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 UAA170 application circuit was taken from Siemens' own integrated circuits manual from 1976....
We found this circuit in the 1960 Mullard transistor reference manual. The phototransistor can be a...
Found in National Semionductor documentation this circuit combines a tone control with an...