This circuit is from an American 1967 documentation and can be implemented with modern equivalent transistors. The circuit serves as a Q multiplier.
This circuit consists of an astable multivibrator whose frequency changes according to the light...
This circuit has a 200 kHz bandwidth and a low input current. The circuit is from the 80's, but...
The sensor can be made using two bare wire or two screen with a piece of tisse between them. One...