Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the Sonalert type with included oscillator.
This timer was found in the Texas Instruments 1996 linear applications manual. The relay must be...
This circuit compares two light intensities, providing the indication on an analog instrument. The...
This circuit was obtained in a 1983 publication. It is a 1-transistor voltmeter, capable of...