This circuit was published in the July 1993 issue of Electronics Now magazine. It uses a sensor from the time and triggers a buzzer with a Sonalert-type oscillator.
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...