to a weak AMbroadcast station as the detector. Tune the oscillatoruntil you hear a low-frequency beat note. This beatnote is the difference between the signal of abroadcast station and this oscillator. Do not bring theradio any closer than necessary. The best position iswhere the levels of the two signals are about equal.This gives maximum sensitivity.

Try using keys, plastic objects, coins, and so on, assample objects. Of course, a real metal detectordoes not have a small ferrite coil like this. It usuallyuses an air-core coil shielded with an aluminumelectrostatic shield called a Faraday electrostaticshield.

If the oscillator does not oscillate no matter what youdo, try reversing the wire connections on terminals 9and 10. If this fixes the problem, reverse the wireconnections underneath the board so you can usethe proper terminals for this and other similarprojects.

Notes:

EXPERIMENT #128: METAL DETECTOR

Schematic

-150-

Wiring Sequence:

o 6-11-85-47o 8-12-119o 9-109o 10-79-86-46o 48-72o 71-80-110-124o 121-122

This electronic circuit is a radio transmitter/alarmdevice used to monitor rising water levels such ason rivers, dams, and spillways. Its alarm signals arereceived by a standard AM radio. When the water-contact plates or wires are out of the water, thecircuit is not complete and there is no RF output.When the contacts are connected by water, an RFoutput received by the radio indicates that the waterlevel has reached the height of the contacts.

The emitter of the NPN transistor in the RF oscillatorcircuit is connected to the ferrite coil center terminalthrough the 10μF capacitor. The capacitor acts as ashort circuit at these frequencies. Feedback to thebase is through the 100pF capacitor. The 470kΩresistor supplies the base current that turns on thetransistor.

Notice that the battery current must flow through thePNP transistor to get to the oscillator circuit andback. With the wires insulated from each other, theonly current that can flow is the leakage currentfrom the collector to the emitter with the base open.This weak current cannot drive the RF oscillator.

When the wires are connected by the water, somecurrent can flow through the water to supply basecurrent to the PNP transistor. This base currentturns on the PNP transistor so that oscillator currentcan flow between the collector and the emitter of thePNP transistor with little resistance. Without thisresistance, the PNP transistor could be burned outby excessive current, especially if the probes wereaccidentally touched directly together.

When the transistor is on, the RF oscillatorproduces an RF signal. These probes can be madeof almost any insulated conductor, but large surfaceareas provide the quickest results.

Place an AM radio receiver nearby and tune it to aweak station. Then, adjust the oscillation frequencywith the tuning capacitor to a point where you canhear through the radio.

Notes:

EXPERIMENT #129: WATER LEVEL ALARM

-151-

Wiring Sequence:

o 47-11-6-ANTo 7-93-113-41o 8-12-97o 40-87o 42-119o 46-98-94o 48-73o 74-114-120-WATERo 88-WATER

Schematic

This project uses the LED and an audio oscillatoralarm to indicate three different levels of water in acontainer. The water is used as a conductor tocomplete the circuits and show the water level.

When the water is below all three of the wireconnections, only the bottom segment (D) of theLED is on (indicating a low water level).

When the water rises to a level that touches the twolong wires connected to terminals 77 and 124 (but isbelow the shorter wire), the base current turns ontransistor Q2 and the middle segment of the LED (G)turns on (indicating a moderate water level).

If the water reaches a level high enough to touch allthree wires, the base current is supplied to transistorQ1, and the top segment of the LED (A) lights. Theaudio oscillator is also activated as a warning of ahigh water level.

Of course, you can modify this wiring to make theLED display show other letters of symbols to indicatethe different water levels. Can you think of any goodsymbols? (How about L = low, C = center, and H =high?)

Notes:

EXPERIMENT #130: THREE-STEP WATER LEVEL INDICATOR

-152-

Wiring Sequence:

o 1-29o 2-30o 3-103-109o 4-17-41-87o 5-47-110o 20-42-45-119o 22-44o 25-48-124-WIREo 40-76o 43-78o 46-104-88o 75-WIREo 77-WIREo 121-122

Schematic

INDEX

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We’ve added this listing to aid you in findingexperiments and circuits that you might beespecially interested in. Many of the experiments arelisted two, three, or four times - since they can beused in many ways. You’ll find some listed asentertainment-type circuits, even through they werenot organized that way in the sequence of projects.However, you may find some of these same circuitsto be good for other uses too.

Do you want to learn more about a specific type ofcircuit? Use this Index to look up all the other usesand applications of any specific circuit - then turn tothose and read what we’ve told you in each one.You’ll find by jumping back and forth and around, youoften will pick up a lot more circuit details than justby going from one project to the next in sequence.

Use this Index and your own creative ability and weknow you will have a lot of extra fun with your LabKit.

BASIC ELECTRONIC CIRCUITS AND COMPONENTS

Capacitors: 2, 5, 6, 15, 16, 17, 22, 32,48, 49, 60, 67, 120 ,124

Diodes: 27, 29, 34, 88, 90, 99,106, 107, 115

Integrated: 34, 70

Multivibrators: 48, 50, 53, 87, 88

Resistance: 1, 6, 12, 17, 20, 26, 65,72, 79, 82, 89, 107, 109,116, 125, 128

Set / reset: 55, 56

Timing: 10

Transformers: 119

ENTERTAINMENT CIRCUITS

Alarm: 55, 68, 69, 83, 94, 99,100, 125, 128, 129

Audio Oscillators: 49

Buzzin: 53, 54, 83, 100

Code Transmitter: 112

Electronic Cat: 3

Grandfather Clock: 10

Machine Gun: 5

Metal Detector: 127

Metronome: 9, 88

Motorcycle: 6

Musical: 9, 11, 107

Persistence of Vision: 14

Radio: 4, 5, 12, 44, 109, 110, 11,112, 113, 114, 122, 123,127, 128

Rain Detector: 125

RF Signal Tracer: 123

Shot in the Dark: 59

Siren: 7, 8, 18, 84, 85, 86, 87, 94

Sound: 1, 2, 3, 4, 5, 6, 8, 9, 10,11, 12, 16, 18, 21, 49, 52,53, 54, 55, 56, 57, 58, 60,68, 69, 75, 84, 85, 86, 87,94, 98, 99, 101, 107

Strobe: 13

Timer: 51, 52, 89, 100, 101, 105,124

INTEGRATED CIRCUIT PROJECTS

Amplifier: 21, 70, 71, 72, 73, 74, 75,76, 77, 78, 79, 80, 81, 82,83, 88, 89, 90, 91, 92, 95,97, 102, 103, 108, 126

Amplifier Uses: 21, 75

IC Radio: 114

LED DISPLAY

LED Display: 14, 19, 20, 22, 23, 24, 25,26, 27, 28, 29, 31, 66, 93,96, 102, 104, 129

Logic: 26, 27, 28, 29, 34, 37, 96,104

LOGIC AND COMPUTER CIRCUITS

AND Gate: 27, 36, 40, 41

Data: 47

DTL: 27, 28, 29, 30, 35

Exclusive OR: 30, 38

Flip-flop: 32, 33, 44, 45, 55, 56

Inverting: 70, 75, 76, 77, 80, 95,114

Line: 46

NAND Gate: 29, 43

NOR Gate: 39

OR Gate: 37, 38, 39, 42

Power Supply: 27, 75, 76, 77, 78

TTL: 34, 35, 36, 37, 38, 39, 40,41, 42, 43, 44, 45, 46, 47,48, 49, 50, 51, 52, 65, 87,89, 110, 128

NATURAL SCIENCE PROJECTS

Electrical Energy: 58

Fish: 5

OSCILLATORS

Blocking: 17

Oscillators: 4, 49

Sinewave: 118, 119, 120

Square wave: 64, 81, 82, 123

SWITCHING AND CONTROL CIRCUITS

Relay: 25

Transistor: 32, 33, 63, 64, 80, 106,111, 117

TEST EQUIPMENT

Transistor Checker: 117

Voltmeters: 26, 61

Water Level: 130

TRANSMITTERS

Code: 109, 112

Tone: 7, 8, 11, 16, 49, 60, 62,65, 69, 79, 109, 112, 113,118, 121

Voice: 10, 58, 95, 99, 103, 113

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PARTS LIST

Bar Antenna with Holder

Battery Box Plastic (2)

Capacitors

10pF, ceramic disc type

100pF, ceramic disc type

0.001μF, ceramic disc type

0.01μF, ceramic disc type

0.02μF, ceramic disc type

0.05μF, ceramic disc type (2)

0.1μF, ceramic disc type

3.3μF, 25V electrolytic type

10μF, 16V electrolytic type

100μF, 10V electrolytic type

470μF, 10V electrolytic type

CdS Cell

CdS Holder Plastic

Digital Display PCB Assembly

LED Digital Display LT-312

PCB for Digital Display

Resistor 360Ω (8)

Diode Germanium 1N34A (2)

Diode Silicon 1SS53 / 1N4148

Earphone, ceramic type

Frame, Plastic (L)

Frame, Plastic (R)

Integrated Circuit 74LS00

Integrated Circuit BA728

Key Switch

Knob, Tuning Capacitor, Plastic

Knob, Control, Metal

Light Emitting Diode (3)

Nut 2mm

Paper Bottom Panel

PCB for 74LS00

PCB for BA728

Resistors

100Ω 5% 1/4W (4)

470Ω 5% 1/4W

1kΩ 5% 1/4W

2.2kΩ 5% 1/4W

4.7kΩ 5% 1/4W

10kΩ 5% 1/4W (2)

22kΩ 5% 1/4W

47kΩ 5% 1/4W

100kΩ 5% 1/4W

220kΩ 5% 1/4W

470kΩ 5% 1/4W

Screw 2.4 x 8mm (4)

Screw 2.5 x 3mm

Screw 2.8 x 8mm (2)

Slide Switch

Speaker, 8Ω

Spring (138)

Transformer

Transistors

2SA733 PNP (2)

2SC945 NPN

Variable Capacitor (tuning)

Variable Resistor (control)

Washer 10mm (4)

Wires

White, 75mm (20)

Red, 150mm (30)

Blue, 250mm (20)

Yellow, 350mm (5)

Black, 380mm (2)

Green, 3M (2)

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DEFINITION OF TERMS

AC Common abbreviation foralternating current.

Alternating Current A current that is constantlychanging.

AM Amplitude modulation. Theamplitude of the radio signal isvaried depending on theinformation being sent.

Amp Shortened name for ampere.

Ampere (A) The unit of measure for electriccurrent. Commonly shortenedto amp.

Amplitude Strength or level of something.

Analogy A similarity in some ways.

AND Gate A type of digital circuit whichgives a HIGH output only if allof its inputs are HIGH.

Antenna Inductors used for sending orreceiving radio signals.

Astable Multivibrator A type of transistorconfiguration in which only onetransistor is on at a time.

Atom The smallest particle of achemical element, made up ofelectrons, protons, etc.

Audio Electrical energy represent-ingvoice or music.

Base The controlling input of an NPNbipolar junction transistor.

Battery A device which uses achemical reaction to create anelectric charge across amaterial.

Bias The state of the DC voltagesacross a diode or transistor.

Bipolar Junction A widely used type ofTransistor (BJT) transistor.

Bistable Switch A type of transistorconfiguration, also known asthe flip-flop.

Capacitance The ability to store electriccharge.

Capacitor An electrical component thatcan store electrical pressure(voltage) for periods of time.

Carbon A chemical element used tomake resistors.

Clockwise In the direction in which thehands of a clock rotate.

Coil When something is wound in aspiral. In electronics thisdescribes inductors, which arecoiled wires.

Collector The controlled input of an NPNbipolar junction transistor.

Color Code A method for marking resistorsusing colored bands.

Conductor A material that has lowelectrical resistance.

Counter-Clockwise Opposite the direction in whichthe hands of a clock rotate.

Current A measure of how fastelectrons are flowing in a wireor how fast water is flowing in apipe.

Darlington A transistor configuration whichhas high current gain and inputresistance.

DC Common abbreviation for directcurrent.

Decode To recover a message.

Detector A device or circuit which findssomething.

Diaphragm A flexible wall.

Differential Pair A type of transistorconfiguration.

Digital Circuit A wide range of circuits inwhich all inputs and outputshave only two states, such ashigh/low.

Diode An electronic device that allowscurrent to flow in only onedirection.

Direct Current A current that is constant andnot changing.

Disc Capacitor A type of capacitor that has lowcapacitance and is used mostlyin high frequency circuits.

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Electric Field The region of electric attractionor repulsion around a constantvoltage. This is usuallyassociated with the dielectric ina capacitor.

Electricity A flow of electrons betweenatoms due to an electricalcharge across the material.

Electrolytic Capacitor A type of capacitor that hashigh capacitance and is usedmostly in low frequencycircuits. It has polaritymarkings.

Electron A sub-atomic particle that hasan electrical charge.

Electronics The science of electricity andits applications.

Emitter The output of an NPN bipolarjunction transistor.

Encode To put a message into a formatwhich is easier to transmit.

Farad, (F) The unit of measure forcapacitance.

Feedback To adjust the input tosomething based on what itsoutput is doing.

Flip-Flop A type of transistorconfiguration is which theoutput changes every time itreceives an input pulse.

FM Frequency modulation. Thefrequency of the radio signal isvaried depending on the information being sent.

Forward-Biased The state of a diode whencurrent is flowing through it.

Frequency The rate at which somethingrepeats.

Generator A device which uses steam orwater pressure to move amagnet near a wire, creating anelectric current in the wire.

Germanium A chemical element that isused as a semiconductor.

Ground A common term for the 0V or“–” side of a battery orgenerator.

Henry (H) The unit of measure forInductance.

Inductance The ability of a wire to createan induced voltage when thecurrent varies, due to magneticeffects.

Inductor A component that opposeschanges in electrical current.

Integrated Circuit A type of circuit in whichtransistors, diodes, resistors,and capacitors are allconstructed on asemiconductor base.

Kilo- (K) A prefix used in the metricsystem. It means a thousand ofsomething.

Light Emitting Diode A diode made from gallium(LED) arsenide that has a turn-on

energy so high that light isgenerated when current flowsthrough it.

Magnetic Field The region of magneticattraction or repulsion around amagnet or an AC current. Thisis usually associated with aninductor or transformer.

Magnetism A force of attraction betweencertain metals. Electriccurrents also have magneticproperties.

Meg- (M) A prefix used in the metricsystem. It means a million ofsomething.

Micro- (μ) A prefix used in the metricsystem. It means a millionth(0.000,001) of something.

Microphone A device which converts soundwaves into electrical energy.

Milli- (m) A prefix used in the metricsystem. It means a thousandth(0.001) of something.

Modulation Methods used for encodingradio signals with information.

Morse Code A code used to send messageswith long or short transmitbursts.

NAND Gate A type of digital circuit whichgives a HIGH output if some ofits inputs are LOW.

NPN Negative-Positive-Negative, atype of transistor construction.

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Ohm’s Law The relationship betweenvoltage, current, andresistance.

Ohm, (Ω) The unit of measure forresistance.

Oscillator A circuit that uses feedback togenerate an AC output.

Parallel When several electricalcomponents are connectedbetween the same points in thecircuit.

Pico- (p) A prefix used in the metricsystem. It means a millionth ofa millionth (0.000,000,000,001)of something.

Pitch The musical term for frequency.

Printed Circuit Board A board used for mountingelectrical components.Components are connectedusing metal traces “printed” onthe board instead of wires.

Receiver The device which is receiving amessage (usually with radio).

Resistance The electrical friction betweenan electric current and thematerial it is flowing through;the loss of energy fromelectrons as they movebetween atoms of the material.

Resistor Components used to controlthe flow of electricity in a circuit.They are made of carbon.

Resistor-Transistor- A type of circuitLogic (RTL) arrangement used to construct

digital gates.

Reverse-Biased When there is a voltage in thedirection of high-resistanceacross a diode.

Saturation The state of a transistor whenthe circuit resistances, not thetransistor itself, are limiting thecurrent.

Schematic A drawing of an electrical circuitthat uses symbols for all thecomponents.

Semiconductor A material that has moreresistance than conductors butless than insulators. It is usedto construct diodes, transistors,and integrated circuits.

Series When electrical componentsare connected one after theother.

Short Circuit When wires from different partsof a circuit (or different circuits)connect accidentally.

Silicon The chemical element mostcommonly used as asemiconductor.

Speaker A device which convertselectrical energy into sound.

Switch A device to connect (“closed” or“on”) or disconnect (“open” or“off”) wires in an electric circuit.

Transformer A device which uses two coilsto change the AC voltage andcurrent (increasing one whiledecreasing the other).

Transient Temporary. Used to describeDC changes to circuits.

Transistor An electronic device that usesa small amount of current tocontrol a large amount ofcurrent.

Transmitter The device which is sending amessage (usually with radio).

Tuning Capacitor A capacitor whose value isvaried by rotating conductiveplates over a dielectric.

Variable Resistor A resistor with an additionalarm contact that can movealong the resistive material andtap off the desired resistance.

Voltage A measure of how strong anelectric charge across amaterial is.

Voltage Divider A resistor configuration tocreate a lower voltage.

Volts (V) The unit of measure for voltage.

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IDENTIFYING RESISTOR VALUESUse the following information as a guide in properly identifying the value of resistors.

BANDS

METRIC UNITS AND CONVERSIONS

Abbreviation Means Multiply Unit By Orp pico .000000000001 10-12

n nano .000000001 10-9

μ micro .000001 10-6

m milli .001 10-3

– unit 1 100

k kilo 1,000 103

M mega 1,000,000 106

1. 1,000 pico units = 1 nano unit

2. 1,000 nano units = 1 micro unit

3. 1,000 micro units = 1 milli unit

4. 1,000 milli units = 1 unit

5. 1,000 units = 1 kilo unit

6. 1,000 kilo units = 1 mega unit

IDENTIFYING CAPACITOR VALUESCapacitors will be identified by their capacitance value in pF (picofarads), nF (nanofarads), or μF (microfarads).Most capacitors will have their actual value printed on them. Some capacitors may have their value printed inthe following manner. The maximum operating voltage may also be printed on the capacitor.

Second Digit

First Digit

Multiplier

Tolerance*

Note: The letter “R”may be used at timesto signify a decimalpoint; as in 3R3 = 3.3

103K100V

The letter M indicates a tolerance of +20%The letter K indicates a tolerance of +10%The letter J indicates a tolerance of +5%

Maximum Working Voltage

The value is 10 x 1,000 =10,000pF or .01μF 100V

*

Electrolytic capacitors have a positiveand a negative electrode. Thenegative lead is indicated on thepackaging by a stripe with minussigns and possibly arrowheads.

Warning:If the capacitoris connectedwith incorrectpolarity, it mayheat up andeither leak, orcause thecapacitor toexplode.

PolarityMarking

BAND 11st Digit

Color DigitBlack 0Brown 1

Red 2Orange 3Yellow 4Green 5Blue 6Violet 7Gray 8White 9

BAND 22nd Digit

Color DigitBlack 0Brown 1Red 2Orange 3Yellow 4Green 5Blue 6Violet 7Gray 8White 9

Multiplier

Color MultiplierBlack 1Brown 10Red 100Orange 1,000Yellow 10,000Green 100,000Blue 1,000,000Silver 0.01Gold 0.1

ResistanceTolerance

Color ToleranceSilver ±10%Gold ±5%Brown ±1%Red ±2%Orange ±3%Green ±0.5%Blue ±0.25%Violet ±0.1%

1 2 Multiplier Tolerance

MultiplierFor the No. 0 1 2 3 4 5 8 9

Multiply By 1 10 100 1k 10k 100k .01 0.1

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