Simple liquid level sensor (CB20729E)

This sensor with two transistors triggers a relay according to the supply voltage. The power source must be isolated from the power grid.

Audio limiter (CB7398E)
This circuit was found in documentation from the 1980s. It is powered by the audio signal that must...
Damped Oscillator LM108 (CB19097E)
Damped oscillators can be used to produce sound from percussion instruments such as the triangle, bell,...
IR remote control ON OFF test (CB7820E)
Found in Radio Electronics from the 90s, this circuit produces pulses to test an infrared...