IES60972B2 - Alarm device - Google Patents

Description

ALARM DEVICE FIELD OF THE INVENTION The present invention relates to alarm devices for use in a neighbourhood alarm network for summoning assistance from neighbours and others. Such networks are well known.

BACKGROUND ART United States Patent No. 2,663,864 to Cundiff describes an electric burglar alarm system for interconnection between plural stations situated in locations of the small business establishment type. In the Cundiff system, a switch is provided at each of the several interconnected stations to be operated secretly by a person on the premises for providing an indicating signal at the other ones of the stations.

United States Patent No. 3,133,276 to Millar and Millar provides an alarm system in which means are provided for automatically triggering the alarm switches at all other stations of a group upon unlawful entry at any remaining station of the group.

United States Patent No. 4,109,139 to Ortega describes a network - 2 in which an undesired disturbance at one of a number of stations will be made known with characteristic identification at all remaining stations in the system.

Published United Kingdom Patent Application No. 2,009,478 A in the name Walter Holzer describes an alarm system including a high-frequency transmitter which transmits an alarm signal over the electricity mains and a high frequency receiver tuned to the common carrier frequency of the transmitters, whereby when the alarm is raised at one station the alarm devices of all the other stations are operated.

Published PCT Application W0 84/02216 in the names Them and Holmgren describes a system in which each station includes a transmitter which repeatedly transmits a locality signature signal to the remaining stations of the group and includes a receiver for receiving said signals. When a correct locality signature signal is not received a corresponding indication is given to the remaining stations.

Published United Kingdom Patent Application No. 2,159,649 A in the names Roman and Peeters describes an intercommunicating alarm network, in which each of a plurality of premises is provided with a respective alarm station of the kind wherein the alarm signal is generated a predetermined time after an initiation signal is made, the alarm signal being cancellable by a person in the premises at any time up to the moment of generation. In practice the alarms may be initiated by a suspicious occupant of the premises, and subsequently cancelled within the predetermined time if the suspicions prove false.

Published European Patent Application No. 0,148,708 Al in the names Grand and Piquet-Gauthier describes a system in which each station is provided with a siren and a light and the stations are interconnected not only by the mains electrical connection but also by an alarm bus and a series of branches to each of the different stations.

United States Patent No. 4,731,810 to Watkins describes a system which is a backup security system for the telephone company lines of a - 3 protected home. When the system senses that the telephone company lines for the protected home have been cut by an intruder, the system provides a signal to neighbouring homes.

Published PCT Application WO 90/07170 in the name Donovan describes a system for separate and spaced premises or locations in which each premises or location is linked to each other premises or location by radio signal transmitting and receiving means.

Published European Patent Application No. 0,229,198 Al in the name Hansons Neighbourhood Alarms Pty. Limited describes a computer controlled radio network linked neighbourhood alarm system in which the communication system used comprises a packet switching network.

In the case of systems of this type, once the alarm has been raised the occupant of the premises is then faced with deciding what to do while awaiting assistance. Options include vacating the premises, hiding within the premises, aggressively confronting the intruder, or attempting to negotiate with the intruder. In each case this is a frightening time for the occupant. It is difficult to know which option to exercise. A wrong choice may lead to violence.

OBJECT AND SUMMARY OF THE INVENTION An object of the present invention is to assist the occupant in determining the correct approach to be taken viz-a-viz the intruder.

The invention provides a local alarm device for use in a neighbourhood alarm network consisting of a plurality of such devices 30 comprising: signal transmission means for transmitting an alarm signal indicative of said device; signal receiving means for receiving an alarm signal from another such device indicative of said other device; characterized in that the signal transmission means is manually operable to transmit an acknowledgment signal to another device in response to an alarm signal received from said other device; and in that the signal receiving means is operable to receive an acknowledgment signal from another such device in response to an alarm signal transmitted from the device.

An advantage of the system of the invention is that the person who raises the alarm may receive an indication as to whether or not assistance is on the way. This indication may influence the persons choice of which option to exercise.

Preferably, the signal transmission means is operable to transmit an acknowledgment signal indicative of the device sending the acknowledgment signal, and the receiving means is operable to receive an acknowledgment signal indicative of the device sending the acknowledgment signal.

As a result, the person raising the alarm not only knows that help is coming, but also knows from which quarter, for example knows whether help is coming from the immediately adjacent house or from some house at a greater distance, and may also have some idea of which person will render the assistance and how long it is likely to take.

Preferably the signal transmission means and signal receiving means include a radio transmitter and a radio receiver.

As a result the device may be included in a network where physical connection of all devices is not possible.

Preferably, the signal transmission means includes a voice synthesizer associated with the transmitter for transmitting a voice alarm signal indicative of said device.

As a result a mobile patrolman carrying a conventional two way radio (walkie talkie) may be alerted.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described more particularly with reference to the accompanying drawings which show, by way of Example only, one construction of device according to the invention, a network of such devices, and variants of the network. In the drawings: Figure 1 is a front view of a device according to the invention as installed in the home, showing a control and display panel; Figure 2 illustrates part of a network, and in particular shows two devices as shown in Figure 1 each connected to a communications bus; Figure 3 is a block diagram of the device of Figure 1; Figure 4 is a detailed circuit diagram of the device of Figure 1 and Figure 4A shows the circuit diagram of Figure 4 divided into the blocks of Figure 3; Figure 5 shows a remote alarm button and remote bell siren associated with the device of Figure 1; Figure 6 shows a miniature radio alarm transmitter associated with the device of Figure 1; Figure 7 shows a variant of the network of Figure 2 in which part of the communications bus is replaced by a radio communication link; Figure 8 shows a variant of the network of Figure 2 in which one device is connected to the network via a radio communication link; Figure 9 is a block diagram of a radio modem for use in such a radio communication link; Figure 10 shows a network in which all of the devices are interconnected by means of radio communication links; Figure 11 shows a variant of the network of Figure 2 in which a radio link is provided to a mobile patrolman; Figure 12 shows a block diagram of an interface for the radio link to the mobile patrolman; Figure 13 shows a microprocessor controller forming part of the circuit of Figures 3, 4 and 4A; Figure 14 shows a line transmitter forming part of the circuit of Figures 3, 4 and 4A; Figure 15 shows a line receiver forming part of the circuit of Figures 3, 4 and 4A; Figure 16 shows a low pass line filter forming part of the circuit of Figures 3, 4 and 4A; Figure 17 shows a voltage regulator and standby battery circuitry forming part of the circuitry of Figures 3, 4 and 4A; Figure 18 illustrates the format of signals used in a network in accordance with the invention; Figure 19 shows an acoustic warning device forming part of the circuit of Figures 3, 4 and 4A; Figure 20 is a detailed circuit diagram of the radio modem of Figure 9 and Figure 20A shows the circuit diagram of Figure 20 divided into the blocks of Figure 9, and Figure 21 is a detailed circuit diagram of the interface of Figure 12.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS General Description of the Device and its Operation Referring to Figure 1, initially the device and its operation will be described from the point of view of a user, without going into engineering detail.

The device 100 consists of a box installed at a convenient location in a house, for example mounted on a wall in the kitchen or hall. The box has a front panel 101 which includes controls and a display. The device 100 is one of a number of such devices 100 installed one each in neighbouring houses and interconnected. Up to sixteen devices 100 may be interconnected.

In the event that the occupant of a house becomes alarmed, the occupant should simultaneously press both red ALARM buttons 102. As a result, an alarm signal is sent to the other houses, two ALARM SENT lamps 103 in the form of light emitting diodes (LED's) become illuminated. The requirement to press two buttons 102 simultaneously is intended to prevent accidental tripping of the alarm system.

At each other house the alarm is raised by means of a siren sound produced by an acoustic warning device 104 not shown in Figure 1 but contained within the box 100. In response to the siren sound, the 20 occupant of the other house should look at the control panel in his house. Each control panel has sixteen location indicator lamps 105 in the form of light emitting diodes (LED's), one lamp corresponding to each of the interconnected devices. Each location indicator lamp 105 has a number from 1 to 16 and the control panel also provides spaces 106 in which further particulars such as the name, address, or other description of the various houses may be entered. That location indicator lamp 105 which corresponds to the house in which the alarm was raised is illuminated on the panels 101 at each other house. Thus, the occupant of a house in which a siren sounds will know not only that 30 the alarm is being raised, but will also know to which house assistance should be rendered.

Before rendering any assistance the occupant of the house in which a siren sounds should press the RESET button 107 on his control panel 35 101. As a result, the siren sound at his house stops, an acknowledgment signal is transmitted back to the house from which the alarm was initially raised. This acknowledgment signal is received in the form of an illuminated location indicator lamp 105 on the control panel 101 at which the alarm was raised corresponding to the house from which the acknowledgment signal is received. Thus the person who raises the alarm may very quickly receive acknowledgment signals from a number of other houses and will know that help is on the way, and will know from where that help is coming.

By way of Example the occupant of house ,l9 may raise the alarm, in which case location indicator lamp 105 numbered 9 will illuminate in all the other houses, and by way of further example the occupants of houses numbered 2, 7 and 16 may send acknowledgments in which case location indicator lamps 105 numbered 2, 7 and 16 will illuminate at house 9.

The alarm may be cancelled at the house where the alarm was initiated by pressing the RESET button 107. As a result the two red ALARM SENT lamps 103 are extinguished on the control panel from which the alarm was raised. After a delay of ten seconds a cancellation signal is sent to the other houses, stopping any siren sounds which have not already been stopped by the occupants of the other houses, and after a further ten seconds the location indicator lamp 105 at each other house is extinguished. The two ten second delays mentioned above prevent misuse of the alarm, in particular prevent the occupant of a house from activating siren sounds at other houses and then cancelling these siren sounds before the occupants of other houses have time to identify the source.

The siren sounds will sound for a maximum of fifteen minutes. At the end of this time, if not already switched off by either the initiator or the receiver, the siren sounds switch off automatically.

Testing Still referring to Figure 1, the control panel 101 also includes a TEST button 109 which may be depressed by the occupant of a house to test communication with the other houses without however producing any audible or visual signal at the other houses. In response to pressing the TEST button 109, the TEST SENT lamp 110 is illuminated and for each other house that automatically replies to the test call the corresponding location indicator lamp 105 is illuminated for approximately five seconds, during which time the acoustic warning device 104 (not shown in Figure 1) in the device 100 emits rapid pips. Testing may be carried out regularly to test the complete network integrity and also to isolate network faults.

In addition to the manually initiated test mentioned above, each device 100 also automatically carries out periodic testing. Every ten minutes each device 100 polls each other device 100 in sequence, in 10 each case waiting until a valid reply is received. If a device 100 succeeds in receiving a valid reply from any other device 100 then a new ten minute period starts. If a device 100 fails to receive a valid reply from any other device then this failure is indicated by short pips being emitted from the acoustic warning device 104 every two to three seconds. The pips may be stopped by depressing the RESET button 107 and a new ten minute period starts.

Installation Still referring to Figure 1, to facilitate installation, and in particular to facilitate distinguishing sixteen apparently identical devices from one another, a feature is provided whereby pressing and holding the RESET button 107 causes the location indicator lamp 105 corresponding to the device 100 being installed to flash three times and then go steady accompanied by pips from the acoustic warning device 104 every two seconds. The device 100 is then restored to its normal state by releasing and then briefly depressing the RESET button 107.

On application of mains power to a device 100, for the first time or after a mains failure and total discharge of optional internal standby battery, the location indicator lamp 105 corresponding to that device 100 is illuminated and short pips every two seconds are emitted by the acoustic warning device 104. The device 100 may be restored to its normal state by depressing the RESET button 107, or is restored to its normal state on receipt of a signal from another device 100 in the network. - 10 Network Referring now to Figure 2, a network consists of a two wire communication line 120 or bus extending between houses and up to sixteen devices 100 connected to the communication line (only two devices 100 are shown in Figure 2). In each case the device 100 is connected through a junction box 121 to the communication line, and the junction box 121 is connected to the power supply wall plug 122.

Overview of Electrical Circuitry Referring now to Figure 3, there is shown a block diagram of the circuitry contained within one device 100. The heart of the device is a microprocessor controller 130. Inputs to the microprocessor controller 130 include the RESET button 107, the TEST button 109, the two ALARM buttons 102, connection 131 for an optional external alarm 150 (not shown in Figure 3), connections 132 for an electricity supply, voltage regulator 133, optional stand by batteries 134, a signal receiver 135 connected through a low pass filter 136 to the two wire communication line 120, and an optional radio receiver 137 and decoder 138 for receiving radio signals from a portable personal attack button 139 (not shown in Figure 3). Outputs from the microprocessor controller 130 includes a line transmitter 140 connected by means of the low pass filter 136 to the two wire communication line 120, the acoustic warning device 104, a connection 142 to an external siren 150 (not shown in Figure 3 but shown in Figure 5), and the various lamps 103, 105, 108 and 110 (lamps 105 and 108 have been conveniently grouped together for illustrative purposes). Finally, the microprocessor controller 130 is connected to a rotary hex switch memory 142 for storing the address of the house in which it is located and this address i.e. numbers 1 to 1116 is unique to the particular device 100 and is the only difference between otherwise identical interconnected devices 100.

Referring now to Figures 4 and 4A, the circuitry is shown in considerably more detail. Inspection of the circuit diagram will reveal the particulars to one skilled in the art, and it is not proposed to describe each component. However, the more important components and associated circuitry will be pointed out and described.

Microprocessor Controller 130 Referring to Figure 13, the microprocessor controller 130 is of the ICIMC68HC705C8 type. This is a low power CMOS device providing all the input/output and processing functions of the device 100.

The microprocessor controller 130 operates at an internal instruction speed of 2 MegaHertz, this speed is derived from the external crystal XLI and associated components Cl, C2 and R18 which together with an amplifier within the microprocessor 130 form an oscillator circuit at 4 MegaHertz. This 4 MegaHertz signal is internally divided by two to form the basic system clock of 2 MegaHertz from which all the internal functions of the microprocessor controller 130 derive their timing instructions.

In addition to an internal power-up-reset system within the microprocessor controller 130 an external power-up-reset circuit is provided by transistor Q8 and associated components C15 and R63, this circuit ensures that when power is first applied, or when external power is re-applied to device 100 following a period of standby operation, the microprocessor controller 130 is forced to re-commence instructions in an organised manner from a pre-defined point within the stored software programme.

Transistor Q7, Zener Diode ZD1 and associated components signal the microprocessor controller 130 when the supply voltage falls below 12 volts, that is when the system is operating from the standby batteries 134. Under these conditions the Power On light emitting diode is extinguished due to the excess voltage drop across the Zener Diode ZD1.

Line Transmitter 140 Referring now to Figure 14, the line transmitter 140 receives logic level serial binary data from the microprocessor controller 130, and converts this into +12 volt or -12 volt opto-isolated, balanced - 12 transmission signals suitable for connection to the two wire line 120.

Logic level (0-5 Volt) Data signals are presented to the line transmitter section from the microprocessor controller 130. Logic Gate, IC6/A inverts the data signal which passes via the transmitter enable gate IC6/B to the opto isolator IC4, PINS 2, 3. The non inverted data signal passes via the transmitter enable gate IC6/C to the opto isolator IC4, PINS 6, 7.

Thus when the incoming data signal level is at + 5 Volts the output of IC6/C PIN 4 is at O.V. and the output of IC6/B PIN 11 is at + 5 Volts. Thus the opto Coupler Diodes 3/4 and 5/6 in IC4 are conducting and emitting light. Opto Coupler diode 1/2 and 7/8 are reverse biased and not emitting light. Thus the photo sensitive transistors 13/14 and 11/12 are conducting.

When photo transistor 11/12 conducts, this causes switching of the + 12 Volt supply via current limiting fusable resistor R36 to the line output ' B'.

When photo transistor 13/14 conducts, this causes switching of the Zero Volt (-Ve) side of the supply via current limiting resistor R35 to the 1ine output Ά'.

When the incoming data signal changes state from + 5 Volt to 0 (Zero) Volt, photo transistor 13/14 and 11/12 are non conducting and photo transistor 15/16 and 9/10 are conducting resulting in the voltage polarity on the output lines A/B being reversed.

The output signal to the transmission line is therefore 24 Volt peak to peak square wave derived from a 5 Volt peak input data signal from the microprocessor controller 130.

When the line transmitter 140 is not required to transmit data the Enable input is brought high (+ 5 Volts) resulting in both IC6/B output and IC6/C output being at Zero Volts, consequently no current flows in the light emitting diodes and none of the photo transistors are conducting, thus the two wire line 120 is effectively disconnected - 13 from the circuit and therefore free and available for other device 100 units to transmit.

Logic gate IC5 inverts the polarity of the Enable control signal 5 and via transistor Q5 illuminates the red TX LED D18 when the transmitter is enabled. This is used for service purpose only as an indication of transmitter status. The output of IC5 is also used to inhibit the line receiver 135 from receiving data signals from the two wire line 120 whilst the line transmitter 140 is transmitting.

The application of opto isolator IC4 provides isolation between the two wire line 120 and the logic circuits IC6 and preceding stages such as the microprocessor controller 130. These logic elements are very low current high impedance devices which are very prone to damage 15 if subjected to voltage in excess of 5 Volts such as are present or may be induced in the two wire line 120 by static electricity or the inadvertent misconnection of the two wire line 120 to a voltage source on a third party premises.

The use of a balanced transmission line (i.e. neither side of the line connected to ground) improves the quality of the transmitted signal as received at a third party premises particularly if that premises is a long distance away. A non-balanced system using one side of the circuit or two wire line 120 connected to ground could suffer interference and therefore signal degradation from differences in earth potential at physically separated premises.

The Darlington photo transistors of IC4 are capable of delivering over 100 mA to the two wire line 120 which is well in excess of the requirements for 16 receiver units each of which draw 2.5 mA of current from the common two wire line 120.

Line Receiver 135 Referring now to Figure 15, the line receiver 135 detects low level current reversal signals on the two wire line 120, transmitted from other parts of the network. A special opto-coupled flip-flop circuit provides line isolation and converts the incoming signals into - 14 logic level. The line receiver circuitry also generates synchronisation pulses which are fed to the microprocessor controller 130.

The input to the line receiver 135 section is connected to the two wire line 120 via the line filter 136.

The purpose of the line receiver 135 is to convert voltage polarity reversal signals with an amplitude range of 6 to 24 Volts into a stable logic level (0 - 5 V) signal suitable for inputting to the microprocessor controller 130. A further part of line receiver 135 detects the voltage reversal edges of the incoming signal and generates SYNC pulses which are fed to the microprocessor controller 120 to flag a polarity change.

Photo transistor IC7 and IC8 with their associated resistors form a Bi-stable circuit. The two stable states of this circuit are either IC7 photo transistor conducting and IC8 photo transistor not conducting or IC7 photo transistor not conducting and IC8 photo transistor conducting.

The stable state of line receiver 135 is reversed by switching on whichever photo transistor is presently in an off condition. Switching is achieved by illuminating the photo transistor from its associated light emitting diode. This photo transistor now conducting switches off, via the resistor bias network, the photo transistor that was in a stable on state.

A line input signal is applied to input AB with line A at positive potential with respect to line B. This produces light emitting diode IC7 forward biased and conducting and light emitting diode IC8 reverse biased and non-conducting. With a light emitting diode illuminating photo transistor IC7 this transistor is switched into a conducting state resulting in a potential of one volt on transistor collector pin 5 representing a logic zero level, photo-transistor IC8 is switched into a non conducting state via the feedback resistor network.

When the line input signal applied to AB reverses polarity, with - 15 line B at positive potential with respect to line A, photo transistor IC7 is switched into a non conducting state as a consequence of photo transistor IC8 conducting, the potential on Pin 5 of photo transistor IC7 now changes to four volts representing a logic one level.

Diodes D28 and D29 protect the sensitive photo diodes from high levels of reverse polarity. Constant current devices CC1 and CC2 limit the current drawn through the photo diodes to a nominal 2.4 mA. This not only protects the photo diodes from high current surges but also ensures that all devices 100 share equally the available line current irrespective of whether they are close to the sending line transmitter 140 or a kilometre of cable away.

The data output from the opto-coupled receiver stage is converted in logic gate IC5/C, this gate is used to block the data signal when the transmitter section of device 100 is sending.

Logic gates IC9 with associated components form a dual monostable arrangement, Gate IC9/D and IC9/B produce a negative pulse on IC9/B pin 4 for every positive transition of the data out signal. Logic gate IC9/D and IC9/C produce a negative pulse on IC9/C pin 10 for every negative transition of the data out signal.

These two sources of negative pulses are combined and inverted in logic gate IC9/A to form a synchronisation pulse train which is again inverted in logic gate IC5/B before passing to the microprocessor controller 130 interrupt input.

Logic gate IC5/B is also used to buffer the device 100 alarm switch signal into the microprocessor controller 130 interrupt input.

Logic gate IC5/A and IC6/A with associated components integrate the sync pulse train to form a steady state high logic level at IC6/A pin called the squelch signal indicating the presence of an incoming data message, a local indicator LED D19 is illuminated indicating the presence of a squelch signal. The purpose of this indicator is for service use only. - 16 The squelch signal output is fed to the microprocessor controller 130 to indicate that the network is busy and not available for this device 100 to transmit a message.

Low Pass Filter 136 Referring now to Figure 16, the low pass filter 136 prevents the high frequency content from the line transmitter 140 from reaching the two wire communication line 120. This prevents what might otherwise be a potential source of interference to other equipment users such as television/radio from becoming a problem. The low pass filter 136 also helps to block high frequency signals which might be induced onto the two wire line 120 and conducted back to the line receiver 135 corrupting an otherwise valid signal.

The filter 136 comprising inductors LI and L2 and capacitors C18 and C19 form a low pass filter network placed between the two wire line 120 and the device 100 transmit/receive circuits.

This filter 136 serves two functions as follows: (a) The line transmitter 140 output is a square wave voltage polarity reversal signal with a fundamental frequency of 1000 Hertz. However, a square wave by its nature, is made up of its fundamental frequency together with harmonics of the fundamental frequency up to tens of thousands of Hertz. It is undesirable for these harmonics to be present on the two wire line 120, since the higher frequency components in particular may radiate from the line in the form of radio frequencies and cause interference to radio receivers.

The line filter 136 removes or greatly attenuates these higher frequency components of the square wave from reaching the two wire line 120. (b) The two wire line 120 which may be up to a kilometre in length is capable of picking up a wide range of unwanted signals such as radio broadcasts from high power transmitters where the long wire acts as an aerial, or unwanted signals may be inducted onto the two wire line 120 - 17 due to the proximity of cables running close to the two wire line. The low pass filter 136 removes or severely attenuates the level of these unwanted signals before they reach the line receiver 135.

User Display The user display includes the sixteen location indicator lamps 105, one for each potential subscriber on the system. These lamps 105 are driven from the microprocessor controller 130 via a Darlington driver circuit.

Voltage Regulator 133 and Standby Batteries 134 Referring now to Figure 17, the voltage regulator IC10 and associated components C8 and C13 provide the logic elements within device 100 with a stable 5 Volt supply.

The optional standby battery system comprises two 9 volt nominal nickel cadmium rechargeable batteries 134 described individually as BAT.l and BAT.2.

Battery BAT.l provides standby power to all the logic circuits and when in standby mode the terminal voltage on the battery BAT.l may fall as low as six Volts and maintain a fully functional system.

Battery BAT.2 provides standby power to the line transmitter 140 only. As current is drained from the battery BAT.2 only during transmission of a message the terminal voltage on the battery BAT.2 remains close to 10 Volts even after eight hours of standby operation, thus maintaining line transmission signal level at close to its normal 12 Volt level.

When the device 100 is supplied with normal external power at 12 Volts from power supply 122 the batteries 134 are trickle charged via resistors R16 and R62. When in discharge/standby mode, current is supplied from the batteries 134 via diodes D35 and D36 which are characterised by a very low forward voltage drop. - 18 Personal Attack Receiver 137 / Decoder 138 The radio personal attack receiver 137/decoder 138 (shown in Figure 3) may be optionally fitted within the box of the device 100. This modular receiver 137/decoder 138 receives a radio alarm signal from a hand held personal attack unit 139 (shown in Figure 5) and, provided a code match is valid, an alarm activation signal is input to the microprocessor controller 130.

Network Signals Referring now to Figure 18, the signals employed in the network will now be described in more detail. A data code employing voltage reversal was selected. A logical 1 is represented by a +12 volt signal. A logical 0 is represented by a -12 volt signal. Each logical 1 is in practice is transmitted as a 101 voltage reversal sequence. Each logical 0 is in practice is transmitted as a 010 voltage reversal sequence. Any sequence of signals can therefore contain no more than two consecutive l's or two consecutive 0's. The voltage on the two wire communication line 120 is therefore an alternating voltage with an average direct current value of 0 volts. The system is consequently capable of working over alternating current coupled lines (i.e. employing isolating transformers should they be required).

In order to minimise costs the system is designed to operate over a two wire 600 ohm telephone type cable, this cable is the most widely produced and available cable throughout the world and as such is inexpensive.

To achieve the maximum transmission distance a signalling frequency range compatible with this cable must be employed. A centre frequency of 800 Hz produces the minimum attenuation and hence the greatest range. The design range of 1,000 metres is comfortably exceeded using these parameters.

By selecting an individual bit length of 500 microseconds and a telegram structure where there are no more than two successive binary ones or two successive binary zeros but never two successive ones - 19 followed by two successive zeros or two successive zeros followed by two successive ones the lowest fundamental frequency employed is 650 Hz and the highest, fundamental frequency is 1,000 Hz.

To comply with the above limitation each binary information bit is transmitted as three signalling bits with a binary one being transmitted as a 101 voltage reversal signal and each binary zero being transmitted as a 010 voltage reversal on the two wire line 120.

Consequently, the actual information bit transmission rate is one third of the transmission bit rate.

Binary information required to be transmitted from a sending device 100 to a receiving device 100 are as follows: Address information: Groups information Type of messages Party check bit Header word unique addresses A or B types information bits information bit information bits information bit information bits Synchronisation information bits Words one and two are synchronisation bits transmitted as a succession of ones and zeros, this section of the telegram takes 24 ms and is used primarily to allow the two wire line 120 to stabilise and the radio modems (described in more detail later) to have a validatible structure to trigger the keying of the radio modem transmitter which in turn requires an identifiable data structure before repeating the radio received telegram onto the next section of the two wire line 120 and device 100's.

The header marks the start of the decoded information. The unique binary number 00011100 cannot be valid in any other frame and is used to define with a very high degree of probability the position of the data section of the telegram which contains the unit address condition code and parity bit information. - 20 The post sync is primarily spare bits for future options, however the most significant bit is used to define the group A or B to which the device 100 belongs.

Since the two wire line 120 is common to all device 100's on the system only one unit can transmit at any given time if successful decoding is to occur. Before commencing transmission each device 100 monitors the line to ensure that no other device 100 is transmitting before it sends a telegram itself.

If a device 100 wishes to send a telegram and finds the line occupied then it only needs to wait a maximum of 60 ms before the line is free.

The bit rate and message length are selected to provide the optimum transmission distance together with the shortest time occupancy of an individual transmission on the common two wire line 120 in order to minimise interference between messages from different devices 100 transmitting signals at the same time.

In order to provide maximum isolation of the electronic circuitry in each device 100 from the two wire communication line 120, an opto-coupled transmitter/receiver stage is used.

External Alarm 150 Referring now to Figure 5 the device 100 is provided with an external alarm siren 150 driven by the device 100 and connected to the device 100 via a simple connection at the junction box 121. The siren 150 output is activated only by an incoming alarm signal and is useful in situations where the siren sound produced by the acoustic warning device 104 (described in more detail below) may not be heard due to the size of the premises or other factors. The drive for the external alarm 150 may also be used to activate the other devices. The device 100 is also connected via the junction box 121 to a remote alarm activation button or personal attack button 139, typically located at the bedside, entrance door or other high risk locations. - 21 Acoustic Warning Device 104 Referring now to Figure 19, the acoustic warning device 104 within device 100 is a ceramic plate resonator employing an amplifier in a positive feedback oscillator arrangement.

When current supply is applied to this oscillator a finite time is required for the oscillation to build to maximum output level.

This feature is employed to produce low acoustic level signals from the acoustic warning device by switching on the circuit for very short periods of time typically less than 100 milliseconds. The result is to produce short duration acoustic output pulses with a greatly reduced audio level, typically described as a pip.

This same acoustic warning device 104 may also be used to produce very high level acoustic signals typically described as a siren by applying current continuously.

The external alarm 150 driver circuit in parallel with the acoustic warning device 104 employs a slow attack fast release transistor switch arranged such that the switch only responds to the prolonged application of current (siren level) and not the short duration application of current (pip level).

By this means an externally connected siren 150 will only sound for incoming third party alarm activations and not operate for any of the test and monitor functions which produce a pip signal on the internal acoustic warning device 104.

Personal Attack Feature Referring now to Figure 6 the device 100 is fitted with a personal attack radio receiver module 160, capable of receiving a signal from a miniature radio transmitter 161 incorporating an alarm activation button and worn on clothing. This arrangement provides extra security for those users at high risk such as the elderly living alone, lone workers or the like. The hand activated radio transmitter 161 is similar to the type used for conventional car alarm activation/deactivation and may typically be carried in a pocket, on a wrist strap, pinned to clothing or hung around the neck.

Alternative Networks - including Radio Links Referring now to Figure 7, it may in some cases be impractical to connect all of the houses by means of a two wire communication line 120. This may be true for example where some of the houses are on one side of a street and the other houses are on the other side of the street. In this case the network may be coupled by a radio link with radio signals being transmitted between two radio modems 170.

Referring now to Figure 8, an isolated house may be connected to the remainder of the network by means of a radio link including two radio modems 170, one associated with the isolated house and the other associated with the network.

Radio Modem 170 Referring now to Figure 9, 20 and 20A, the radio modem 170 block diagram will now be described in more detail. A radio receiver 171 receives an incoming radio signal and this is sent to the control logic 230 and then to the line transmitter 240 which converts this signal into a +12 volt or -12 volt opto-isolated, balanced transmission signal suitable for connection to the two wire communication line 120. A low pass filter 236, line receiver 235, voltage regulator 233 and line transmitter 240 serve the same functions as corresponding components in the device 100 described with reference to Figure 3.

The radio receiver 171 is a proprietary module employing FM demodulation. Demodulated binary data is sent to the control logic 230 in addition to a carrier detect squelch signal. An internal dipole antenna (xyz) is connected to the input of the radio receiver 171, however a facility is provided to connect to an external antenna if greater receiving range is required.

The radio transmitter 175 is a low power proprietary module - 23 employing FM modulation. The radio transmitter 175 is keyed by the control logic circuit 230 in response to an incoming signal on the line receiver 235. The FSK data modulation is derived from the line receiver 235 via the control logic. An internal dipole antenna (xyz) is connected to the output of the radio transmitter 175, however a facility is provided to connect to an external antenna if greater transmission range is required.

The control logic 230 controls the direction of data transmission through the radio modem 170. This control is necessary since only a single radio frequency is employed and only one or other of sending or receiving is possible at any given time on the two wire communication line 120. A first come first served principle is employed in determining the direction of data flow.

The circuit diagram in Figure 19 is shown divided into blocks in Figure 19A for the purpose of analysis.

The purpose of the radio,modem 170 is to convert two wire line 120 telegrams into a frequency shift keyed (FSK) modulated radio signal and correspondingly to receive FSK modulated radio signals and convert these into a data telegram suitable for transmission on the two wire line 120.

The low pass line filter 236 of the radio modem 170 is identical in all respects and function to the low pass line filter 136 used in the device 100.

The voltage regulator 233/standby batteries 234 are identical in all respects and function to the voltage regulator 133/standby batteries 134 used in the device 100.

The first stage of the line receiver 235 is identical in form and function to that of line receiver 135 of device 100. The synchronisation extraction stage is omitted since the logic controller 230 of radio modem 170 operates in a continuous data input software monitor loop rather than a service requesting interrupt mode employed by the microprocessor controller 120 of the device 100. - 24 The opto-isolator stage of line transmitter 240 of radio modem 170 is identical in form and function to the opto-isolator stage of line transmitter 140 of device 100. Since the logic controller 230 of radio modem 170 has a higher output current drive capability than the microprocessor controller 130 employed in the device 100, the driver integrated circuits IC6 and associated components of line transmitter 140 are not required in line transmitter 240.

The radio transmitter 175 is a proprietary module employing FSK frequency modulation techniques at a frequency depending on the licensing authority of the country of use.

The logic controller keys the radio transmitter 175 by applying current via switching transistors QI and Q2. The data modulation telegram output from the logic controller is buffered via transistor Q3.

The radio receiver 171 is a proprietary module employing frequency de-modulation techniques at an identical frequency to that used by the transmitter 175.

The demodulated received radio signal is passed directly to the logic controller 230 for analysis. An additional output from the radio receiver 171 indicates to the logic controller 230 when a radio signal on the receiver frequency is detected, this signal is buffered via transistor Q4.

The Control Logic 230 of the Radio Modem The control logic 230 employs a minimum instruction set micro controller type PIC 16C54. The embedded control programme/software serves two basic functions as follows: (a) radio data receiver to two wire line transmitter validation and send, (b) two wire line receiver to radio transmitter validation and send. - 25 As the radio channel may be used by other services the control logic 230 performs timing measurements on any incoming radio telegram to verify that the data is a valid signal from a companion radio modem 170 before passing this signal to the two wire line 120 for onward transmission to other device 100's. Additionally, since a valid telegram is 60 ms in duration a received telegram of duration greater than 60 ms is deemed to be invalid. When the logic controller 230 is in radio receive/two wire line transmit mode any signal arriving from the two wire line receiver is ignored.

Similarly, when the logic controller 230 is in the two wire line receiver/radio transmit mode any signal arriving from the radio receiver is ignored.

A number of light emitting diode indicators are provided to assist with installation and service as follows: (a) Line squelch: Illuminates when a telegram is received on the two wire line 120 (b) Radio squelch: Illuminates when a telegram is received via the radio receiver 171 (c) Transmit: Illuminates when the radio transmitter 175 is keyed.

Further Network - Radio Links only Referring now to Figure 10 there is shown a network in which all of the devices 100 are connected to one another by radio links. Each device is provided with an associated radio modem 170 capable of transmitting to the radio modems 170 of all of the other devices 100 and capable of receiving from the radio modems 170 of all of the other devices.

Further Network - Voice Synthesizer to send signal to Mobile Patrolman Referring now to Figure 11, the network includes a communication device for communicating with a mobile patrolman, for example a police - 26 man or security guard. The drawing shows device 100 at location 7, device 100 at location 8 from which an alarm signal has been transmitted, device 100 at location 9, and shows a patrolman's radio voice synthesizer interface 181 and an associated radio transmitter 182 for transmitting a voice signal to a patrolman provided with a conventional radio receiver 183. Typically a security man patrolling an area would receive on his personal radio receiver 183 a synthesized voice message, for example Alarm Activation Unit No. 8. This message is repeated a number of times or at regular intervals until the activated alarm is reset.

Referring now to Figure 12, there is shown a circuit block diagram of the patrolman's radio voice synthesizer interface 181 of Figure 11. The interface 181 is connected to the two wire communication line 120 or to a radio modem 170 in a similar fashion to the other devices 100 forming part of the network. Voltage regulator 333, standby batteries 334, line transmitter 340, line receiver 335 and low pass line filter 336 shown in Figure 11 serve the same functions as the corresponding components 133, 134, 140, 135 and 136 respectively in the device 100 illustrated in Figure 3.

The area code selector switch 284 is used to define a higher order address within the voice message, so that a patrolman who is on duty in relation to a number of different networks of houses will know to which network he must go, and to which house within that network. For example if the area code switch 284 is set to 3 the synthesizer voice message would be as follows: Alarm Activation - Area 3, Unit No. 8.

The voice synthesizer 285 takes instructions from the microprocessor controller and, from a pre-stored menu of words puts together a composite message. The composite audio signal is passed via an isolating transformer 286 to the modulation input of the radio transmitter 282 which then transmits the voice signal to the patrolman. A switched output 287 to key the radio transmitter 182 is also provided. The monitor loudspeaker 288 is used to speak the message locally so as to allow the quality of the message to be monitored for service purposes. - 27 Operation of the patrolman's radio interface will now be described by way of Example. Assuming that the alarm is raised in Network No. 3, House No. 8, the patrolman will hear a message as follows: Alarm Activation - Area 3, Unit No. 8 and this message is repeated a number of times. An occupant of another house within the network, for example House No. 4, may acknowledge the alarm signal and in this case the patrolman will receive a synthesized voice message as follows: Alarm Respond - Area 3, Unit 4. If the occupant who raised the alarm resets the alarm the patrolman will receive a synthesized voice signal as follows: Alarm Restore - Area 3, Unit 8. If the patrolman's interface 281 loses mains power, and assuming the interface 281 is fitted with optional standby batteries 334, the patrolman will receive a signal as follows: Power Fail - Area 3. This message is transmitted at regular intervals. If the power is restored, the patrolman will receive a synthesized voice message as follows: Power Restored - Area 3. The patrolman's radio interface unit 281 is programmed in such a way that when switched on the radio interface unit 281 automatically carries out a poll of the network and stores in memory a record of all the devices 100 in the network that replied. Regular polls of the networks are carried out, and in the event of by way of example house 9 that previously replied now fails to reply, the patrolman receives a synthesized voice message as follows: Link Fail Area 3, Unit 9. If that house is subsequently polled successfully the patrolman receives a synthesized voice message as follows: Link Restore - Area 3, Unit 9.

Mobile Patrolman's Radio Interface Circuitry Referring now to Figure 21, consideration of the detailed circuit diagram of the patrolman's radio interface will show that it is identical in many respects to the standard device 100. A number of items have been omitted as they are not required such as the acoustic warning device, radio alarm receiver socket and associated components, radio alarm decoder socket and associated components, front panel alarm indicator light emitting diodes, and alarm, test and reset button conditioning circuits.

Whereas in device 100 the output ports of the microprocessor controller 130 are used to drive the alarm location indicator diodes, in the patrolman's radio interface these microprocessor controller output ports pass addresses information to the proprietary voice storage device. The address information points to pre-stored words within the voice storage device. The synthesized voice output from the voice storage device is output on pins 14 and 15 to an isolation transformer and monitor loudspeaker. The secondary winding of the isolation transformer is grounded on one side and the other side is connected to connector CON 5 Pin 3. Switching transistors Q3 which was used as a remote siren output driver in device 100 is used in the patrolman's radio interface as a key output for the patrolman's radio.

Granny Mode In a further modification, not illustrated in any of the drawings, a device 100 may be capable of initiating an alarm call, but not of receiving such a call. A device 100 having this feature may be used in the home of an old person who may wish to raise the alarm but should not be expected to respond to an alarm raised by someone else. The device 100 is modified for this purpose by disconnecting the appropriate circuit wire link within the device 100.

Two Groups of Houses, One Communication Line 120 Also in accordance with the invention and not illustrated in the drawings, the various houses connected to one two wire communication line 120 may be divided into two essentially independent groups, the members of each group communicating only with other members of the same group, but using a common communications line 120 for this purpose. Such an arrangement is useful in cases where immediate neighbours are not good friends. To allow for this arrangement the device 100 includes two group addresses, Group A and Group B. Only devices 100 with the same group setting will communicate with each other.

Group B is selected by removing a selector wire link within device 100.

Claims (5)

1. A local alarm device for use in a neighbourhood alarm network consisting of a plurality of such devices comprising: signal transmission means for transmitting an alarm signal indicative of said device; signal receiving means for receiving an alarm signal from another such device indicative of said other device; characterized in that the signal transmission means is additionally manually operable to transmit an acknowledgment signal to another device in response to an alarm signal received from said other device; and in that the signal receiving means is operable to receive an acknowledgment signal from another such device in response to an alarm signal transmitted from the device.

2. A local alarm device in accordance with claim 1 in which the signal transmission means is operable to transmit an acknowledgment signal indicative of the device sending the acknowledgment signal, and the receiving means is operable to receive an acknowledgment signal indicative of the device sending the acknowledgment signal.

3. A local alarm device in accordance with claim 1, in which the signal transmission means and signal receiving means include a radio transmitter and receiver.

4. A local alarm device for use in a neighbourhood alarm network consisting of a plurality of such devices including signal transmission means comprising a voice synthesizer and associated radio transmitter for transmitting a voice alarm signal indicative of said device.

5. A local alarm device or network substantially as herein described with reference to and as shown in the accompanying drawings.