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.
This 10 kHz filter is based on a 741 operational amplifier. The circuit is from Electronics Now...
We found this circuit in a994 documentation. It has a visual and a time signature indicator in...
This control circuit using a low voltage switch was found in the September 1987 Radio Electronics...