EP0233735A1

EP0233735A1 - Communication system

Info

Publication number: EP0233735A1
Application number: EP87301054A
Authority: EP
Inventors: John Richard Hawke; Alastair Ian Stirling; Wieslaw Andrzej Stepien
Original assignee: Monicell Ltd
Current assignee: Monicell Ltd
Priority date: 1986-02-19
Filing date: 1987-02-06
Publication date: 1987-08-26
Also published as: GB8702828D0; GB2187015A; JPS6323440A; GB8604052D0

Abstract

A communications 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. Each component unit is responsive to 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 a part. The system allocates its own code in accordance with a predetermined routine, and transmits a characteristic response on the channel whenever the allocated code is transmitted on the channel by another system. The code allocated routine selects a provisional code, transmits the provisional code on the channel, monitors the channel for any transmission of the characteristic response, and allocates the provisional code to the system if the characteristic response is not detected, but repeats the provisional code selection and transmission sequence if the characteristic response is detected.

Description

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 component units each connected to a power supply network in a building or dwelling. For example, published 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 that the system can be installed without any additional wiring being required.
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 the type described in the above mentioned European specification. It is expected that the number of systems transmitting control signals over the mains 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 particular consumer's premises. The filters would be designed to prevent any of the control signals appearing on the power supply network within the premises from travelling beyond those premises. Unfortunately this introduces 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 supply to their premises in order to 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 out the 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 by that unique code. Unfortunately either the code capacity would have to be so large that no two systems would ever have the same code number or the 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 the suppliers informed of the transfer of a system from one area to another, for example as a result of a user moving his 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 communications systems may also be connected, wherein each component unit is responsive to 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 a part, the system further comprising initialising means for allocating the code to 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 provisional code, means for transmitting the provisional code on the channel, means for monitoring the channel 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 communications systems connected to a common communications channel, each system comprising a plurality of component units connected to the 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 by the 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, 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 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 it is only those systems which are geographically close together that can effectively interfere in any event. Systems of this type can accordingly be purchased in the knowledge that no modifications to the power supply network will be necessary and yet there is substantially no risk of control signals generated by one system affecting the operation of a similar system located in adjacent premises.
Preferably, each system will comprise a master unit which oversees the code allocation procedure and a number of standard units which communicate with the master unit. When the system is initialised the master unit will select an address at random and transmit a message incorporating that address and a status report command. It will then await a reply from another master unit. If another master unit replies by sending a characteristic status report the master unit which selected the random address will know that that address is already in use and will then select another address at random for transmission. When the ma-ster unit receives no reply to the transmission of the randomly selected address it will accept that address for use by its own system. Additional units can be added to or taken out of a particular system providing an appropriate initialisation procedure is followed.
An embodiment of the present invention will now be described by way of example, with reference in part to the accompanying drawing, which is a schematic block illustration of the component parts of one component unit of a system in accordance with the invention.
Referring to the drawing, the illustrated unit has at its heart a single chip microcomputer and serial communications interface 1 which on the one hand receives and interprets infra-red signals and ultrasonic signals from its local environment and on the other hand communicates with other similar units via a main supply cable network to which it is connected by a simple plug engaged in a conventional socket outlet. An infra-red detector 2 detects infra-red radiation resulting from, for example, an intruder or a fire and an ultrasonic receiver 3 receives ultrasonic signals reflected to it by for example an intruder from 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 amplifier 8 through which signals are transmitted. The output of the limiting amplifier 7 is fed via a demodulator 9 to the microcomputer and a transmit signal is fed to the coupling amplifier 8 via a modulator 10. A select signal is used to either enable the demodulator 9 for signal reception or the modulator 10 for signal transmission, the effective switching function of the select signal being schematically indicated by a switch 11.
The output of the infra-red detector comprises infra-red signals generated by for example fire or an intruder. Signals generated by a hand held infra-red "torch" (not shown) of the type used to control, for example, 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 example fire or an intruder are passed via a low pass response amplifier 13 and a discriminator 14 which monitors the 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 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.
The unit illustrated in the accompanying drawings provides an audible output from a loud speaker 20 driven by an amplifier 21 in response to signals from the microcomputer 1 supplied via buffer 22.
A manual three-position slider switch 23 enables the unit to be manually switched between three conditions, that is "full on" in which the unit is responsive to both fire and intruder generated signals, "fire", that is responsive only to signals resulting from fire, and "off" in which the unit is unresponsive to infra-red or ultrasonic signals resulting from fire or intruders.
Finally there is a "panic" button 24 which 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 they form 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.
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 it to monitor and control the system as a whole. This one unit is referred to as the master unit. The master unit will detect fire and intruder, and respond to panic in the same way as any other unit. It will be possible to turn the system on or off from any one of the units using the hand-held infra-red torch.
The infra-red torch has two push bottons and one slider switch allowing the following series of functions:
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 may be cut from a standard blank by a simple mechanical key-cutting type of operation. Thus duplicate keys may be provided. Alternatively, the "key" may be provided in the form of a customised chip in the torch circuitry. The chip will include a small PROM area which contains the system key. The chip will be programmed at the time of manufacture of the chip.
Each unit will have its own battery power supply to at least maintain essential system data in the event of a mains power failure. One of the units may have an external bell connected to it in addition to its loudspeaker 20.
The units communicate over the local mains wiring 5. Different systems are distinguished from one another by a unique code or "system address". Up to 1024 different addresses will be provided for which will 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 subaddresses are coded via a simple mechanical process. Subaddresses 0 will be reserved for the master unit. 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 may be 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. To 'program' a unit with its unit- address, an insert is pushed into a slot at the back of the unit. The pins on the underside of the insert break PCB tracks to program the unit with a binary code. Catching lugs will ensure that once an insert has been pushed home, it cannot be removed without damaging it or the unit. This is to prevent the user from 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 set to position 1. The torch is then directed at the master unit and button A on the torch is depressed. This transmits the torch "key" and an instruction to initialise the system.
After a preset period of a few seconds, the master unit will bleep, prompting for button A to 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 but which may be recovered in the event of loss of the torch.
The master unit will then select a system address at random. It will transmit the selected system address and the received key to all other units to initialise them. Once the units have been initialised, they will only respond to mains transmissions which contain the system address, and they will only respond to torch commands which contain the system key. Once initialised, each unit will bleep, allowing the user to check 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 set to position 1, and the torch is directed at the master unit as described above. The master unit will transmit the 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 issue the reset signal.
The system may be armed from any unit using the infra-red torch. The slider switch on the infra-red torch is set to position 0. The torch is directed at t.he unit selected from arming, and buttom A on the torch is pressed. An arming signal is sent from the selected unit to all other unit. Before the units are armed, the system will monitor itself (as described below) and then the unit from 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.
The system will report detection of either fire 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 unit will start a 30 second timeout. This will allow the user time to disarm the system if he or she has just entered the protected premises. The system may be disarmed from any unit using the "Disarm" option on the infra-red torch. When a unit receives the torch "Disarm" signal, it will send the reset signal to all units to 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 unit which may be provided will also sound.
In the case of an intruder, the alarm will sound for two minutes after which it will turn off automatically and the system will continue to monitor its surroundings. Further activation of the intruder sensor will cause the alarm to sound for another two minutes. The alarm sound for an intruder is an alternating tone. The intruder alarm may be switched off within the two minute period if required, using the "Disarm" option on the infra-red torch.
In the event of a fire alarm, the alarm will not turn itself off but will have to be turned off using the "Disarm" option on the infra-red torch. The alarm sound for fire is a constant tone.
The system may be 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 may be switched off using the "Disarm" option on the infra-red torch.
A test mode is provided which may be activated from the infra-red torch whenever the system is disarmed. The test will be invoked by pressing button B on the torch with the torch slider switch in position 1. If before 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 will not be sounding. To turn a unit off while in test mode, the torch "Disarm" option should be used. The slider switch is set to position 0 and button B is pressed.
Battery backup can be made available at three levels of support. The user may choose which option he would like for each unit in the system. The three options are as follows:-1. Battery backup is provided for essential system data only. No signalling, detection or sounding facilities are supported during a mains supply failure.
With this option, the system will become disarmed in the event of a mains supply failure and will not be rearmed when the supply returns. This is because there would be no means of the user disarming the system during the supply failure.
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.
If this level of backup is supplied to a unit, then such a unit will continue to operate throughout a supply failure. The system may be disarmed via any such backed up unit and may in the same way be rearmed.
3. Battery backup is provided for all functions. The same considerations apply as with level 2 support as far as arming and disarming the system during a supply failure are concerned and also detection under these conditions. In addition, support is provided for the sounder for up to 24 hours operation.
In the event of arming taking place during a supply failure, only units with level 2 or 3 support will be armed.
For a 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 supply failure, it will have to be done via the level 2 unit.
In the event of tampering 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 be set internally on the bell unit. When a system self check occurs, the bell unit will be excluded from the master unit's list of correctly functioning units.
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 ultrasonic transceiver on any unit.
4. Presence on the mains of signals which prevent reliable communications between units over a long period.

If the mains supply to a unit with battery backup fails, operatwion will continue on battery support. When the supply voltage on battery support falls below a preset threshold, the unit will be deemed faulty.
In the event of the supply voltage to a unit without battery backup falling below a preset threshold, the unit will be deemed faulty if the mains is present.
If a unit is deemed faulty, a flag will be set internally on the unit, which will be detected when a system self check next occurs. A faulty unit will not be included in the master units list of correctly functioning units. When the system is next armed, the arming unit will only sound a bleep for each correctly functioning unit.
If communications is interrupted by the presence on the mains of a rogue signal which persists for more 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 over the 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 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 1's, in order to allow the receiver to synchronise to the transmitter clock.
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 only two, in order to keep the overall duration of transmissions to a minimum.
A message will begin with a ten bit system address followed by a four bit command and a two bit checksum. This will normally complete a message. However an additional third byte will be transmitted in the case of the two twenty-four bit messages for which the command number is 8.
Each sixteen bit message has the following format:
The two twenty-four bit messages have the following formats:
Sixteen commands, accommodated within the four bit command field of a message, are as set out below:
Commands 0 to 7 are addressed commands. They will only be acted upon by the specific unit for which the command is intended. The SR commands 0 to 7 are status reports whose usage is described below.
Command 8 caters for two commands, each of which is three bytes long. The commands are decoded from the first bit of the extra byte. If this bit is set, a system initialisation message will be sent from 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 sent from the master unit to be interpreted by the unit from 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 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 signals SR1 to SR7 respectively. During a status report sequence, the SRO signal is issued by the master unit and then each other unit issues its own SR signal only after receipt of the SR signal of the unit having a number one less than itself. This is described in more detail below. However, it will be appreciated that the master unit will 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. It then transmits a message with this address and the _SR7 command in the command field. It will then await a reply from another master unit. If another master unit replies by sending an SRO signal, the initialising master unit will know that the address is already in use and it will try another randomly chosen address. When the master unit transmits an _SR7 signal and receives no reply, it will use the address chosen.
In order to 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 periodically sounding a bleep, until a command 10 reset signal is received.
Whenever a unit is added to the system and needs to be initialised, the master unit, when triggered by the 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 have the system address and key already latched in memory. Any uninitialised unit will respond to the message by periodically sounding a bleep until a command 10 reset signal is received.
When the infra-red torch is directed at a unit in order to 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 transmitting an SRO signal.
Whenever any unit sees an SR signal which is numbered one less than the number of the unit, it will increment the command number and transmit the renumbered SR signal. It- will then start a timer. The unit will reset its arming flag either when the timer runs out or when the unit sees an SR signal from the next unit in numerical order.
The master unit will monitor the mains during the whole of the report sequence. It will "fill in" for any unit which does not generate a report. This covers the possibility of a system comprising a faulty unit or less than eight units.
The timeout on the arming flag reset will permit retries of the master unit's fill-in transmissions. If after three tries, a unit still does not generate a report, the master unit will "map" the unit as unarmed. It will then restart the report sequence at the next unit in numerical order.
By the time the last unit has reported or retries on that unit are complete, the master unit will know which units have been armed.
The master unit will then transmit a command 8 initialisation/arming status message with bit 16 reset. Thus, the message will contain arming status information in byte three of the message. This transmission will be detected by all units but only the unit which the system is being armed from will act upon the master unit's signal. The arming unit will read the arming status field (bits 17 to 23 in the message) to determine how many units were successfully armed. It will then sound a series of short bleeps, one bleep for each successfully armed unit.
If the highest numbered unit is unit 7, then during the report sequence its status report signal may result in an SRO signal being received by the system from an external system's master unit. Thus, the system address must already be in use. This will provide another check in addition to the SR7 signal which is transmitted by the master unit at initialisation.
If an SRO signal is received from another master unit, this will be acted upon by the master unit in the system being armed. When the master unit transmits its command 8 with arming status information, the arming status field in the message will contain 7F. When this transmission is detected by the arming unit, it will interpret the arming status field as "address already in use" and will indicate this to the user by sounding a series of long bleeps. The user should then reinitialise the system. The response of each of the other units to the 7F transmission 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

1. A communications 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 responsive to 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 a part, the system further comprising initialising means for allocating the code to 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 provisional code, means for transmitting the provisional code on the channel, means for monitoring the channel 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.

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 form of a characteristic status report, and to respond to receipt of the characteristic status report by selecting another address at random and transmitting 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. 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 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 by the 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, 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 monitoring steps if the characteristic response is detected.