GB2187015A - Communication system - Google Patents

Description

GB 2 187 015 A 1

SPECIFICATION

Communication system 5 The present invention relates to a communication system comprising a plurality of component units intended to be connected to a common communications channel, and to a method for preventing interference between two or more such systems connected to a common communications channel.

Various proposals have been made to provide communication systems incorporating a number of compo- nent units each connected to a power supply network in a building or dwelling. For example, published 10 European Patent Specification No. 0102229 describes an alarm system in which fire and intruder detection units are plugged into power socket outlets and controlled by signals transmitted from a master control unit which is also plugged into a power socket outlet. The advantage of using the existing power supply network for communication between the various components of such an alarm system is thatthe system can be installed without any additional wiring being required. 15 The installation of additional wiring can often represent a substantial proportion of the cost of an alarm system, particularly where considerable skill and care is required to install the wiring in a concealed manner.

There have been many proposals for using the power supply network of domestic premises to carry control signals to various devices in addition to alarm units of thetype described in the above mentioned European specification. It is expected thatthe number of systems transmitting control signals overthe mains 20 power supply network will increase significantly in the future and this will bring with it possible problems of interference between systems installed in adjacent premises as steps must be taken to prevent signals generated by one system affecting a system in adjacent premises. It has been proposed to overcome this possible problem by installing filters in the mains supply at the point at which that supply enters a particularcon- sumer's premises. The filters would be designed to prevent any of the control signals appearing on the 25 power supply network within the premises from travelling beyond those premises. Unfortunately this intro duces a major disadvantage from the marketing point of view in that it means that systems cannot be simply supplied to consumers for immediate use as the consumers will have to interfere with the mains power supplyto their premises in orderto install the necessary filters. Mutual interference between systems could still occur however if the filters malfunction or are incorrectly installed or are not capable of filtering outthe 30 wide range of possible signal formats which might be used by different systems obtained from different suppliers.

The above mentioned problem could be overcome by allocating to each system a unique code to be transmitted with all communications and arranging for the various system components to be unresponsive to any signals not identified bythat unique code. Unfortunately eitherthe code capacitywould have to be so 35 large that no two systems would ever have the same code number orthe allocation of codes would have to be carefully controlled to prevent duplication within a particular geographical area. In the first case a significant increase in system complexity would result and in the second case a large administrative burden would be imposed not only on the system suppliers but also on the users who would need to keep thesuppliers informed of thetransfer of a system from one area tQ another, for example as a result of a user moving his 40 residence.

It is an object of the present invention to obviate or mitigate the problems outlined above.

According to the present invention there is provided a communications system comprising a plurality of component units intended to be connected to a common communication channel to which other com- munications systems may also be connected, wherein each component unit is responsive to signals trans- 45 mitted on the channel only if the signals are identified by a unique code allocated to the system of which the component unit is a part, the system further comprising initialising means for allocating the code of the system, and means for transmitting a characteristic response on the channel whenever the allocated code is transmitted on the channel by another system, the initialising means comprising means for selecting a prov isional code, means fortransmitting the provisional code on the channel, means for monitoring the channel 50 for any transmission of the characteristic response, and means for allocating the provisional code to the system if the characteristic response is not detected, and for initiating the repetition of the provisional code selection and transmission if the characteristic response is detected.

The present invention also provides a method for preventing interference between two or more com munications systems connected to a common communications channel, each system comprising a plurality 55 of component units connected to the channel, each system being allocated to unique code, and each compo nent unit being responsive to signals transmitted on the channel only if the signals are identified bythe code allocated to the respective system, wherein each system controls the allocation of its own unique code and transmits a characteristic response on the channel whenever its own code is transmitted on the channel by another system, code allocation being achieved bythe system selecting a provisional code, transmitting the 60 provisional code on the channel, monitoring the channel forthe characteristic response, and allocating the provisional code to each unit of the system if the characteristic response is not detected, and repeating the selecting, transmitting and monitoring steps if the characteristic response is detected.

Thus, the present invention effectively transfers responsibility for system code allocation to each system and by so doing a relatively small number of code possibilities is sufficient to prevent mutual interference as 65 2 GB 2 187 015 A 2 it is only those systems which are geographically close together that can effectively interfere in anyevent.

Systems of thistypecan accordingly be purchased inthe knowledgethat no modifications to the power supply networkwill be necessary and yet there issubstantially no riskof control signals generated byone system affecting the operation of a similarsystem located in adjacent premises.

Preferably, each systernwill comprise a masterunitwhich overseesthe code allocation procedureand a 5 numberof standard unitswhich communicate with the masterunit.When the system is initialisedthe master unitwill select an address at random and transmit a message incorporating that address and a status report command. Itwill then await a replyfrom another master unit. If another master unit replies by sending a characteristic status reportthe master unitwhich selected the random address will knowthatthat address is already in use and will then selectanother address at random for transmission. When the master unit re- 10 ceives no replyto the transmission of the randomly selected address itwill acceptthat address for use by its own system. Additional units can be added to ortaken out of a particular system providing an appropriate initialisation procedure isfollowed.

An embodimentof the present invention will now be described byway of example, with reference in partto the accompanying drawing,which is a schematic block illustration of the component parts of one component 15 unitof a system in accordancewith the invention.

Referring to the drawing,the illustrated unit has at its heart a single chip microcomputer and serial com munications interface 1 which on the one hand receives and interprets infra-red signals and ultrasonic signaisfrom its local environmentand on the other hand communicates with other similar units via a main supply cable networkto which it is connected by a simple plug engaged in a conventional socket outlet.An 20 infra-red detector2 detects infra-red radiation resulting from, for example, an intruder ora fire and an ultra sonic receiver3 receives ultrasonic signals reflected to it byfor example an intruderfrom an ultrasonic transmitter 4. The mains supply 5 is coupled to the microcomputer 1 via a receiving transformer 6, and a limiting amplifier 7, and via a mains coupling am p] ifier 8 through which sig nals are transmitted. The output of the limiting amp] ifier7 is fed via a demodulator 9 to the microcomputer and a transmit signal is fed to the 25 coupling amplifier 8 via a modulator 10. A select sig nal is used to either enable the demodulator 9 for sig nal reception orthe modulator 10 for signal transmission, the effective switching f unction of the select signal being schematically indicated by a switch 11.

The output of the infra-red detector comprises infra-red signals generated for example fire or an intruder.

Signals generated by a hand held infra-red "torch" (not shown) of the type used to control, forexample, 30 television receivers, are decoded by a decoder 12 and fed to the microcomputer 1 to enable control of the unit and of similar units connected to the mains supply 5. The infra-red signals resulting from for examplefire or an intruder are passed via a low pass response amplifier 13 and a discriminator 14which monitorsthe characteristics of the received infra-red signal to discriminate between flame generated signals and intruder generated signals. Discriminator 14 provides a flame signal to a threshold detector 15 and an intruder signal 35 to a threshold detector 16. The output of the ultrasonic receiver is fed via an amplifier 17, a demodulator 18 and a threshold detector 19 to the microcomputer 1.

The infra-red detector and its associated circuitry and the ultrasonic receiver and its associated circuitry may be of any suitable kind, for example of the type described in Published European Patent Specification

No.0103375. 40 The unit illustrated in the accompanying drawings provides an audible outputfrom a loud speaker20 driven by an amplifier 21 in response to signals from the microcomputer 1 supplied via buffer22.

A manual three-position $lider switch 23 enables the unitto be manually switched between three con ditions,that is "full on" in which the unit is responsiveto both fire and intruder generated signals, "fire",that is responsive onlyto signals resulting from fire, and "ofF' in which the unit is unresponsive to infra-red or 45 ultrasonic signals resulting from fire or intruders.

Finallythere is a "panic" button 24which if pressed transmits a panic command via the mains cabling 5.

The components illustrated in the accompanying drawing are in themselves essentially conventional but the integrated system which theyform a part of operates in a novel manner so as to prevent interference between different systems connected to the same mains cabling 5 as is described below. 50 The alarm system consists of a maximum of eight units of the type illustrated generally in the drawing. One of the eight units has extra capabilities which enable itto monitor and control the system as a whole. This one unitis referred to as the master unit. The master unitwill detectfire and intruder, and respond to panic inthe sameway as any other unit. Itwill be possible to turn the system on or off from any one of the units using the hand-held infra-red torch. 55 The infra-red torch has two push buttons and one sliderswitch allowing the following series of functions:

Slider switch position 0: ButtonA- Arm System Button B - Disarm System 60 Slider switch position 1: Button A- Initialise System/ Add new unit Button B - Test 3 GB 2 187 015 A 3 Pressing buttons A and B together in either slider position causes a "Panic" alarm to sound and is thus equivalent to pressing the panic button 24 as shown in the drawing.

The torch contains a "key" which is coded for each system. Keys maybe cut from a standard blank by a simple mechanical key-cutting type of operation. Thus duplicate keys maybe provided. Alternatively, the "key" maybe provided in the form of a customised chip in the torch circuitry. The chip will include a smal 1 5 PROM area which contains the system key. The chip wil I be programmed at the time of manufacture of the chip.

Each unit wil I have its own battery power supply to at least maintain essential system data in the event of a mains powerfailure. One of the units may have an external bel I connected to it in addition to its loudspeaker jo 20. 10 The units communicate over the local mains wiring 5. Different systems are distinguished from one an other by a unique code or "system address". Up to 1024 different addresses wil I be provided forwhichwil I give adequate capacity on a single phase of a mains supply network.

Units within each system are distinguished from one another by respective subaddresses. These sub addresses are coded via a simple mechanical process. SubaddressesOwil I be reversed for the master unit. 15 Units to be added to a system may have the subaddress set either at the point of sale or by the user. As an example of one suitable mechanical coding process, a set of 8 individually different plastic inserts maybe provided with each master unit sold. Each insert is numbered or colour- coded and has on its underside a set of pins whose arrangement represents a binary code. T&prograrn'a unit with its unit address, an insert is pushed into a slot at the back of the unit. The pins of the underside of the insert break PCB tracks to program 20 the unit with a binary code. Catching lugs wil I ensure that once an insert has been pushed home, it cannot be removed without damaging it or the unit. This is to preventthe userfrom attempting to're-program'the unit with a different insert.

To initialise the system, all units must be connected to the mains. The slider switch on the infra-red torch is then setto position 1. The torch is then directed atthe master unit and button A on the torch is depressed. 25 This transmits the torch "key" and an instruction to initialise the system.

After a preset period of a few seconds, the master unitwill bleep, prompting for buttorn Ato be pressed again. The master unit will keep prompting until it has successfully received two consecutive transmissions from the infra-red torch which are the same. It will then latch the received "key" into its memory.

The key will be recorded on the master unit in a way which cannot easily be decoded butwhich may be 30 recovered in the event of loss of thetorch.

The master unit will then select a system address at random. It will transmitthe selected system address and the received key to all other units to initialise them. Once the units have been initialised, theywill only respond to mains transmissions which contain the system address, and theywill only respond totorch commands which contain the system key. Once initialised, each unitwill bleep, allowing the user to check 35 that all the units have been initialised. The bleeping may be turned off using the "Disarm" option on the infra-red torch, which when directed at any unit will cause a reset signal (command 10) to be transmitted to all units.

If a unit is to be added to a previously initialised system, the unit is plugged into the mains to which all the other units are connected. The slider switch on the infra-red torch is setto position 1, and the torch is directed 40 atthe master unit as described above. The master unitwill transmitthe key it has received from the infra-red torch and also the system address it has selected, to all units. Units already initialised will not act on this information. However, the added unit will latch this information into its memory and will bleep until the "Disarm" option on the infra-red torch is used to issuethe reset signal.

The system may be armed from any unit using the inf ra-red torch. The slider switch on the infrared torch is 45 setto position 0. The torch is directed atthe unit selected from arming, and buttorn A on the torch is pressed.

An arming signal is sentfrom the selected unitto all other unit. Before the units are armed, the system will monitor inself (as described below) and then the unitfrom which the system is being armed will sound a series of short bleeps, one bleep for each correctly functioning unit. After a 30 second delay, each unit will be armed for detection according to the setting of its slider switch 23. 50 The system will report detection of eitherfire or intruder when full on or fire only, depending on the setting of the switches 23. When a unit's sensors (infra red / ultrasonic) detect a fire or intruder, it will send a fire or intruder alarm signal to all other units and start a 30 second timeout. Upon receipt of the alarm signal, each unitwill start a 30 second timeout. This will allowthe usertimeto disarm the system if he or she hasjust entered the protected premises. The system may be disarmed from any unit using the "Disarm" option on 55 the infra-red torch. WHen a unit receives the torch " Disarm" signal, itwill send the reset signal to all unitsto disarm them. If the reset signal is not received within the 30 second timeout period, the alarm loudspeaker will sound on each unit and any external bell unitwhich may be provided will also sound.

In the case of an intruder, the alarm will sound fortwo minutes afterwhich itwill turn off automatically and the system will continue to monitor its surroundings. Further activation of the intruder sensorwill causethe 60 alarm to sound for anothertwo minutes. The alarm sound for an intruder is an alternating tone. The intruder alarm may be switched off within thetwo minute period if required, using the "Disarm" option on the infra red torch.

In the event of a fire alarm, the alarm will notturn itself off butwill have to be turned off using the "Disarm" option on the inf ra-red torch. The alarm sound for fire is a constant tone. 65 4 GB 2 187 015 A 4 The system maybe triggered for panic either by pressing the panic button on any unit or by pressing both buttons on the infra-red torch. The system will respond by sounding the alarm on each unit, even when the system is disarmed. The alarm maybe switched off using the "Disarm" option on the infra-redtorch.

Atest mode is provided which maybe activated from the infra-red torch wheneverthe system is disarmed.

The testwill be invoked by pressing button B on the torch with the torch slider switch in position 1. If before 5 disarming, the system had alarmed, the unit which detected the alarm condition will periodically sound a bleep until turned off by the infra-red torch. Otherwise, all units will sound a periodic bleep until turned off by the infra-red torch. While in the test mode, it is possible to find inoperative units because they wil I not be sounding. To turn a unit off while in test mode, the torch "Disarm" option should be used. The slider switch is setto position 0 and button B is pressed. 10 Battery backup can be made available atthree levels of support. The user may choose which option he would like for each unit in the system. The three options are asfollows:1. Battery backup is provided for essential system data only. No signalling, detection or sounding facilities are supported during a mains supplyfailure.

With this option,the system will become disarmed in the event of a mains supply failure and will not be 15 rearmed when the supply returns. This is because there would be no means of the user disarming the system during the supplyfailure. 2. Battery backup is provided for essential system data, signalling and detection but not for sounding.

Any number of units in the system may have this battery backup option. However, if any unit has battery backup, the master unit must have battery backup. 20 If this level of backup is supplied to a unit, then such a unitwill continue to operate throughout a supply failure. The system maybe disarmed via any such backed up unit and may in the same way be rearmed.

3. Battery backup is provided foraU functions. The same considerations apply as with level 2 support asfar as arming and disarming the system during a supply failure are concerned and also detection underthese conditions. In addition, support is provided for the sounder for up to 24 hours operation. 25 In the event of arming taking place during a supply failure, only units with level 2 or 3 support will be armed.

Fora system with at least one unit with level 2 support, if the supply fails while the system is armed,then the system will be fully rearmed when the supply returns. If the user wishes to disarm the system during the supplyfailure, it will have to be done via the level 2 unit. 30 In the event of tamperting with an external bell unit which has, for example, a microswitch fitted and is connected as an external device to a unit on the alarm system, the system will respond by sounding the alarm for intruder if it has been armed. If the system is disarmed, a flag will beset internally on the bell unit. When a system self check occurs, the bell unit will be excluded from the master unit's list of correctlyfunctioning units. 35 Fault conditions which may arise in the system include - 1. Failure of the power supply to any unit.

2. Power supply voltage falling below a certain threshold if battery backup is provided on a unit and the mains supply has failed.

3. Failure of a units ultrasonictransceiveron any unit. 40 4. Presence on the mains of signals which prevent reliable communications between units over along period.

If the mains supply to a unit with battery backup fal Is, operatwion will continue on battery support. When the supply voltage on battery support fails below a preset threshold, the unit will be deemed faulty.

In the event of the supply voltage to a unit without battery backup failing below a preset threshold, the unit 45 will be deemed faulty if the mains is present.

If a unit is deemed faulty, a flag will beset internally on the unit, which will be detected when a system self check next occurs. Afaulty unit will not be included in the master units list of correctly functioning units.

When the system is next armed, the arming unit wi 11 only sound a bleep for each correctly functioning unit.

If communications is interrupted bythe presence on the mains of a rogue signal which persists for more 50 than two minutes, the system will alarm.

Having described the operation of the system in general terms, a more detailed description of the signal format and signalling procedure is given below.

The signals which are transmitted overthe mains are FSK (Frequency Shift Keying) signals. The pulse code used is Manchester Code to maximise noise immunity. Baud rate is at least 100 baud. Each byte transmitted 55 has one start bit, one stop bit and one parity bit. Even parity is used. A message is preceded by an idle string consisting of a complete frame of consecutive Vs, in order to a] low the receiverto synchronise to thetrans mitterclock.

Message length is either sixteen or twenty four bits, depending on the data to be sent. The number of messages which require a twenty-four bit message length is onlytwo, in orderto keep the overall duration of 60 transmissionsto a minimum.

A messagewill begin with aten bitsystem addressfollowed by a four bitcommand and a two bit checksum. Thiswill normally complete a message. However an additional third bytewill be transmitted in the case of thetwo twenty-four bit messages for which the command number is& Each sixteen bit message hasthefollowing format: 65 GB 2 187 015 A 5 0-9 10-13 14-15 Address Command<>8 Checksum 5 The two twenty-four bit messages have the following formats:

0-9 10-13 14-15 16 17-23 lo Address Command13 Checksum 0 Arming Status 10 0-9 10-13 14-15 16 17-23 Address Command 8 Checksum 1 System Key Sixteen commands, accommodated within thefour bitcommand field of a message, are as set out below:

15 0 SRO - Status Report 0 1 SR1 -Status Report 1 2 SR2 - Status Report 2 3 SR3 - Status Report 3 4 SR4 - Status Report 4 20 SR5 - Status Report 5 6 SR6 - Status Report 6 7 SR7 - Status Report 7 8 Initialise/Arming Status (three byte command) 9 Arm 25 Reset 11 Test 12 Intruder 13 Fi re 14 Panic 30 Spare Commands 0 to 7 are addressed commands. They will only be acted u pon by the specific u n it for which the command is intended. The SR commands 0 to 7 are status reports whose usage is described below.

Command 8 caters fortwo commands, each of which is three bytes long. The commands are decoded from 35 the first bit of the extra byte. If this bit is set, a system initialisation message will be sentfrom the master unit to all other units to inform them of the system address and system key. If the first bit of byte three is reset, an arming status signal will be sentfrom the master unitto be interpreted by the unitfrom which the system is being armed. Command 8 will only be sent by the master unit.

Commands 9 to 14 are global commands which will normally be acted upon by all the units. They can be 40 transmitted by any unit.

Each status report signal can be issued by only one of the units, the master unit issuing signal SRO and units 1 to 7 issuing sig nals SR1 to SR7 respectively. Du ring a status report sequence, the SRO signal is issued bythe master unit and then each other unit issues its own SR signal only after receipt of the SR signal of the unit having a num ber one less than itself. This is described in more detai 1 below. However, it will be apprecia- 45 ted thatthe master unitwill respond to receipt of an SR7 command by issuing the SRO command.

As described above, during initialisation the master unit chooses an address at random. Itthen transmits a message with this address and the SR7 command in the command field. It will then await a replyfrom another master unit. If another master unit replies by sending an SRO signal, the initialising master unitwill know that the address is al ready in use and it wil 1 try another randomly chosen address. When the master u nit 50 transmits an SR7 signal and receives no reply, itwill use the address chosen.

In orderto initialise the units on the system with the system address and key, the master unit will transmit an initialisation message. The message contains the system address in the address field, command 8 in the command field, bit 16 set and the system key in the remainder of byte three. Each unit will respond to this initialisation message by peridiodically sounding a bleep, until a command 10 reset signal is received. 55 Whenever a unit is added to the system and needs to be initialised, the master unit, when triggered bythe infra-red torch, will transmit a command 8 initialisation message containing the system address and key.

This message will not be acted upon by units which have already been initialised since they will havethe system address and key already latched in memory. Any u ninitial ised u nit wil 1 respond to the message by periodically sounding a bleep until a command 10 reset signal is received. 60 When the infra-red torch is directed at a unit in orderto arm the system, that unit will send a command 9 arming signal to all other units. The units which receive the arming signal will set an internal arming flag. The master unit will then start a "status report sequence" by transmitti ng an SRO sig nal.

Whenever any unit sees an SR signal which is numbered one less than the number of the unit, itwill increment the command nu m ber and transmit the renumbered SR signal. It will then start a timer. The unit 65 6 GB 2 187 015 A 6 will reset its arming flag either when the timer runs outorwhenthe unitsees an SR signal from the nextunit in numerical order.

The masterunitwill monitorthe mainsduring thewholeof the reportsequence. Rwill "fill in" foranyunit which does notgenerate a report. This covers the possibilityof a system comprising a faultyunit or lessthan eight units. 5 Thetimeout on the arming flag resetwill permit retries of the master unit's fill-in transmissions. If after three tries, a unit still does not generate a report, the master unitwill "map" the unit as unarmed.Itwill then restartthe report sequence atthe next unit in numerical order.

Bythe time the last unit has reported or retries on that unit are complete, the master unitwill knowwhich units have been armed. 10 The master unitwill then transmit a command 8 initialisation/arming status messagewith bit 16 reset.

Thus,the messagewill contain arming status information in bytethree of the message. This transmission will be detected by all units but onlythe unitwhich the system is being armed from will act upon the master unit's signal. The arming unitwill read the arming status field (bits 17to 23 in the message) to determine how many unitswere successfully armed. [twill then sound a series of short bleeps, one bleep for each success- 15 fully armed unit.

If the highest numbered unit is unit7, then during the report sequence its status reportsignal may resultin an SRO signal being received bythe system from an external system's master unit. Thus,the system address must already be in use. Thiswill provide anothercheckin addition tothe SR7 signal which istransmitted by the master unit at initialisation. 20 If an SRO signal is received from another master unitthis will be acted upon bythe master unit in the system being armed. When the master unittransmits its command 8 with arming status information,the arming statusfield in the message will contain $7F. When this transmission is detected by the arming unit. it will interpretthe arming status field as "address already in use" and will indicate this to the user bysounding a series of long bleeps. The user should then reinitialise the system. The response of each of the other unitsto 25 the $7Ftransmission will be to stop its arming timeout, which is normally run before the unit is armed for detection according to the setting of its three-position slider switch.

Claims (3)

1. 30 1. Acommunications system comprising a plurality of component units intended to be connected to a common communication channel to which other communications systems may also be connected, wherein each component unit is responsiveto signals transmitted on the channel only if the signals are identified by a unique code allocated to the system of which the component unit is apart, the system further comprising initialising meansfor allocating the code to the system, and means for transmitting a characteristic response 35 on the channel whenever the allocated code is transmitted on the channel by another system, the initialising means comprising means for selecting a provisional code, means fortransmitting the provisional code on the channel, means for monitoring the channel for any transmission of the characteristic response, and meansfor allocating the provisional code to the system if the characteristic response is not detected, and for initiating the repetition of the provisional code selection and transmission if the characteristic response is 40 detected.
2. 2. A communications system according to claim 1, comprising a master unit which oversees the code allocation procedure, and a number of standard units which communicate with the master unit, the master unit being operative when the system is initialised to select an address at random and transmit a message incorporating that address and a status report command, to await a reply from another master unit in the 45 form of a characteristic status report, and to respond to receipt of the characteristic status report by selecting another address at random and transmiting the other address with a status report command, and to respond to non-receipt of the characteristic status report by allocating the transmitted address to its own system.
3. 3. A method for preventing interference between two or more communications systems connected to a common communications channel, each system comprising a plurality of component units connected to the 50 channel, each system being allocated a unique code, and each component unit being responsive to signals transmitted on the channel only if the signals are identified bythe code allocated to the respective system, wherein each system controls the allocation of its own unique code and transmits a characteristic response on the channel whenever its own code is transmitted on the channel by another system, code allocation being achieved by the system selecting a provisional code, transmitting the provisional code on the channel, 55 monitoring the channel for the characteristic response, and allocating the provisional code to each unit of the system if the characteristic response is not detected, and repeating the selecting, transmitting and monitor ing steps if the characteristic response is detected.

   60 Printed for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd,7187, D8991685. Published by The Patent Office, 25Southamptan Buildings, London WC2A l AY, from which copies maybe obtained.