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 requires an input current of only 20 fA (femto amps) which corresponds to a...
This circuit for frequencies of 20 to 2 kHz was obtained in English documentation from 1966. The...
This timer can control loads up to 240 W. We found it in a 1967 RCA documentation. The main...