This circuit was obtained in an Electronics Now from the 90s. The circuit uses operational amplifiers from the time and the indicator is of the Sonalert type with internal oscillator.
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...