Using a common crystal diode and a 741, this circuit can be used to detect microwaves. The circuit is from old documentation and the switch selects the gains.
Found in an EDN this 80's circuit allows a microcontroller to be used to regulate a battery. The...
This circuit, which can serve as a reference for restorations, was found in the October 1989 issue...
Found in Unitrode documentation, this oscillator uses some unusual components today such as PU and...