Intercommunication system

Claim 2

In an intercommunication system having plural stations which may originate or receive calls, with circuits connected between stations, an operating control, comprising: means for establishing in said circuits a first electrical condition when the circuit is free and a second electrical condition when said circuit is in use; means in a call originating station for sensing the electrical condition of the circuit connected with an intended call receiving station; an amplifier in the call originating station; means responsive to said sensing means for rendering said amplifier operative and completing the call connection if said circuit is free; means responsive to said sensing means for maintaining said amplifier in an inoperative state if said circuit is in use; and means for manually overriding said maintaining means to render said amplifier operative for transmission of a message to the intended call receiving station.

Claim 3

In an intercommunication system having plural stations which may originate or receive calls through two-wire balanced lines connected between stations, an operating control comprising: means for establishing in said lines a first electrical condition in which they float when free and a second electrical condition in which they are connected with a reference potential means when in use; means in a call originating station for sensing the electrical condition of the lines connected with an intended call receiving station; means responsive to said sensing means for completing the call connection if said lines are free; a semiconductor switch responsive to said sensing means to connect said two-wire balanced lines with said reference potential means upon completion of the call connection; and a station selector switch with a section in series with said semiconductor switch, said switch section being operated to open condition upon termination of the call to interrupt the circuit of said semiconductor switch.

Claim 4

In an intercommunication system having plural stations which may originate or receive calls through two-wire balanced lines connected between stations, an operating control comprising: means for establishing in said lines a first electrical condition in which they float when free and a second electrical condition in which they are connected with a reference potential means when in use; means in a call originating station for sensing the electrical condition of the lines connected with an intended call receiving station; means responsive to said sensing means for completing the call connection if said lines are free; a semiconductor switch responsive to said sensing means to connect said two-wire balanced lines with said reference potential means upon completion of the call connection; and a station selector switch with a section in series with said semiconductor switch, said switch section being operated to open condition upon termination of the call to interrupt the circuit of said semiconductor switch.

Claim 5

In an intercommunication system having plural stations which may originate or receive calls, with circuits connected between stations, an operating control, comprising: means for establishing in said circuits a first electrical condition when the circuit is free and a second electrical condition when said circuit is in use; means in a call originating station for sensing the electrical condition of the circuit connected with an intended call receiving station; an amplifier at the call originating station, the operation of which is necessary to complete a call connection; and means responsive to said sensing means for rendering said amplifier operative at the end of said time delay if said circuit is free, and maintaining said amplifier inoperative if said circuit is in use including an amplifier control circuit having an input, and an output coupled to said amplifier, said control circuit respectively rendering said amplifier inoperative and operative when its input is in first and second electrical states, a first transistor for switching said control circuit input to said first state in response to a signal at its base when enabled, a second transistor for providing said signal in response to said station connecting circuit being in said first electrical condition, said second transistor only providing said signal when not disabled, and a third transistor associated with said time delay means and coupled to the control circuit input and said first and second transistors, said third transistor changing states, at the end of said time delay to enable said first transistor to switch said control circuit input to said first state, if said signal is being provided, and switching said input to said second state at the end of said time delay and disabling said second transistor, if said signal is not being provided.

Claim 6

In an intercommunication system having plural stations which may originate or receive calls, with circuits connected between stations, an operating control, comprising: means for establishing in said circuits a first electrical condition when the circuit is free and a second electrical condition when said circuit is in use; means in a call originating station for sensing the electrical condition of the circuit connected with an intended call receiving station; an amplifier at the call originating station, the operation of which is necessary to complete a call connection; and means responsive to said sensing means for rendering said amplifier operative at the end of said time delay if said circuit is free, and maintaining said amplifier inoperative if said circuit is in use including an amplifier control circuit having an input, and an output coupled to said amplifier, said control circuit respectively rendering said amplifier inoperative and operative when its input is in first and second electrical states, a first transistor for switching said control circuit input to said first state in response to a signal at its base when enabled, a second transistor for providing said signal in response to said station connecting circuit being in said first electrical condition, said second transistor only providing said signal when not disabled, and a third transistor associated with said time delay means and coupled to the control circuit input and said first and second transistors, said third transistor changing states, at the end of said time delay to enable said first transistor to switch said control circuit input to said first state, if said signal is being provided, and switching said input to said second state at the end of said time delay and disabling said second transistor, if said signal is not being provided.