This high sensitivity circuit was found in the July 1992 Radio Electronics magazine. The circuit drives a buzzer, but a relay can be used to activate an external load.
This circuit was obtained in a 1979 101 Electronics Projects. The circuit can be assembled easily,...
Suggested by a 90's Linear Databook, this circuit compensates for capacitor hysteresis. The main...
This circuit serves to isolate analog signals, for example, audio signals in a secure link...