SPECIFICATIONIntruder Detection SystemThis invention relates to an intruder detection system of the kind, hereinafter referred to as of the kind specified, comprising a detector unit having a transmitter for transmitting ultrasonic sound waves into a protected area (as herein defined), a receiver for receiving reflected waves i.e. echoes of the transmitted waves from objects within or the boundary of, the protected area, means to detect any change in the nature of the echoes from a prior echo, and to provide an alarm signal to an alarm unit when any such change is detected, and a method of operating the same.
Intruder detection systems which operate using ultrasonic waves are well known. Usually such systems operate using the Doppler effect and detect changes in the frequency of the echoes received, due to movement of a reflecting object, such as an intruder, within the protected area.
However, in such systems it is necessary for the ultrasonic sound waves to be continuously transmitted and received which means that power consumption of such systems is high. This makes battery operation only viable for short periods, and it is more usual for the system to be mains powered with a battery standby. However, if the battery becomes unable to produce the necessary current to operate the system, and power from the mains is lost, this renders the system useless for detecting intruders.
Accordingly, an entirely battery powered system is preferred which necessitates a low power consumption.
Further, because the ultrasonic sound waves are continuously transmitted and received, it is necessary for two separate ultrasonic transducers to be provided, one for transmitting, and the other for receiving the ultrasonic sound waves.
To reduce the risk of interference between the two, they generally have to be physica!ly separated a substantial distance apart. Where a large area is to be protected, it may even be necessary to split the detection unit into two separate parts, one part having the receiver, and the other the transmitter, with the necessary wiring interconnecting the two. This is obviously undesirable, inconvenient and uneconomic.
Accordingly it is an object of the present invention to provide a new or improved intruder detection system.
According to one aspect of the invention we provide an intruder detection system of the kind specified characterised in that the sound waves are transmitted intermittently, and the receiver receives echoes from the protected area, only during the periods for which the transmitter is inoperative.
Thus the ultrasonic waves are transmitted in pulses rather than continuously.
By "protected area", we mean that area into which the ultrasonic sound waves travel, and from which the waves are reflected back to the detector unit, for example from a stationary or moving object within that area, or the boundary of that area, for example walls, ceilings or floors, where the protected area is within a room.
Thus the disadvantages of known ultrasonic intruder detection systems discussed above, are entirely alleviated.
Because the ultrasonic sound waves are not transmitted continuously, power consumption of the detector unit is low, and thus the unit may conveniently be entirely battery powered. Further, it is possible to use a single ultrasonic transducer to both transmit and receive the ultrasonic sound waves and thus there is no necessity to separate the detector unit into two separate parts or to provide any interconnecting wiring therebetween.
it will be appreciated that the system operates in an entirely different principle to known ultrasonic detection systems in that the frequency of received echoes may only be one parameter which could be compared with the prior echo to detect said change in the nature of the echo.
Because ultrasonic sound waves are not being transmitted at the same time as being received, the intensity and general characteristic of the received echo from said prior echo can be compared, or any other selected information from the echoes can be compared.
Thus a more reliable, more accurate, intruder detection system is provided compared to those which operate on the Doppler effect principle.
If desired, the system may include a control unit which may comprise part of the detection unit or be remote therefrom, to give command signals to the detector unit to render the detector unit operable or inoperable.
The alarm unit may be part of the detector unit and/or the control unit, or may be remote from both.
It is preferred for the detector unit, control unit, and alarm unit, to be remote from one another, or at least for the control unit to be remote from a combined detector/alarm unit, or for the detector unit to be remote from a combined control/alarm unit, or for the alarm unit to be remote from a combined control/detector unit. However, at present, such a system would require the installation of wiring interconnecting the various units.
Obviously, where an intruder detection system is to be installed in an existing building, such known systems are very inconvenient because it is necessary to install the interconnecting wiring.
It would of course be preferred for the need to install any interconnecting wiring to be entirely eliminated, whilst retaining the facility to provide separate control and/or detector and/or alarm units as required.
Accordingly, it is another object of the invention to provide an intruder detection system which overcomes this problem also.
According to a second aspect of the invention we provide an intruder detection system of the kind specified characterised in that the detector unit is at a first location, the alarm unit is at a second location, and a control unit is provided at a third location to give command signals to the detector unit, to render the detector unit operable or inoperable, the detector unit and/or the alarm unit and/or the control unit being interconnected solely by mains wiring.
Thus there is no need to install any special wiring to interconnect the units, but existing mains wiring can be used.
The first location may be the same as the second location but spaced from the third location, or the second location may be the same as the third location but spaced from the first location, or the third location may be the same as the first location but spaced from the second location.
Of course where two of the units are at the same location, they need not be interconnected by mains wiring.
The first, second and third locations may each be within the same building although it is within the scope of the invention for the first and/or the second location to be in a separate building or separate buildings to the third location, provided that the buildings are each supplied with electricity from the same mains.
Thus the command signal from the control unit and the alarm signal from the detector unit, may pass along said mains wiring to the detector unit and the alarm unit respectively.
It will be appreciated that the intruder detection systems according to the first and/or second aspect of the invention each provide a novel and useful improvement over known intruder detection systems.
Preferably however, the intruder detection system according to the second aspect of the invention incorporates the features of the intruder detection system according to the first aspect of the invention.
The detector unit of the system may comprise a memory to store selected information from a calibration echo, and comparator means to compare similar selected information from subsequent echoes, with the selected information from the calibration echo, stored in the memory, to detect any changes in the nature of the subsequent echoes, from the calibration echo, and means to provide the alarm signal to the alarm unit when any such change is detected.
Thus the invention may provide a novel method of calibrating and operating an intruder detection system without any need for manual calibration as in known systems.
Accordingly, it is another object of the invention to provide a new or improved method of operating an intruder detection system of the kind specified.
According to a third aspect of the invention we provide a method of operating an intruder detection system of the kind specified, said method comprising the steps of:(a) actuating the detector unit,(b) storing selected information from a calibration echo in a memory,(c) comparing similar selected information from subsequent echoes with the selected information from the calibration echo stored in the memory to detect any change in the nature of the subsequent echoes from the calibration echo,(d) providing an alarm signal to the alarm unit when any such change is detected.
Thus the system, is automatically calibrated, and there is no need for manual adjustment to adjust the sensitivity of the system according to environment.
The calibration and subsequent echoes are preferably compared using a comparator means which may be integral with a microprocessor control.
The detector unit may include an address and priority matrix whereby the detector unit is responsive to predetermined command signals only, from the control unit. For example, the matrix may be responsive only to specified digitally encoded command signals from the control unit, to render the detector unit operable or inoperable.
Thus the system may only be actuated or deactuated upon receipt of a specific command signal by the detector unit which signal would be coded for each system, the matrix being programmed only to be responsive to the correctly coded command signals.
The command signals may be coded within the control unit upon a specific sequence of instructions being fed into the control unit. For example, the control unit may have a plurality of digital inputs which may be selected in a specific order to provide said specific sequence of instructions in which case, the control unit may be in the form of a keyboard having a plurality of code keys, for example which could be numbered 1 to 9, at least some of which keys would have to be operated in a specific order to provide said coded sequence of instructions.
Alternatively, the control unit may comprise a voice detection unit which provides a command signal, in response to a particular voice or voices, and/or a particular word or words only.
Preferably, the command signal has, in addition to said code, to which the address and priority matrix responds, an instructing part, whereby an operator can give an instruction either to actuate or deactuate the detection unit.
The instructing part may be derived in the control unit to give the required command, for example by means of an "arm" or "disarm" key, after the code keys have been operated. Alternatively, where a voice detector is provided, the matrix may respond to a particular voice or voices whilst the microprocessor is programmed to respond to the actual word or words used to carry out a particular command.
Any other means may be used to cause the control unit to provide a correctly coded command signal, and instructions to the detector unit, such as a remote ultrasonic transmitter, or even a message given over a telephone line.
Preferably, upon the command signal being received by the detector unit, the detector unit responds by issuing an acknowledgement signal, to the control unit, so that an operator knows that his command signal has been received by the detector unit.
For example, the control unit may be provided with an audible or visual means which are actuated by the acknowlegement signal to indicate to the operator that his command signal has been received.
In each case, the microprocessor of the detector unit will only be operative to arm or disarm the intruder detection system, where the predetermined command signal is given.
The detector unit may include an interface between the mains wiring to which the unit is connected, and the remainder of the unit, which interface may include a discriminator, to discriminate between the command signal and the mains frequency, and any other signal such as an interference or other parasitic signal which may be on the mains. The interface, or a separate interface may be operable to respond to an instruction from the microprocessor to transmit the alarm signal into the mains and, where the microprocessor is arranged to give an acknowledgement signal to the control unit to the command signal, the interface, the separate interface, or another separate interface may be operable to transmit the acknowledgement signal onto the mains.
Of course, the control unit would also require such an interface to isolate the remainder of the control unit from the mains and to transmit the command signal onto the mains, and where appropriate to receive an acknowlegement signal.
The detector unit may include an ultrasonic analogue section which is arranged to transmit ultrasonic sound waves into the protected area via an ultrasonic transducer thereof, and to receive ultrasonic sound waves from the protected area, both under the direction of the microprocessor.
The ultrasonic transducer may be operated by an oscillator which is switched on and off under the control of the microprocessor, and the ultrasonic transducer, or a separate ultrasonic transducer, may receive the echoes from the protected area.
A receiver circuit of the analogue section may convert the output from the ultrasonic transducer when receiving echoes, into a signal which is compared with that derived from a prior calibration echo. For example, the signal converted from the output from the ultrasonic transducer when receiving, may comprise a series of binary levels.
The receiver circuit may include an amplifier, the gain of which is controlled by the microprocessor so that said signal converted from the output from the ultrasonic transducer, has an amplitude above a minimum level.
A control section of the detector unit may provide power to the microprocessor and the analogue section, upon receiving an "arm" command signal from the control unit.
The microprocessor may then be arranged to decode the command signal from the interface and issue the acknowledgement signal to the control unit, where the command signal is correctly coded.
An override operative for testing purposes may be provided so that the alarm unit is not given an alarm signal when the alarm unit would otherwise be given such a signal.
The override may be provided on the control unit or detection unit.
The memory of the detector unit may be programmed to store two sets of information, namely a decoding programme to decode incoming command signals from the interface to provide an input to the address and priority matrix which responds where the command signal is correctly coded, and a detection programme in which selected information from the calibration echo from the analogue section, is stored. For example, where the output from the analogue section is a series of binary levels, the detection programme may store these series of binary levels of the calibration echo.
Preferably, said comparator means are part of the microprocessor and compare the series of binary levels stored in the detection programme with the series of binary levels obtained from subsequent echoes.
It is preferred for the detection unit to be operative to recalibrate itself regularly, for example every three or four minutes to account for atmospheric changes in the protected area such as changes of temperature which can affect reflection of the- ultrasonic waves. This is conveniently done within the detection programme of the memory, at these regular intervals, by selecting a subsequent echo received by the analogue section, and treating this echo as a calibration echo.
Preferably, the detector unit and/or the control unit is battery powered, although if required rechargeable batteries may be provided along with a trickle charger, so that the batteries are continuously recharged from the mains as power is drawn from the batteries. However because of the low power consumption of the detector unit, even on failure of the mains supply, the batteries have been found to power the unit for a substantial period of time.
It will be appreciated that once the control unit has issued a correctly coded command signal to "arm" the system, and the command signal is acknowledged, where this facility is provided, that the control unit has no further function and thus may be disconnected from the system until it is required to give a "disarm" command signal. Thus where the system is installed in a building, such as a dwelling, office or factory building, an operator can carry the control unit with him after arming the system, whilst the remainder of the system is operable to detect intruders.
Alternatively, the control unit may be fixed at a particular location, but a remote signalling device, such as an ultrasonic transmitter, may be used to operate the control unit remotely.
Where the control unit is operated from within a building, or even from within the protected area, the system may have an inbuilt time delay to enable the operator to "arm" the system and leave the building or protected area, or enter the building or protected area and disarm the system without any risk of the detector unit issuing an alarm signal to the alarm unit.
The detector unit may include an internal alarm which indicates audibly or visually that an intruder is present, when an alarm signal is given to the remote alarm unit.
The alarm unit may be battery or mains powered, but preferably is battery powered, with means such as a trickle charger, to recharge the batteries from the mains, as power is consumed by the unit.
In either case, it would be necessary for the unit to be connected to the mains to receive any alarm signal from the detector unit.
Thus the alarm unit may include an interface between the mains wiring to which the unit is connected, and the remainder of the unit, which interface may include a discriminator to discriminate between the alarm signal and the mains frequency, and any other signal such as an interference signals or other parasitic signals, which may be on the mains.
The alarm unit preferably includes means to identify a predetermined alarm signal, whereby the unit is responsive to the predetermined alarm signal only.
Said identifying means may comprise a memory in which a decoding programme is stored, which decodes an incoming signal, to operate an alarm means only where the signal is recognised.
The identifying means and alarm means may conveniently be microprocessor controlled.
The alarm means may be an audible or visible alarm and/or may initiate means, such as a telephone dialing mechanism, to transmit a signal to a remote location, such as a police station, that the alarm unit has been actuated and thus that an intruder has been detected.
Preferably, the alarm unit also includes an address matrix whereby the unit may also respond to a correctly coded command signal containing the necessary instruction to operate or discontinue operation of the alarm means. In the former case, the system may also be used as a panic device, for example if an occupant of a building is aware that the building is being broken into, in which case the occupant may override the detection unit and instruct the alarm unit direct.
The alarm unit may comprise a control section operable to actuate the remainder of the unit upon receipt of an alarm or command signal (not necessari!y the predetermined alarm or command signal).
Thus the alarm unit consumes minimum power until actuated and even if mains power is interrupted, the power stored in the batteries is adequate to operate the unit for a considerable period of time.
The invention will now be described with the aid of the accompanying drawings in which:Figure 1 is a schematic diagram of an intruder detection system in accordance with theinvention.
Figure 2 is a block circuit diagram of thedetector unit of the system of Figure 1.
Figure 3 is a block circuit diagram of aninterface of the circuit of Figure 2.
Figure 4 is a block circuit diagram of anultrasonic analogue section of the circuit of Figure 2.
Figure 5 is a block circuit diagram of a controlsection of the circuit of Figure 2.
Figure 6 is a block circuit diagram of thecontrol unit of the system of Figure 1.
Figure 7 is a block circuit diagram of the alarmunit of the system of Figure 1.
Referring first to Figure 1, an intruder detectionsystem in accordance with the inventioncomprises three main units, a detector unit 10, acontrol unit 1 and an alarm unit 12.
As will be appreciated from the followingdescription, the system is not limited to the threeunits as shown, but could have more than onedetector unit 10 and/or more than one controlunit 1 and/or more than one alarm unit 12.
As shown, the detector unit 10 is mounted in aloudspeaker cabinet for concealment, but couldbe concealed in any other type of cabinet, or neednot be mounted in a cabinet at all.
The control unit 11 as shown, comprises akeyboard although again, as will be apparent fromthe ensuing description, this need not be a keyboard, but could be a voice detection unit forexample or could comprise a receiver to receivesignals from a remote handset e.g. an ultrasonicor radio controlled hand set, or a telephone line.
The alarm unit 12 preferably includes anaudible alarm such as a bell, buzzer or highpitched transmitter (shriek device) and mayinclude a visual indicating means such as a flashinglight and/or the alarm unit may be arranged tooperate an auxiliary alarm such as lights within abuilding, or arranged to convey a predeterminedmessage such as on a tape, to a remote locationsuch as a police station over the telephone line ora radio link.
The units 10, 11 and 12, are interconnectedsolely by means wiring, along which varioussignals can be transmitted and received from theunits, although the operation of the units 10, 11,12, is not dependent upon mains power. Hencethe mains wiring acts merely as aninterconnection. The units 10 to 12 may belocated each in the same building, although it ispossible for the various signals to be transmittedfrom one building to another where the buildingsare all supplied with electricity from the samemains and there is no isolating means betweenthe buildings, and provided of course that thetransmitted signals are strong enough. Thus theunits 10 to 12 may each be located in separate buildings or two of the units may be located in a building separate from the third unit.
Alternatively, two of the units could be located at the same location. For example, the control means 11 could comprise an integral part of the detector means 10 or alarm unit 12, or the alarm unit 12 and detector unit 10 may comprise an integral unit separate from the control unit 11.
The system shown operates using ultrasonic sound waves which are transmitted from and received by the detection unit 10, and the received signals are analysed in the detection unit 10.
Where an intruder is detected within a protected area (as hereinbefore defined) which may be a room or part of a room, the detection unit 10 sends an alarm signal to the alarm unit 12 along the mains wiring, to operate the alarm.
The system is armed and disarmed by a coded command signal issued by the control unit 11.
The control unit 11 will transmit a correctly coded command signal only upon a specific sequence of instructions being fed into the unit 11. In the present case, this is achieved by depressing the keys 13 of the keyboard in a predetermined sequence, although where another type of control unit is provided, this may be achieved in any other way. For example, where a voice detection unit is used, the unit 11 may be responsive only to a particular voice and/or word or words.
The unit 11, in addition to transmitting signals to the detection unit 10, may also receive an acknowledgement signal transmitted from the detector unit 10.
The individual unit 10, 11, 12, will now each be individually described in more detail.
The Detector UnitThe circuit of the detection unit 10 is schematically shown in Figure 2. The unit 10 is microprocessor controlled, the microprocessor being indicated at 1 5. The unit 10 further includes a power supply 16, an interface 17 with mains wiring 18, and an ultrasonic analogue section 19 for transmitting and receiving ultrasonic waves, a control section 20 to control the various functional components, and an address and priority matrix 21 An external memory 22 is also provided along with an internal alarm 23.
As shown, the power supply 1 6 comprises a plurality of batteries arranged in series. Because of the lower power consumption of the unit 10, the batteries are able to power the unit 10 for a long period of time. If desired, the batteries could be rechargeable from the mains by the inclusion of a trickle charger similar to that shown as in Figure 7.
The interface 17 isolates the remainder of unit 10 from the mains supply 18, and upon receipt of a command signal from the mains 18, is arranged to send a "wake up" signal to control section 20 along line24, which signal in turn renders the microprocessor 1 5 and ultrasonic analogue section 1 9 operative;.
Thus the detector unit 10 is thus activated from a quiescent state in which only the interface is "live" and in which there is minimum power consumption.
The interface 17 is also operable to transmit the acknowledgement signal and/or the alarm signal into the mains wiring 1 8 or if required, the unit may include a separate interface or interfaces to achieve this.
The ultrasonic analogue section 19 is operable to transmit ultrasonic sound waves into a protected area, and to receive sound waves reflected from the area.
The control section 20 returns the detection unit to its quiescent state upon receipt of a "end of cycle" signal from the microprocessor 15, along line 62.
The control section 20 also includes a light emitting diode circuit which causes a light emitting diode to be lit up when an intruder is detected within an initial callibration period, as hereinafter described.
The address and priority matrix 2 1 provides a means for coding the system to receive a predetermined command signal only so that the system cannot be controlled by any unauthorised person.
The address and priority matrix 2 1 also provide a means for coding an individual detector unit 10 so that where more than one unit 10 is provided, each detection unit 10 may be individually identified and controlled.
The memory 22 stores the two main programmes, namely a decoding programme and a detection programme.
The decoding programme decodes an incoming command signal and feeds the decoded signal to the address and priority matrix which determines whether the command signal is correctly coded or not and thus whether the unit 10 should respond to the signal.
The detection programme stores selected information from a calibration echo from the ultrasonic analogue section 19 which is compared with selected information from subsequent echoes, to determine whether an intruder is detected or not.
The internal alarm 23 is optional, but where provided, is operable to give a visual and/or audible indication that an intruder has been detected.
The microprocessor 1 5 connects all the component sections 1 6 to 23 and controls operation of the unit as described below.
The interface 17 will now be described in more detail with particular reference to Figure 3.
InterfaceThe interface 1 7 comprises a receiver section R and a transmitter section T, and an isolator means which in the present case comprises a suitably wound coil C.
The receiver section R (and coil C) are tuned to reject the usual 50 or 60 Hertz mains frequency signal, and any interference or other parasitic signal on the mains and to identify and accept a command signal having a predetermined high frequency carrier signal.
The receiver section R includes a demodulator 26 to demodulate the command signal from the carrierfrequency, and also provides a further filter for removing interference and other parasitic signals from the incoming signal.
The demodulated signal is fed to a further filter and wave shaping circuit indicated at 27, which may provide three outputs, namely, a "wake up" signal to the control section 20 via line 24, the coded command signal from the control unit 11 to the microprocessor 1 5 via line 29, and a further "interrupt" signal via line 30 to the microprocessor 1 5, to enable interruption of the cycle of operation hereinafter described, so that the microprocessor 1 5 will accept a new command.
The transmitter section T comprises a modulator 35 (e.g. 100 KHz) for modulating a signal received from the microprocessor 15, along the line 36, which signal is transmitted via a buffer circuit 37 which converts the modulated signal to a signal suitable for feeding to coil C connected to the mains wiring 1 8.
Preferably, the incoming command and outgoing transmitted signals are amplitude modulated, although they could be frequency modulated or digitally encoded as required.
The ultrasonic analogue section 19 will now be described with particular reference to Figure 4.
Ultrasonic Analogue SectionThis section 19 includes a single ultrasonic transducer 40 which is operable both to transmit and receive ultrasonic waves, although if required separate receiving and transmitting transducers may be provided. However, the section 1 9 is characterised in that the ultrasonic waves are not received or transmitted simultaneously.
The section 19 has a transmitter section T' and a receiver section R'.
The transmitter section T' comprises an oscillator circuit 41 to produce a signal, e.g. 40 kHertz signal, which the transducer 40 converts to ultrasonic sound waves.
The oscillator 41 only operates the transducer 40 when a control switch 42 completes the transmitter circuit, under the control of a signal from the control section 20 via line 43.
The control section 20 is caused to signal the switch 42 to switch on and off in response to an instruction from the microprocessor 1 5.
The receiver section R' includes a power line 46, also fed with power from the control section 20, but not when the control section 20 instructs the switch 42 to close and thus the waves are transmitted in pulses.
Thus when the receiving section R' is operative, the oscillator 41 is switched off, and when the oscillator 41 is switched on, the receiver section R' is switched off.
The receiver section R' includes an input amplifier 47 to amplify any signal of ultrasonic frequency received from the transducer 40 (when the oscillator 41 is switched off) before further processing.
The receiving section R' further includes a band pass tuned amplifier 48 to further filter and amplify the incoming signal to provide a signal of maximum amplitude around 40 kHertz, or other frequency corresponding to that of the transmitted ultrasonic waves.
The now filtered and strong signal is next fed to a detector circuit 49 which converts the signal from amplifier 48 into a fluctuating DC voltage.
It will be appreciated that the signal received from the transducer 40 will be amplitude modulated compared to the transmitted signal, as the received signal will comprise reflected signals from objects within the protected area. The nature of the modulations will depend on the nature of the reflected waves which will in turn depend upon the nature of the objects in the protected area.
It can be seen that the amplifier 48 and detector 49 are part of a gain control network, which includes further circuitry indicated at 50 and 51.
The circuitry 51 provides a reference signal to a comparator 52 according to the strength of the signal derived from the output of amplifier 47.
This is because the signals reaching the input amplifier 47 from remote objects are weaker than the signals reflected from the nearer objects. The variable reference signal from the circuitry 50 provides the means for the comparator 52 to identify the pattern of the protected area. The reference signal is also controlled by the circuitry 51 from the microprocessor 1 5. Depending on an input to circuitry 51 from the microprocessor 1 5, the gain at the output of comparator 52 is raised until the number of echo levels switched by switch 53 reaches a predetermined number.
There is a four bit input to circuitry 51 from the microprocessor and thus the gain may be adjusted to any of sixteen levels. There is a four bit input to circuitry 51 from the microprocessor 1 5 and thus the gain may be adjusted to any one of sixteen levels.
The comparator 52 compares the processed signal from detector 49, with the original signal after initial amplification by amplifier 47, fed via circuitry 50 to the comparator 52, to determine whether the detected signal is significant. This indicates that an echo has been received by transducer 40, above any interference or background noise. When a significant signal is present, the comparator 52 opens a switch 53 to permit the signal to pass to the microprocessor 1 5 via a line 54.
Detailed operation of the control section 20 will now be described with reference to Figure 5.
Control SectionThe control section 20 has a main control circuit 60 which has five inputs and two (three notional) outputs.
A first input via line 61 is from the battery power source 1 6 to provide power, and a second input is from the filter and wave shaping circuitry of the interface 17, via line 24. The remaining three inputs are from the microprocessor 15, one of which feeds, via line 62, an arm or disarm instruction to circuit 60, another of which feeds, via line 63, a signal to set the rate of the on/off periods of the ultrasonic analogue section 1 9, and the last of which feeds, via line 64, an "end of cycle" signal to signal the end of the programme cycle of the microprocessor 1 5.
The outputs of the main control circuit 60 are as follows.
A first output is the signal via line 43 to provide power to switch the oscillator 41 of the transmitter section of the ultrasonic analogue section 19, on and off.
Thus upon receipt of the "wake up" signal, via line 24, and assuming the system to be armed, the output via line 43 causes the transmitter section T' of the ultrasonic analogue section 19, to be switched on.
The other output via line 65 from the main control circuit 60, provides power to both the receiver section R' of the ultrasonic analogue section 1 9, and the microprocessor 15, and a "reset" signal to the microprocessor.
However, the power applied to the ultrasonic analogue section 1 9 and microprocessor 15 and reset signal to the microprocessor, are delayed by delay circuit 66 to enable the transmitted ultrasonic sound wave to be transmitted into the protected area and reflected back to receiver R'.
By the time the reflected wave is received by the ultrasonic transducer 40, the receiver section R' of the ultrasonic analogue section 19 is rendered operative via the output from power line 46, and at the same time the output from the main control circuit 60 via line 43 to the transmitter section of the ultrasonic analogue section 19, is discontinued.
Simultaneously, power is fed via a line 68 to the microprocessor 1 5 which then processes the signal.
The purpose of reset signal is to set and re-set the microprocessor 1 5 at the beginning of each programme cycle and at the end of the programme cycle when an "end of cycle" signal is given. Delay circuit 69 prevents the reset signal being applied before the microprocessor 1 5 is fully powered via line 68. At this time, delay circuit 67 has no function.
Conversely, when power to the microprocessor and analogue section 1 9 is switched off, delay circuit 67 prevents power being removed before the microprocessor 1 5 is completely re-set. At this instant the delay circuit 69 has no function.
The signal from the delay circuit 67 to the ultrasonic analogue section 1 9 and microprocessor 1 5 via line 68, is regulated by a power supply circuit 75 which ensures a steady even non fluctuating voltage is applied to the microprocessor 1 5 and ultrasonic analogue section 1 9.
The control section 20 also includes a walk test LED indicator circuit 76 which receives a signal from the microprocessor via a line 77 to cause a light emitting diode of the control section to light up when the detector unit detects an intruder during a test cycle which may be carried out during a calibration period immediately after the system is first actuated.
It will be appreciated that when the system is unarmed, the control secton 20 has to remain in a "live" state so as to respond to any "wake up" signal from the control unit 11.
However, when in this state, the control section 20 consumes minimal electricity and thus battery life is prolonged.
When armed, because the detector unit is microprocessor controlled, again minimal battery power is consumed.
Control UnitAs mentioned above, the control unit 11 comprises a keyboard having a plurality of keys 13.
As shown in Figure 6, twelve keys are provided, nine of which are marked with a number 1 to 9, and are used to enter a code which will be recognised by the address and priority matrix 21 of the detector unit 1 0.
The remaining three keys are instruction keys to "arm" (key 'on') or disarm (key 'off') the system, or to override the detection unit and cause the alarm unit 12 to give an alarm.
The twelve keys provide a seven bit input 79 to an encoding and transmitting circuit 80 which encodes the signal to a pulse position modulated signal comprising a series of binary levels which then pass to a buffer circuit 81 similar to circuit 37 of Figure 3, to enable the signal to be passed to a coil 82 similar to coil 25 of Figure 3 to transmit the encoded signals into the mains wiring 18.
The control unit 11 also has a receiver section comprising a receiving and filtering circuit 83 which receives incoming acknowledgement signals from the coil 82.
The receiver circuit 83 only operates when the transmitter is not transmitting, and thus a control signal is fed via a line 84 to achieve this.
Upon receipt of a predetermined acknowledgement signal, a buzzer 85 is caused to sound, or another audible or visual indicating means caused to indicate the incoming signal.
Alarm UnitThe alarm unit is shown in Figure 7, and is microprocessor controlled, the microprocessor being shown at 90. The unit includes an interface 91 between the mains wiring 18, similar to that shown at 1 7 in Figure 2, although no facility is provided to transmit signals onto the mains 1 8.
The interface 91 has an input coil 92, receiver and filtering circuits 93, and further filter and wave shaping circuits 94 to discriminate between the main signal and any interference or other parasitic signals in the mains, and an alarm signal given by the detection unit 10 or control unit 11.
The interface 91 may give three outputs. A first output provides a "wake up" signal in line 95 which is sent to a control section 100 which sends a reset signal via line 99 to switch the microprocessor 90 on, and a pulse position modulated signal (PPM signal) to the microprocessor 90 along a line 104, which signal is processed by the microprocessor 90 to determine whether to switch on alarm 101, and an interrupt signal along line 105 which is processed by the microprocessor 90 to determine whether to switch the alarm 101 off or not.
Power for the interface 91 and the remainder of the unit 12 is via a power pack 95 comprising batteries which are recharged via a trickle charger from the mains, via line M.
Power is fed from the pack 95 to the interface 91 via a line 96.
The unit 12 further comprises a power regulating circuit 97 to ensure an even nonfluctuating power supply to the microprocessor 90 via line 98.
Upon actuation of the alarm 101, the microprocessor 90 is programmed to actuate the alarm for a preselected time, for example three minutes, and then to switch the alarm 101 off.
This is achieved by the microprocessor 90 sending an "end of cycle" signal along line 102 to the control section 100 which then sends a reset signal along line 99 back to the microprocessor 90.
In another example, the alarm 101 may be arranged to be switched on for a different period of time or continuously until an interrupt signal is received by the interface 91.
The alarm 101 is fed with power via a line 108 from the microprocessor 90, and in the present case comprises an audible warning such as an alarm bell but could comprise a visual warning, or a means to actuate a remote alarm via a telephone line, cable or radio link, such as an alarm within a police station.
A memory 109 contains a decoding programme to decode incoming PPM or "interrupt" signals to determine whether the alarm 101 should be switched on or off.
Preferably, the alarm unit 12 is arranged only to respond to a predetermined alarm signal recognised by an address matrix 110, which matrix may also be arranged to recognise only a coded alarm signal from the control unit 11, or the detection unit 1 0.
Operation of the system will now be described.
OperationThe units 10, 11, 12, are each connected to the mains wiring 18, for example by beingprovided with plugs which are inserted into various mains outlet sockets.
The detector unit TO is located within the area to be protected whilst the location of theremaining units 11, 12, is not critical.- In oneexample, the control unit 11 may be plugged intoa mains socket outlet near a door of a building so that the operator can leave the building during an initial callibration period without any risk of actuating the alarm.
Next, the operator inputs a predetermined code into the keyboard 11 by depressing the requisite keys. For example, the code may be a four digit number such as 1 346, which the code would be unique for the system and thus only known to authorised persons.
Next, the operator presses an instruction key to "arm" the system i.e. the 'on' key shown in Figure 6.
The input includes an address code i.e. the code number and an instruction code i.e. "the arm" instruction and this signal is then converted in the control unit 11 to a command signal which is transmitted into the mains wiring 18 along which it travels to the detection unit 10.
Upon receipt of the command signal, the detection unit 10 "wakes up" from its quiescent state and begins to transmit and receive ultrasonic waves. Providing that the command signal received is correctly identified by the address and priority matrix 21, the detectiori unit 10 issues an acknowledgement signal which is received by the control unit 11 and registers as a short buzz, bleep, or whatever indication is given on the indicator 85.
The detector unit 10 then initiates a callibration period.
There is an inbuilt delay, for example 45 seconds, before any alarm signal can be generated by the unit 10, which should give an operator ample time to check that the systeni is operating and to leave the protected area.
Initially, a signal derived from an echo of the ultrasonic sound waves, is processed by the microprocessor 1 5 and selected information.
therefrom e.g. the wave form of the reflected waves, is. programmed into the memory 22.
Subsequent echoes are similarly processed and compared by the microprocessor, with the stored programme until any variation is sensed.
During the delay period, if any significantly different echo is noticed,-the light emitting diode will light up, but no alarm signal will be given.
Thus an operator may perform a walk test to check whether the system is operating, by entering the protected area. The operator will be detected by the. detector unit 10 as an intruder, because the echo patterns will change.
At the end of the delay period, any subsequent intrusion into the protected area will cause an alarm signal to be generated by the detector unit 10 to actuate the alarm unit 12.It will be appreciated that once the system is armed, that the circuit 11 can be disconnected from the mains until it is required to give a disarm or override instruction as hereinafter explained.
The detector unit 10 once armed, will cycle between transmitting and receiving ultrasonic waves at a rate dependant upon the programming of the microprocessor 1 5 i.e, the signals sent to the control section 20 via line 63, the cycles being separated by "end of cycle" and "reset" signals.
The detector unit 10 may subsequently be arranged to recalibrate itself regularly for example every three or four minutes, to compensate, for example, for changes in temperature in the protected area which could effect the reflection characteristic of the echoes.
If an intruder enters the protected area, selected information from the echo detected will differ from that present in the memory 22. As adouble check, the system may be arranged torecalibrate itself immediately once again and to again analyse subsequent echoes.
Thus any change in position of the intruder will be sensed, and an alarm signal will be generated and transmitted along the mains wiring to the alarm unit 12.
Upon the alarm unit 12 receiving an alarm signal from the detector unit 10, the unit 12 "wakes up" and the incoming PPM signal is decoded by the microprocessor 90 using the programme stored in the memory 109, and, assuming the decoded signal is recognised by the address matrix 110, the alarm 101 is operated for a predetermined period of time. At the end of that time, the alarm 101 is rendered inoperative and the unit 12 is returned to a quiescent state.
Of course, if the moving intruder is still present in the protected area, the sequence will be repeated.
If it is required ta interrupt the alarm whilst the alarm is being given, an operator can, by inserting the correct code on the control unit 13; and thenby depressing the "disarm" key "off" issue an"interrupt" signal which would be recognised by the alarm unit and the alarm will be stopped.
Further, if an operator wishes to overridedetection unit 10, and operate the alarm unit 12 direct, he can achieve this by entering the codeinto the control unit 11 and pressing the 0 key togenerate the appropriate PPM alarm signal in thecontrol unit 11 which is transmitted to the alarmunit 12 to cause the alarm to operate.
Where more than one detector unit 10 isprovided, of course more than one area can beprotedted. Each unit 10 may be armed byinsertion of the correct code and instructions on the control unit 11. Each unit may be arranged toprovide an acknowledgement signal in turn, sothat the operator knows that each unit hasresponded.
The control unit may be arranged to warn theoperator should the condition of the battery inthat unit reach a row level, for example byoperation of the buzzer 85 or other indicator.
Similarly, the detector and alarm unit 10, 12,may also have means to warn of a low batterycondition, should this occur.
As well as acknowledging "arming", thedetector unit 10 may be arranged to acknowledge"disarm" so that the operator will know that if heenters the protected area, a false alarm will not begiven.