The integrated circuit used in this 2002 project is not very common. It is powered directly by the telephone line, requiring no power supply.
This circuit is from 1975 documentation. Transistors such as 2N3055 can be used and the...
In this circuit from the 60s, the power supply is made with 22.5 V, which is the voltage of the...
I found this simple circuit from an English magazine from 1984. The circuit can be easily...