Elenco Circuit Maker Sound Plus 200 - Manual (Page 42)

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Project #82
Place this circuit near a bright light. Turn the slide switch (S1) on and
move the adjustable resistor (RV) control all the way up. The brightness
of the lamp (L4) is at maximum. Now, move the adjustable resistor
control down until the lamp goes out. Set the control up a little and the
lamp lights dimly.
Move your hand from side to side over the photoresistor (RP). As your
hand blocks the light, the lamp goes out.
Wave your hand over the photoresistor (RP) and the lamp 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
lamp to the negative (–) side of the battery (B3). Wave your hand over
the photoresistor at different distances. The lamp gets brighter the farther
away your hand is.
Motion Detector
Project #83
The amount of light changes the resistance of the photoresistor and the
current flow to the base of the NPN transistor (Q2). The transistor acts like
a switch. Its base current is supplied through the photoresistor. As the base
current changes, so does the current flow through the LED. With no base
current, the LED goes out.
LED Motion Detector
There are many applications for the use of the
detector. The most common is in the alarm system
industry. Some other applications are automatic
door openers, light switches in hallways, stairways
and areas that increase safety for the public.
CM-200_Manual_031914.qxp_CM-200_Manual_031914 4/2/14 12:04 PM Page 42