We found this circuit in the Texas Instruments optoelectronics manual. Field effect transistors can be BF245 and bipolar BC548. The sensor is a photodiode in the photo-generator mode.
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...