When the voltage supplying the circuit falls below the zener value, the LED lights up, and if a low current buzzer is used, it is activated. The circuit is from a 1999 American publication.
We found this circuit in the January 1992 issue of Radio Electronics magazine. The circuit...
The 60 Hz hum or noise from the power grid (hum, in English) is one of the biggest enemies of...
This circuit was found in old English documentation. We have the same version found in this...