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 circuit is from the time when cars used contact breakers. This 80's version measures the dwell...
In the fist circuit the alarm triggers on when any sensor is CUT. In the second circuit the alarm...
We found this Vox in a 1969 Motorola documentation. Transistors support modern equivalents and the SCR can...