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.
This circuit was found in a 90s Electronic Design. It uses integrated circuits that are not common...
The frequency of this oscillator depends on the crystal used and has a threshold given by the...
This circuit is from a 1993 Italian magazine, but it can be easily assembled today. For 110 V,...