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Project #69, Space war siren project #70, Sunrise light – Elenco Electronics 202 User Manual

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Project #69

OBJECTIVE: To combine effects from the space war and alarm
integrated circuits.

Build the circuit shown on the left and turn on the slide switch (S1).
Press and hold the press switch (S2) to make the lamp (L2) brighter.

Space War Siren

Project #70

OBJECTIVE: To learn about one device that is used to delay
actions in electronics.

Sunrise Light

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. Press the press switch (S2) and reset the circuit.

The resistance of the photoresistor controls how long it takes to
charge up the 470

μF capacitor (C5). Once the capacitor is charged,

current can flow into the NPN transistor (Q2) and turn on the LED.
Pressing the press switch discharges the capacitor.