This telephone circuit was found on a 90's EDN. It keeps a flashing LED to indicate that there was a call in your absence. The components admit equivalents.
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....