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.
Found in EEE documentation, this circuit can have the duration and frequency adjusted separately....
This amplifier provides up to 15 W of output when powered by a simple 12 V source. The integrated...
This sweep generator or current-controlled oscillator was found in Popular Electronics from...