Voltage level detector (CB21504E)

This circuit was found in a 1966 EEE. The circuit can be implemented with modern general-purpose transistors.

Anti Sleep Alarm (CB18464E)
This circuit is from a 1998 Poptronics. The circuit triggers a buzzer after a certain time, waking...
Voltage Indicator (CB16366E)
An integrated circuit 741 (operational amplifier is the basis of this voltage indicator, which can also...
Voltage Converter (CB22525E)
This transistorized voltage converter is one of the oldest that we find in technical publications. It...