This circuit was found in a 73 magazine for radio amateurs from the 90s. The circuit uses high voltage transistors and the relay is high voltage as well.
This circuit is from a Popular Electronics from the 90s. The integrated circuit admits equivalents...
This very interesting project was obtained in a 1980 publication. It consists of a device that is...
This circuit beeps when the sensor is triggered by the opening of the freezer door or other...