Undervoltage detector with the LM3900 (CB25172E)

The figure shows how to implement an undervoltage detector using a Norton amplifier and a zener diode as the main elements.

XTAL 10 to 20 MHz oscillator (CB13847E)
This circuit was found in a documentation for radio amateurs in 1974. It can be used to generate...
Sine and square generator (CB21949E)
This circuit was found in a publication by Gernsback from 1960. The circuit generates signals from...
Simple Touch Switch (CB16945E)
The touch sensor of this circuit consists of a single plate that must be touched to obtain an...