Metal Detector (CB21929E)

This two-transistor metal finder was found in a Raytheon manual from the 1950s. The transistors are germanium from the time.

Microphone Preamplifier (CB10228E)
This circuit is from a 1986 Revista Española de Electrónica. It consists of an amplifier with...
4 LEDs Flasher (CB16325E)
This is the project was found in a 1982 publication. As shown in the figure, these are two...
Water Pump Automatic Control (CB18677E)
This very simple circuit uses two stripped wires as sensors that must be at the drive level. The...