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Project #104 Spacey Fan
OBJECTIVE: To build a fan with space war sounds that
Place the fan onto the motor.
Space war sounds are heard if
light shines on the
photosensitive resistor 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
The alarm will sound, as long as light is present. Slowly cover the
photosensitive resistor (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 photosensitive resistor (less light means more
resistance). The photosensitive resistor 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
This light alarm circuit uses two
(2) transistors 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 light turns on. You could
replace the jumper with a longer
wire and run it across a doorway
to signal an alarm when
someone enters.
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