This circuit was obtained from a Radio Electronics issue from January 1989. The indicator is a ceramic transducer, and the frequency of the emitted sound is given by C3.
This class B push-pull amplifier circuit with a few hundred milliwatts of power was found in an...
In the figure we have a window detector that uses only a voltage comparator. The circuit can use...
This circuit was found in an old American documentation. The operational used is of the...