We found this circuit in April 1979 Radio Electronics magazine. The circuit is based on the 555 and an integrated circuit of the time, including the audible warning and the activation of a relay.
This well-known configuration that appears elsewhere on the site is from an English documentation. In it,...
We found this simple operating tester 741 in a European publication in 1991. The circuit...
Found in Radio Electronics, this circuit doubles the voltage of the 117V power grid to activate...