Found in American documentation from the 1980s, this circuit can be designed with equivalent components. The microphone can be of the piezoelectric type.
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...