Interface connecting machine to telephone network - uses optical couplers to avoid danger of mains voltage reaching exchange line

摘要

The circuit (1) provides galvanic isolation between a subscriber's machine, e.g. a telefacsimile machine, and the lines (2,3) of the public switched telephone network. The terminals (4,5,6,7,8) are connected via amplifiers, a demodulator (17) and a modulator (14) to optocouplers (9,10,11,12,13). In the case of the transmit and receive data signals, the optical signals are demodulated or modulated and fed to a conventional hybrid gyrator (19) and bridge rectifier (18). The other three signals control the interchange of data and handle the `calling' process.