This circuit with the CA3059 was found in the July 1995 Elexctronics Now magazine. The signal must be DC, and the circuit is not isolated from the mains.
Found in an Electronic Design from the 90s, this circuit measures the phase difference between two...
This circuit was found in the 2005 Linear Technology Linear Circuit Manual. It is a sensor with large...
This circuit was obtained in an old Elektor and can be adapted to use white power LEDs. The...