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.
Found in a 1963 documentation, this circuit employs germanium transistors of the time. Transformer and...
In the figure we have a way of receiving ultrasonic signals of a single frequency using a PLL 567....
This traditional circuit generates a 200 Hz sinusoidal signal. The frequency depends on the...