This circuit is intended to detect when current flows through the opening of a car door. The circuit fires the horn for 90 seconds. The FET can be the BF245 and the NPN transistors can be the BD135.
This circuit was found in a 1960s book of projects by Gernsbak. The circuit uses germanium...
This circuit was originally designed for testing crystals used in color televisions, but it works...
The circuit of a 1968 publication can be implemented with more modern transistors such as BC548 for...