This high-gain circuit was found in an American publication from the 1990s. The circuit can use general purpose transistors and powered from a source or battery.
With a touch of the sensor wire X1, which can also be a pressure switch, the LED lights for a time...
This alarm with automatic shutoff was found in the April 1975 Radio Electronics magazine. The...
This Colpitts crystal oscillator was found in an American publication for amateurs in the 1980s....