This simple tester was found in a Popular Electronics from the 90s. The circuit is powered by two 9 V batteries since it requires a symmetrical source.
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...