Abstract: A multi-line, multi-instrument telephone system having no key service unit and wherein decentralized or local indicator lamp and paging circuit management functions are provided which are operative independently in each station set to operate and control the indicator lamps and paging circuits through selective local generation and alteration of control signals and comparison of the control signals with locally generated reference voltage signals to provide basis for decisions on required visual and audible indicator status. The system is connected in loop fashion with each instrument being connected across a common, multiconductor buss wherein a single conductor supports lamp supervision signaling for the multiple lines and another single conductor supports intercom status signaling, intercom audio, paging audio, and the ring signal.

Abstract: Each of the station sets in the system generates a continuous, current-modulated digital data stream carrying information concerning the status of pushbutton-actuated switches associated with a particular service or feature. This data stream is transmitted via a phantom pair over standard four-wire cable to an associated station card in the key service unit, which receives and decodes the data, implements any service requested at the associated station set by closure of a pushbutton-actuated switch in the station set, and generates a continuous voltage-modulated digital data stream carrying instructions for the connection of the station set speakerphone to either the first or second talk path formed by the first and second conductor pairs in the standard four-wire cable, for energization of light-emitting diodes associated with the pushbutton-actuated switches in the station set, and for controlling background music transmission to the associated station set.

Abstract: A key telephone set is disclosed having a programmed digital computer which signals a central switching and control unit of a key telephone system of the status of a plurality of function switches and receives signals from the central switching and control unit that certain electrical connections and visual indicators in the key telephone set are to be initiated or controlled. Two independent audio communication circuits are provided in the key telephone set for interconnection to either the hybrid network of the handset or the built in speakerphone unit. Central office lines are accessed via individual function switches. Intercom calls are initiated via one function switch, and are answered hands-free via the speakerphone or are answered via the hybrid network. A wide range of features are signalled via the function switches and are visually monitored by means of visual indicators. The key telephone set may be used interchangeably with either dial pulse signalling units or tone signalling units.

Abstract: The disclosure relates to a four conductor circuit arrangement providing two communication channels between a control unit and a terminal device. Power feed and bi-directional signalling are accomplished simultaneously over the same four conductors used for the two commmunication channels without interference. The signalling from the control unit to the terminal is accomplished by means of a voltage modulator circuit in the control unit by which voltage pulses are transmitted via a phantom circuit arrangement over the four conductors to the terminal unit. The voltage pulses are sensed from the phantom circuit in a data receiver which is located at the terminal unit. Connected to the phantom circuit in the terminal unit is a voltage regulator circuit which receives power from the control unit via the four conductor phantom circuit interconnecting the control unit and the terminal. In series with the voltage regulator circuit is a constant current sink and an inductor.