This filter was found in an old publication from 1977. The circuit must use a simple two-voltage source and the components can be changed for operation at other frequencies.
This circuit that we found in a 1990 documentation uses an LED as a sensor. The operational...
This 1988 circuit makes a back-and-forth of LEDs whose speed is controlled by P1. All components used...
This simple circuit can drive a reed-relay when light falls onto the photo-transistor. The...