This circuit makes use of an optical coupler to isolate the telephone line. The circuit is from 1970s documentation. The components admit equivalents.
We have in the figure as a monostable a proximity switch where our body capacitance (estimated at 200...
Suggested by Siliconix in documentation from the 90s, this circuit can present gains of digitally...
This amplifier with old germanium transistors is from a 1957 documentation. The power is a few...