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.
Found in a 1965 Radio Shack documentation this oscillator can be used with modern general purpose...
In the figure we have a voltage / frequency converter circuit that can be used as a transducer interface...
This small stereo amplifier for headphones was found in a documentation on integrated circuits from...