The time of this timer depends on C1. The circuit was found in the July 1994 Electronics Now magazine. The supply voltage depends on the relay and can go up to 12 V.
The opening of the sensor in this circuit of the 70's causes an integrated buzzer of the Sonalert type...
We found this circuit in a Harris Semiconductor Databook of 1977. The circuit can be implemented with any...
The time of this timer depends on C1. The circuit was found in the July 1994 Electronics Now...