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

Think of the CdS cell as a resistor that changes its
resistance with the amount of light that falls on it. In
darkness the resistance is very high, around 5
megohms (M

Ω

, 5 million ohms); in bright sunlight, it

increases to about 100

Ω

, or less.

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

You can use the NPN transistor as a switch. As we
saw in the last project, it turns on when sufficient
positive voltage is applied to its base. The positive
voltage leads from the positive terminal of the
battery, to the CdS cell, to the control, to the 10k

Ω

resistor.

The amount of voltage applied to the base is
determined by the total resistance value of the CdS,
the control, and the 10k

Ω

resistor. The amount of

light striking the cell and the setting of the control
change the base voltage – making it low or making
it high enough to turn on the transistor. Use your
voltmeter on the control and try changing the control
position while casting a shadow over the CdS to
verify this voltage change. Adjust the control so that
the transistor turns on and off when the light
changes over the CdS.

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

Notes:

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

Wiring Sequence:

o

15-21-23-119

o

16-28

o

25-47

o

124-26-48

o

27-82

o

46-81

o

121-122

Schematic

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Содержание EP-130

Страница 1: ...y any means electronic photocopying or otherwise without written permission from the publisher ELECTRONIC PLAYGROUND TM and LEARNING CENTER MODEL EP 130 Elenco Electronics Inc Wheeling IL USA 99 Washington Street Melrose MA 02176 Phone 781 665 1400 Toll Free 1 800 517 8431 Visit us at www TestEquipmentDepot com ...

Страница 2: ...r 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 52 37 TTL OR Gate 53 38 TTL Exclusive OR Gate 54 39 TTL NOR Gate 55 40 TTL Three Input AND Gate 56 41 TTL AND Enable Circuit 57 42 TTL OR Enable Circuit 58 43 TTL NAND Enable Circuit 59 44 TTL R S Flip Flop 60 45 T...

Страница 3: ...9 Operational Amplifier Winking LED 108 90 LED Flashing Light 109 91 Two LED Winker 110 92 One Shot Light 111 93 LED Initials 112 94 Wake Up Siren 113 95 Voice Activated LED 114 96 Logic Tester 115 IX MORE ADVENTURES WITH OPERATIONAL AMPLIFIERS 116 97 Alternating Current Sound 117 98 Light Control Sound Circuit 118 99 Sound Alarm Circuit 119 100 Study Timer 120 101 Kitchen Timer 121 102 Three Inpu...

Страница 4: ...arious components in your lab kit are printed next to each component You ll notice that we often refer to a Volt Ohm Meter VOM for making measurements A VOM or multimeter is a device that measures voltage current amperes or amps and resistance ohms Ω We will tell you more about these later If you are going to understand electronic circuits it is important that you learn to measure circuit values f...

Страница 5: ...ist the strands together You can remove the insulation with a wire stripper tool or a penknife Be very careful doing this as a penknife is very sharp MAKING WIRING CONNECTIONS Your kit has more that 30 separate components If this is your first experience with electronics you probably don t know the difference between a resistor and a transistor If so don t worry the general purpose fo each compone...

Страница 6: ...t the control is You can use it as a light dimmer a volume control and in many other circuits where you d like to be able to change resistance easily and quickly This is a normal resistor with an additional arm contact that can move along the resistive material and tap off the desired resistance Capacitors Capacitors can pass alternating current AC signals while blocking direct current DC signals ...

Страница 7: ...prevent you from burning out the display with excess current Integrated Circuit As you might already know after the transistor was invented in the middle 1940 s the next big breakthrough in electronics was the integrated circuit in the early 1960 s The great advantage of ICs as we call them is that the equivalent of hundreds or even thousands of transistors diodes and resistors can be put into a s...

Страница 8: ...lectricity back into mechanical form to drive machinery and appliances Speaker A speaker converts electrical energy into sound It does this by using the energy of an AC electrical 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 air pressure variations You need high cur...

Страница 9: ... and so on Wires You will use the wires to make connections between terminals The parts and spring terminals are mounted onto a platform If you look underneath it you can see how wires are used to connect the parts and their terminals BUILDING YOUR FIRST PROJECT There is a simple wiring sequence listing for each project You should connect appropriate length wires between the terminals listed in ea...

Страница 10: ... container You might turn it in as a Science Fair project at school and make a major research project out of it TROUBLESHOOTING If you assemble each project according to its wiring sequence you should have no problem getting the projects to work properly But if you do have a problem you can usually find and correct it by using the following troubleshooting steps These steps are similar to those us...

Страница 11: ... 11 I ENTERTAINMENT CIRCUITS ...

Страница 12: ...venient control for carrying the kit outside as you try to attract birds with your bird caller Try different combinations of resistance and capacitance in place of the 1kΩ resistor and the 100μF capacitor To change the 100μF capacitance to 470μF disconnect the wire at terminal 116 and reconnect it to terminal 118 Then transfer the wire attached to terminal 115 to terminal 117 Now your bird might s...

Страница 13: ...the first transistor Q1 is cut 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 10μF and the 100μF capacitors and hear what happens These capacitors control the amount of electricity reaching the transistors through connections to the transistor bases Remember...

Страница 14: ...effect does it have on the circuit s operation Set the switch to A and try again Now the sound is lower and lasts longer as if the cat is begging for a dish of milk You can experiment with this circuit to produce a variety of other sounds But don t change the value of the 0 05μF capacitor to more than 10μF or reduce the value of the 10kΩ resistor otherwise the transistor might be damaged Notes EXP...

Страница 15: ...ur school place your kit near the aquarium glass and see if fish are attracted to the sound Or you can actually try it out while fishing Get another speaker and attach it to terminals 1 and 2 using long lengths of insulated wire Carefully wrap the speaker in a waterproof plastic bag or seal it inside a jar Be sure no water can reach the speaker Now lower it into the water Then cast a line into the...

Страница 16: ...re used to produce sounds Super fast oscillators produce radio frequency signals RF signals These RF signal oscillators turn on and off millions of times per second The number of times an oscillator turns on and off each second is called the frequency of the oscillator and is measured in units called hertz Hz This oscillator has a frequency of about 1 to 12Hz The frequency of a radio frequency sig...

Страница 17: ...CdS cell With a strong light on the CdS cell you can control the operation entirely by exerting more pressure on the wires in your hand Use your hand to make a shadow over the CdS cell and see what happens When you hold the ends of the wires you make yourself another part of the circuit a resistor Changing your grip changes the resistance to the current in the project With some practice you will b...

Страница 18: ...he tone lowers You can control the tone the same way police and ambulance drivers do This is the same type of oscillator circuit used in many other projects When you press the key another capacitor is added to the circuit to slow down the oscillator action Notes EXPERIMENT 7 TWO TONE PATROL CAR SIREN Wiring Sequence o 1 29 o 2 30 o 3 104 106 110 o 4 85 120 o 5 41 109 o 40 137 105 86 o 103 138 o 42...

Страница 19: ...ns you might want to try 1 Change the 10μF capacitor to a 100μF or 470μF This gives a very long delay for both turn on and turn off 2 Change the circuit to eliminate the delays by temporarily disconnecting the 10μF capacitor Simply disconnect one of the wires from terminal 113 or terminal 114 Sounds dead in comparison doesn t it 3 Change the 0 02μF capacitor to a 0 01μF and then to a 0 05μF Notes ...

Страница 20: ...rol That is they are connected end to end so that the current runs through both components Also try a different capacitor in place of the 100μF capacitor and see what effect this has on circuit operation Remember to keep track of the results in your notes Try connecting the 470μF capacitor to the batteries to hear the difference a stronger capacitor makes Connect terminal 117 to terminal 119 and t...

Страница 21: ...ady monotonous ticking can put animals and people into a restful state of mind If you have traveled on a train you know how sleepy you get as you hear the click click click of the wheels Now want to scare this clock to stop Yell into the speaker How about that You can momentarily stop the clock The speaker acts as a microphone The sound of your voice vibrates in the speaker and upsets the electric...

Страница 22: ...e circuitry The first instrument of this type was invented by a man named Leon Theremin so the instrument was named Theremin in his honor When you complete the wiring press the key and wave your hand over the CdS cell With a little practice you will be able to play tunes with this magical electronic musical instrument Experiment with the CdS cell light shield for more light control Have fun Notes ...

Страница 23: ...ount of light of the CdS cell determines the resistance value of the cell More resistance from the cell slows down the frequency of the music sound waves The basic music is produced by the oscillator circuit When a circuit controls the frequency of an oscillator we call it FM or frequency modulation An FM radio signal is something like this but at much higher frequencies Notes EXPERIMENT 12 HORROR...

Страница 24: ...ey and watch LED 1 It turns on and off at certain intervals You can control the blinking rate with the 50kΩ control This lets you see how an oscillator works Try substituting a lower value capacitor for the 100μF capacitor What do you think will happen Were you right Notes EXPERIMENT 13 STROBE LIGHT Wiring Sequence o 3 115 o 4 27 138 o 5 31 o 28 80 o 33 47 o 79 116 112 46 o 111 48 121 o 119 137 Sc...

Страница 25: ...D by changing the wiring of the LED Connect the appropriate terminals to form letters or numbers to terminal 71 in place of terminals 21 and 23 The connections for the number 3 would be 17 21 22 23 20 71 You might want to try different values of capacitors and see their effects but don t use a capacitor value higher than 10μF or the transistor might be damaged by excessive current Notes EXPERIMENT...

Страница 26: ... 26 II BASIC SEMICONDUCTOR AND COMPONENTS CIRCUITS ...

Страница 27: ... picture of each part along with its schematic symbol and a brief description at the beginning of this manual You ll notice on the schematics that some lines cross each other and there s a dot at the point where they cross This means that the two wires represented by the lines are connected at the point indicated by the dot You ll usually find a terminal number beside the dot If two lines cross wi...

Страница 28: ...lied by a battery or other power source or more accurately by the quantity of electrons displaced in one of the capacitor s electrodes The quantity of electrons in an electrode of a capacitor is measured in coulombs One coulomb is a quantity of 6 280 000 000 000 000 000 electrons 6 25 x 1018 To determine the charge in either electrode of the capacitor Q multiply the capacitance C by the voltage ac...

Страница 29: ...o separate channels What do you think happens to the total capacitance when you connect two capacitors in parallel You might have guessed wrong When two capacitors are connected in parallel the total capacitance increases The increased capacitance causes the tone to be lower Now release the key and move the switch from B to A but do not press the key while the switch is set to A The transistor can...

Страница 30: ... resistance in a parallel connection is not as easy as calculating resistance in a series connection You must multiply the values together then divide the product by the sum of the values In this case the total resistance is Now connect terminals 13 14 As shown in the schematic this connects the 22kΩ resistor in parallel with the two 10kΩ resistors Any change in the LED It flashes on and off at sh...

Страница 31: ...nsistor base and the LED stays on When you turn the switch off you remove the battery from the circuit and the capacitor begins the discharge through the transistor and the LED The L gradually dims until the 100μF fully discharged If you want a slower dimmer circuit replace the 100μF capacitor with the 470μF capacitor Simply replace connections 25 116 124 with connections 25 118 124 and replace co...

Страница 32: ...ress the key 1 is displayed To increase the base current of the NPN transistor decrease the value of the 47kΩ resistor connected to the base terminal 46 Simply disconnect terminals 87 and 88 and replace them with connections to another resistor For example change connections 87 42 and 46 88 to 83 42 and 84 46 to change the 47kΩ resistor to a 10kΩ resistor Each time you use a lower value resistor m...

Страница 33: ...he connections the NPN transistor is on because positive voltage is applied to its base through the 1kΩ resistor This turns on the upper half of the LED At the same time the PNP is off because no current can flow to its base Current flows from the PNP emitter to the base of the NPN transistor but this flow is blocked from the PNP base by the diode When you press the key the NPN is turned off becau...

Страница 34: ...k about the transformer The transformer has a copper wire wound hundreds of turns We call it a coil A transformer has two coils separated by a plate When electricity flows through a coil it creates a magnetic field The reverse is also true if a coil is subjected to a change in its magnetic field strength electricity flows through it So when electricity flows through the first or primary as we ofte...

Страница 35: ... projects For the moment try a different value for the capacitors to see their effects on the speed of operation See if you can rewire the LED to display numbers other than 1 and 2 You can try different higher values in place of the 2kΩ and 4 7kΩ resistors Do not use lower values for any of the resistors or you might damage the transistors Notes EXPERIMENT 22 FLIP FLOP MULTIVIBRATOR WITH LED DISPL...

Страница 36: ... 36 III LED DIGITAL DISPLAY CIRCUITS ...

Страница 37: ... flow through the LED display The series resistors determine how much current flows from the batteries to the diodes Complete the wiring as shown to connect the 3V supply with the LED segments and the decimal point Dp What numbers and letters can you display At this low battery voltage you can reverse the polarity of the circuit by reversing the connections to the battery Change 25 120 and 119 WIR...

Страница 38: ...minal terminal 25 to the negative side of the battery and any anode segment terminals as required to the positive side of the battery LEDs operate extremely fast An LED can turn on and off hundreds of times each second so fast you can t see it blink Unlike an incandescent lamp there is no warm up time and no great amount of heat is produced Perform the following experiment to see how fast the LED ...

Страница 39: ...ortant for you to remember A PNP transistor turns on when negative voltage is applied to its base the current flows from collector to emitter An NPN transistor turns on when positive voltage is applied to its base the current flows from emitter to collector Now that the current can flow through the NPN transistor it can travel a complete path from the negative side of the batteries to the NPN tran...

Страница 40: ...nt of voltage applied to the base is determined by the total resistance value of the CdS the control and the 10kΩ resistor The amount of light striking the cell and the setting of the control change the base voltage making it low or making it high enough to turn on the transistor Use your voltmeter on the control and try changing the control position while casting a shadow over the CdS to verify t...

Страница 41: ... 41 IV A TOUR THROUGH DIGITAL CIRCUITS ...

Страница 42: ... H only when you connect terminal A and terminal B to terminal 124 the high terminal If you connect terminal A or B or both to terminal 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 terminal 126 and or terminal 128 is connected to terminal 119 positive voltage is applied to the PNP transi...

Страница 43: ...rminal 124 What happens The output 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 we won t explain the whole operation for you here Compare the two projects and make notes of their similarities and differences See if you follow the circuit on the schematics diagram Notes EXPERIMENT 28 DTL OR CIRCUIT WITH LED ...

Страница 44: ...t the output The function is represented AB When either or both terminals A and B are connected to terminal 124 the logic low terminal negative current flows through the diode s and the NPN transistor stays off The LED remains off When both inputs are connected to terminal 119 the logic high terminal both diodes allow positive voltage to flow through them This positive voltage turns the NPN transi...

Страница 45: ...igh input Is there any change in LED 1 Release the key to make both inputs low Now set the switch to A and make the input traveling through the switch high What does LED 1 do now Leave the switch at A and press the key to make both inputs high You can see that in an XOR circuit two high inputs produce a low output You can also build an XNOR circuit exclusive NOR We won t build one here but you mig...

Страница 46: ... circuit is shown with the schematic The function is written as A B The symbolizes the OR circuit and the bar over the symbol indicates the circuit is inverted When you connect either A or B or both to terminal H the NPN transistor turns on completing the current path for the LED When you connect both A and B to L the transistor turns off and LED goes off Notes EXPERIMENT 31 TRANSISTOR NOR CIRCUIT...

Страница 47: ... is charging and discharging through its base The 4 75kΩ resistor and the control keep transistor Q2 on after the 100μF capacitor has discharged Now the 10μF capacitor has received a charge and is discharging through the 47kΩ resistor the battery and the Q2 Remember when transistor Q2 is on this means current can flow through its collector to its emitter Transistor Q1 remains off as long as the ch...

Страница 48: ...y the LED 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 that flip flop circuits can remember things When you leave a circuit in a certain condition it stays in that condition until you want to change it Many flip flops that are controlled by a single toggle signal can remember many things That is how computers ...

Страница 49: ... 49 V MORE ADVENTURES WITH DIGITAL CIRCUITS ...

Страница 50: ...omponent with more digital circuits in other projects This gate circuit is called a buffer because it is used to keep two portions of a device isolated from each other Refer to the schematic as you build this project We take the output from one NAND gate and use it for both inputs to the second note the two inputs for the two NANDs are always the same From what you know about NANDs what do you thi...

Страница 51: ...are 0 and the LEDs go out When the switch is set to B we no longer have all inputs at 1 and the LEDs come back on One amazing thing to think about is how large the RTL and DTL circuits were that we played with in earlier projects Believe it or not four of those circuits have been shrunk down to fit inside this tiny IC There s a special type of IC a bit bigger than the ICs in your kit which is actu...

Страница 52: ... the inputs 1 causing the overall output to be 1 Can you flow the 1 input through the circuit until you reach a 1 output Try it and don t peek at the answer It works like this each 1 input goes into the first NAND gate This causes the output of the NAND to be 0 This 0 output is used for both inputs to the second NAND The 0 inputs to the second NAND cause its output to be 1 and the LED lights So tw...

Страница 53: ...aves like other OR gates you ve played with If at least one or the other of the inputs is 1 the output to the LED is 1 Have you traced what happens from input to output yet The explanation is in the next paragraph but no fair peeking Let s say you press the key with the switch set to B This enters 1 as both inputs of the NAND causing the NAND s output to become 0 This 0 output is one of the inputs...

Страница 54: ...o Leave the switch at A and press the key What happens to LED 1 now The output is 1 as long as the inputs are different If both inputs are the same either 0 or 1 the output of the XOR gate is 0 Put on your thinking cap and follow each 0 or 1 input through the circuit until you reach the output It might help if you mark 0 or 1 on the schematic at the input and output of each NAND gate Notes EXPERIM...

Страница 55: ...see this project behaves just like other NOR gates we ve built Both of the NANDs marked A and B have input of 1 So they each have an output of 0 when the input is 1 Their outputs are used as inputs to the NAND marked C NAND C has an output of 1 as long as one or both of its inputs are 0 This 1 output is used for the inputs of the next NAND causing an output of 0 Thus LED 1 does not light As you ca...

Страница 56: ...d then read on to see if you were right Here s how this circuit works the key and switch are both connected to one NAND When they each provide 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 see it on the schematic There it makes up one input along with the input from terminals 13 and 1...

Страница 57: ... see LED 2 light and turn off at the same time at LED 1 The two NAND gates make up an AND gate remember this circuit from Project 36 TTL AND GATE In this circuit LED 1 is called the data input LED 2 is called the output These terms are often used with enable circuits They will pop up from time to time when we talk about digital electronics You might suspect by now that we can use other digital cir...

Страница 58: ... two projects After you finish the wiring connect terminals 13 and 14 to turn the power on What does LED 1 do And what is LED 2 doing Now set the switch to B What happens to LED 1 and LED 2 now We simplify the circuit by saying that setting the switch to A blocks the flow of data from LED 1 to LED 2 This is called the inhibit status But when the switch is at B data can flow from LED 1 to LED 2 Thi...

Страница 59: ... indicating that something is preventing the signal at LED 1 from reaching LED 2 Now set the switch to A and observe LED 1 What is happening Is the same thing happening to both LED 1 and LED 2 You can see that LED 1 and LED 2 take turns going on and off This is because we make one of the two inputs to the NAND equal 1 when the switch is set to A The multivibrator sends 0 and signals to the other N...

Страница 60: ...inals 13 and 14 in turn What happens to LED 1 and LED 2 When LED 2 lights the R S flip flop is in the set state When LED 1 lights the R S Flip flop is reset After you set or reset the flip flop remove the long wire from the circuit and see what happens Now you can see one of the prime characteristics of the R S flip flop Once the circuit is set or reset the circuit keeps that state until an input ...

Страница 61: ...r thinking cap and try to trace what happens from the key input to LED 1 Two of the four NANDs function as an R S flip flop See if you can figure out what the remaining NANDs are doing This circuit is an inverter because it takes inputs and reverses them Notes EXPERIMENT 45 TOGGLE FLIP FLOP CIRCUIT MADE FROM NAND GATE Wiring Sequence o 13 75 85 81 49 31 42 o 14 119 o 33 57 61 87 o 40 88 o 41 74 77...

Страница 62: ...to A or B controls the inputs to the two NANDs that light LED 2 and LED 3 With the switch at A the NAND controlling LED 2 gets one steady input of 1 The output of the multivibrator supplies the other input As the multivibrator s output switches from 0 to 1 the NAND controlling LED 2 switches its output from 1 to 0 The opposite happens when you set the switch to B Now the NAND controlling LED 3 get...

Страница 63: ...ng happening yet Now press the key and see what happens to LED 1 and LED 3 LED 3 goes on and off at the same time as LED 1 Now set the switch to B LED 3 turns on and according to the blinking of LED 2 You can use either of the two sources as the input to determine the output of LED 3 Now put on your thinking cap and try to follow the inputs from the multivibrator to the key to the setting of the s...

Страница 64: ... 64 VI THE WORLD OF TRANSISTOR TRANSISTOR LOGIC ...

Страница 65: ...dn t have much trouble figuring out how this particular circuit works The 100μF capacitor makes it all possible Try using other electrolytic capacitors in place of the 100μF capacitors and see what effect they have on LED 1 Be sure to use the correct polarity By now you can see why NAND gate ICs are so useful The quad two input NAND IC in your kit is one of the most widely used electronic componen...

Страница 66: ...g the value of the capacitors from 0 1μF to 0 5μF What effect does this have on the sound you hear You might also want to try different capacitors in this project Don t try using any of the electrolytic capacitors however terminals 111 118 Try to arrange the circuit so you can switch different value capacitors in and out of this circuit to vary the tone Can you think of ways to use this circuit wi...

Страница 67: ...sed today in place of transistor multivibrators Can you think of some reasons why Write down any reasons you think TTL multivibrators would work better than regular transistor multivibrators TTL multivibrators take up much less space than transistor multivibrators TTL ICs also use less current than similar transistor arrangements Notes EXPERIMENT 50 WINKING LEDS Wiring Sequence o 13 49 31 34 o 14 ...

Страница 68: ...t fires one shot This means that it can be used in many circuits as a timer You might also see this circuit called a monostable multivibrator Since this is a multivibrator you might suspect that there s some way to vary the time it produces an output You re right there is a way and we ll let you try to figure out what it is Actually you shouldn t have much trouble discovering which parts you need ...

Страница 69: ...ks and you hear a sound from the speaker The sound will continue until the 100μF capacitor discharges keeping the first transistor from operating The output of the first NAND becomes 0 stopping the multivibrator The sound will last about 10 seconds with the 22kΩ resistor Try replacing the 22kΩ with the 47kΩ or the 100kΩ resistor and find out what happens After you ve experimented with this project...

Страница 70: ...tor is affected by the NAND multivibrator If you say yes how is it affected Try using other electrolytic capacitors in place of the 100μF capacitor in the NAND multivibrator to see what effects they have on the circuit Try changing the transistor multivibrator and see how you can alter its operation You can use the speaker instead of the earphone with this project by connecting the NPN transistor ...

Страница 71: ...ppens Study the schematic and when you think you have the answer read on to check your guess When the output of the NAND multivibrator is 0 current can flow through LED 1 to light it but the transistor multivibrator won t work because the left transistor has a 1 signal applied to its emitter When the output of the NAND multivibrator is 1 LED 1 won t light but a 0 signal is applied to the emitter o...

Страница 72: ...ow move the switch to position B and press the key one more time What happens now Circuits like this can be used in alarms They are very useful since intruders often can t figure out how to make the sound stop You might also want to experiment using light from LEDs instead of sound to tell you that the circuit has been set or reset Notes EXPERIMENT 55 SET RESET BUZZER 1 Wiring Sequence o 13 77 75 ...

Страница 73: ... and press the key and the sound will stop Compare the operation of this project with the previous one What makes them different from each other Can you think of some situations where one circuit might be better suited than the other Be sure to make some notes about what you learn Notes EXPERIMENT 56 SET RESET BUZZER 2 73 Wiring Sequence o 13 49 42 45 138 o 14 119 o 81 32 41 o 33 59 60 62 36 121 o...

Страница 74: ...ize this familiar circuit Notice that we re also using two NAND gates to make a multivibrator The NAND gate multivibrator affects the operation of the transistor multivibrator which sends its output through the NPN transistor to the audio amplifier The result is the sound you hear from the speaker You can change the sound this circuit makes by substituting a different value for the 470μF capacitor...

Страница 75: ... the amount of the signal from the earphone that is amplified The two NAND gates in series control the lighting of LED 1 Trace 0 s and 1 s as they change from input to output To use this circuit set the switch position A and set the control to position 5 Yell into the earphone and watch LED 1 It probably lights If so try turning the control counter clockwise to make it more difficult to light LED ...

Страница 76: ...rom about five feet or so As your aim improves try increasing the distance When you are really good you can try hitting the CdS cell simply by switching your flashlight on and off rather than using a continuous stream of light You might have to adjust the control knob very carefully to have LED 2 come on when light strikes the CdS cell For the best results be sure you have the kit in a completely ...

Страница 77: ... 77 VII APPLICATION CIRCUITS BASED ON THE OSCILLATOR ...

Страница 78: ...inals 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 Is there any change in the sound Now connect terminals 13 and 14 and press the key Try both settings of the switch with terminals 13 and 14 connected and see what happens Which combination gives you the highest tone The lowest What does this tell you about how capacitor...

Страница 79: ...it negative The current that flows to charge the capacitor is called charging current or displacement current When the capacitor is discharging the same amount of current must flow in the opposite direction This current is called discharge current or displacement current If you have a VOM use it to measure the charge on the capacitor with the voltmeter function The displacement current can be meas...

Страница 80: ...llector current of the PNP transistor vary with the temperature of the transistor Build this project and you will hear a sound from the speaker Adjust the 50kΩ control so that the sound is low or a series of pulses Now warm up the PNP transistor by holding it between your fingers You hear the tone become higher as the transistor temperature increases Notes EXPERIMENT 62 TEMPERATURE SENSITIVE AUDIO...

Страница 81: ...a greater output The capacitor determines the frequency of the oscillation The project starts with the 0 01μF capacitor in the circuit but you can experiment with different value capacitors The control adjusts the voltage leading to the base of the NPN transistors It changes the tonal quality as well as the frequency You should be sure to record your results like a professional scientist so you ca...

Страница 82: ...switch to position A to turn on the power Note the sound from the speaker because we will be using square wave signals in later projects This oscillator circuit works well with low DC voltage supplies For this reason scientist and technicians use DC to AC converters and DC to DC inverters with supply voltages of about 0 5 to 12 volts Another characteristic of this oscillator is that it makes a max...

Страница 83: ...ker After you complete the wiring make a very heavy pencil mark on a sheet of paper a soft lead pencil works best The mark needs to be about an inch wide and 5 to 6 inches long Now slide the switch to position A to turn on the power and hold one of the probes to one end of the mark or attach it with tape Move the other probe back and forth along the mark You hear the pitch rise and fall as you mov...

Страница 84: ...presenting the two different voltage values When the output from the emitter of the PNP transistor supplies the base current to the NPN transistor as in this circuit shorter pulses are generated Try experimenting by changing the value of the 3 3μF capacitor to 10μF You can also vary the 1kΩ resistor and change the 470kΩ resistor to 220kΩ The frequency of this oscillator is controlled by the rate o...

Страница 85: ... and off You can replace it with the slide switch Also you can change the tonal range by changing the 10μF and 3 3μF capacitor values Try using the switch or the key to add extra components to the circuit like an extra capacitor in parallel with the 10μF or 3 3μF so you can change from one tonal range to another quickly These changes will make a more complete organ from this project Be sure to kee...

Страница 86: ...ol so that the right amount of light will set off the bird and wake you up in the morning not too early and not too late We have changed only a few component values and rearranged the circuit schematic from the original electronic bird See if you can spot the changes and rearrange the circuit so that it looks like Project 1 Use the space below to redraw the schematic Notes EXPERIMENT 68 DAYLIGHT E...

Страница 87: ...the project and press the key to hear the alarm sound coming from the speaker You hear the alarm sound turning on and off as the pulse oscillator turns on and off This intermittent sounding alarm is more effective than a continuous tone because it is more noticeable You can experiment with this project by varying the values of the 22kΩ 47kΩ and 100kΩ resistors and the 0 02μF capacitor Notes EXPERI...

Страница 88: ... 88 VIII BASIC OPERATIONAL AMPLIFIER CIRCUITS ...

Страница 89: ...ltages The voltage that is compared is the input voltage The reference voltage in this project is about 3 7V It is connected to terminal 68 of one of the integrated circuits Input voltage flows to terminal 69 of the same IC The LED lights if this voltage is higher than the reference voltage and stays off if it is lower In this circuit the operational amplifier acts as an inverting amplifier for th...

Страница 90: ...itch position A This eliminates the 10kΩ resistors from the circuit so the amplifier s positive input terminal receives the full 1 5V input voltage Using the above equation you can see that the output voltage of the operational amplifier is now 1 5V X 220kΩ 100kΩ 1 4 8V The LEDs light dimly because the voltage supplied to them is more than 3V Let s change the amplification factor Slide the switch ...

Страница 91: ... First set the switch to position A and press the key while watching LED 1 It is dimmer when the key is closed This is because both LED 1 and LED 2 are in the circuit when the key is closed The load the amount of energy used by the LEDs in this circuit increases but the current remains constant So the LED becomes dimmer Now set the switch to position B with the key off Do you see any change in LED...

Страница 92: ...slowly through resistor R and the LEDs become brighter Setting the switch to position B discharges the capacitor and turns the LEDs off Set the switch to position B before completing the project to discharge the capacitor Set the switch to position B and hold the key down to see LEDs 1 2 and 3 become brighter They reach maximum brightness in about 5 seconds Set the switch to B to discharge the cap...

Страница 93: ...eriment First leave the key off The operational amplifier works as a comparator in this state When you rotate the control LEDs 1 and 2 take turns lighting at some point Note that this point doesn t change whether you turn the control clockwise or counterclockwise Now press the key on and you ll have a Schmitt trigger circuit that produces hysteresis loops as shown in Figure 1 The width of hysteres...

Страница 94: ...that you put in 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 dual operational amplifier uses two power sources 4 5V for the circuit and 9V for the IC Note that the dual operational amplifier has two input terminals the positive and negative terminals 69 and 68 The non inverting input is applied to the positiv...

Страница 95: ...ast project IC 1 used as a buffer of gain 1 and IC 2 as an inverting amplifier Input reaches this inverting amplifier through its negative terminal not the positive one as in our last project Its gain is about 100 as determined by R1 R2 100k 1k The gain becomes larger if you increase R1 or decrease R2 See what happens to the gain when you change the value of R2 to 470 Notes EXPERIMENT 76 INVERTING...

Страница 96: ...this microphone amplifier It is still determined by R1 and R2 but now it s much larger Can you see why Yes we use the 100kΩ resistor in place of the 1kΩ resistor from the last two projects Try changing R2 to 1kΩ and the gain drops to the level of the last projects In this project two power sources are connected in series to operate the dual operational amplifier at 9V But the operational amplifier...

Страница 97: ...used as a normal speaker electricity flows through the coil and a magnetic field is created around the coil The magnet attracts or repulses the coil depending on the magnetic field created by the coil So the coil moves this movement is transferred to the cone paper attached to it and this creates the sound you hear Here the speaker is used as a microphone so the opposite takes place When sound mak...

Страница 98: ...s tone with another You can change the two separate tones by changing the values for the two 10kΩ resistors Thus the tone mixing amplifier allows you to mix two tones together by changing resistances with no need to change the other circuits Notes EXPERIMENT 79 TONE MIXING AMPLIFIER Wiring Sequence o 1 29 o 2 30 o 3 49 91 119 124 o 5 67 90 o 50 51 85 106 o 52 53 54 87 86 o 55 88 105 113 o 56 57 75...

Страница 99: ...ker to produce the sound This circuit is called a single ended push pull circuit SEPP You have learned about push pull circuits Single ended means the circuit has only one output Most amplifiers have a second output that is connected to the negative side of the battery Notes EXPERIMENT 80 POWER AMPLIFIER USING OPERATIONAL AMPLIFIER 99 Wiring Sequence o 1 29 o 2 30 o 3 90 67 47 44 o 5 94 48 119 124...

Страница 100: ...e voltage through terminal 27 of the control changes the 0 01μF capacitor s charging discharging time also changes causing a change in the frequency of the oscillator Current that shows a triangular wave travels from terminal 67 of the first operational amplifier to terminal 65 of the second amplifier which acts as a comparator The comparator releases output from terminal 64 current that shows a s...

Страница 101: ...s you ll see later The oscillating circuit of this buzzer is an astable multivibrator and works as an oscillator producing current that shows a square wave Changing the control changes the tone of the sound because it changes the frequency of the signal The frequency is determined by the resistance from the battery input and the resistance from the capacitor that is connected to the battery termin...

Страница 102: ...est the alarm detach the wire from terminal 13 The speaker gives out a beep This beep is the alarm that tells you a burglar is about the break into your house As you can see in the schematic this burglar alarm uses the dual operational amplifier as an astable multivibrator as the electronic buzzer in the last project did You can change its frequency by using different values for the 10kΩ resistor ...

Страница 103: ...hear the speaker give out a sudden roaring siren sound The sound is low at first and becomes higher then changes to a steady tone in about 3 to 4 seconds When you press the key and release it the capacitor discharges and starts the siren sound again Refer to the schematic IC 1 works as a buffer and IC 2 as an astable multivibrator The pitch changes when the 100kΩ resistor increases the voltage app...

Страница 104: ...ecomes progressively lower Press the key to start the sound again Like the siren in our last project this siren uses IC 1 as a buffer and IC 2 as an astable multivibrator The capacitor C and the resistor R change the pitch of the siren sound The pitch changes slowly when you increase the values of C and R and it changes quickly when you decrease their values Use the 3 3μF capacitor for C and notic...

Страница 105: ...hear the siren sound change pitch as you expected IC 1 is an oscillator that produces current that forms a triangular wave so when you press the key it produces a triangular wave output Then the output is sent to IC 2 which acts as an astable multivibrator In projects 84 85 and 86 the astable multivibrator produces the siren sound and the pitch changes according to the values of R and C Find out h...

Страница 106: ...n is made up of two astable multivibrators IC 2 provides the normal beep sound that we heard in Project 82 Operational Amplifier Buzzer and IC 1 produces the signal that changes the pitch of its sound at regular intervals Let s perform a small experiment now Detach the 22kΩ resistor and you find that the siren gives out an intermittent beep instead of the two pitch sound Can you figure out why Yes...

Страница 107: ... rotate the control clockwise and the beats come faster Now take a look at the schematic IC 1 and IC 2 are used as astable multivibrators as in our last project But you ll notice that IC 1 uses diodes to generate short pulses and the control is used to adjust the speed of the pulses The transistor turns on each time a pulse is generated and produces a sound Notes EXPERIMENT 88 MUSICAL TEMPO GENERA...

Страница 108: ...al operational amplifier works as an astable multivibrator of a low frequency You can change the period of oscillation that is the LED blinking rate by using different values for R and C See what happens to the blinking rate when you change the value of R to 220kΩ One last thing the dual operational amplifier has a high input impedance resistance to input so it loses very little input current This...

Страница 109: ...position A and lightly tap the key The LED starts blinking immediately Even if you don t press the key this LED flasher starts flashing shortly after you turn on the power if you press the key it begins blinking immediately Just like the LED winker in the last project this LED flasher uses a dual operational amplifier as an astable multivibrator but its flashing time is much shorter because of the...

Страница 110: ...few seconds The LEDs light and turn off alternately The dual operational amplifier works as an astable multivibrator as in previous projects When the output is high LED 1 lights when it is low LED 2 lights You can change the speed of the winking by using different values for R and C See how the speed of the pulses change when you change the value of R to 220kΩ Notes EXPERIMENT 91 TWO LED WINKER Sc...

Страница 111: ...liding the switch to position A The LED lights but quickly turns off Now press the key and see what happens The LED lights and stays on for 2 to 3 seconds and then turns off You can change the amount of time the LED is on by using different values for C Change the value of C from 10μF to 100μF and see what happens to the LED It stays on much longer Notes EXPERIMENT 92 ONE SHOT LIGHT 111 Schematic ...

Страница 112: ...position A to turn on the power and you ll see the letters E and P lighting alternately on the LED display IC 1 works as an astable multivibrator and displays the letter E IC 2 is used as an inverter with an output that is opposite to that of IC 1 it displays the letter P Now that you ve successfully displayed the letters E and P why not try displaying other letters It should be a cinch if you tak...

Страница 113: ...light When you cast a shadow over the CdS the siren sound stops Like the electronic buzzer in Project 82 Operational Amplifier Buzzer the alarm siren uses a multivibrator and controls its operation with the CdS Turn on the power for this project when you go to bed at night and sleep with your room dark Then the alarm siren will wake you up the next morning Notes EXPERIMENT 94 WAKE UP SIREN 113 Sch...

Страница 114: ...1 acts as a microphone amplifier a non inverting amplifier with a gain of about 100 IC 2 works as a comparator Its positive input terminal receives a reference voltage from the battery The output of the microphone amplifier goes to the comparator s negative input terminal When this input voltage is higher than the reference voltage the comparator s output level becomes low and the LED lights Notes...

Страница 115: ...erminal to terminal 122 to apply 4 5V The display changes to 1 Look at the schematic The dual operational amplifier works as a comparator A reference voltage of about 3V is applied to its negative input terminal When the input applied to its positive terminal is higher than this reference voltage the comparator s output level becomes high turning off the transistor Q1 Segments A E F and D of the d...

Страница 116: ... 116 IX MORE ADVENTURES WITH OPERATIONAL AMPLIFIERS ...

Страница 117: ...he CdS cell near an electric lamp Can you hear a hissing sound coming from the earphone This is the sound of the alternating current Now place the CdS cell under a fluorescent lamp and listen for a similar sound This circuit greatly amplifies the signals of light on the CdS cell through the operational amplifier Adjust the quantity of light on the CdS cell with your hand You can probably hear the ...

Страница 118: ...ulate the approximate value of the frequency of the signal by using the equation 1 2 x C1 x R1 However R1 in this project is the CdS and is not constant You can change the value of the output frequency by changing C1 In this experiment the speaker is equipped with a buffer so that the light control sound circuit is not affected when the speaker emits sounds Notes EXPERIMENT 98 LIGHT CONTROL SOUND ...

Страница 119: ...ile speaking into the microphone and set the control in a position where the LED light only when you speak into the microphone Stop speaking and you will see the LED turn off Now see what happens when you disconnect the wire between 57 and 62 and reconnect it between 57 and 32 When you blow into the microphone earphone the LED and the speaker sounds Notes EXPERIMENT 99 SOUND ALARM CIRCUIT 119 Wiri...

Страница 120: ... a lot of patience but it is necessary for making sure your timer works accurately After you set the calibration make a graph showing each control position and the time it takes for the buzzer to sound Now your tester is ready for use Look at the schematic The control changes the reference voltage of the comparator IC 1 The timer setting is determined by the resistor R and the capacitor C When the...

Страница 121: ...nds the timer sounds for 1 to 2 seconds and stops Use the graph you 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 a time lag of 1 to 2 seconds produced by R and C the transistor Q1 turns on to stop the multivibrator The silicon diode discharges C and restores the circuit to the original state when the timer i...

Страница 122: ...rminals are connected to the negative terminal so they do not cause the LED to light Terminal 14 is connected to the positive terminal so it is the logic 1 terminal When you connect terminals 125 127 and 129 to terminal 14 in various combinations you see that the LED lights and shows H only when terminals 125 127 and 129 are all connected to terminal 14 logic 1 Notes EXPERIMENT 102 THREE INPUT AND...

Страница 123: ...ls through the PNP transistor and then becomes the positive input for the first operational amplifier The output of this operational amplifier is stored at the 100μF capacitor The voltage of the capacitor lowers as it slowly discharges through the 47kΩ resistor As the voltage decreases the LED grows dim At the same time the voltage that lights the LED flows to the negative input of the first opera...

Страница 124: ...ing and now it is stabilized Set the switch to position B to switch the power back to 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 The operational amplifier acts as a comparator The negative terminal receives the reference voltage of about 5 4V When the switch is at position B the positive terminal receives about ...

Страница 125: ...n the resistance is large and faster when the resistance is small This charging speed 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 seconds later This 5 to 7 second time difference is the delay time that is set by the CR time constant Now turn off the power ...

Страница 126: ...eans the frequency is doubled to 1 000Hz Now let s see how this frequency doubler works Transistor Q1 receives signals from the operational amplifier through its transistor base The base voltage changes with the oscillations This results in the opposite phase signals appearing at the collector and emitter when one signal is at a wave peak the other is at the bottom The two outputs from transistor ...

Страница 127: ...that is generated when you apply a reverse voltage to the base and the emitter of transistor Q1 IC 1 acts as an oscillator The output of this oscillator is rectified remember this term from Project 99 Sound Alarm Circuit by diodes D1 and D2 and flows to Q1 IC 2 amplifies the noise so that you can hear it through the earphone Notes EXPERIMENT 107 WHITE NOISE GENERATOR 127 Wiring Sequence o 64 90 13...

Страница 128: ... a comparator that examines the voltage increase When the input voltage to IC 2 is more than 5V the LED lights By the way did you try rotating the control How does it affect the circuit In this circuit the control is used as a fixed resistor of 50kΩ Rotating the control has no effect Sorry if we had you worried Notes EXPERIMENT 108 DC DC CONVERTER WITH OPERATIONAL AMPLIFIER 128 Wiring Sequence o 3...

Страница 129: ... 129 X COMMUNICATION CIRCUITS ...

Страница 130: ... 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 the earphone Simply disconnect the speaker and connect the earphone to terminals 27 and 28 With these connections the control acts as a volume control as well as a tone control You can replace the control with a fixed resistance if you want a fixed tone and volume When you a...

Страница 131: ...ne that results in the best reception Short antennas 50 feet or less work best on terminal 95 Longer antennas work best on terminal 97 The part of the radio circuit that includes the antenna coil and the tuning capacitor is called the tank circuit When a coil and the tuning capacitor are connected in parallel the circuit resonates only at one frequency So the circuit picks up only the frequency th...

Страница 132: ...he basic rules of radio reception are the same as in Project 110 Crystal Set Radio Simple Diode Radio The tuning capacitor selects the radio station frequency The diode and 0 02μF capacitor rectify detect the audio signal changing it from AC to DC This signal is so weak that we must amplify it to be able to hear it through the speaker Transistor Q1 amplifies the signal first then the control adjus...

Страница 133: ...nications receiver without tuning to another station if the communications receiver has a beat frequency oscillator BFO The BFO beats with your transmitter s CW signal and produces the tone This oscillator sends out an RF signal because the frequency is very high 500 000Hz to 1 600 000Hz When you tune to a weak AM station first and then send a signal slightly off from the station frequency you can...

Страница 134: ... feet so place your AM radio close to the kit Transistor Q1 amplifies the audio frequency signal The amplified signal controls the amplitude of the RF oscillator signal The tuning capacitor and antenna coil tune the RF signal to the setting on your AM radio dial and send it through the antenna Transistor Q2 helps control the amplitude of the RF signal The NPN transistor is a part of the RF oscilla...

Страница 135: ...implest way to use this IC Slide the switch to position B and assemble the project When you complete the circuit put up the antenna connect it to the circuit set the control to the 12 o clock position and slide the switch to position A to turn on the power Turn the tuning capacitor until you hear a station To pick up weaker stations try using the earphone in place of the speaker in connections to ...

Страница 136: ... 136 XI TESTING AND MEASURING CIRCUITS ...

Страница 137: ... unless they have been damaged If you look at the schematic you will see that the output from the transistor goes through the transformer to the 0 02μF capacitor and then to the base of the transistor The emitter of the transistor is connected to the TEST terminal When something that allows electricity to flow is connected to the terminal the transistor starts to oscillate You can safely check alm...

Страница 138: ...100kΩ If the LED does not light the resistance is greater than 100kΩ If the LED lights connect terminals 93 and 86 and see if the LED stays on or turns off If it turns off the resistance is in the range of 10Ω to 100kΩ If it stays on remove the wire from terminal 86 and connect it to terminal 84 If the LED turns off the resistance is in the range of 1 to 10kΩ If the LED still doesn t turn off remo...

Страница 139: ...trol fully counter clockwise Then press the key and turn the control clockwise If you hear a sound from the speaker the transistor is a working PNP transistor If you hear no sound at all change connections 4 124 and 119 138 to 4 119 and 124 138 and repeat the test If you get a sound from the speaker this time the transistor is a working NPN type If you get no sound from the speaker using either se...

Страница 140: ...z sinewave has A 0 1μF capacitor connecting terminals 3 and 5 of the transformer to form a tank circuit that resonates at about 600Hz A 470kΩ resistor to turn on the base of the transistor only a small amount An adjustable feedback circuit that includes the control and the 0 05μF capacitor A 100Ω resistor connected to the emitter to help stabilize the circuit and keep the sound from being distorte...

Страница 141: ...s C make up the path for the circuits to the transistor base Every time the signals pass the RC circuits a slight time lag occurs In other words the rise and fall of the wave the phase shifts slightly That s why we call it phase shift After the signal has traveled through the circuit the phase shifts 180 degrees When the collector voltage rises this rise is fed back to the collector with the phase...

Страница 142: ...it to obtain pure sinewave output as in the previous two projects Adjust the control very slowly over its entire range until you hear a tone in the earphone that is very low and resembles the lowest note of a large pipe organ This control setting should be between 7 and 10 on your dial Once the oscillation has started adjust the control carefully for the setting that gives the purest sounding low ...

Страница 143: ...ly in less than 0 0001 seconds charges the 0 05μF to about 4V or so with a polarity negative on the transformer side and positive on the transistor base lead side Output activates the speaker only while the current flows in the transformer The charging of the 0 05μF capacitor stops when the induced voltage from the top half of the transformer winding stops Then the capacitor begins to charge again...

Страница 144: ...out damaging the circuit The amplifier circuit is a common emitter type That is the transistor s emitter is connected directly to the input and the output of the earphone Its base current is the self current type The current from the transistor collector provides current to the base through the 470kΩ resistor This provides some stabilizing negative DC feedback You can use this amplifier to check a...

Страница 145: ...ans and BOLD technicians but there are no OLD BOLD technicians Connect the probes between grounded objects and other metallic objects that can act as antennas You will find that this circuit allows you to receive all kinds of AM signals as well as noise For example if you have citizens band transmitters you can hear these signals if the transmitter is close enough to the signal tracer Some of the ...

Страница 146: ...own below Build this circuit and you will hear the sound produced by a square wave signal You can vary the pitch and the frequency of the signal by adjusting the control This varies the current supplied to the PNP transistor bases Notes EXPERIMENT 124 SQUARE WAVE AUDIO OSCILLATOR Schematic 146 Wiring Sequence o 77 75 48 27 124 o 28 81 83 o 40 107 84 o 41 106 76 o 119 42 45 80 EARPHONE o 43 105 82 ...

Страница 147: ...f the capacitor exceeds the voltage of the voltage divider 1 6V the transistors turn on and provide a path for the 0 1μF capacitor to discharge quickly Now the transistors turn off again and the capacitor begins to slowly charge to repeat the cycle You can change the oscillator frequency by changing the values of the components in the timer circuit the control the 100kΩ resistor and the 0 1μF capa...

Страница 148: ...tallic plates laid out on an insulated surface When water completes the circuit by spanning the two wires or plates the alarm turns on This oscillator is the basic pulse type that we ve used several times in this kit The 22kΩ resistor protects the circuit against excess base current in case the wires are shorted together The 100kΩ resistor keeps any transistor leakage current from turning on the o...

Страница 149: ...uch the two output terminals with your fingers If the speaker makes a sound again the electricity is flowing through your body because the wire lead is in contact with sweat This project uses two dual operational amplifiers IC 1 works as a comparator The IC s negative input terminal has a reference voltage of about 1 6V When a voltage exceeding 1 6V is applied to the positive input terminal the ou...

Страница 150: ...beat note This beat note is the difference between the signal of a broadcast station and this oscillator Do not bring the radio any closer than necessary The best position is where the levels of the two signals are about equal This gives maximum sensitivity Try using keys plastic objects coins and so on as sample objects Of course a real metal detector does not have a small ferrite coil like this ...

Страница 151: ...he only current that can flow is the leakage current from 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 some current can flow through the water to supply base current to the PNP transistor This base current turns on the PNP transistor so that oscillator current can flow between the collector and the emitte...

Страница 152: ...ent of the LED G turns on indicating a moderate water level If the water reaches a level high enough to touch all three wires the base current is supplied to transistor Q1 and the top segment of the LED A lights The audio oscillator is also activated as a warning of a high water level Of course you can modify this wiring to make the LED display show other letters of symbols to indicate the differe...

Страница 153: ...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 Transmitt...

Страница 154: ...8 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 ...

Страница 155: ...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...

Страница 156: ...p flop Capacitance The ability to store electric charge Capacitor An electrical component that can store electrical pressure voltage for periods of time Carbon A chemical element used to make resistors Clockwise In the direction in which the hands of a clock rotate Coil When something is wound in a spiral In electronics this describes inductors which are coiled wires Collector The controlled input...

Страница 157: ...rm for the 0V or side of a battery or generator Henry H The unit of measure for Inductance Inductance The ability of a wire to create an induced voltage when the current varies due to magnetic effects Inductor A component that opposes changes in electrical current Integrated Circuit A type of circuit in which transistors diodes resistors and capacitors are all constructed on a semiconductor base K...

Страница 158: ...rent Schematic A drawing of an electrical circuit that uses symbols for all the components Semiconductor A material that has more resistance than conductors but less than insulators It is used to construct diodes transistors and integrated circuits Series When electrical components are connected one after the other Short Circuit When wires from different parts of a circuit or different circuits co...

Страница 159: ...at times to signify a decimal point as in 3R3 3 3 103K 100V 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 positive and a negative electrode The negative lead is indicated on the packaging by a stripe with minus signs and po...

Страница 160: ...99 Washington Street Melrose MA 02176 Phone 781 665 1400 Toll Free 1 800 517 8431 Visit us at www TestEquipmentDepot com ...

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