Elenco Electronics Snap Circuits Light User manual

Copyright © 2003 by ElencoTM Electronics, Inc. All rights reserved. No part of this book shall be reproduced by 753104
any means; electronic, photocopying, or otherwise without written permission from the publisher.

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Table of Contents
Basic Troubleshooting 1
Parts List 2
MORE About Your Snap Circuits Parts 3
MORE Advanced Troubleshooting 4
MORE DO’s and DON’Ts of Building Circuits 5
Project Listings 6, 7
Experiments 306-511 9 - 57
More Snap Circuits Projects 58
1. Most circuit problems are due to
incorrect assembly, always double-
check that your circuit exactly
matches the drawing for it.
2. Be sure that parts with
positive/negative markings are
positioned as per the drawing.
3. Sometimes the light bulbs come
loose, tighten them as needed.
4. Be sure that all connections are
securely snapped.
5. Try replacing the batteries.
ElencoTM Electronics is not responsible
for parts damaged due to incorrect
wiring.
Basic
Note: If you suspect you have
damaged parts, you can follow the
Advanced Troubleshooting
procedure on page 5 to determine
which ones need replacing.
How To Use It
WARNING: SHOCK HAZARD - Never connect snap circuits to
the electrical outlets in your home in any way! WARNING: Always check your wiring before turning on a circuit.
Never touch the motor when it is spinning at high speed. Never
leave a circuit unattended while the batteries are installed.
The snap circuit kit uses building blocks with snaps to build
the different electrical and electronic circuits in the projects.
Each block has a function: there are switch blocks, lamp
blocks, battery blocks, different length wire blocks, etc.
These blocks are in different colors and have numbers on
them so that you can easily identify them. The circuit you will
build is shown in color and numbers, identifying the blocks
that you will use and snap together to form a circuit.
For Example:
This is the switch block which is green and has the marking
on it.
This is a wire block which is blue and comes in different wire
lengths.
This one has the number , , , , , or on it
depending on the length of the wire connection required.
There is also a 1-snap wire that is used as a spacer or for
interconnection between different layers.
To build each circuit, you have a power source block
number that need two (2) “AA” batteries (not included
with the snap circuit kit).
A large clear plastic base grid is included with this kit to help
keep the circuit block together. You will see evenly spaced
posts that the different blocks snap into. You do not need this
base to build your circuits, but it does help in keeping your
circuit together neatly. The base has rows labeled A-G and
columns labeled 1-10.
Next to each part in every circuit drawing is a small number in
black. This tells you which level the component is placed at.
Place all parts on level 1 first, then all of the parts on level 2,
then all of the parts on level 3, etc.
The 2.5V and 6V bulbs come packaged separate from their
sockets. Install the 2.5V bulb in the lamp socket , and the
6V bulb in the lamp socket whenever those parts are
used.
Place the fan on the motor whenever that part is used,
unless the project you are building says not to use it.
Some circuits use the jumper wires to make unusual
connections. Just clip them to the metal snaps or as
indicated.
Note: While building the projects, be careful not to
accidentally make a direct connection across the battery
holder (a “short circuit”), as this will damage and/or quickly
B1
L1
M1
2 3 4 5 6
S1
7
L2

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Qty. ID Name Symbol Part # Qty. ID Name Symbol Part #
32-Snap Wire 6SC02 1Analog Meter 6SCM2
15-Snap Wire 6SC05 1SCR 6SCQ3
1Diode
1N4001 6SCD3 1Relay 6SCS3
17-Segment
LED
Display 6SCD7 1 Transformer 6SCT1
1FM Module 6SCFM 1 Recording
Integrated
Circuit 6SCU6
You may order additional / replacement parts at our website: www.elenco.com/snapcircuits
Q3
M2
FM
D3
5
2
S3
T1
U6
D7
Note: There are additional part lists in your other project manuals. Part designs are subject to change without notice.
Important: If any parts are missing or damaged, DO NOT RETURN TO RETAILER. Call toll-free [phone] or e-mail us at:
[email protected]. Customer Service • 150 W. Carpenter Ave. • Wheeling, IL 60090 U.S.A.
Parts List (Colors and styles may vary) Symbols and Numbers

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(Part designs are subject to change without notice).
The FM module (FM) contains an integrated FM radio circuit.
Refer to the figure below for the pinout description:
The meter (M2) The meter is a very important indicating and
measuring device. You’ll use it to measure the amount of current
or voltage depending on the circuit configuration. Notice the meter
has + sign, indicating the positive terminal (+ power from the
batteries). The other snap is the negative terminal (- power return
to batteries).
The recording IC module (U6) contains an integrated recording
circuit. You can record a message up to eight seconds long.
There are also three pre-recorded songs. Refer to the figure below
for the pinout descriptions:
The relay (S3) is an electronic switch with contacts that can be
closed or opened. It contains a coil that generates a magnetic field
when current flows through it. The magnetic field attracts an iron
armature, which switches the contacts (see figure).
The transformer (T1) consists of two coils windings on one core.
One coil is called the Primary (input) and other the Secondary
(output). The purpose of the transformer is to increase the amount
of AC voltage applied to the primary. This transformer is a step-up
transformer. The secondary has more windings than the primary.
Diode (D3) - You can think of a diode as a one-way valve that
permits current flow in the direction of the arrow. The anode
(arrow) is the positive side, and the cathode (bar) is the negative.
The diode conducts or turns on when the voltage at the anode is
0.7V or greater.
MORE About Your New Snap Circuits Parts (Note: There is additional information in your other project manuals).
(+)
OUT
(–)
FM Module:
(+) - power from batteries
(–) - power return to batteries
T - tune up
R - reset
OUT - output connection
See project 307 for example of
proper connections.
(+)
OUT
(–)
Recording IC Module:
(+) - power from batteries
(–) - power return to batteries
RC - record
Play - play
OUT - output connection
Mic + - microphone input
Mic – - microphone input
See project 308 for example of
proper connections.
RCPlay
Mic –
Mic +
COM Relay:
Coil - connection to coil
Coil - connection to coil
NC - normally closed contact
NO - normally open contact
COM - Common
See project 341 for example of
proper connections.
Coil
Coil NO
NC
S
CT
S
Transformer:
P - primary (input)
P - primary (input)
S - secondary (output)
S - secondary (output)
CT - center tap
See project 347 for example of
proper connections.
P
P
Anode
Diode:
Anode - (+)
Cathode - (–)
Cathode
(+)
(–)
Meter:
(+) - power from batteries
(–) - power return to batteries

ElencoTM Electronics is not responsible for parts damaged due to incorrect wiring.
If you suspect you have damaged parts, you can follow this procedure to systematically
determine which ones need replacing:
1 - 20. Refer to project manuals 1 & 2 (projects 1-101, 102-305) for testing steps 1-20, then
continue below.
21. FM Module (FM): Build project #307, you should hear FM radio stations.
22. Meter (M1): Build the mini-circuit shown here, the meter (M2) should
deflect full scale.
23. Recording IC (U6): Build project 308. Make an 8 second recording, then listen to the three
prerecorded songs.
24. Relay (S3): Build project #353. Turn on the switch (S1) and you should hear a buzzing sound
from the relay.
25. Transformer (T1): Build the mini-circuit shown here.
Pressing the switch (S2) flashes the LED. Connect the
jumper wire to the CT point. Pressing the switch (S2)
flashes the LED.
26. Diode (D3): Build the mini-circuit shown here, the LED should light.
Reverse the direction of D3, the LED should not light now.
27. SCR (Q3): Build the mini-circuit shown here. Turn on the switch
(S1) and the motor should not spin. Press switch S2, the motor
should start spinning. Now open and close switch S1, the motor
should not spin.
28. 7-Segment Display (D7): Build project #337. All segments light, displaying the number 8.
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SCR (Q3) - An SCR is a three pin (anode, cathode
and gate) controlled silicon diode. Like a standard
diode, it permits current flow in only one direction. It
will only conduct in the forward direction when
triggered by a short pulse or steady voltage applied
to between the gate and cathode terminals.
A high
current may damage this part, so the current must
be limited by other components in the circuit.
The 7-segment display (D7) is found in many
devices today. It contains 7 LEDs that have been
combined into one case to make a convenient
device for displaying numbers and some letters.
The display is a common anode version. That
means that the positive leg of each LED is
connected to a common point which is the snap
marked +. Each LED has a negative leg that is
connected to one snap. To make it work you need
to connect the + snap to positive three volts. Then
to make each segment light up, connect the snaps
of each LED to ground. In the projects, a resistor is
always connected to the + snap to limit the current.
A high current may damage this part, so the
current must be limited by other components in
the circuit.
SCR:
A - Anode
K - Cathode
G - Gate
7-segment Display:
(+) - power from batteries
A - Segment A
B - Segment B
C - Segment C
D - Segment D
E - Segment E
F - Segment F
G - Segment G
DP - Decimal Point
See project 337 for example
of proper connections.
MORE Advanced Troubleshooting (Adult supervision MORE About Your Snap
Circuits Parts (continued)

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MORE DO’s and DON’Ts of Building Circuits
After building the circuits given in this booklet, you may wish to experiment on
your own. Use the projects in this booklet as a guide, as many important design
concepts are introduced throughout them. Every circuit will include a power
source (the batteries), a resistance (which might be a resistor, lamp, motor,
integrated circuit, etc.), and wiring paths between them and back. You must be
careful not to create "short circuits" (very low-resistance paths across the
batteries, see examples below) as this will damage components and/or quickly
drain your batteries.Only connect the ICs using configurations given in the
projects, incorrectly doing so may damage them. ElencoTM Electronics is not
responsible for parts damaged due to incorrect wiring.
Here are some important guidelines:
ALWAYS include at least one component that will limit the current through a
circuit, such as the speaker, lamp, whistle chip, capacitors, ICs (which
must be connected properly), motor, microphone, photo resistor, or
fixed resistors.
ALWAYS use the 7-segment display, LEDs, transistors, the high frequency IC,
the SCR, the antenna, and switches in conjunction with other
components that will limit the current through them. Failure to do
so will create a short circuit and/or damage those parts.
ALWAYS connect the adjustable resistor so that if set to its 0 setting, the current
will be limited by other components in the circuit.
ALWAYS connect position capacitors so that the “+” side gets the higher voltage.
ALWAYS disconnect your batteries immediately and check your wiring if
something appears to be getting hot.
ALWAYS check your wiring before turning on a circuit.
ALWAYS connect ICs, the FM module, and the SCR using configurations
given in the projects or as per the connection descriptions for the
parts.
NEVER try to use the high frequency IC as a transistor (the packages are similar,
but the parts are different).
NEVER use the 2.5V lamp in a circuit with both battery holders unless you are
sure that the voltage across it will be limited.
NEVER connect to an electrical outlet in your home in any way.
NEVER leave a circuit unattended when it is turned on.
NEVER touch the motor when it is spinning at high speed.
For all of the projects given in this book, the parts may be arranged in different
ways without changing the circuit. For example, the order of parts connected in
series or in parallel does not matter — what matters is how combinations of these
sub-circuits are arranged together.
Examples of SHORT CIRCUITS - NEVER DO THESE!!!
You are encouraged to tell us about new circuits you create. Upon
review, we will post them with your name, age, and hometown in a special
section on our website. If we use them in future manual revisions, we will
send you a copy of the manual so you can show your family and friends.
Send your suggestions to ElencoTM Electronics.
WARNING: SHOCK HAZARD - Never connect snap circuits to the
electrical outlets in your home in any way!
Placing a 3-snap wire directly
across the batteries is a
SHORT CIRCUIT.
This is also a
SHORT
CIRCUIT.
When the switch (S1) is turned on, this large circuit has a SHORT
CIRCUIT path (as shown by the arrows). The short circuit prevents any
other portions of the circuit from ever working.
!
!
!!
NEVER
DO!
NEVER
DO!
NEVER
DO!
NEVER
DO!
NEVER
DO!
!

Project # Description Page #
306 AM Radio 8
307 Adjustable Volume FM Radio 8
308 Playback & Record 9
309 Playing Music 9
310 Light-Controlled Music 9
311 Touch-Controlled Music 9
312 Power Amplified Playing Music 10
313 Power Playback & Record 10
314 Power Light-Controlled Music 10
315 Power Touch-Controlled Music 10
316 FM Radio 11
317 Mega Circuit 11
318 SCR 2.5V Bulb 12
319 SCR & Motor 12
320 Music Alarm 13
321 Light-Music Alarm 13
322 Light-Controlled SCR 13
323 1mA Meter 14
324 0-3V Meter 14
325 Function of Variable Resistor 15
326 Function of Photo Resistor 15
327 Meter Deflect by Motor 16
328 SCR 6V Bulb 16
329 Principle of Segment LED 17
330 Display #1 17
331 Display #2 17
332 Display #3 17
333 Display #4 17
334 Display #5 18
335 Display #6 18
336 Display #7 18
337 Display #8 18
338 Display #9 18
339 Display #0 18
Project # Description Page #
340 Music Meter 18
341 LED & Relay 19
342 Manual 7 Second Timer 19
343 Half Wave Rectifier Circuit 20
344 Half Wave Rectifier Circuit (II) 20
345 LED vs. Diode 20
346 Current & Resistance 20
347 Telegraph 21
348 Mosquito Sound 21
349 Mosquito Sound (II) 21
350 Mosquito Sound (III) 21
351 Touch-Control Mosquito Sound 21
352 Bulb & Relay 22
353 Relay Buzzer 22
354 Transistor Timer 23
355 Light-Controlled Relay 23
356 Bulb Alert Relay 23
357 Adjustable Light Control 24
358 Meter Deflection 24
359 AC to DC Current 25
360 Current Meter 25
361 Buzzer, Relay, & Transformer 26
362 Buzzer & Relay 26
363 Display Capital Letter “F” 27
364 Display Capital Letter “H” 27
365 Display Capital Letter “P” 27
366 Display Capital Letter “S” 27
367 Display Capital Letter “U” 27
368 Display Capital Letter “C” 27
369 Display Capital Letter “E” 27
370 Display “.” 27
371 Display Letter “b” 28
372 Display Letter “c” 28
373 Display Letter “d” 28
Project # Description Page #
374 Display Letter “e” 28
375 Display Letter “h” 28
376 Display Letter “o” 28
377 Alarm by SCR 29
378 Light Space War Alarm 29
379 Alarm by SCR 29
380 Light & Alarm IC 29
381 Delay Light 30
382 Delay Fan 30
383 Delay Fan (II) 30
384 Recording LED Indicator 31
385 Playback & Record with Meter 31
386 Alarm Light 32
387 Alarm Light (II) 32
388 Night Police Car 33
389 Night Machine Gun 33
390 Night Fire Engine 33
391 Night Ambulance 33
392 Daytime Light Police Car 34
393 Daytime Light Machine Gun 34
394 Daytime Light Fire Engine 34
395 Daytime Light Ambulance 34
396 Flashing 8 35
397 Flashing 8 with Sound 35
398 Musical Space War 35
399 Oscillation Sounds 36
400 Oscillation Sounds (II) 36
401 Oscillation Sounds (III) 36
402 Oscillation Sounds (IV) 36
403 Touch-Control Oscillator 36
404 Oscillator Sound 37
405 Oscillator Sound (II) 37
406 Oscillator Sound (III) 37
407 Oscillator Sound (IV) 37
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Project Listings

-7-
Project # Description Page #
408 Oscillator Sound (V) 37
409 Transistor Tester 38
410 Adjustable Voltage Divider 38
411
Automatic Display Capital Letter “C” 39
412
Automatic Display Capital Letter “E” 39
413
Automatic Display Capital Letter “F” 39
414
Automatic Display Capital Letter “H” 39
415
Automatic Display Capital Letter “P” 39
416
Automatic Display Capital Letter “S” 39
417
Automatic Display Capital Letter “U” 39
418
Automatic Display Capital Letter “L” 39
419 Whistle Chip Sounds 40
420 Whistle Chip Sounds (II) 40
421 Whistle Chip Sounds (III) 40
422 Whistle Chip Sounds (IV) 40
423 Whistle Chip Sounds (V) 40
424 Whistle Chip Sounds (VI) 40
425 LED Music 41
426
Light-Controlled LED Time Delay 41
427
Touch-Controlled LED Time Delay 41
428 Alarm Recorder 42
429 Alarm Recorder (II) 42
430 Machine Gun Recorder 42
431 Time Delay 1-7 Seconds 43
432 Time Delay 43
433 Manual 7 Second Timer (II) 44
434 15 Second Alarm 44
435 Flashing “1 & 2” 45
436 Flashing “3 & 4” 45
437 Flashing “5 & 6” 45
438 Flashing “7 & 8” 45
439 Flashing “9 & 0” 45
440 Flashing “C & E” 46
441 Flashing “F & H” 46
442 Flashing “P & S” 46
Project # Description Page #
443 Flashing “U & L” 46
444 Flashing “b & c” 46
445 Flashing “d & e” 46
446 Flashing “h & o” 46
447 Bird Sounds 47
448 Bird Sounds (II) 47
449 Bird Sounds (III) 47
450 Bird Sounds (IV) 47
451 Bird Sounds (V) 47
452 Touch-Control Bird Sound 47
453 Motor Sound Recording 48
454 Motor Sound Indicator 48
455 Relay & Buzzer 49
456 Relay & Speaker 49
457 Relay, LED, & Bulb 49
458 Electronic Cat 50
459 Electronic Cat (II) 50
460 Electronic Cat (III) 50
461 Electronic Cat (IV) 50
462 Buzzer Cat 50
463 Buzzer Cat (II) 50
464 Buzzer Cat (III) 50
465 Lazy Cat 50
466 Meter Deflection (II) 51
467 Automatic Display #1 51
468 Automatic Display #2 51
469 Automatic Display #3 52
470 Automatic Display #4 52
471 Automatic Display #5 52
472 Automatic Display #6 52
473 Automatic Display #7 52
474 Automatic Display #8 52
475 Automatic Display #9 52
476 Automatic Display #0 52
477 Variable Oscillator 53
Project # Description Page #
478 Variable Oscillator (II) 53
479 Variable Oscillator (III) 53
480 Variable Oscillator (IV) 53
481 Photo Variable Oscillator 53
482
Photo Variable Whistle Chip Oscillator 53
483 Slow Adjusting Tone 53
484 Slow Adjusting Tone (II) 53
485 Fixed-Voltage Divider 54
486 Simple Illumination Meter 54
487 LED Voltage Drop 55
488 Open/Closed Door Indicator 55
489 Hand-Control Meter 56
490 Light-Control Meter 56
491 Electric-Control Meter 56
492 Sound-Control Meter 56
493 Fixed-Voltage Divider 57
494 Resistor Measurement 57
495 Automatic Display Letter “b” 58
496 Automatic Display Letter “c” 58
497 Automatic Display Letter “d” 58
498 Automatic Display Letter “e” 58
499 Automatic Display Letter “h” 58
500 Automatic Display Letter “o” 58
501 Hand-Control Display 1 & 4 59
502 Hand-Control Display 1 & 0 59
503 Hand-Control Display 1 & 7 59
504 Hand-Control Display 1 & 8 59
505 Hand-Control Display 1 & 9 59
506
Monitor a Capacitor Charging & Discharging 60
507 Hand-Control Space Meter 60
508 Rhythm Swinging Meter 61
509
Police Car Sound with Whistle Chip 61
510
Fire Engine Sound with Whistle Chip 61
511
Ambulance Sound with Whistle Chip 61
Project Listings

-8-
Project #306 OBJECTIVE: To build a one IC AM radio.
Turn on the slide switch (S1) and adjust the variable capacitor (CV) for
a radio station.
AM Radio
Project #307
OBJECTIVE: To build a working FM radio with adjustable
volume.
Turn on the switch (S1) and press the R and then the T button. When
a station is heard, adjust the volume using the variable resistor (RV).
The resistor controls the amount of signal into the power amp.
Turn on the switch (S1) and press the R button. Now press the T
button and FM module scans for a radio station. When a station is
found, it locks on to it and you hear it on the speaker. Adjust the
volume using the variable resistor (RV). The resistor controls the
amount of signal into the power amp. Press the T button again for the
next radio station. The module will scan up to 108MHz, the end of the
FM band, and stop. You must then press reset to start at 88MHz
again.
Adjustable Volume
FM Radio

-9-
Project #308
Build the circuit shown. Turn on the switch (S1), you hear a beep
signaling that you may begin recording. Talk into the microphone (X1)
up to 8 seconds, and then turn off the switch (S1) (it also beeps after
the 8 seconds expires).
Press the switch S2 for playback. It plays the recording you made
followed by one of three songs. If you press the switch (S2) before the
song is over, music will stop. You may press the switch (S2) several
times to play all three songs.
Playback & Record
OBJECTIVE: To demonstrate the capabilities of the
recording integrated circuit.
OBJECTIVE: To play the three built-in
songs on the recording IC.
Use the circuit in project 308. Turn on the
switch (S1), then press the switch (S2) to start
the first song. When the music stops, press
the switch (S2) again to hear the second
song. When the second song stops, press the
switch (S2) again, the third song plays.
Playing Music
Project #309
OBJECTIVE: To build circuit that uses light
to control the recording IC.
Light-
Controlled
Music
Project #310
OBJECTIVE: To build circuit that lets you
control the recording IC with your fingers.
Touch-
Controlled
Music
Project #311
Use the circuit in project 308. Replace the
switch (S2) with the photo resistor (RP), then
turn on the switch (S1). Turn the music on and
off by waving your hand over photo resistor.
Use the circuit in project 308. Replace the
switch (S2) with the PNP transistor (Q1) and
then turn on the switch (S1). Turn the music
on and off by touching the base and collector
at the same time. You may need to wet your
fingers.

-10-
Project #312
Connecting the power amp IC (U4) to the output of the recording IC
(U6), you can make much louder music than project 308.
Turn on the switch (S1), you hear a beep signaling that you may begin
recording. Talk into the microphone up to 8 seconds, and then turn
open the switch (it also beeps after the 8 seconds expires).
Press the switch (S2) for playback. It plays the recording you made
followed by one of three songs. If you press switch (S2) before the
song is over, music will stop. You may press the switch (S2) several
times to play all three songs.
Power Amplified
Playing Music
OBJECTIVE: To build a circuit that amplifies the recording IC.
OBJECTIVE: To amplify the output of the
recording IC.
Use the circuit in project 312. Turn on the
switch (S1), then press the switch (S2) to start
the first song. When the music stops, press
the switch (S2) again to hear the second
song. When the second song stops, press the
switch (S2) again, the third song plays.
Power
Playback &
Record
Project #313
OBJECTIVE: Show variations of project 312.
Power Light-
Controlled
Music
Project #314
OBJECTIVE: Show variations of project 312.
Power Touch-
Controlled
Music
Project #315
Use the circuit in project 312. Replace the
switch (S2) with the photo resistor (RP), then
turn on the switch (S1). Turn the music on
and off by waving your hand over photo
resistor.
Use the circuit in project 312. Replace the
switch (S2) with the PNP transistor (Q1) and
then turn on the switch (S1). Turn the music
on and off by touching the base and collector
at the same time. You may need to wet your
fingers.

-11-
Project #316 OBJECTIVE: To build a working FM radio.
The FM module (FM) contains a scan (T) and a reset (R) button. The
R button resets the frequency to 88MHz. This is the beginning of the
FM range. Press the T button, the module scans for the next available
radio station.
Turn on the switch (S1) and press the R button. Now press the T
button and the FM module scans for an available radio station. When
a station is found, it locks on to it and you hear it on the speaker.
Press the T button again for the next radio station. The module will
scan up to 108MHz, the end of the FM band, and stop. You must then
press the reset (R) button to start at 88MHz again.
FM Radio
Project #317 OBJECTIVE: To build a complex circuit.
This is an example of using many parts to create an unusual circuit.
Turn on the switch (S1). As the circuit oscillates, the 7-segment
display (D7) flashes the number 5 and the LEDs flash as well. The
meter (M2) deflects back and forth and the speaker sounds a low tone
at the same rate. The frequency of the circuit can be changed by
adjusting the variable resistor.
Mega Circuit

-12-
Project #318 OBJECTIVE: To learn the principle of an SCR.
This circuit demonstrates the principle of the SCR (Q3). The SCR can
be thought of as an electronic switch with three leads: anode,
cathode, and gate. Like a standard diode, it permits current flow in
only one direction. It will only conduct in the forward direction when
triggered by a short pulse or steady voltage applied between the gate
and cathode terminals. One set of batteries powers the lamp, the
other is used to trigger the SCR.
Turn on the switch (S1) and the bulb (L1) should not light. Now press
the press switch (S2); the SCR turns on and lights the bulb. To turn
off the bulb you must turn off the slide switch (S1).
SCR 2.5V Bulb
Project #319 OBJECTIVE: To activate a motor using an SCR.
In this circuit, the gate is connected to the battery through resistor R2.
When the switch (S1) is turned on, it triggers the gate, the SCR
conducts, and the motor (M1) spins. The motor continues to spin until
the switch is turned off.
SCR & Motor

-13-
Project #320 OBJECTIVE: To build a music alarm.
The alarm circuit activates when you remove the jumper wire from
points A & B. The jumper wire shorts the SCR’s (Q3) gate to ground
and the SCR does not conduct. Removing the jumper wire places a
voltage on the gate and the SCR conducts. This connects the battery
to the music IC (U1) and music is played.
Construct the circuit and you should hear no music. Now remove the
jumper wire and the music starts playing.
Music Alarm
Project #321
OBJECTIVE: To build a light-music alarm.
Light-Music Alarm
Use the circuit in project 320. Replace the resistor R3 with the photo
resistor (RP) and remove the jumper wire. Cover the photo resistor
with your hand. Now slowly remove your hand. When enough light
hits the resistor, the music plays.
Project #322 OBJECTIVE: To build a circuit that activates a bulb and motor
with the amount of light present.
Cover the photo resistor (RP) with your finger. Turn on the switch
(S1), and only the LED (D1) lights. The relay (S3) connects the motor
(M1) and the bulb (L2) to the batteries, but the motor and bulb are
powerless until a voltage is applied to the SCR's gate.
Remove your finger, as light hits the photo resistor, its resistance
decreases and a voltage appears on the gate of the SCR (Q3). The
SCR conducts and the motor and bulb work now.
Light-Controlled SCR

-14-
Project #323 OBJECTIVE: To build a 1mA meter circuit. 1mA Meter
Project #324 OBJECTIVE: To build a voltmeter. 0-3V Voltmeter
Build this 0-3V voltmeter circuit. Using new batteries, place the battery
holder between points A & B. Adjust the variable resistor (RV) so the
meter deflects full scale.
Now you can check your other “AA” batteries by inserting them into the
battery holder.
Inside the meter (M2), there is a fixed magnet and a moveable coil
around it. As current flows through the coil, it creates a magnetic field.
The interaction of the two magnetic fields cause the coil (connected to
the pointer) to move (deflect). By itself, the meter can measure 300µA
or 0.3V. To increase its range, resistors are connected in parallel or
in series to the meter.
Build the circuit shown. Placing the 100Ωresistor (R1) in parallel with
the meter increases the range to 1mA. More current flows through the
resistor than the meter. The lower the resistor value, the wider the
range of the meter.

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Project #325
OBJECTIVE: To understand the function of the variable resistor.
A variable resistor is a normal resistor with an additional arm contact.
The arm moves along the resistive material and taps off the desired
resistance.
The knob on the variable resistor moves the arm contact and sets the
resistance between the left and center pins. The remaining resistance
of the part is between the center and right pins. For example, when the
dial is turned fully to the left, there is minimal resistance between the left
and center pins (usually 0Ω) and maximum resistance between the
center and right pins. The resistance between the left and right pins will
always be the total resistance, (50kΩfor your part).
Adjust the variable resistor (RV) for maximum resistance by setting the
knob to the top. The meter (M2) only deflects ¼ of the way. As you move
the knob down, decreasing the resistance, the meter deflects more.
Function of Variable
Resistor
Project #326
OBJECTIVE: To understand the function of the photo resistor.
Build the circuit shown. The photo resistor (RP) is a light-sensitive
resistor. Its value changes from nearly infinite in total darkness to
about 1000Ωwhen a bright light shines on it.
The meter reading changes as the resistance changes in the circuit.
When the lights are on, the meter (M2) points to the right of the 5 on
the scale. When the lights are OFF, the pointer will be to the left of the
5. This means that the resistance of the photo resistor is changing
according to the amount of light in the room.
Function of Photo
Resistor

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Project #328 OBJECTIVE: To learn the principle of an SCR.
In this circuit, the 6-volt bulb (L2) will not light until the SCR (Q3) is
triggered. Turn on the switch (S1) and the bulb will not light. Now
press the switch (S2) to light the bulb. The bulb will stay lit until the
slide switch is turned off. To protect the SCR, a current limiting 1kΩ
resistor (R2) is placed in series with the gate.
SCR 6V Bulb
Project #327
OBJECTIVE: To change the direction of current flow using a
motor.
A motor generates a current when it rotates. The rotation of the motor
determines the direction current flows. Quickly spin the motor (M1)
clockwise with your hand; the meter (M2) deflects to the right. Now
spin the motor counterclockwise, and the meter deflects to the left.
Meter Deflect
by Motor

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Project #329
OBJECTIVE: To demonstrate how a seven segment LED works.
The display (D7) is made up of seven segments. Each segment
contains an LED connected to an input snap. When the snap is
connected to the negative of the battery the segment lights. For
example, connect the circuit as shown and the letter “L” lights.
Principle of
Segment LED
Project #330
OBJECTIVE: To configure the seven
segment to display the number 1.
Connect B & C to the negative of the
battery.
Display #1
OBJECTIVE: To configure the seven
segment to display the number 2.
Connect A, B, G, E, & D to the
negative of the battery.
Display #2
OBJECTIVE: To configure the seven
segment to display the number 3.
Connect A, B, G, C, & D to the
negative of the battery.
Display #3
OBJECTIVE: To configure the seven
segment to display the number 4.
Connect B, C, F, & G to the negative of
the battery.
Display #4
Project #331
Project #332 Project #333

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Project #334
OBJECTIVE: To configure the seven
segment to display the number 5.
Connect A, F, G, C, & D to the negative of the
battery.
Display #5 Project #335
OBJECTIVE: To configure the seven
segment to display the number 6.
Connect A, C, D, E, F, & G to the negative of
the battery.
Display #6 Project #336
OBJECTIVE: To configure the seven
segment to display the number 7.
Connect A, B, & C to the negative of the
battery.
Display #7
Project #337
OBJECTIVE: To configure the seven
segment to display the number 8.
Connect A, B, C, D, E, F & G to the negative
of the battery.
Display #8 Project #338
OBJECTIVE: To configure the seven
segment to display the number 9.
Connect A, C, D, F, & G to the negative of the
battery.
Display #9 Project #339
OBJECTIVE: To configure the seven
segment to display the number 0.
Connect A, C, D, E, & F to the negative of the
battery.
Display #0
Project #340 OBJECTIVE: See and hear the output of the music IC.
In this circuit, the output of the music IC (U1) is applied to the primary
of the transformer (T1), which lights the LED (D1) and deflects the
meter (M2).
Place the variable resistor (RV) to the bottom position and turn on the
switch (S1). Adjust the variable resistor upwards. This increases the
voltage across the LED and meter. The LED brightens and the meter
deflects more towards 10. Place the speaker (SP) across points A &
B. Now you can hear and see the output of the music IC.
Music Meter

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Project #341
OBJECTIVE: Turn on and off LEDs using a relay.
A relay is an electronic switch with contacts that are opened or closed
using voltage. It contains a coil that generates a magnetic field when
a current flows through it. The magnetic field attracts an iron armature
which switches the contacts. Contact #2 is normally closed,
connecting the green LED (D2) and the resistor across the batteries.
With the slide switch (S1) turned off, the green LED should light. Now
turn on the switch, contact #1 on the relay (S3) will switch to contact
#3, lighting the red LED (D1).
LED & Relay
Project #342
OBJECTIVE: To build a manual timer using a relay.
The transistor (Q2) acts as a switch, connecting the relay (S3) to the
batteries. As long as there is positive voltage on the transistor’s base,
the bulb (L2) will light.
Turn on the switch (S1) and hold down the press switch (S2). The
transistor turns on, capacitor C5 charges up, and the bulb lights.
When the press switch is released, the capacitor discharges through
the base, keeping the transistor on. The transistor will turn off when
the capacitor is almost discharged, about 10 seconds. The relay
contacts will switch and the bulb will turn off.
Change the value of the capacitor and see what happens.
Manual
7 Second Timer