Elenco SC100, SC750 User Manual

Copyright © 2012 by ELENCO®All rights reserved. No part of this book shall be reproduced by 753098
any means; electronic, photocopying, or otherwise without written permission from the publisher.

REV-H Revised 2012

Patent #‘s: 7,144,255, 7,273,377, & other patents pending

Project 242

-1-

Table of Contents

Basic Troubleshooting 1
Parts List 2

MORE

About Your Snap Circuits®Parts 3

MORE

DO’s and DON’Ts of Building Circuits 4

MORE

Advanced Troubleshooting 5
Project Listings 6, 7
Projects 102 - 305 8 - 73
Other Fun Elenco®Products 74

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. Be sure that all connections are securely snapped.

4. Try replacing the batteries.

5. If the motor spins but does not balance the fan, check
the black plastic piece with three prongs on the motor
shaft. Be sure that it is at the top of the shaft.

Elenco

®

is not responsible for parts damaged due to

incorrect wiring.

Basic Troubleshooting

Note: If you suspect you have damaged parts, you can

follow the Advanced Troubleshooting procedure on page 5
to determine which ones need replacing.

Review of How To Use It (See page 3 of the Projects 1-101 manual for more details.)

The Snap Circuits®kit uses building blocks with snaps
to build the different electrical and electronic circuits in
the projects. 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
with numbers, identifying the blocks that you will use
and snap together to form a circuit.

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.

A large clear plastic base grid is included with this kit
to help keep the circuit block together. The base has
rows labeled A-G and columns labeled 1-10.

Install two (2) “AA” batteries (not included) in the
battery holder (B1). The 2.5V and 6V bulbs come
packaged separate from their sockets. Install the 2.5V
bulb in the L1 lamp socket, and the 6V bulb in the L2
lamp socket.

Place the fan on the motor (M1) whenever that part is
used, unless the project you are building says not to
use it.

Some circuits use the red and black 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 may damage
and/or quickly drain the batteries.

WARNING: SHOCK HAZARD -

Never connect Snap Circuits®to
the electrical outlets in your home
in any way!

WARNING FOR ALL PROJECTS WITH A SYMBOL

Moving parts. Do not touch the motor or fan during operation. Do not lean
over the motor. Do not launch the fan at people, animals, or objects. Eye
protection is recommended.

!

!

WARNING: CHOKING HAZARD -

Small parts.
Not for children under 3 years.

!

Batteries:

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

• Insert batteries with correct polarity.

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

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

• Do not mix old and new batteries.

• Remove batteries when they are used up.

• Do not short circuit the battery terminals.

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

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

• Do not connect batteries or battery
holders in parallel.

!

WARNING: Always check your wiring before

turning on a circuit. Never leave a circuit
unattended while the batteries are installed. Never
connect additional batteries or any other power
sources to your circuits. Discard any cracked or
broken parts.

Adult Supervision: Because children’s abilities

vary

so much, even with age groups, adults should
exercise discretion as to which experiments are
suitable and safe (the instructions should enable
supervising adults to establish the experiment’s
suitability for the child). Make sure your child reads
and follows all of the relevant instructions and
safety procedures, and keeps them at hand for
reference.

This product is intended for use by adults and
children who have attained sufficient maturity to
read and follow directions and warnings.

Never modify your parts, as doing so may disable
important safety features in them, and could put
your child at risk of injury.

!

-2-

Qty. ID Name Symbol Part # Qty. ID Name Symbol Part #

r 3

1-Snap Wire 6SC01

r 1

10μF Capacitor 6SCC3

r 3

2-Snap Wire 6SC02

r 1

100μF Capacitor 6SCC4

r 1

3-Snap Wire 6SC03

r 1

470μF Capacitor 6SCC5

r 1

4-Snap Wire 6SC04

r 1

1kΩ Resistor 6SCR2

r 1

7-Snap Wire 6SC07

r 1

5.1kΩ Resistor 6SCR3

r 1

Battery Holder - uses
2 1.5V type AA (not

Included)

6SCB1

r 1

10kΩ Resistor 6SCR4

r 1

Antenna Coil 6SCA1

r 1

100kΩ Resistor 6SCR5

r 1

Green Light Emitting
Diode (LED)

6SCD2

r 1

High Frequency
Integrated Circuit

6SCU5

r 1

6V Lamp 6SCL2

r 1

PNP Transistor 6SCQ1

r 1

Microphone 6SCX1

r 1

NPN Transistor 6SCQ2

r 1

Power Amplifier
Integrated Circuit

6SCU4

r 1

Adjustable Resistor 6SCRV

r 1

0.02μF Capacitor 6SCC1

r 1

Variable Capacitor 6SCCV

r 1

0.1μF Capacitor 6SCC2

You may order additional / replacement parts at our
website: www.snapcircuits.net

D2

A1

B1

7

4

3

2

1

L2

X1

U4

C1

C2

U5

R5

R4

R3

R2

C5

C4

C3

Q1

Q2

RV

CV

Note: There are additional part lists in your other project manuals.

Important: If any parts are missing or damaged, DO NOT RETURN TO RETAILER. Call toll-free [phone] or e-mail us at:

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

Parts List (Colors and styles may vary) Symbols and Numbers

-3-

(Part designs are subject to change without notice).

Note: There is additional information in your other project manual.

The green LED (D2) works the same as the red LED (D1) and the

6V lamp (L2) works the same as the 2.5V lamp; these are

described in the projects 1-101 manual.

Resistors “resist” the flow of electricity and are used to control or
limit the electricity in a circuit. Snap Circuits

®

includes 100Ω (R1),

1KΩ (R2), 5.1KΩ (R3), 10KΩ (R4), and 100KΩ (R5) resistors (“K”

symboliz

es 1,000, so R3 is really 5,100Ω).

Materials like metal
have very low resistance (<1Ω) and are called conductors, while
materials like paper, plastic, and air have near-infinite resistance
and are called insulators.

The adjustable resistor (RV) is a 50KΩ resistor b

ut with a center

tap that can be adjusted between

0Ω and 50KΩ. At the 0Ω setting,

the current must be limited by the other components in the circuit.

The microphone (X1) is actually a resistor that changes in value
when changes in air pressure (sounds) apply pressure to its
surf

ace.

Its resistance typically varies from around 1KΩ in silence

to around 10KΩ when you blow on it.

Capacitors are components that can store electrical pressure
(voltage) for periods of time, higher values have more storage.
Because of this storage ability they block unchanging voltage
signals and pass fast changing voltages. Capacitors are used for
filtering and oscillation circuits. Snap Circuits

®

includes 0.02μF

(C1), 0.1μF (C2), 10μF (C3), 10μF (C4), 470μF (C5) capacitors,
and a variable capacitor (CV). The variable capacitor can be

adjusted from .00004 to .00022μF and is used in high frequency
r

adio circuits for

tuning. The whistle chip (WC) also acts like a

0.02μF capacitor in addition to its sound properties.

The antenna (A1) contains a coil of wire wrapped around an iron
bar.

Although it has magnetic effects similar to those in the motor,
those effects are tiny and may be ignored except at high
frequencies (like in AM radio). Its magnetic properties allow it to
concentrate radio signals for reception. At lower frequencies the
antenna acts like an ordinary wire.

The PNP (Q1) and NPN (Q2) transistors are components that use
a small electric current to control a large current, and are used in
switching,

amplifier, and buffering applications. They are easy to
miniaturize, and are the main building blocks of integrated circuits
including the microprocessor and memory circuits in computers.
Projects #124-125 and #128-133 demonstrate their properties. A
high current may damage a transistor, so the current must be
limited by other components in the circuit.

The power amplifier IC (U4) is a module containing an integrated
circuit amplifier and supporting components that are alwa

ys

needed with it. A description of it is given here for those interested:

MORE

About Your Snap Circuits®Parts

The high frequency IC (U5) is a specialized amplifier used only in
high frequency radio circuits. A description of it is given here for
those interested:

INP

FIL

(+)

OUT

(–)

Power Amplifier IC:

(+) - power from batteries
(–) - power return to batteries
FIL - filtered power from batteries
INP - input connection
OUT - output connection

See project #242 for example of
connections.

High Frequency IC:

INP - input connection (2 points
are same)
OUT - output connection
(–) power return to batteries

See project #242 for example of
connections.

INP INP(–)

OUT

Our Student Guides give much more information about your parts along with a complete lesson
in basic electronics. See www.snapcircuits.net/learn.htm or page 74 for more information.

-4-

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. Elenco®is not responsible for parts damaged

due to incorrect wiring.

Here are some important guidelines:

ALWAYS

USE EYE PROTECTION WHEN EXPERIMENTING ON YOUR OWN.

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, photoresistor, or resistors (the adjustable resistor
doesn’t count if it’s set at/near minimum resistance).

ALWAYS

use LEDs, transistors, the high frequency IC, 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 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.

Note: If you have the more advanced Models SC-500 or SC-750, there are additional
guidelines in your other project manual(s).

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. If they are
unique, we will post them with your name and state on our website at
www.snapcircuits.net/kidkreations.htm. Send your suggestions to
Elenco

®

.

Elenco®provides a circuit designer so that you can make your own Snap
Circuits

®

drawings. This Microsoft®Word document can be downloaded

from www.snapcircuits.net/SnapDesigner.doc or through the

www.snapcircuits.net website.

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 slide 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!

Warning to Snap Rover owners: Do not connect your parts to the

Rover body except when using our approved circuits, the Rover
body has a higher voltage which could damage your parts.

!

!

NEVER

DO!

!

!!

NEVER

DO!

NEVER

DO!

MORE

Advanced Troubleshooting (Adult supervision recommended)

Elenco

®

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. - 9. Refer to project manual 1 (projects 1-101) for testing steps
1-9, then continue below. Test both lamps (L1, L2) and
battery holders in test step 1, all blue snap wires in step 3,
and both LEDs (D1, D2) in step 5.

10. 1KΩ (R2), 5.1KΩ (R3),

and 10KΩ (R4) resistors: Build

project #7 but use each of these resistors in place of the 100Ω
resistor (R1), the LED should light and the brightness
decreases with the higher value resistors.

11. Antenna (A1): Build the mini-

circuit sho

wn here,

you should

hear sound.

12. NPN transistor (Q2): Build the

mini-circuit shown here.

The
LED (D2) should only be on if the
press switch (S2) is pressed. If
otherwise, then the NPN is
damaged.

13. PNP transistor (Q1): Build the
mini-circuit shown here.

The
LED (D1) should only be on if the
press switch (S2) is pressed. If
otherwise, then the PNP is
damaged.

14. Adjustable resistor (RV): Build project #261 but use the 100Ω
resistor (R1) in place of the photoresistor (RP), the resistor
control can tur

n the LED (D1) on and off.

15. 100

ΩK resistor (R5) and 0.02μF (C1),

0.1μ

F (C2), and 10μF

(C3) capacitors: Build project #206, it makes sound unless

the resistor is bad.

Place the 0.02μ

F capacitor on top of the
whistle chip (WC) and the sound changes (pitch is lower).
Replace the 0.02μF with the 0.1μF and the pitch is even lower.
Replace the 0.1μF with the 10μF and the circuit will “click”
about once a second.

16. 100μF (C4) and 470μF (C5) capacitor

s: Build project #225,

press the press switch (S2) and turn

on the slide switch (S1).
The LED (D1) should be lit for about 15 seconds then go out
(press the press switch again to reset this). Replace the 470μF
with the 100μF and the LED is only lit for about 4 seconds now.

17. Power Amplifier IC (U4): Build project #293, the sound from
the speak

er (SP) should be loud.

18. Microphone

(X1): Build project #109, blowing into the

microphone should turn off the lamp (L2).

19. Variab

le Capacitor (CV): Build project #213 and place it near

an AM radio,

tune the radio and the capacitor to verify you hear

the music on your radio.

20. High Frequency IC (U5): Build project #242 and adjust the
variab

le capacitor (CV) and adjustable resistor (RV) until you

hear a radio station.

Note: If you have the more advanced Models SC-500 or SC-750,
there are additional tests in your other project manuals.

ELENCO

®

150 Carpenter Avenue

Wheeling, IL 60090 U.S.A.

Phone: [phone]

Fax: [phone]

e-mail: [e-mail]

Web site: www.elenco.com

You may order additional / replacement parts at:

www.snapcircuits.net

-5-

Project # Description Page #

102 Batteries in Series 8
103 Ticking Screecher 8
104 Spacey Fan 9
105 Two-Transistor Light Alarm 9
106 Light-Controlled Alarm 9
107 Automatic Street Lamp 10
108 Voice-Controlled Rays of Light 10
109 Blowing Off the Electric Light 10
110 Adjustable Tone Generator 11
111 Photosensitive Electronic Organ 11
112 Electronic Cicada 11
113 Light & Sounds 12
114 More Light & Sounds 12
115 More Light & Sounds (II) 12
116 More Light & Sounds (III) 12
117 More Light & Sounds (IV) 12
118 Motor Speed Detector 13
119 Old-Style Typewriter 13
120 Optical Transmitter & Receiver 14
121

Space War Sounds Controlled by Light

14
122 Space War Radio 15
123 The Lie Detector 15
124 NPN Amplifier 16
125 PNP Amplifier 16
126 Sucking Fan 17
127 Blowing Fan 17
128 PNP Collector 17
129 PNP Emitter 17
130 NPN Collector 18
131 NPN Emitter 18
132 NPN Collector - Motor 18
133 NPN Emitter - Motor 18
134 Buzzing in the Dark 19
135 Touch Buzzer 19

Project # Description Page #

136 High Frequency Touch Buzzer 19
137 High Frequency

Water Buzzer 19
138 Mosquito 19
139 High Sensitivity Voice Doorbell 20
140 Louder Doorbell 20
141 Very Loud Doorbell 20
142 Doorbell with Button 20
143 Darkness Announcer 20
144 Musical Motion Detector 20
145 Radio Music Alarm 21
146 Daylight Music Radio 21
147 Night Music Radio 21
148 Night Gun Radio 21
149 Radio Gun Alarm 21
150 Daylight Gun Radio 21
151 Blow Off a Space War 22
152 Series Lamps 22
153 Parallel Lamps 22
154 Fire Fan Symphony 23
155 Fire Fan Symphony (II) 23
156 Fan Symphony 23
157 Fan Symphony (II) 23
158 Police Car Symphony 24
159 Police Car Symphony (II) 24
160 Ambulance Symphony 24
161 Ambulance Symphony (II) 24
162 Static Symphony 25
163 Static Symphony (II) 25
164 Capacitors in Series 25
165 Capacitors in Parallel 25
166 Water Detector 26
167 Salt Water Detector 26
168 NPN Light Control 27
169 NPN Dark Control 27

Project # Description Page #

170 PNP Light Control 27
171 PNP Dark Control 27
172 Red & Green Control 28
173 Current Controllers 28
174 Current Equalizing 28
175 Battery Polarity Tester 28
176 Blow Off a Doorbell 29
177 Blow Off a Candle 29
178 Blow On a Doorbell 29
179 Blow On a Candle 29
180 Screaming Fan 30
181 Whining Fan 30
182 Light Whining 30
183 More Light Whining 30
184 Motor Than Won’t Start 30
185 Whiner 31
186 Lower Pitch Whiner 31
187 Hummer 31
188 Adjustable Metronome 31
189 Quiet Flasher 31
190 Hissing Foghorn 32
191 Hissing & Clicking 32
192 Video Game Engine Sound 32
193 Light Alarm 33
194 Brighter Light Alarm 33
195 Lazy Fan 33
196 Laser Light 33
197 Water Alarm 34
198 Radio Announcer 34
199 Pitch 35
200 Pitch (II) 35
201 Pitch (III) 35
202 Flooding Alarm 35
203 Make Your Own Battery 36

-6-

Project Listings

-7-

Project # Description Page #

204 Make Your Own Battery (II) 36
205 Make Your Own Battery (III) 36
206 Tone Generator 37
207 Tone Generator (II) 37
208 Tone Generator (III) 37
209 Tone Generator (IV) 37
210 More Tone Generator 38
211 More Tone Generator (II) 38
212 More Tone Generator (III) 38
213 Music Radio Station 39
214 Alarm Radio Station 39
215 Standard Transistor Circuit 39
216 Motor & Lamp by Sound 40
217 Fading Siren 40
218 Fast Fade Siren 40
219 Laser Gun with Limited Shots 41
220 Symphony of Sounds 41
221 Symphony of Sounds (II) 41
222 Transistor Amplifiers 42
223 Pressure Meter 42
224 Resistance Meter 42
225 Auto-Off Night-Light 43
226 Discharging Caps 43
227 Changing Delay Time 43
228 Morse Code Generator 44
229 LED Code Teacher 44
230 Ghost Shriek Machine 44
231 LED & Speaker 44
232 Dog Whistle 44
233 Mind Reading Game 45
234 Enhanced Quiet Zone Game 46
235 Capacitor Charge & Discharge 46
236 Sound Wave Magic 47
237 Space War Amplifier 47

Project # Description Page #

238 Trombone 48
239 Race Car Engine 48
240 Power Amplifier 49
241 Feedback Kazoo 49
242 AM Radio 50
243 Fire Engine Symphony 51
244 Fire Engine Symphony (II) 51
245 Vibration or Sound Indicator 51
246 Two-Finger Touch Lamp 52
247 One-Finger Touch Lamp 52
248 Space Battle 53
249 Space Battle (II) 53
250 Multi-Speed Light Fan 53
251 Light & Finger Light 53
252 Storing Electricity 54
253 Lamp Brightness Control 54
254 Electric Fan 54
255 Radio Music Burglar Alarm 55
256 Light Dimmer 55
257 Motion Detector 56
258 Fan Modulator 56
259 Oscillator 0.5 - 30Hz 57
260 Sound Pulse Oscillator 57
261 Motion Detector (II) 57
262 Motor Rotation 58
263 Motor Delay Fan 58
264 Motor Delay Fan (II) 58
265 High Pitch Bell 59
266 Steamboat Whistle 59
267 Steamship 59
268 Light NOR Gate 59
269 Noise-Activated Burglar Alarm 60
270 Motor-Activated Burglar Alarm 60
271 Light-Activated Burglar Alarm 60

Project # Description Page #

272 Photoresistor Control 61
273 Microphone Control 61
274 Pressure Alarm 62
275 Power Microphone 62
276 LED Fan Rotation Indicator 63
277 Space War Sounds with LED 63
278 Sound Mixer 64
279 Sound Mixer Fan Driver 64
280 Electric Fan Stopped by Light 65
281 Motor & Lamp 65
282 Start-Stop Delay 66
283 Mail Notifying System 66
284 Mail Notifying Electronic Bell 67
285 Mail Notifying Electronic Lamp 67
286 Twice-Amplified Oscillator 67
287 Quick Flicking LED 67
288 AM Radio with Transistors 68
289 AM Radio (II) 68
290 Music Amplifier 69
291 Delayed Action Lamp 69
292 Delayed Action Fan 69
293 Police Siren Amplifier 70
294 Lasting Doorbell 70
295 Lasting Clicking 70
296 Quieting a Motor 71
297 Transistor Fading Siren 71
298 Fading Doorbell 71
299 Blowing Space War Sounds 72
300 Adjustable Time Delay Lamp 72
301 Adjustable Time Delay Fan 72
302

Adjustable Time Delay Lamp (II)

73
303 Adjustable Time Delay Fan (II) 73
304 Watch Light 73
305 Delayed Bedside Fan 73

Project Listings

-8-

Project #102

OBJECTIVE: To show the increase in voltage when batteries are
connected in series.

When you turn on the slide switch (S1), current flows from the
batteries through the slide switch, the 100Ω resistor (R1), the LED
(D1), through the LED (D2), and back to the second group of batteries
(B1). Notice how both LED’s are lit. The voltage is high enough to turn
on both LED’s when the batteries are connected in series. If only one
set of batteries is used, the LED’s will not light up.

Some devices use only one 1.5 volt battery, but they make hundreds
of volts electronically from this small source. A flash camera is an
example of this.

Batteries in Series

Project #103

OBJECTIVE: To make fun sounds using light.

Build the circuit as shown, and turn on the slide switch (S1). Vary the
amount of light to the photoresistor (RP) by partially covering it with
your hand. You can make screeching sounds by allowing just a little
light to reach the photoresistor.

If you replace the 10μF capacitor (C3) with a 3-snap wire or any of the
other capacitors (C1, C2, C4, or C5), then the sound will be a little
different.

Ticking Screecher

+

+

-9-

Project #104

Spacey Fan

OBJECTIVE: To build a fan
with sound that is activated by
light.

Place the fan onto the motor (M1).
Sounds are heard if light shines on
the photoresistor (RP) OR if you
press the press switch (S2), the fan
may start to spin, but will only get to
high speed if you do BOTH. Try
various combinations of shining light
and holding down the press switch.

Project #106

OBJECTIVE: To show how light is used to turn an alarm.

The alarm will sound, as long as light is present. Slowly cover the
photoresistor (RP), and the volume goes down. If you turn off the
lights, the alarm will stop. The amount of light changes the resistance
of the photoresistor (less light means more resistance). The
photoresistor and transistor (Q2) act like a dimmer switch, adjusting
the voltage applied to the alarm.

This type of circuit is used in alarm systems to detect light. If an
intruder turned on a light or hit the sensor with a flashlight beam, the
alarm would trigger and probably force the intruder to leave.

Light-controlled Alarm

Project #105

Two-Transistor Light Alarm

OBJECTIVE: To compare transistor circuits.

This light alarm circuit uses two
transistors (Q1 & Q2) and both
sets of batteries. Build the circuit
with the jumper connected as
shown, and turn it on. Nothing
happens. Break the jumper
connection and the lamp (L2)
turns on. You could replace the
jumper with a longer wire and
run it across a doorway to signal
an alarm when someone enters.

!

WARNING: Moving parts. Do

not touch the fan or motor during
operation. Do not lean over the
motor.

Visit www.snapcircuits.net or page 74 to learn about Snap Circuits®upgrade kits, which have more parts and circuits.

-10-

Project #107

OBJECTIVE: To show how light is used to control a street lamp.

Press the press switch (S2) on and set the adjustable resistor (RV) so
the lamp (L2) just lights. Slowly cover the photoresistor (RP) and the
lamp brightens. If you place more light at the photoresistor the light
dims.

This is an automatic street lamp that you can turn on by a certain
darkness and turn off by a certain brightness. This type of circuit is
installed on many outside lights and forces them to turn off and save
electricity. They also come on when needed for safety.

Automatic

Street Lamp

Project #108

Voice-controlled Rays of Light

OBJECTIVE: To show how light is stimulated by sound.

Turn the slide switch
(S1) on. There will be
only a weak light
emitting from the green
LED (D2). By blowing
on the mic (X1) or
putting it near a radio
or TV set, the green
LED will emit light, and
its brightness changes
as the loudness
changes.

Project #109

Blowing Off the Electric Light

OBJECTIVE: To show how light is stimulated by sound.

Install the parts. The
lamp (L2) will be on. It
will be off as long as
you blow on the mic
(X1). Speaking loud
into the mic will
change the brightness
of the lamp.

-11-

Project #110

OBJECTIVE: To show how resistor values change the frequency
of an oscillator.

Turn on the slide switch (S1); the speaker (SP) will sound and the LED
(D1) will light. Adjust the adjustable resistor (RV) to make different
tones. In an oscillator circuit, changing the values of resistors or
capacitors can vary the output tone or pitch.

Adjustable Tone

Generator

OBJECTIVE: To show how resistor values change the frequency
of an oscillator.

Project #112

Electronic Cicada

OBJECTIVE: To show how capacitors in parallel change the
frequency of an oscillator.

Use the circuit from project #110 shown above, replace the
photoresistor (RP) back to the 10kΩ resistor (R4). Place the 0.02μF
capacitor (C1) on top of the whistle chip (WC). Place the slide switch
(S1) on and adjust the adjustable resistor (RV). The circuit produces the
sound of the cicada insect. By placing the 0.02μF capacitor on top of
the whistle chip, the circuit oscillates at a lower frequency. Notice that
the LED (D1) flashes also at the same frequency.

It is possible to pick resistors and capacitors that will make the pitch
higher than humans can hear. Many animals, however, can hear these
tones. For example, a parakeet can hear tones up to 50,000 cycles per
second, but a human can only hear to 20,000.

Use the circuit from project #110 shown above. Replace the 10kΩ
resistor (R4) with the photoresistor (RP). Turn on the slide switch (S1).
The speaker (SP) will sound and the LED (D1) will light. Move your
hand up and down over the photoresistor and the frequency changes.
Decreasing the light on the photoresistor increases the resistance and
causes the circuit to oscillate at a lower frequency. Notice that the LED
flashes also at the same frequency as the sound.

By using your finger, see if you can vary the sounds enough to make this
circuit sound like an organ playing.

Project #111

Photosensitive

Electronic Organ

-12-

OBJECTIVE: To build a police siren with light.

Turn on the slide switch (S1). A police siren is heard and the lamp
(L1) lights.

Project #114

More Light &

Sounds

OBJECTIVE: To show a
variation of the circuit in
project #113.

Modify the last circuit by
connecting points X & Y. The
circuit works the same way but
now it sounds like a machine gun.

OBJECTIVE: To show a
variation of the circuit in
project #113.

Project #116

More Light &

Sounds (III)

OBJECTIVE: To show a
variation of the circuit in
project #113.

Project #117

More Light &

Sounds (IV)

OBJECTIVE: To show a
variation of the circuit in
project #113.

Project #113 Light & Sounds

Project #115

More Light &

Sounds (II)

Now remove the connection
between X & Y and then make a
connection between T & U. Now
it sounds like a fire engine.

Now remove the connection
between T & U and then make a
connection between U & Z. Now
it sounds like an ambulance.

Now remove the connection
between U & Z, then place the
470μF capacitor (C5) between T
& U (“+” side to T). The sound
changes after a few seconds.

To learn more about how circuits work, visit www.snapcircuits.net or page 74 to find out about our Student Guides.

-13-

Project #118

OBJECTIVE: To show how to make electricity in one direction.

When building the circuit, be sure to position the motor (M1) with the
positive (+) side snapped to the 470μF capacitor (C5). Turn on the
slide switch (S1), nothing will happen. It is a motor speed detector,
and the motor isn’t moving. Watch the LED (D2) and give the motor a
good spin CLOCKWISE with your fingers (don’t use the fan blade); you
should see a flash of light. The faster you spin the motor, the brighter
the flash will be. As a game, see who can make the brightest flash.

Now try spinning the motor in the opposite direction (counter­clockwise) and see how bright the flash is — it won’t flash at all
because the electricity it produces, flows in the wrong direction and
won’t activate the diode. Flip the motor around (positive (+) side
snapped to the 3-snap wire) and try again. Now the LED lights only if
you spin the motor counter-clockwise.

Motor Speed Detector

Project #119

OBJECTIVE: To show how a generator works.

Turn on the slide switch (S1), nothing will happen. Turn the motor (M1)
slowly with your fingers (don’t use the fan blade), you will hear a
clicking that sounds like an old-time manual typewriter keystrokes.
Spin the motor faster and the clicking speeds up accordingly.

This circuit works the same if you spin the motor in either direction
(unlike the Motor Speed Detector project).

By spinning the motor with your fingers, the physical effort you exert is
converted into electricity. In electric power plants, steam is used to
spin large motors like this, and the electricity produced is used to run
everything in your town.

Old-Style Typewriter

-14-

Project #120

OBJECTIVE: To show how information can be transmitted
using light.

Build the circuit shown. Connect the photoresistor (RP) to the circuit
using the red & black jumper wires. Place the photoresistor upside
down over the red LED (D1), so the LED goes inside the photoresistor.
Turn on both switches (hold down the press switch button). Music plays
on the speaker, even though the two parts of the circuit are not
electrically connected.

The left circuit, with the LED and music IC (U1) creates a music signal
and transmits it as light. The right circuit, with the photoresistor and
speaker, receives the light signal and converts it back to music. Here
the photoresistor has to be on top of the LED for this to work, but better
communication systems (such as fiber optic cables), can transmit
information over enormous distances at very high speeds.

Optical Transmitter &

Receiver

Project #121

OBJECTIVE: To change the sounds of a multiple space war with
light.

The space war IC (U3) will play a sound continuously. Block the light
to the photoresistor (RP) with your hand. The sound will stop. Remove
your hand and a different sound is played. Wave your hand over the
photoresistor to hear all the different sounds.

Press the press switch down and now two space war sounds are
played. If you hold the press switch down the sound repeats. Press
the press switch again and a different sound is played. Keep pressing
the press switch to hear all the different combinations of sounds.

Space War Sounds

Controlled By Light

-15-

Project #122

OBJECTIVE: To transmit Space War sounds to a AM radio.

Place the circuit next to an AM radio. Tune the radio so no stations are
heard and turn on the slide switch (S1). You should hear the space war
sounds on the radio. The red LED (D1) should also be lit. Adjust the
variable capacitor (CV) for the loudest signal. Push the press switch
(S2) to change the sound.

You have just performed the experiment that took Marconi (who
invented the radio) a lifetime to invent. The technology of radio
transmission has expanded to the point that we take it for granted.
There was a time, however, when news was only spread by word of
mouth.

Space War Radio

Project #123

OBJECTIVE: To show how sweat makes a better conductor.

Turn on the slide switch (S1) and place your finger across points A &
B. The speaker (SP) will output a tone and the LED (D2) will flash at
the same frequency. Your finger acts as a conductor connecting points
A & B. When a person is lying, one thing the body starts to do is
sweat. The sweat makes the finger a better conductor by reducing its
resistance.

As the resistance drops, the frequency of the tone increases. Lightly
wet your finger and place it across the two points again. Both the
output tone and LED flashing frequency increase, and the lamp (L2)
may begin to light. If your finger is wet enough, then the lamp will be
bright and the sound stops - indicating you are a big liar! Now change
the wetness of your finger by drying it and see how it affects the circuit.
This is the same principle used in lie detectors that are sold
commercially.

The Lie Detector

Visit www.snapcircuits.net or page 74 to learn about more Snap Circuits®products to add to your collection.

-16-

Project #124

OBJECTIVE: To compare transistor circuits.

There are three connection points on an NPN transistor (Q2), called
base (marked B), emitter (marked E), and collector (marked C). When
a small electric current flows from the base to the emitter, a larger
(

amplified

) current will flow from the collector to the emitter. Build the
circuit and slowly move up the adjustable resistor (RV) control. When
the LED (D2) becomes bright, the lamp (L2) will also turn on and will
be much brighter.

NPN Amplifier

Project #125

OBJECTIVE: To compare transistor circuits.

The PNP transistor (Q1) is similar to the NPN transistor (Q2) in project
#166, except that the electric currents flow in the opposite directions.
When a small electric current flows from the emitter to the base, a
larger (

amplified

) current will flow from the emitter to the collector.
Build the circuit and slowly move up the adjustable resistor (RV)
control. When the LED (D1) becomes bright, the lamp (L2) will also
turn on and will be much brighter.

PNP Amplifier

-17-

Project #126 Sucking Fan

OBJECTIVE: To adjust the speed of a fan.

Project #128 PNP Collector

OBJECTIVE: To
demonstrate adjusting the
gain of a transistor circuit.

OBJECTIVE: To build a fan that
won’t come off.

Modify the circuit from project #126 by
reversing the position of the motor
(M1), so the positive (+) side is
towards the PNP (Q1). Turn it on, and
set the adjustable resistor (RV) for the
fan speed you like best. Set it for full
speed and see if the fan flies off - it
won’t! The fan is blowing air upward
now! Try holding a piece of paper just
above the fan to prove this.

Project #127

Blowing Fan

Project #129

PNP Emitter

OBJECTIVE: To compare
transistor circuits.

Compare this circuit to that
in project #128. The
maximum lamp (L2)
brightness is less here
because the lamp
resistance reduces the
emitter-base current, which
contacts the emitter­collector current (as per
project #128). The point on
the PNP (Q1) that the lamp
is now connected to (grid
point C4) is called the
emitter.

Build the circuit, and be sure to orient the motor (M1)
with the positive (+) side down as shown. Turn it on,
and set the adjustable resistor (RV) for the fan speed
you like best. If you set the speed too fast then the fan
may fly off the motor. Due to the shape of the fan
blades and the direction the motor spins, air is sucked
into the fan and towards the motor. Try holding a piece
of paper just above the fan to prove this. If this suction
is strong enough then it can lift the fan blades, just like
in a helicopter.

The fan will not move on most settings of the resistor,
because the resistance is too high to overcome friction
in the motor. If the fan does not move at any resistor
setting, then replace your batteries.

Build the circuit and vary
the lamp (L2) brightness
with the adjustable resistor
(RV), it will be off for most
of the resistor’s range. The
point on the PNP (Q1) that
the lamp is connected to
(point E4 on the base grid)
is called the collector,
hence the name for this
project.

!

WARNING: Moving parts. Do not touch the fan or

motor during operation. Do not lean over the motor.

-18-

Project #130

NPN Collector

OBJECTIVE: To compare
transistor circuits.

Project #131

NPN Emitter

Compare this circuit to that in
project #128, it is the NPN
transistor (Q2) version and
works the same way. Which
circuit makes the lamp (L2)
brighter? (They are about the
same because both transistors
are made from the same
materials).

OBJECTIVE: To compare
transistor circuits.

Compare this circuit to that in
project #129. It is the NPN
transistor (Q2) version and
works the same way. The same
principles apply here as in
projects #128-#130, so you
should expect it to be less bright
than #130 but as bright as #129.

Project #132

NPN Collector - Motor

OBJECTIVE: To compare
transistor circuits.

Project #133

NPN Emitter - Motor

This is the same circuit as in
project #130, except that it has
the motor (M1) instead of the
lamp. Place the motor with the
positive (+) side touching the
NPN and put the fan on it.

The fan will not move on most
settings of the resistor, because
the resistance is too high to
overcome friction in the motor. If
the fan does not move at any
resistor setting, then replace your
batteries.

OBJECTIVE: To compare
transistor circuits.

This is the same circuit as in
project #131, except that it has
the motor (M1) instead of the
lamp. Place the motor with the
positive (+) side to the right and
put the fan on it. Compare the
fan speed to that in project #132.
Just as the lamp was dimmer in
the emitter configuration, the
motor is not as fast now.

!

WARNING: Moving parts. Do not touch

the fan or motor during operation.

Do

not lean over the motor.

Visit www.snapcircuits.net or page 74 to learn about Snap Circuits®upgrade kits, which have more parts and circuits.

!

WARNING: Moving parts. Do not touch the fan or

motor during operation.

Do not lean over the motor.

-19-

Project #134

OBJECTIVE: To make a circuit that
buzzes when the lights are off.

Buzzing in

the Dark

Project #136

High Frequency

Touch Buzzer

OBJECTIVE: To build a high frequency
human buzzer oscillator.

Replace the speaker (SP) with the 6V lamp
(L2). Now touching your fingers between B1
and D1 creates a quieter but more pleasant
buzzing sound.

Project #137

High Frequency

Water Buzzer

OBJECTIVE: To build a high frequency
water buzzer oscillator.

Now connect two (2) jumpers to points B1 and
D1 (that you were touching with your fingers)
and place the loose ends into a cup of water.
The sound will not be much different now,
because your body is mostly water and so the
circuit resistance has not changed much.

Project #138

Mosquito

OBJECTIVE: To make a buzz like a
mosquito.

Place the photoresistor (RP) into the circuit in
project #137 across where you were
connecting the jumpers (points B1 and D1 on
the grid, and as shown in project #134). Now
the buzz sounds like a mosquito.

Project #135

Touch Buzzer

OBJECTIVE: To build a human buzzer
oscillator.

Remove the photoresistor (RP) from the
circuit in project #134 and instead touch your
fingers across where it used to be (points B1
and D1 on the grid) to hear a cute buzzing
sound.
The circuit works because of the resistance in
your body. If you put back the photoresistor
and partially cover it, you should be able to
make the same resistance your body did, and
get the same sound.

This circuit makes a high-frequency
screaming sound when light shines on
the photoresistor (RP), and makes a
buzzing sound when you shield the
photoresistor.

-20-

Project #139

Project #141

Very Loud

Doorbell

OBJECTIVE: To build a very
loud, highly-sensitive, voice­activated doorbell.

Replace the antenna coil (A1)
with the speaker (SP), the sound
is much louder now.

OBJECTIVE: To build a press­activated doorbell.

Project #143

Darkness

Announcer

OBJECTIVE: To play music
when it gets dark.

OBJECTIVE: To detect when
someone spins the motor.

Project #142

Doorbell

with Button

Replace the microphone (X1)
with the press switch (S2) and
wait until the music stops. Now
you have to press the slide switch
(S1) to activate the music, just
like the doorbell on your house.

Replace the press switch (S2)
with the photoresistor (RP) and
wait until the sound stops. If you
cover the photoresistor now the
music will play once, signaling
that it has gotten dark. If the
speaker (SP) is too loud then you
may replace it with the antenna
coil (A1).

Replace the photoresistor (RP)
with the motor (M1), oriented in
either direction. Now spinning the
motor will re-activate the music.

Project #144

Musical

Motion Detector

OBJECTIVE: To build a loud
highly sensitive voice-activated
doorbell.

Replace the 6V lamp (L2) with
the antenna coil (A1), the sound
is louder now.

Project #140

Louder

Doorbell

OBJECTIVE: To build a
highly sensitive voice-activated
doorbell.

Build the circuit and wait until the
sound stops. Clap or talk loud a
few feet away and the music
plays again. The microphone
(X1) is used here because it is
very sensitive.

High

Sensitivity

Voice Doorbell

-21-

Project #145 Radio Music

Alarm

OBJECTIVE: To build a radio music alarm.

Project #147

Night Music

Radio

OBJECTIVE: To build a dark­controlled radio transmitter.

Put the 100kΩ resistor back in as
before and instead connect the
photoresistor between X & Y (you
also need a 1-snap and a 2-snap
wire to do this). Now your radio
plays music when it is dark.

OBJECTIVE: To build a dark­controlled radio transmitter.

Project #149

Radio Gun

Alarm

OBJECTIVE: To build a radio
alarm.

OBJECTIVE: To build a light­controlled radio transmitter.

Project #148

Night Gun

Radio

Replace the music IC (U1) with
the alarm IC (U2). Now your
radio plays the sound of a
machine gun when it is dark.

Remove the photoresistor (RP).
Now connect a jumper wire
between X & Y on the drawing.
If you remove the jumper now,
the machine gun sound will play
on the radio indicating your alarm
wire has been triggered.

Remove the jumper wire.
Replace the 100kΩ resistor (R5)
with the photoresistor (RP). Now
your AM radio will play the
machine gun sound as long as
there is light in the room.

Project #150

Daylight Gun

Radio

OBJECTIVE: To build a light­controlled radio transmitter.

Project #146

Daylight

Music Radio

Remove the jumper wire.
Replace the 100kΩ resistor (R5)
with the photoresistor (RP). Now
your AM radio will play music as
long as there is light in the room.

You need an AM radio for this project. Build the
circuit on the left and turn on the slide switch
(S1). Place it next to your AM radio and tune the
radio frequency to where no other station is
transmitting. Then, tune the adjustable
capacitor (CV) until your music sounds best on
the radio. Now connect a jumper wire between
X and Y on the drawing, the music stops.

If you remove the jumper now, the music will
play indicating your alarm wire has been
triggered. You could use a longer wire and wrap
it around a bike, and use it as a burglar alarm!

To learn more about how circuits work, visit www.snapcircuits.net or page 74 to find out about our Student Guides.

-22-

Project #151

OBJECTIVE: To turn off a circuit by blowing on it.

Blow Off a Space War

Project #152

Series Lamps

OBJECTIVE: To compare types of circuits.

Turn on the slide
switch (S1) and both
lamps (L1 & L2) will
light. If one of the
bulbs is broken then
neither will be on,
because the lamps are
in series. An example
of this is the strings of
small Christmas lights;
if one bulb is damaged
then the entire string
does not work.

Project #153

Parallel Lamps

OBJECTIVE: To compare types of circuits.

Build the circuit and turn it on,
you hear a space war. Since it is
loud and annoying, try to shut it
off by blowing into the
microphone (X1). Blowing hard
into the microphone stops the
sound, and then it starts again.

Turn on the slide
switch (S1) and both
lamps (L1 & L2) will
light

. If one of the
bulbs is broken then
the other will still be
on, because the
lamps are in parallel.
An example of this is
most of the lights in
your house; if a bulb is
broken on one lamp
then the other lamps
are not affected.

-23-

Project #154 Fire Fan Symphony

OBJECTIVE:

To combine sounds
from the music, alarm, and space war
integrated circuits.

OBJECTIVE:
See project #156.

The preceding circuit may be too
loud, so replace the speaker (SP)
with the whistle chip (WC).

Project #157

Fan

Symphony (II)

OBJECTIVE:
See project #154.

Project #155

Fire Fan

Symphony (II)

Project #156

Fan Symphony

OBJECTIVE:

To combine sounds
from the music, alarm, and space war
integrated circuits.

Modify the circuit from project #154 to
match the circuit shown on the left.
The only differences are the
connections around the alarm IC
(U2). It works the same way.

The preceding circuit may be too
loud, so replace the speaker (SP)
with the whistle chip (WC).

Build the circuit shown and add the
jumper to complete it. Note that in one
place two (2) single snaps are stacked
on top of each other. Also, note that
there is a 2-snap wire on layer 2 that
does not connect with a 4-snap wire that
runs over it on layer 4 (both touch the
music IC). Turn it on and press the press
switch (S2) several times and wave your
hand over the photoresistor (RP) to hear
the full spectrum of sounds that this
circuit can create. Have fun!

!

WARNING: Moving parts. Do not touch

the fan or motor during operation. Do
not lean over the motor.

!

WARNING: Moving parts. Do not touch

the fan or motor during operation. Do
not lean over the motor.

-24-

Project #158 Police Car Symphony

OBJECTIVE: To combine sounds
from the integrated circuits.

OBJECTIVE:
See project #160.

The preceding circuit may be too
loud, so replace the speaker (SP)
with the whistle chip (WC).

Project #161

Ambulance

Symphony (II)

OBJECTIVE:
See project #158.

Project #159

Police Car

Symphony (II)

Project #160 Ambulance Symphony

OBJECTIVE:

To combine sounds
from the music, alarm, and space war
integrated circuits.

Modify the circuit from project #158 to
match the circuit shown on the left.
The only differences are the
connections around the alarm IC
(U2). It works the same way.

The preceding circuit may be too
loud, so replace the speaker (SP)
with the whistle chip (WC).

Build the circuit shown and add the two (2)
jumper wires to complete it. Note that in one
place two (2) single snaps are stacked on
top of each other. Turn it on and press the
press switch (S2) several times and wave
your hand over the photoresistor (RP) to
hear the full spectrum of sounds that this
circuit can create. Have fun!
Do you know why the antenna (A1) is used
in this circuit? It is being used as just a 3­snap wire, because it acts like an ordinary
wire in low frequency circuits such as this.
Without it, you don’t have enough parts to
build this complex circuit.

Visit www.snapcircuits.net or page 74 to learn about more Snap Circuits®products to add to your collection.

-25-

Project #162 Static Symphony

OBJECTIVE:
See project #162.

Project #163

Static

Symphony (II)

Project #164 Capacitors in Series

OBJECTIVE: To compare types of circuits.

Project #165 Capacitors in Parallel

OBJECTIVE: To compare types of circuits.

Turn on the slide switch (S1), then press and release the press switch (S2). The LED (D1)
becomes bright when the 470μF capacitor charges up with the press switch on, then the LED
slowly gets dim after you release the press switch.

Now turn off the slide switch. Repeat the test with the slide swtich off; you’ll notice the LED goes
out much faster after you release the press switch. The much smaller 100μF capacitor (C4) is
now in series with the 470μF and so reduces the total capacitance (electrical storage capacity),
and they discharge much faster. (Note that this is opposite to how resistors in series work).

Turn off the slide switch (S1), then press and release the press switch (S2). The LED (D1)
becomes bright when the 100μF capacitor charges up with the press switch on, then the LED
slowly gets dim after you release the press switch.

Now turn on the slide switch and repeat the test; you’ll notice the LED goes out much slower
after you release the press switch. The much larger 470μF capacitor (C5) is now in parallel
with the 100μF and so increases the total capacitance (electrical storage capacity), and they
discharge much slower. (Note that this is opposite to how resistors in parallel work.)

OBJECTIVE: To combine sounds from the
integrated circuits.

For a variation on the preceding
circuit, you can replace the 6V
lamp (L2) with the LED (D1), with
the positive (+) side up, or the
motor (M1) (do not place the fan
on it).

Build the circuit shown. Note that in some places
parts are stacked on top of each other. Turn it on and
press the press switch (S2) several times and wave
your hand over the photoresistor (RP) to hear the full
spectrum of sounds that this circuit can create. Have
fun!

-26-

Project #166

OBJECTIVE: To show how water conducts electricity.

Build the circuit at left and connect the two jumpers to it, but leave the
loose ends of the jumpers lying on the table initially. Turn on the slide
switch (S1) - the LED (D1) will be dark because the air separating the
jumpers has very high resistance. Touch the loose jumper ends to
each other and the LED will be bright, because with a direct
connection there is no resistance separating the jumpers.

Now take the loose ends of the jumpers and place them in a cup of
water, without letting them touch each other. The LED should be dimly
lit, indicating you have detected water!

For this experiment, your LED brightness may vary depending upon
your local water supply. Pure water (like distilled water) has very high
resistance, but drinking water has impurities mixed in that increase
electrical conduction.

Water Detector

Project #167

OBJECTIVE: To show how adding salt to water changes water’s
electrical characteristics.

Place the jumpers in a cup of water as in the preceding project; the
LED (D1) should be dimly lit. Slowly add salt to the water and see how
the LED brightness changes, mix it a little so it dissolves. It will slowly
become very bright as you add more salt. You can use this bright LED
condition as a saltwater detector! You can then reduce the LED
brightness by adding more water to dilute the salt.

Take another cup of water and try adding other household substances
like sugar to see if they increase the LED brightness as the salt did.

Saltwater Detector

-27-

Project #168

NPN Light Control

OBJECTIVE: To compare
transistor circuits.

Project #169

NPN Dark Control

Turn on the slide switch (S1),
the brightness of the LED (D2)
depends on how much light
shines on the photoresistor
(RP). The resistance drops as
more light shines, allowing more
current to the NPN (Q2).

OBJECTIVE: To compare
transistor circuits.

Turn on the slide switch (S1),
the brightness of the LED (D2)
depends on how LITTLE light
shines on the photoresistor
(RP). The resistance drops as
more light shines, diverting
current away from the NPN
(Q2).

Project #170

PNP Light Control

OBJECTIVE: To compare
transistor circuits.

Project #171

PNP Dark Control

Turn on the slide switch (S1),
the brightness of the LED (D1)
depends on how much light
shines on the photoresistor
(RP). The resistance drops as
more light shines, allowing more
current through the PNP (Q1).
This is similar to the NPN (Q2)
circuit above.

OBJECTIVE: To compare
transistor circuits.

Turn on the slide switch (S1),
the brightness of the LED (D1)
depends on how LITTLE light
shines on the photoresistor
(RP). The resistance drops as
more light shines, so more
current gets to the 100kΩ
resistor (R5) from the
photoresistor path and less from
the PNP-diode path. This is
similar to the NPN circuit above.

Visit www.snapcircuits.net or page 74 to learn about Snap Circuits®upgrade kits, which have more parts and circuits.

-28-

Project #172

Red & Green Control

OBJECTIVE: To demonstrate
how the adjustable resistor
works.

Project #173

Current Controllers

Turn on the circuit using the slide
switch (S1) and/or the press
switch (S2) and move the
adjustable resistor’s (RV) control
lever around to adjust the
brightness of the LED’s (D1 &
D2). When the adjustable resistor
is set to one side, that side will
have low resistance and its LED
will be bright (assuming the
switch on that side is ON) while
the other LED will be dim or OFF.

OBJECTIVE: To compare
types of circuits.

Build the circuit and turn on the slide
switch (S1), the LED (D1) will be lit.
To increase the LED brightness, turn
on the press switch (S2). To
decrease the LED brightness, turn
off the slide switch.

With the slide switch on, the 5.1KΩ
resistor (R3) controls the current.
Turning on the press switch places
the 1KΩ resistor (R2) in parallel with
it to decrease the total circuit
resistance. Turning off the slide
switch places the 10KΩ resistor (R4)
in series with R2/R3 to increase the
total resistance.

Project #174

Current Equalizing

OBJECTIVE: To compare
types of circuits.

Project #175

Battery Polarity Tester

In this circuit the LED’s (D1 &
D2) will have the same
brightness, but the lamp (L1) will
be off. When connected in
series, all components will have
equal electric current through
them. The lamp is off because it
requires a higher current
through the circuit to turn on
than the LED’s do.

OBJECTIVE: To test the
polarity of a battery.

Use this circuit to check the
polarity of a battery. Connect
your battery to X & Y on the
drawing using the jumper cables
(your 3V battery pack (B1) can
also be snapped on directly
instead). If the positive (+) side
of your battery is connected to
X, then the red LED (D1) will be
on, if the negative (–) side is
connected to X then the green
LED (D2) will be on.

-29-

Project #176 Blow Off a Doorbell

OBJECTIVE: To turn off a circuit
by blowing on it.

OBJECTIVE: To turn on a
circuit by blowing on it.

Replace the speaker (SP) with
the 6V lamp (L2). Blowing into
the microphone (X1) turns on the
light, and then it goes off again.

Project #179

Blow On a

Candle

OBJECTIVE: To turn off a
circuit by blowing on it.

Project #177

Blow Off a

Candle

Project #178 Blow On a Doorbell

OBJECTIVE: To turn on a circuit
by blowing on it.

Build the circuit and turn it on, music
plays for a few moments and then
stops. Blow into the microphone (X1)
and it plays; it plays as long as you
keep blowing.

Replace the speaker (SP) with
the 6V lamp (L2). Blowing hard
into the microphone (X1) turns
off the light briefly.

Build the circuit and turn it on; music
plays. Since it is loud and annoying,
try to shut it off by blowing into the
microphone (X1). Blowing hard into
the microphone stops the music, and
then it starts again.