Telephone intercom system
First Claim
1. In a subscriber telephone system of the type including a first electrical circuit comprising a pair of conductors on the subscriber'"'"'s premises connectable to each of a plurality of telephone sets on the premises, each of the telephone sets including a dial circuit for transmitting dial pulse signals over the first circuit and a talk circuit for transmitting and receiving voice signals over the first circuit, the first circuit being connected to a telephone company line extending from a central office for carrying central office calls to and from the subscriber'"'"'s premises, apparatus for enabling at least two of the telephone sets on the premises to be used for intercom calls as well as central office calls, said apparatus comprising:
- A. a second electrical circuit for carrying intercom calls comprising a pair of conductors on the premises connectable to each of the telephone sets to be used for intercom and central office calls;
B. means at the premises for supplying power to said second circuit to enable the transmission of voice signals thereover;
C. line selection means associated with each of the telephone sets to be used for intercom and central office calls for switching the talk circuit therein between the first circuit and said second circuit;
D. intercom signalling means separate from said dial circuit associated with each of the telephone sets to be used for intercom and central office calls and connectable to said second circuit, said intercom signalling means including an intercom call alerting signal generator for generating an intercom call alerting signal in an audio frequency range and at a level substantially above that of the voice signals transmitted over said second circuit and an intercom switch for activating said intercom call alerting signal generator to transmit the intercom call alerting signal over said second circuit; and
E. intercom signal detecting means associated with each of the telephone sets to be used for intercom and central office calls and connectable to said second circuit, each of said intercom signal detecting means including means responsive to the presence of the audio frequency intercom call alerting signal on said second circuit for providing provide an indication that an intercom call is desired and threshold means for selectively attenuating the relatively low level voice signals on said second circuit in advance of said indication providing means.
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Accused Products
Abstract
Standard four prong, plug-in telephone sets are modified to enable intercommunication among the sets on the subscriber'"'"'s premises. In a subscriber telephone system including a single central office circuit, only two of the standard four prongs and associated receptacle sockets are used for establishing connection to the central office circuit. In the disclosed system, a local intercom circuit is added to the premises and connects to the remaining two sockets in each receptacle so that each set that is plugged in is also connected to the intercom circuit. The sets are modified to include a line selector switch which enables the talk circuits therein to be switched back and forth between the central office circuit and the intercom circuit. An intercom call signal generator and detector is also added to each set for intercom call signalling over the intercom circuit. In a subscriber telephone system that includes two separate central office circuits, the system is adapted to enable one of the two circuits to be used for intercom calls as well as central office calls. Switching back and forth between an intercom mode and a central office mode on that one circuit is accomplished by a suitable command such as a hook flash. The two central office circuit system also allows the standard four prong plug-in arrangement to be retained for the telephone sets. Calls may also be placed on hold and conference connections made in the two central office system upon the generation of appropriate hook flash commands.
45 Citations
14 Claims
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1. In a subscriber telephone system of the type including a first electrical circuit comprising a pair of conductors on the subscriber'"'"'s premises connectable to each of a plurality of telephone sets on the premises, each of the telephone sets including a dial circuit for transmitting dial pulse signals over the first circuit and a talk circuit for transmitting and receiving voice signals over the first circuit, the first circuit being connected to a telephone company line extending from a central office for carrying central office calls to and from the subscriber'"'"'s premises, apparatus for enabling at least two of the telephone sets on the premises to be used for intercom calls as well as central office calls, said apparatus comprising:
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A. a second electrical circuit for carrying intercom calls comprising a pair of conductors on the premises connectable to each of the telephone sets to be used for intercom and central office calls; B. means at the premises for supplying power to said second circuit to enable the transmission of voice signals thereover; C. line selection means associated with each of the telephone sets to be used for intercom and central office calls for switching the talk circuit therein between the first circuit and said second circuit; D. intercom signalling means separate from said dial circuit associated with each of the telephone sets to be used for intercom and central office calls and connectable to said second circuit, said intercom signalling means including an intercom call alerting signal generator for generating an intercom call alerting signal in an audio frequency range and at a level substantially above that of the voice signals transmitted over said second circuit and an intercom switch for activating said intercom call alerting signal generator to transmit the intercom call alerting signal over said second circuit; and E. intercom signal detecting means associated with each of the telephone sets to be used for intercom and central office calls and connectable to said second circuit, each of said intercom signal detecting means including means responsive to the presence of the audio frequency intercom call alerting signal on said second circuit for providing provide an indication that an intercom call is desired and threshold means for selectively attenuating the relatively low level voice signals on said second circuit in advance of said indication providing means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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Specification