Elenco Electronics 202 - Manual (Page 86)

Project #198 Fire Engine Symphony
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Project #199
OBJECTIVE: To build a light dimmer.
Press the press switch (S2) to complete the current's path flow. You
might expect the LED (D1) to light instantly but it takes about a second.
The charging current flows into the 100 μF capacitor (C4) first. As the
capacitor charges, the charging current decreases, input current to the
PNP transistor (Q1) increases. So current begins to flow to the LED
and the LED gradually brightens.
Now release the press switch. The capacitor begins to discharge,
sending input current to the transistor. As the capacitor discharges,
the input current reduces to zero and gradually turns off the LED and
the transistor.
Light Dimmer
OBJECTIVE: To combine sounds from the music, alarm, and
space war integrated circuits.
Build the circuit shown. Turn it on, 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!