Motorcycle headlight monitor (CB9117E)

This simple circuit was found in Popular Electronics from the 1980s. The circuit uses an LED as an indicator.

Wien Bridge Oscillator with Diode Regulator (CB25908E)
This circuit for 1 kHz sinusoidal signals uses a common operational amplifier circuit and is...
Negative Peak Detector (CB5166E)
We find this circuit in an American manual from the 80's. The circuit can be implemented with more...
48 V Fast Current Sensor (CB5242E)
For -48 V voltages, this fast sensor was found in a 2005 Linear Technology application manual. The...