Alarm Light; Alarm Light (Ii) - Elenco Electronics Snap Circuits Instruction Manual

Project #386
Project #387

Alarm Light

OBJECTIVE: To light a bulb to indicate an open circuit.
This is another example of a alarm that activates when the circuit is
broken. Connect the jumper wire across points A & B and then turn
on the switch (S1). The bulb (L2) will not light until the jumper wire is
disconnected. Turn off the switch to turn the bulb off again.

Alarm Light (II)

OBJECTIVE: To light a bulb to indicate an open circuit.
This project is similar to project 386, but uses a transistor (Q2). The
bulb (L2) will not light until the jumper wire is disconnected. The
jumper wire grounds the base of the transistor, keeping it off. Remove
the jumper and the voltage on the base rises; turning the transistor
and SCR (Q3) on, and lighting the bulb. Note, the variable resistor
(RV) is used as a fixed value.
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