Elenco Electronics 202 - Manual (Page 87)

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Project #200
OBJECTIVE: Build a circuit that detects motion.
Set the adjustable resistor (RV) to the center position. Turn the slide
switch (S1) on and the LED (D1) lights. Wave your hand over the
photoresistor (RP) and the LED turns off and on. The resistance
changes as the amount of light strikes the photoresistor. As the light
decreases, the resistance increases. The increased resistance lowers
the voltage at the base of the NPN transistor (Q2). This turns off the
transistor, preventing current flowing through the LED to the negative (–)
side of the battery (B1). Wave your hand over photoresistor at different
distances. The LED gets brighter the farther away your hand is.
Motion Detector
Project #201
OBJECTIVE: To modulate the brightness of an LED.
Using the fan outline as a guide, cut a 3" circle out of a piece of paper.
Then, cut a small triangle in it as shown. Tape the circle onto the fan
and then place it onto the motor (M1). Set the adjustable resistor (RV)
to the center position and turn the slide switch (S1) on. Press the
press switch (S2), the fan spins and the lamp (L2) lights. As the
triangle opening moves over the photoresistor (RP), more light strikes
it. The brightness of the LED (D1) changes, or is
modulated. As in AM
or FM radio, modulation uses one signal to modify the amplitude or
frequency of another signal.
Fan Modulator
3” dia.
!
WARNING: Moving parts. Do not touch the fan or
motor during operation.