This circuit was found in the January 1999 issue of Electronics Now magazine. The circuit uses an integrated circuit from the period and has earphone listening.
This 4-function, high-pass, low-pass, band-pass and rejector filter was found in French...
Passing between a light source and the sensor will trigger on the relay by a time interval...
This circuit was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...