Elenco Electronics 202 - Manual (Page 116)

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Project #272
OBJECTIVE: To show how capacitors delay circuit changes.
Turn on the slide switch (S1) and the LED (D1) comes on if there is
light on the photoresistor (RP). If you cover the photoresistor now then
the LED will stay on for a while, until the 100
μF capacitor (C4)
discharges.
You can replace the 100 μF capacitor with the other values to change
how long the LED stays on for when the photoresistor is covered.
Slow Light Dimmer
Project #271
OBJECTIVE: To make a brief sound.
Turn on the slide switch (S1) and you a siren sound for only a second or
two, increase the light on the photoresistor (RP) to make it last longer.
Short-time Sound