This current switch was found in a Radio Electronics from November 1957. It triggers the current determined by the electromechanical sensor, a polarized relay of the time.
This circuit was obtained in a 1979 publication. The operational amplifier is of the type with...
This circuit was obtained in a 90’s Popular Electronics. The frequency depends on C1, a component...
Because it uses TTL integrated circuits, this siren must be powered by 5 V or as indicated with D1 to...