This simple circuit is a continuity test that, in addition to testing resistors, can also test other components. Power is provided by batteries and the LED can be of any color.
This circuit was found in Radio Electronics from the 90s. The components used are common, and the...
This circuit was found in an American publication called Ham Radio. The circuit uses still current...
This circuit was obtained from a 1997 publication. It is an alarm that has a lock and a bistable...