SUBSCRIBER LINE CIRCUITS USING HALL EFFECT DEVICES

摘要

Telephone subscriber line circuits and an all-electronic telephone exchange are described wherein Hall effect devices are incorporated to detect line looping, dialing and ring-trip. The line circuit includes direct current feed means coupled via transformer w m dings, each of which windings are connect-ed between the direct current supply and one of a pair of line wires; an additional winding from the transformer through which an AC ringing current is applied to the line wires; a Hall effect device for detecting the presence of direct current in the line wires and a magnetic circuit coupled to the Hall effect device and to the transformer windings.