Abstract: Signal data is generated by interconnected non-inverting and inverting voltage followers and is transmitted on power-carrying conductors to a remote detection circuit comprising a differential amplifier which receives equal in-phase signal inputs of opposite polarity, thereby effecting cancellation of any externally-induced noise which might accompany the signal data.

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 switching matrix in the key service unit of a key telephone system is formed by several groups of relays, each group being associated with a particular station set and each relay in each group also being associated with a particular central office line. All of the relays, except one in each group, disconnect the associated station set from the associated line when the relay is de-energized. One relay in each group functions in the opposite manner to connect the associated station set to the associated line upon failure of the local power supply.

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 is directed to a calling circuit which controls the connection of two different audio signal sources to a single audio signal transmission path for broadcasting the audio signals over a telephone set loudpseaker as well as controlling the energization of indicators in the telephone set and at the main control circuit. Only four conductors are used to connect the telephone set with the main control circuit, two of which are power supply conductors which may supply other circuits as well.

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.

Abstract: A communication switching system of PABX uses a number of time division multiplexed send and receive highway pairs each servicing a plurality of peripheral devices or ports providing two-way communication with the outside world by means of associated telephones, trunk line interfaces, or similar apparatus. All highway pairs are multiplexed in accordance with the same time division format and the maximum number of two-way peripheral devices serviced by each highway pair is dependent on the number of time slots of the format assigned for audio communication. Each peripheral device transmits on a given audio time slot of its send highway. Switching to establish communication paths between peripheral devices is achieved in part by receiving means in each peripheral device responsive to command signals transmitted on command time slots on the associated receive highway instructing each peripheral device on which audio time slots of its receive highway to receive.

Abstract: A counting circuit is disclosed which generates an electrical representation corresponding to the number of pulses in a plurality of pulse trains, each pulse train containing at most ten pulses. The circuit does not start to count the number of pulses in individual pulse trains until a first pulse train with more than a preselected number of pulses is received. The circuit then counts each pulse in subsequently received pulse trains for a preselected number of pulse trains. The circuit is particularly useful in key telephone dial pulse signalling apparatus as a register circuit which is not responsive to false pulses generated by lifting the handset.

Abstract: The disclosure relates to a dial impulse relay circuit including a three-winding relay which repeats a pulse train generated by a first circuit onto a second circuit with substantially no pulse ratio distortion.

Abstract: The disclosure is for key telephone system line control circuitry which provides telephone station line status signals for central office ring, busy, idle and station hold conditions by means of a single control line.

Abstract: The disclosure relates to a key telephone system intercom line circuit which uses only three leads to connect plural telephones and an intercom line control circuit. These leads comprise two talking circuit leads and one control lead. Exclusion circuits in each of the telephones are controlled by signals applied on the single control lead (1) to allow a telephone to seize the intercom line circuit when it is in an idle state, (2) to allow a called telephone (signalled via a separate pair of calling leads) to answer without being excluded and (3) to exclude all other telephones from the intercom line circuit after the calling telephone has seized the intercom line circuit.

Abstract: A timing circuit is disclosed in which the charging time constant in response to positive or negative pulses can be independently controlled. The discharging time constant in response to the removal of all signal pulses from the input of the circuit can be fixed differently from the charging time constants.

Abstract: The invention is a toll restricting method and apparatus which restricts toll telephone calls from telephone stations by interrupting dialing sequences if from the station there is dialed (a) a restricted digit during a first predetermined number of digits, or (b) more than a second predetermined number of digits. Restricted dialing sequences are interrupted by disconnecting the telephone from the central office line for a period sufficient to release all the registered digits and to return central office dial tone to the telephone. Also provided are a method and apparatus for allowing absorb digits to be dialed before the counting of digits begins. A method and apparatus are additionally provided for restricting a telephone from which delays between digits dialed are greater than a predetermined time delay.

Abstract: There is disclosed herein an improved dial assembly suitably adapted to provide an expanded capability for a touch-tone telephone system or to replace existing rotary dial assemblies in various equipment manufacturers' subsets with a touch-tone like assembly. In particular the improved dial assembly includes an upper frame and a pushbutton arrangement similar to known touch-tone dial assemblies. Longitudinal and transverse rods positioned in separate planes immediately below the upper frame convert the downward movement of a particular depressed button into rotational movement. The rotational movement of the rods is utilized by suitably positioned cooperating sets of switches to connect in the necessary manner the various telephone circuits within and/or external to the particular subset. The improved dial assembly above expands the capability of present day assemblies in that it enables the provisioning of ancillary telephone functions, such as repertory dialing, toll restricting circuitry, etc.