This sensor circuit for currents of the order of nanoamperes was found in an American documentation from the 1980s. The components are from that time.
The purpose of this interesting circuit found in a 1977 documentation is to complete the last...
The optocoupler in the figure uses common transistors and a phototransistor to drive a sensitive relay...
The coil consists of 100 turns of wire 28 in a wooden or PVC tube from 2 cm to 2.5 cm in diameter with...