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.

4-Band Rectangular Generator (CB25327E)
This circuit generates signals in four frequency bands with the threshold values indicated in...
Dark switch (CB8256E)
This twilight switch or pass switch was obtained from a 1967 Philips documentation. The circuit...
Noise Generator (CB7078E)
Published in Popular Electronics with the curious name of Obnoxious Noisemaker, this 1968 circuit...