Found in 1980s Electronic Engineering, this circuit uses common phototransistors as sensors. The circuit is CMOS using an integrated 4011.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...