This circuit was found in documentation from the 1980s. Transistors are general-purpose types like the BC548 for NPN and the BC558 for PNP.
This circuit can be implemented with discrete transistors. We found it in General Electric's 1964...
The operational amplifier used on this Raytheon circuit is similar to the 741. The circuit is from...
This circuit detects light variations using two LDRs as sensors. Operational amplifiers and...