This telephone recording circuit was found in the June 1979 issue of Radio Electronics magazine. The components are common at the time and the power is supplied by the power grid.
The circuit shown was obtained in American documentation from 1968. MOSFETs can be replaced by...
This circuit is more elaborate than the previous one, employing an integrated amplifier circuit of the...
This circuit activates a relay when the conducting bars (probes) are held by a person. The circuit is...