This circuit was found in a 80’s American documentation. The adjustment trimpot is from 47k to 100k. The diodes are general-purpose types use and the supply voltage depends on the relay.
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....