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 a year 2000 documentation. It must be powered by a voltage of 5 V as it...
This circuit was found in the February 1990 issue of Radio Electronics magazine. The circuit uses...
Voltage comparators, such as those in the LM139/239/339 series, consist of devices that can be...