Timed Alarm (CB6423E)

We found this circuit in a 90's Popular Electronics. The circuit produces a loud sound if S2 is not pressed to reset.

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Bistable Using Relay and SCR (CB541E)
This set-rest relay uses two SCR and two switches to control a DC relay. The circuit can be used...
LM386 Amplifier with 741 Preamplifier (CB1003E)
This simple circuit of low power with an LM386 includes the highly sensitive audio preamplifier...
Electronic Relay (CB504)
circuit is used to increase the sensivity of a relay. A 50 to 100 mA relay can be triggered with...