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 is from 1975 documentation. Transistors such as 2N3055 can be used and the...
In this circuit from the 60s, the power supply is made with 22.5 V, which is the voltage of the...
I found this simple circuit from an English magazine from 1984. The circuit can be easily...