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.
With this circuit it is possible to obtain an input resistance of 100Gohms for a multimeter, with...
This amplifier, to detect biological signals in implanted transmitters, uses transistors such as...
This application is not modern since few computers have parallel ports. But you can use this...