Dtmf activated remote telephone line switching and testing

Abstract

DTMF (dual-tone multi-frequency) activated apparatus for remote switching and testing of a four-wire telephone line system is disclosed. The telephone line provides four-wire service between a first location and a plurality of second remote locations. By using a standard twelve button or expanded sixteen button telephone DTMF key pad, the switching and testing apparatus provides the capability at the first location of controlling switching circuits at any one of the remote locations. Each remote switching and testing circuit is provided with a DTMF detector and digital logic responsive to the detector for recognizing an assigned address code and any one of the command codes corresponding to the looped mode, the terminated mode, the milliwatt source mode, and the in-data mode. A programmable three digit address, for example, allows use of up to one thousand switching and testing circuits on one line. When the digital logic of a switching and testing circuit recognizes its assigned address, the circuit is enabled to respond to a following command code which causes the circuit to assume the corresponding mode. In addition to the four codes for each of the four modes of the switching and testing circuit, there is a 'master reset' code which allows all units, or all units within a group, to be returned to the in-data mode.