This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is based on a 741 that activates a buzzer with oscillator. R5 adjusts the sensitivity.
This circuit can be used as shield or to drive powerful loads from low current switches such as...
This circuit was found in a 1968 documentation. It makes use of both NO and NC reed-switches and small...
This circuit keeps an LED on briefly when S1 is pressed. The time depends on C1. The circuit is...