We found this circuit in a Popular Electronics from the 90s. Its purpose is to monitor a power line. The circuit uses optical couplers of the time.
With this circuit, signals in the range of 10 kHz to 150 kHz can be received at close to 4 MHz...
This limiting circuit with an operational amplifier has an adjustable cut-off point and can use...
Published by Philips in 1965 documentation, the sensor for this circuit is a common LDR. The...