Using an LDR as a sensor, this circuit is from the Radio Electronics magazine of December 1984. The operational amplifier is the 741 and the source must be symmetrical.
This circuit uses a loop antenna to receive and amplify signals from the 60 kHz long wave band....
The frequency of this oscillator depends on R and C (see math section for electronics). The...
This common operational configuration can be implemented with modern equivalent. Next to the...