Elenco Electronics 202 - Manual (Page 122)

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Project #288
OBJECTIVE: To build a space war timer.
Turn on the switch (S1) and the lamp (L2) lights and you hear the
speaker (SP) sound. Now press the press switch (S2); the LED (D1)
lights and the lamp turns off as the speaker sounds. You can change
the length of time the speaker sounds by changing the values of C4
and R5.
Space War Timer
Project #289
OBJECTIVE: To change the speed of the alarm IC sound.
Set the adjustable resistor (RV) at the bottom position and turn on the
slide switch (S1). The lamp (L2) lights and the speaker (SP) sounds.
Now slowly adjust RV up. The lamp dims and the sound slows down. As
you move RV up, the voltage at the base of Q1 increases as the collector
and input of U2 decrease. This lowers the output frequency and
brightness the bulb. You can only adjust RV about a quarter of the way
up before the sound stops.
Alarm Speed Adjuster