Published in a PE Hobbyst Handbook of 1991, this sensor uses an integrated circuit that is unusual today. The circuit is based on a high frequency oscillator.
This circuit for audio signals was found in the March 1990 Radio Electronics magazine. The circuit...
In the figure we have the way to implement a sinusoidal oscillator with the 4093 IC. The component...
Equivalent transistors, like the BC548 and BC558 pair can be used in this circuit that we find in an...