This circuit was found in an 80's Electronic Engineering. The power supply must be symmetrical. The no value components are calculated for the desired frequency.
We found this circuit on Radio Electronics from July 1990. It triggers a relay with a touch of the...
These three circuits have different treble responses. We found them in the February 1970 issue of...
This photoelectric cell light relay was found in Radio Electronics magazine from April 1958. The...