GB2157920A - Telecommunication switching system - Google Patents

Abstract

A system for providing an internal communication facility in private houses utilises the house telephone wiring 10, 12 and a plurality of ordinary telephones each connected to a station unit (35) or the master unit 14. Communication between the master unit 14 and the station units (35) is via an unused wire of the house wiring. Each unit has a coded signal transmitter and receiver. A station unit can selectively signal the master unit to obtain exchange access and to put the exchange line on hold, and when in intercom mode can call other station units. Each station unit has a QUIET button which controls activation of a buzzer inhibit circuit and a corresponding status LED. The master unit can detect an incoming call and signal this to the station units. <IMAGE>

Description

SPECIFICATION Telecommunication switching system This invention relates to telecommunication switching systems and station units for use therein and particularly but not exclusively to station units and a switching system for providing an internal communication facility (intercom) between several telephone extensions in an ordinary private single exchange line arrangement.

There are available many key telephone systems which provide intercom facilities fora multiplicity of telephone extensions. Such systems are large, expensive and generally require special wiring, and are thus totally unsuitable forthe domestic environment where a private customer having several telephone extensions (in, for example, hall, kitchen, sitting room, study, bedroom or garage) would wish to call one telephone extension from another.

Asystem is also known which employstwo unused wires in the telephone wiring in a house as an intercom pair and also forthe transmission of data.

Each telephone extension is coupled to the wiring via a "page" unit, and a control unit is also coupled to the wiring. This system provides a number offunctions selectable by the customer via buttons of a keypad such as exchange line button, hold button, all page button.

According to one aspect ofthe present invention there is provided a station unitforuse in a switching system and comprising an inputterminal for connection, in use, to a conductor of a multi-conductorbus (normally the telephone wiring in a building); coding means having an output coupled to the input terminal and being arranged to generate respective coded signals corresponding to input signals; selector means arranged to apply an input signal to the coding means selectable from a range of input signals representing station unit addresses and system functions; presettable decoding means having an input coupled to the input terminal and having an output coupled to a sound indicator means, the decoding means being preset such asto activate the indicator means in responseto receipt of certain coded signals; inhibit means responsive to respective signal from the selector means for inhibiting the response ofthe indicator means; and a respective visual indicator arranged to provide a visible indication ofthe operation state ofthe inhibit means.

A station unit of this first aspect enables the customer to inhibit sound calling ata station and to have a visual indicator activated to indicate the status ofthe sound calling.

The inhibit means preferably has a toggle operation wherebythe response of the indicator means is alternately inhibited and enabled upon successive respective signals from the selector means.

Preferably the selector means comprises a keypad wherein each key representing a station unit address incorporates or is associated with a key label which displays the respective station address and is of such material that a user can erasably write thereon.

According to a second aspect of the present invention there is provided a switching system comprising a multi-conductor bus; a plurality of telephones having their speech circuits and calling number generators coupled to a pair of conductors of the bus; a station unit as referred to above for each of the telephones; and a master unit comprising ringing condition detecting means and a coding means responsive thereto for sending a coded signal to the station unit via said conductor.

A specific embodiment of a switching system will now be described by way of example with reference to the drawings in which Figure lisa schematic diagram of a master unit ofthe system and Figure 2 is a schematic diagram of a station unit of the system.

A pair 10 of ordinary exchange wires is connected to a master socket 11 in accordance with British Telecom wiring practice. Normally a six core cable 12 (one core not shown) leaves socket 11 and is connected two a number of ordinary sockets or outlets 13 at selected places in a customer's house, for example, sitting room, study, kitchen and bedroom. To implement the switching system ion a housethecable 12is removed from socket 11 and an additional socket 13 is provided adjacent to socket 11. The free end of cable 12 is then terminated atthe additional socket 13, asshown in Figure 1.

A master or control unit 14 of the switching system is positioned near sockets 11 and 13 and is coupled to them by means of cables 15 and 16, respectively. The cables 15 and 16 have a plug, not shown, at each end and the housing 17 ofthe master unit 14 has respective sockets, not shown, mounted therein.

Alternatively, the cables 15 and 16 may have one end connected internallyofthe housing 17 and have respective plugs on their free ends.

The incoming exchange pair is connected to the normally-closed contacts of a pair of change-over relay contact sets 18-1, 18-2, whose poles are connectedvia cable 1 6to the corresponding wires in the house wiring. By this means, the system is fail-safe in that the house wiring would be connected to the exchange pair in the event of a power failure affecting the master unit 14.

Also mounted in the housing 17 is a furthersocket 19 having the same wiring configuration as socket 13 whereby a telephone can be connected to the system close to the master socket 11. It will be appreciated thatfora house having unmodified wiring a main telephone would normally be plugged into the master socket 11, usually in the hall.

A powersupply 21 provides a pair of power lines 22 connected to the normally-open contacts ofthe relay contact sets 18-1 and 18-2. A pair of wires 23 connected to socket 19 and coupled in use to the house wiring via socket 13 is connected to the power supply 21 for supplying powerto circuitry in station units to be described later. It would be normal forthe master unit 14to be mains powered but it could be battery powered if desired.

A fifth wire 24 ofthe house wiring is used forthe transmission and reception of data signals and is connected to a receiver 25 and a transmitter 26. The receiver 25 is formed by a proprietary receiver type 926 and is connected to decoder 27 formed by a proprietary decodertype 4514 which decodes the receiver output into a 1 -out-of-1 6 signal. The transmit- ter26 comprises a proprietary type 490 transmitter and a preselected pair of its control terminals are coupled togethervia relay contact 29-1 of a relay 29 (not shown).

Aringing currentdetector30 is coupled to the incoming exchange pair 15 (this coupling is shown schematically in Figure 1 since the ringing current detector30 may or may not utilise a capacitor which is provided in the master socket 11) and incorporates the relay 29 which is energised in response to detected ringing current, whereby a respective code is applied to the data line 24 by the transmitter 26.

When receiver 25 detects the code corresponding to a request for a telephone to have access to the exchange pair, the decoder 27 sends the corresponding decoded output signal to a relay drive circuit 28 which then deactivates relay 18 to cause the poles of its contact sets to be connected to the normally-closed contacts as shown in Figure 1, and also deactivates relay 32 referred to below.

When receiver 25 detects a signal corr ;ponding to a hold request, then relay drive circuit 28 receives the corresponding signal from decoder 27 and energises relay 18, and also relay 32 which closes its relay contacts 32-1 to couple a holding resistor31 acrossthe exchange pair.

It will be appreciated that ifthere is a failure ofthe mainssupplythen both relays will be unenergised and the exchange line pairwill be coupled through the housewiringandatthesametimeholding resistor3l will not be in circuit.

The master unit 14 includes a keypad 41, constituting a selector means ofthe present invention, having station address keys and system function keys and being connected to the transmitter 26 in known mannerto enablethe output of signals corresponding to the keys ofthe keypad. A buzzer circuit 39 is connected to the outputs of decoder 27 via a presettable selector40 by means of which the buzzer circuit 39 can be triggered in response to any one or any combination of the outputs of decoder 27. The receiver25, decoder 27 and selector 40 together constitute a presettable decoding means of the present invention. A hold LED 43 and an exchange LED 44 are coupled to respective drive signals ofthe relay drive means 28 and indicate respective states of the system.

An auto hold circuit 33 coupled to the data line 24 detects any coded signal on line 24 and applies to transmitter 26 an input corresponding to an auto hold signal for a predetermined period when the detected code signal ceases. Thus a user on an exchange call can press a station key to call that station and upon release of the key, auto hold circuit 33 will cause transmission of a short burst of the auto hold code signal which w;ll trigger the relay drive circuit 28to energisethe relays 18 and 32 and put the system on hold. This auto hold signal is also used to set an R-S flip flop 45 which energises an auto hold LED 42 to indicate that the system is in intercom mode and is in use.

When tho-- userfinishes the intercom call and requires the exchange line again he presses the exchange line function key and relay drive means 28 responds to the corresponding exchange output signal to deenergize the relays 18 and 32. To avoid the auto hold circuit attempting to auto hold atthe end of the exchange code signal, the outputfrom decoder 27 used to a suitable point as an inhibit signal.

When the user finishes the exchange call he will press the hold key to cause relays 18 and 32to be energized again. The hold output signal from the decoder 27 is also used to reset the R-S flip flop 45 to extinguish LED 42 and indicate that the call has finished. Again, the auto hold circuit 33 must not treat the hold code signal as a station code signal and follow itwith an auto hold signal, and the hold output signal from decoder 27 is fed to a suitable point of circuit 33 as an inhibitsignal.

The auto hold circuit also provides initialisation of the system on power-up. By use of a capacitor (not shown) coupled so as to sink current from a source terminal of the transmitter 26, the auto hold code is generated. The presence of a code signal is detected and a further signal is applied to the sourceterminal to latch the auto hold signal. However,the auto hold outputfrom the decoder 27 is fed to circuit 33 where it is applied to a delaycircuitand used to inhibitthe furthersignal and releasethelatch on the source terminal thus ceasing transmission of the auto hold code signal. The system is now in intercom mode but with R-S flip flop 45 set.Itis required to leaveflipflop 45 in its reset state and this is achieved by the auto hold circuit 33 generating a short pulse from the trailing edge ofthe auto hold output signal from decoder 27, selecting only the first such short pulse in known manner, and using itto drive a transistor (not shown) coupled across the hold contacts ofthe keypad. This will generate a corresponding short burst of hold code signal to resetflip-flop 45, but it is necessaryforthe auto hold circuitto be similarly inhibited in known mannerforthe duration ofthis pulse.

Atoggle circuit 48 receives an outputfrom decoder 27 corresponding to a buzzer control key (QUIET button) ofthe keypad 41, and provides an output to a control inputofthe buzzer circuit 39, and to an LED 49 which indicates the operational state ofthe buzzer circuit 39. Thus successive presses ofthe buzzer control key cause the buzzer circuit 39 to be alternately enabled and disabled, and this is indicated by means of LED 49.

In this embodiment, the inhibit means of the present invention is formed by circuit48 and the elements which provide communication between it and the keypad 41. Circuit 48 could alternatively be directly controlled bythe keypad. Furthermore, ifthetransmitting receiving and decoding functions are performed buy a suitably programmed microprocessor, then that would constitute the inhibit means.

In Figure 2 is shown a station unit 35 having a housing 36 in which there are mounted two sockets 19' and 37; for convenience both sockets are the same type as socket 19 of the master unit 14.

Two wires 38 corresponding to the exchange line pair in the house wiring are connected directly from socket 37 to socket 19'. Two further wires 23' are connected to the electrical circuitry ofthe station unit 35 for supplying electrical power. Afurther wire 24' is used forthe transmission and reception of data signals and is connected to a receiver 25' and a transmitter 26', associated with receiver 25' is a decoder 27', and these three devices are the same type asthe corresponding devices in the master unit 14.

A buzzer circuit 39' is connected to the outputs of decider27' via a selector40' by means of which the buzzer circuit 39' can be triggered in response to any one or any combination ofthe outputs of decoder 27'.

A keypad 41 is connected to transmitter 27' to provide manual selection from a range of input signals for the transmitter 26' corresponding to addresses of station units ofthe switching system and system facilities including hold and exchange requests and buzzer off (QUIET).

An R-S fl ip flop 47 receives hold and exchange outputsignalsfrom decoder 27' and drives a hold LED 43' and an exchange LED 44' which indicate respective states ofthe system.

An R-S flipfiop 45' receives the auto hold signal from decoder 27' on its set input and drives an auto hold LED42'to indicatethatan auto hold intercom state exists. The reset input of flip flop 45' is connected to the hold output of decoder 27' so that when the user finishes using the telephone and puts the master unit back into hold state then LED 42' is extinguished.

The station unit also comprises a corresponding toggle circuit 48' and state indicator LED 49' for control ofthe station buzzer.

The switching system comprises a master unit 14 coupled to a master socket 11 and the adjacent additional socket 13 with a main telephone (not shown) ofthe house normally being connected to socket 19, at leastone other station unit 35 and associated telephone coupled to the house wiring at any ofthe other sockets 13.

Although the above described master unit utilizes a line splitting relay 18,the present invention is equally applicable where the line is not split and a station unit contains a line relay to connect its telephone to wires 23' orto wires 38.

Claims (5)

1. Astation unit for use in a switching system and comprising an inputterminal for connection, in use, to a conductor of a multi-conductorbus(normallythe telephonewiring in a building); coding means having an output coupled to the input terminal and being arranged to generate respective coded signals corresponding to input signals; selector means arranged to apply an input signal to the codng means selectable from a range of input signal representing station unit addresses and system functions; presettable decoding means having an input coupled to the input terminal and having an output coupled to a sound indicator means, the decoding means being preset such as to activate the indicator means in response to receipt of certain coded signals; inhibit means responsive to a respective signal from the selector means for inhibiting the response of the indicator means; and respective visual indicator arranged to provide a visible indication ofthe operation state ofthe inhibitor means.

2. A station unit as claimed in claim 1 wherein the inhibit means has a toggle operation whereby the response of the indicator means is alternately inhibited and enabled upon successive respective signals from the selector means.

3. A station unit as claimed in either claim 1 or claim 2 wherein the selector means comprises a keypad wherein each key representing a station unit address incorporates or is associated with a key label which displays the respective station address and is of such materialthata user can erasablywritethereon.

4. A station unit substantially as herein described with referenceto Figure 2 of the drawings.

5. Aswitching system comprising a multi-conductor bus; a plurality oftelephones having their speech circuits and calling number generations coupled to a pair of conductors ofthe bus; a station unit as claimed in any one of claims 1 to 4for each of the telephones; and a master unit comprising ringing condition detecting means and a coding means responsive thereto for sending a coded signal to the station unit via said conductor.