H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/17, 379/33
H04M 3/42 (2006.01) H04M 9/00 (2006.01)
Patent
CA 1122338
Abstract of Disclosure A line/interface circuit for a key telephone system, which system is of the type including a subscriber telephone line manifesting a pair of conductors. The conductors emanate from a central office or PBX and the line/interface circuit pro- vides interconnections between a key subset associated with said subscriber and said central office via said telephone line. The line/interface circuit has a photo-coupler for producing a signal indicative of ringing to indicate an incoming call. A transistor and a first relay are coupled to the photo-coupler to access the subset with an alternate signal. The subset is coupled for the transmission of voice signals to the telephone lines by means of a transformer to provide isolation. Two further relays are provided to enable operation of the subset in a hold condition without releasing a connection between a connected party and the subset. The line circuit provides a fourth relay to enable the subset to initiate a call by access- ing the telephone lines, which access is accomplished rapidly with a minimum of interferences in regard to the telephone lines. Due to the nature of the coupling and operation of the line circuit, the line circuit performs all required switching and supervisory functions with a minimum of interference to the telephone lines, thus avoiding the use of an interface.
331320
International Standard Electric Corporation
Smart & Biggar
LandOfFree
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