This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is based on a 741 that activates a buzzer with oscillator. R5 adjusts the sensitivity.
Suggested by Sprague in the 90's documentation, this circuit applies to AC motors. The...
The diodes in this circuit are used for waveform correction. The circuit is from Electronics Now...
This 5.1 MHz oscillator was found in a 1980s American documentation. The used operational...