Elenco Circuit Maker Skill Builder 125 - Manual (Page 61)

Project #124 Light-controlled Lamp
Project #125
Motor-controlled Lamp
Project #123 Sunrise Light
-60-
Build the circuit to the left. Cover the photoresistor (RP), turn the slide switch
(S1) on, and notice that the lamp (L1) is off after several seconds. Place the
unit near a light and the lamp turns on. Cover the photoresistor again. The
lamp turns off. The resistance of the photoresistor decreases as the light
increases. The low resistance acts like a wire connecting point C to the
positive (+) side of the battery activating the music IC (U1).
Use the circuit from Project #124. Remove the photoresistor (RP) and connect
the motor (M1) across points A & B. The lamp (L1) lights for a few seconds and
then turns off. Turn the slide switch (S1) on and turn the shaft of the motor and
the lamp will light. As the motor turns, it produces a voltage. This is because
there is a magnet and a coil inside the motor. When the axis turns the magnetic
field will change and generate a small current in the coil and a voltage across
its terminals. The voltage then activates the music IC (U1).
Cover the photoresistor (RP) and turn on the slide switch (S1). The
LED (D1) is off, but if you wait a long time then it will eventually light
up. Uncover the photoresistor and the LED will light up in just a few
seconds. Push the press switch (S2) and reset the circuit.
The resistance of the photoresistor controls how long it takes to charge
up the 470mF capacitor (C5). Once the capacitor is charged, current
can flow into the NPN transistor (Q2) and turn on the LED. Pushing the
press switch discharges the capacitor.
CM-125_Manual_031514.qxp_CM-125_Manual_031514 4/2/14 12:20 PM Page 61