This circuit is from old documentation, using a component that cannot be found easily today. The indicator is a galvanometer, and the input voltage is in the order of 1 V.
Found in an English documentation from 1989, this font uses current components. Rectifier bridges can...
This sensor circuit for currents of the order of nanoamperes was found in an American...
This TTL sequential flasher circuit was found in the January 1981 issue of Radio Electronics...