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 requires an input current of only 20 fA (femto amps) which corresponds to a...
This circuit for frequencies of 20 to 2 kHz was obtained in English documentation from 1966. The...
This timer can control loads up to 240 W. We found it in a 1967 RCA documentation. The main...