WO1991016219A2

WO1991016219A2 - Security device

Info

Publication number: WO1991016219A2
Application number: PCT/GB1991/000598
Authority: WO
Inventors: Surrendra Patel
Original assignee: Krypton Car Security Limited
Priority date: 1990-04-18
Filing date: 1991-04-17
Publication date: 1991-10-31
Also published as: GB2244163A; GB9108250D0; GB9008640D0; WO1991016219A3

Abstract

A vehicle security device uses a micro-controller (10) to interpret signals received from sensors (11, 18, 19) by comparison of characteristics of those signals with stored values, thereby discriminating between hostile and non-hostile stimulation of the sensors. Door locking relays (25) are provided to perform central door-locking of the vehicles doors and windows, information about the operation of the central locking of different vehicles being stored in a memory of the micro-controller and selected, according to the model of the vehicle, by a user selecting the position of a hexadecimal switch (26).

Description

SECURITY DEVICE

The present invention relates to a security device and particularly, although not exclusively, to a security device for a vehicle.

Conventional vehicle security devices or alarms may well activate even though no hostile act has been committed towards the vehicle or its contents. In the case of alarms which detect movement or shock to the vehicle, this unwanted activation may be due to another heavy vehicle passing by the protected vehicle and causing it to rock on its suspension due to the air-pressure wave associated with the passing vehicle.

In the case of alarms which detect changes in voltage in the vehicle's electrical systems, (such as occur when an attempt to start, the vehicle is made or a door of the vehicle is opened causing the interior light to turn on) , the unwanted activation may be due an electric fan switching on due to a rise in temperature. The switching on of the fan causes a voltage drop across the vehicle battery which triggers the alarm.

Activation of an alarm in non-hostile conditions is a nuisance to the general public since loud noises and flashing headlamps, etc typically accompany such an activation. In addition to this nuisance factor, the battery of the vehicle may lose much of its charge after several accidental activations.

Typically this kind of problem may be observed in car parks at airports, where the pressure wave associated with the take-off of a large aeroplane is often sufficient to activate alarm devices in several of the parked vehicles. In prior vehicle alarm systems a sensor such as a shock sensor stands alone. When it is triggered it sends a signal to a controller. The two possible conditions are

SIGNAL or NO SIGNAL. If the controller has been sent a signal, it activates a siren.

Unwanted activation e.g. due to non-hostile interference is lessened to some degree by reducing the sensitivity of the sensor. Problems with de-sensitising are that if the sensor is made too insensitive it may not always respond when it should, i.e. when a genuinely hostile act has been committed or, conversely if the sensor is not de-sensitised sufficiently, unnecessary activation may become too frequent.

Accordingly, preferred embodiments of the present invention aim to provide a security device which is less susceptible to non-hostile activation.

According to one aspect of the present invention there is provided a security device for a vehicle, the security device comprising a sensor, processing means and alarm means, the processing means being arranged to process a signal from the sensor and to operate the alarm means according to a characteristic of the signal from the sensor.

Preferably the processing means operates the alarm means if the characteristic of the signal from the sensor is indicative of a hostile stimulation of the sensor.

Alternatively or additionally the processing means may not operate the alarm means if the characteristic of the signal from the sensor is indicative of a non-hostile stimulation of the sensor. The processing means may compare the characteristic of the signal with a predetermined value to determine whether the characteristic is indicative of a hostile or a non-hostile stimulation of the sensor.

Preferably the processing means operates the alarm means if the characteristic of the signal exceeds a predetermined value.

Alternatively the processing means may operate the alarm means if the characteristic is below a predetermined value.

In a preferred arrangement the processing means converts an analogue signal from the sensor into a digital signal.

The characteristic may be an amplitude of the signal.

The characteristic may be a frequency of the signal.

The signal may consist of a number of discrete pulses and the characteristic may be the magnitude of the pulses.

The signal may consist of a number of discrete pulses and the characteristic may be the number of the pulses present in a predetermined time period.

Preferably the processing means comprises a micro- processor.

Preferably there is provided a plurality of sensors.

The sensor may comprise transmitting means arranged to transmit a transmission signal, receiving means arranged to receive a reception signal and detector means arranged to detect differences between the transmission signal and the reception signal to produce a difference signal, in which the signal supplied to the processing means is the difference signal.

The sensor may comprise an ultrasonic sensor arranged to transmit and receive ultrasonic signals.

One of the sensors may comprise a voltage sensor arranged to sense a change in voltage of a voltage source.

One of the sensors may comprise a shock sensor.

Preferably the alarm means comprises a siren.

According to a second aspect of the present invention there is provided control means for controlling an electrical door-locking circuit of a vehicle, the control means comprising processing means, a memory and switching means, the memory being arranged to store information about an operating characteristic of the electrical door- locking circuit, the processing means being arranged to operate the switching means in accordance with the stored information in the memory.

Preferably the memory is arranged to store information about a plurality of operating characteristics of the electrical door-locking circuit.

Preferably the memory is arranged to store sets of information about the operating characteristics of electrical door-locking circuits of different vehicles. The stored information may include information about the type of electrical signal required to operate the door-locking circuit.

The stored information may include information about the duration of the electrical signal required to operate the door-locking circuit.

Preferably the control means is arranged to control the locking and the unlocking of a door of a vehicle.

Preferably the control means is arranged to control an indicator lamp of a vehicle.

Preferably the switching means comprises a relay.

Preferably there is provided control means having only two electrical connections to the door-locking circuit, one to provide a lock signal to the locking circuit and one to provide an unlock signal to the locking circuit.

Preferably the control means is arranged to control the closure of a window of a vehicle.

According to a third aspect of the present invention there is provided a method of operating a security device for a vehicle, the security device comprising alarm means, a sensor and processing means, the method comprising converting an analogue signal from the sensor into a digital Signal, processing the digital signal and operating the alarm means if a characteristic of the digital signal is indicative of hostile stimulation of the sensor. Preferably the method comprises comparing the characteristic of the digital signal with a pre¬ determined, stored value.

The characteristic compared may be a frequency of the digital signal.

Alternatively or additionally, the characteristic compared may be an amplitude of the digital signal.

The characteristic compared may be a pulse-height of the digital signal.

The characteristic compared may be a number of pulses in a sample of the digital signal.

Preferably the method comprises transmitting a transmitted signal and monitoring a received signal from a sensor and identifying whether the received signal is indicative of a hostile stimulation of the sensor by temporarily ceasing transmission of the transmitted signal and monitoring any received signal, the persistence of a received signal being an indication that the received signal is not indicative of a hostile stimulation of the sensor.

According to a fourth aspect of the present invention there is provided a method of recording the activity of a security device for a vehicle, the method comprising storing in a memory of the security device information about hostile stimulation of a sensor of the security device.

The invention also includes a vehicle incorporating a security device or employing a method substantially as herein described with reference to the accompanying drawings.

Specific embodiments of the invention will now be described by way of example, with reference to the accompanying drawings.

Figure 1 is a schematic circuit diagram according to one embodiment of security device.

Figure 2 is a flow diagram of a verification routine for an ultrasonic sensor of the security device of Figure 1.

Figure 3 shows variations in the voltage of a vehicle battery due to, in Figure 3a the activiation of a courtesy lamp, and in Figure 3b the activation of a radiator fan.

Figure 4 is a flow diagram of a verification routine for a voltage sensor of the security device of Figure 1.

Figure 5 is a flow diagram of a verification routine for a shock sensor of the security device of Figure l.

Figure 6 is a schematic circuit diagram of door- locking circuitry of the security device of Figure 1.

Figure 7 is a flow diagram of a setting mode of the security device of Figure 1 and

Figure 8 is a flow diagram of a diagnostic mode of the security device of Figure 1.

Referring particularly to Figure 1, a itiicro- controller 10 controls the operation of a security device for use in a vehicle (not shown) according to one embodiment of the present invention.

An ultrasonic sensor 11 includes a transmitter 12 driven by a 40khz driver 13, and a receiver 14 the output of which is fed to a tuned filter 15 and then into a detector 16. The 40khz driver 13 received a 40khz signal from a micro-controller 10 and both the 40khz signal from the micro-controller 10 together with the output of the tuned filter 15 are fed into the detector 16.

The detector 16 is arranged to detect any disturbances in the received ultrasonic signal, which disturbances might be caused by a moving object in the cabin of the vehicle. The output of the detector 16 is fed into a first analogue-digital converter AD1 of the micro-controller 10.

A shock sensor 18 is connected to a second analogue- digital converter AD2 of the micro-controller 10.

A courtesy light sensor 19 detects a fall in the voltage across a battery of the vehicle due to the operation of a courtesy light of the vehicle. Such an operation of the courtesy light of the vehicle would occur in the event that a door of the vehicle was opened. When this happens, a signal is sent from the courtesy light sensor 19 to the micro-controller 10 via a third analogue- digital converter AD3.

Input switch sensors 20 provide a signal to the port P2 of the micro-controller 10 in the event that the ignition of the vehicle is switched live or in the event that either the boot or bonnet of the vehicle is opened. An internal siren 21 is driven by a siren driver 22 which is activated by the micro-controller 10 in the event of triggering of the security device.

Similarly, door interlock relays 23 are driven by a driver 24 from a port P3 of the micro-controller 10. The door-interlock relays are arranged to operate the central locking of the doors and boot of the vehicle.

The micro-controller 10 has an electrically erasable programmable read only memory 25.

A Hexadecimal switch 26 is connected to the micro¬ controller 10 at its port P4.

Relay outputs 27 are connected to micro-controller 10 via its port P5, which relay outputs include outputs to the siren of the vehicle, external LED's located in the cabin of the vehicle, an ignition-cut-out of the vehicle, and right and left indicators of the vehicle.

In addition, the device has a local power supply (not shown) which provides the necessary power for the device in the event that its fusible link with the battery of the vehicle is broken.

The security device is armed/disarmed by a user operating a small radio remote control transmitter which usually takes the form of a keyfob (not shown) .

The purpose of the ultrasonic sensor 11 is to detect any unwanted intrusion into the vehicle. The transmitter

12 and receiver 14 are mounted in the cabin of the vehicle. The micro-controller 10 produces a 40khz signal which is fed into the driver 13 to drive the transmitter 12. The transmitted 40khz ultrasonic signal is reflected from the inside of the cabin of the vehicle and is received at receiver 14. The received signal is then passed through a tuned filter 15 and finally into the detector 16. The original 40khz signal produced by the micro-controller 10 is also fed into the detector 16.

When no moving object is present in the cabin of the vehicle the received signal is a sine wave of substantially the same frequency i.e. 40khz, as the transmitted square-wave signal. However when there is a moving object in the cabin of the vehicle the received signal comprises the 40khz siren wave with a signal of different frequency superimposed on it due to doppler effects on the 40khz signal as it is reflected from the moving object. When this composite signal is fed into the detector 16 is subtracts the transmitted 40khz component to leave only the "difference" signal caused by the moving body. This difference signal is then amplified and fed into the analogue-digital converter AD1 of the micro¬ controller.

The difference signal, which indicates that something is moving in the cabin of the vehicle, could arise due to a moving body of air or due to an insect or some other non-hostile source. Because of this, the micro-controller 10 performs a verification routine as shown in Figure 2, to substantially reduce the risk of unwanted, non-hostile activation of the security device.

Referring to Figure 2, the digitised signal is sampled by the micro-controller, and the number N_! of pules in time Tj which are greater than a pre-determined threshold are counted. If the number of pulses is less than 50 the micro-controller returns to its counting (this corresponds to an_. idling condition) . If, however, the number of pulses above the threshold level is greater than 50 in time T_lf the micro-controller shuts down the transmitter by ceasing its 40khz output. The number N₂ of pulses in time T₃ which are greater than the threshold are counted. If the count is greater than 10 the micro¬ controller delays momentarily, before re-starting the transmitter and returning to the "idle" counting.

The reason for this shut-down is that, if the pulses being picked up represent signals induced in the wiring of the device due to a non-hostile source such as a high- power electromagnetic signal operating in the vicinity (or even, it has been shown, to a radio signal from e.g. a taxi) these pulses will persist when the transmitter is shut down. If, however, when the pulses being picked up due to a signal from a moving body in the vehicle, then the pulses will cease when the transmission ceases.

Therefore if the number of pulses above the threshold level in time T₃ are less than 10 the micro-controller re¬ starts the transmitter and counts the number N₃ of pulses above the threshold in time T. If N₃ is greater than 10 there is deemed to be a hostile intrusion into the vehicle and a valid trigger situation arises. The micro¬ controller 10 will then activate a siren 21, a vehicle siren and vehicle indicators, and ignition cut-out through relay outputs 27.

The purpose of the threshold levels, below which pulses are effectively ignored, is to allow for the inevitable effect of noise on the system. The threshold levels of the pulses and the threshold numbers of the pulses are pre-deter ined and are stored in memory locations of the micro-controller as described in more detail below. The threshold levels and numbers have been selected by the inventor in such a way as to virtually eliminate the likelihood of triggering of the security device in non-hostile conditions. For example, a body of moving air in the vehicle cabin will provide a "difference" signal by doppler shifting the transmitted 40khz signal to some extent. However, the pulses derived from the difference signal due to a moving body of air will have a slower rise time and a longer duration than those due to e.g.a moving human hand which are shorter. There will therefore be fewer of them in a given time period. The inventor has investigated the difference signals produced by different moving bodies and has chosen the values of the threshold numbers and threshold levels accordingly to reduce the risk of unnecessary triggering of the device.

Whereas prior art ultrasonic detectors simply amplify the "difference" signal and if it is above a certain level activate the alarm means, the signals received by the ultrasonic detector of this embodiment of the present invention are interpreted by the micro-controller which discriminates between those which should give rise to a valid triggering of the device and those which should not.

An alternative to the above-described transmitter /receiver arrangement is a single transmitter /receiver which puts out a pulse train and then "listens" to detect the reflected signal. This so called "echo location" system is known in the field of ultrasonic detection in ve icle alarm systems- However, wh r ^.ς before the "difference" signal between the transmitted and received signals is merely amplified and, where it exceeds a threshold level, activates an alarm of the security device according to an embodiment of the present invention uses the echo location system with a verification routine similar to that described with reference to Figure 2.

As shown in Figure 1, the courtesy light sensor 19 monitors changes in the voltage of the battery of the vehicle, such as would occur when a door of the vehicle was opened and the courtesy light of the vehicle was activated. As compared with prior art security devices which operate on this principle and which merely detect the presence or absence of a voltage drop across the battery of the vehicle, this embodiment of the present invention involves the measuring of the degree to which the voltage across the battery of the vehicle has dropped and the length of time for which it has dropped. This helps to overcome the problem of unwanted activation of the device due to a drop in the voltage across the battery of the vehicle caused by for example activation of the vehicle's electric fan.

The courtesy light sensor 19 monitors the voltage experienced at the positive power lead of the security device. Changes in this voltage are amplified and the amplified signal is fed into an analogue-digital converter AD3 which digitises the signal.

Referring to Figure 3, this shows the fall in voltage across a vehicle battery from its operating voltage due to activation of the courtesy light (Figure 3a) and activation of the radiator fan (Figure 3b) . Although the signals appear similar the scale is very different. The signal shown in Figure 3a represents the courtesy light being activated (eg by opening a door of the vehicle) at time T=T₀, almost instantaneously, falling to a value of -18.5mV and then quickly recovering to less than half of that voltage drop at T=Tj. The signal shown in Figure 3b represents the radiator fan being activated at time T=T₀, falling almost instantaneously to a value of - 283mV and then partially recovering to approximately half of that voltage drop at time T=T,.

The reason for the fall in voltage across the vehicle battery is due to a current being drawn. The current drawn by a courtesy light bulb is small compared to that drawn by a radiator fan (i.e. initially -18.6mV as compared with - 283mV) . The initial current drawn (eg T- T₀) is much greater than that drawn in the steady state (eg T-T_j) since, in the case of the courtesy light, the bulb element is initially cold and therefore of a lower resistance so more current is drawn and more voltage is dropped. When the element becomes hot it has a greater resistance and so draws less current. Hence there is a lower voltage drop.

The signal from the courtesy light sensor 19, digitised by the analogue-digital converter AD3 is sampled by the micro-controller 10. A verification routine as shown in Figure 4 is carried out on the signal, again to reduce the risk of non-hostile triggering of the device.

Referring to Figure 4, the micro-controller firstly samples the digital signal from AD3. If the signal does not exceed a pre-determined threshold level the micro¬ controller continues sampling the signal. If, on the other hand, the signal exceeds a pre-determined threshold level the micro-controller checks whether the signal is maintained for a pre-determined time T_λ. if not then the micro-controller returns to its sampling. The purpose of this is to eliminate triggering, due to a short, high spike of noise. If the signal is maintained above the threshold level larger than T_x the signal checks whether the signal is maintained for a time T_y where T_y > T_x. If the signal is maintained for a time greater than or equal to T_y the micro-controller returns to its sampling. If not, a valid trigger condition has been reached and the micro-controller will initiate the various alarm procedures indicated above. The times T_x and T_y are chosen such that if the signal is maintained above the threshold level for a time greater than or equal to T_y the signal is likely to correspond to a voltage drop caused by activation of the fan.

If the signal persists longer than T_x but not as long as T_y the signal is likely to represent a voltage drop caused by activation of the courtesy light and is therefore probably indicative of a hostile intrusion into the car.

The threshold levels and times T_x and T_y are chosen according to data produced from tests performed on different cars.

As an alternative to the courtesy light sensor (in the case that this was unsuitable for whatever reason) the micro-controller can be fed by signals from auxiliary sensors which are hard-wired to either the courtesy light circuit of the vehicle or to mechanical switches on the doors etc of the vehicle. Again the signals would be digitised, sampled and, if a threshold level was exceeded for a time greater than a pre-determined interval, the micro-controller would reach a valid triggering condition.

Referring again to Figure 1, shock sensor 18 is arranged to detect physical shocks to the vehicle, such as might be caused by breaking of a window of the vehicle or some other hostile act. The shock sensor 18 comprises a custom made piezo-electric transducer. A piezo-electric crystal is housed inside a plastic mounting case which is mounted inside a protective case of the security device (not shown) . When the piezo-electric crystal experiences a shock, due for example, to a hammer blow on the car, the crystal becomes partially deformed and a tiny voltage signal appears across it. This voltage signal appears very noisy due to the sensitivity of the sensor. The noisy signal is "cleaned" in the sensor, mainly by filtering off to ground any very high frequencies, and the "clean" signal is fed into an analogue-digital converter AD2 of the micro-controller. The digitised signal is then sampled and the verification routine is performed by the micro-controller to reduce the risk of non-hostile triggering of the device due to eg vibrations caused by a passing heavy lorry.

Referring to Figure 5, the micro-controller compares the sampled signal to a pre-determined threshold level. If the signal does not exceed this level the micro¬ controller continues sampling. If the threshold level is exceeded the micro-controller counts the number of pulses above the threshold level in a time T,. If this number is greater than a pre-determined valve N the micro-controller delays for a short time and then returns to its sampling. If, on the other hand the number of pulses above the threshold level in time Tj is less than N there is a valid trigger condition and the micro-controller commences an alarm procedure as described above. The value of the threshold level is chosen so as to reduce triggering of the device due tc noise such as electrical signals induced in the wires of the device by strong local electric fields eg radio transmissions. This is necessary due to the very high sensitivity of the apparatus. The pre-determined number N is chosen so as to reduce the likelihood of the device being triggered due to a heavy lorry passing or roadworks taking place nearby. In these cases, there would be a periodic vibration which the shock sensor would pick up and which would be effectively ignored by the micro-controller because the pulse count would exceed N. If, however, a person breaks a window of the vehicle or kicks the vehicle, the resulting signal produced by the short sensor would have a small number of high peaks before dying away, but would not be periodic and so the pulse count would be below N causing a valid triggering of the device.

Security devices which use a radio remote control unit are often used to operate the central locking of a vehicle. Prior security devices typically include a universal locking circuit which is capable of operating four varieties of vehicle locking circuitry. Usually, such prior devices include seven wires which must be configured.

This embodiment of the present invention uses only two wires to connect to the central locking circuit of the vehicle. When the central locking of the doors (and, in some cases closure of the windows) is required to take place upon arming of the security device (and, also unlocking etc upon disarming) it is usually desirable to provide a flash of the indicator lamps to indicate that the security device is armed and the doors locked. In order to achieve these functions it is necessary to take account of five characteristics of the particular vehicle, namely:

i. Whether the locking pulse should be a positive or negative-going pulse. ii. Whether the unlocking pulse should be a positive or negative-going pulse.

iii. The duration of the locking pulse required.

iv. Whether there is a separate circuit for window- closure or whether this is automatically achieved by the locking/unlocking pulses.

v. The polarity of the indicator lamps.

Prior security devices use hard-wiring to enable the central locking of the vehicle to be operated remotely ie. when the device is installed several wires must be connected appropriately to allow for correct operation of the circuit, dependent upon the make and model of the car.

This embodiment of the present invention uses the circuit shown in Figure 6 to achieve the central door locking functions, along with window closure and indicator activation using only two wires A and B. Exceptionally there is the requirement of a third wire C for vehicles which have a separate window closure circuit (e.g Mercedes) which must be energised for closure of the windows as opposed to other vehicles which utilise the door locking circuit to automatically close any open window.

Referring particularly to Figure 6, a hexadecimal switch 30 is connected to micro-controller 31 via four bit-lines BL_! to BL₄. The hexadecimal switch 30 has 16 possible different "positions" or 4-bit words which can be read by the micro-controller 31. The micro-controller 31 reads the setting of the hex switch when the security device is initially connected and afterwards stores the 4- bit word, corresponding to the setting of the hex switch 30 in its internal memory (not shown) . Each different 4- bit word corresponds to a set of memory addresses in the micro-controller read-only memory 32 in which are written the five abovementioned characteristics for each model of car. For example if the hex switch 30 is set to position 1 which causes the micro-controller to read a 4-bit word of 0001 when first connected, this will correspond to a set of memory addresses in the ROM 32 in which is written the following data:

i. (locking pulse) POSITIVE 12V ii. (unlocking pulse) POSITIVE 12V iii. (duration) 0.7 sec. iv. (separate window circuit?) FUNCTION NOT

AVAILABLE v. (polarity of indicators) POSITIVE

That data tells the micro-controller that it must apply positive 12V pulse for 0.7 seconds to lock the doors, there being no provision for remote window-closure and that the indicators operate on a positive polarity. Accordingly when the remote radio control transmitter is activated to remotely lock the vehicle doors, the micro- controller will know to activate the left and right indicators relay 33 with a positive polarity selected by the polarity selector 34, the positive (locking) driver 35 providing a pulse of +12V switched through the locking relay 36 for 0.7 seconds to wire A, connected to the central door-locking circuit of the vehicle. Similarly if the radio remote control transmitter was used to unlock the vehicle door the micro-controller would activate the left and right indicators relay 33 with a positive polarity selected by the polarity selector 34, the positive (unlocking) driver 37 providing a pulse of +12 volt switched through the unlocking relay 38 for 0.7 seconds to wire B, connect to the central door-unlocking circuit of the vehicle.

The negative (locking) driver 39 and the negative (un-locking) driver 40 are to provide OV through the locking/unlocking relays to the locking/unlocking circuits if the vehicle-model requires this.

A short-circuit relay 41 is provided as some vehicle- models require the locking/unlocking relays to be shorted during non-use. A separate window-closure relay 42 is provided to operate separate window-closure circuits through wire C for those models which have them.

Once the micro-controller 31 has first read the 4-bit word of the hex switch at initial connection it ignores the hex switch and merely relies upon the 4-bit word stored in its internal memory. This is useful to prevent any tampering with the central locking by altering the position of the hex switch. The only time that the micro¬ controller 31 will re-read the hex switch 30 is when there has been a disconnection and a re-connection of the security device. It has been found that the central door locking characteristics of most popular vehicle-models can be catered for in just 11 of the 16 positions of the switch 30 (or 11 of the 16 sets of addresses in the micro controllers ROM) . The data for the five characteristics for each of the 11 hex-switch-settings is programmed into the micro-controller ROM by the manufacturer prior to installation. When the security device is installed the installer need only consult a chart supplied with the device to learn which position the switch must be set to for that particular vehicle model. The two (or, in exceptional cases, three) wires are then all that need to be connected for the central locking operation.

The two positive drivers 35 and 37 are arranged to have current sensors (not shown) which are sensitive to very high currents such as might be drawn if the door interlocking unit was connected wrongly during installation causing a short-circuit. If the current sensors detect a rising current of too great a magnitude the drivers shut down until that current is no longer detected. This is to protect the semiconductor devices. When the current sensors cut-out a diagnostic signal is sent to the micro-controller to tell it either not to drive the drivers or to pulse the drivers, as required.

Again referring to Figure 1, the electrically- erasable programmable read-only memory (EEPROM) 25 of the micro-controller 10 stores the values of the preset sensitivity threshold levels of the various sensors. It is intended that these levels should be programmed into the memory at the manufacturing stage. A single variable resistor may be employed to enter each of the sensitivity levels and this is accomplished using the routine schematically shown in Figure 3. It should be pointed out that, once the values have been written in the memory, the micro-controller does not "see" the resistance of the variable resistor.

The device is calibrated by using a single potentiometer which directly connects to an analogue- digital converter input of the micro-control]er 10_ This has two advantages:

1) A physically large potentiometer can be used making the set up mechanically straightforward. 2) The potentiometer can be effectively disabled after set up so that it is not subject to inadvertent or illicit interference.

The unit operates by storing a value of the potentiometer during calibration and using this value as an internal sensitivity parameter when reading the input sensor information.

The threshold levels of sensitivity for each sensor are entered into the electrically erasable programmable and only memory (EEPROM) 25 using a potentiometer. The common connection of the potentiometer is connected to an analogue-digital converter input of the micro-controller and the other two connections of the potentiometer are connected to OV and 5V respectively.

Prior to installations of the device, the manufacturer calibrates each sensor by entering into the EEPROM 25 a range of valves which the threshold level of that sensor may assume using a potentiometer. A D.C. Voltage level is converted to a digital value in an 8-bit word by the analogue-digital converter. If the range of valves for the particular sensor's threshold level is, for example, required to be 1.5V to 4.0V, then the micro¬ controller stores the 4.0V value as the minimum digital value 0 (or in binary 00000000) and the 1.5V value as the maximum digital value 255 (ie binary . The micro-controller, having the maximum and minimum valves for the threshold level stored in its memory, then proceeds to create a table in its memory for each binary number between 00000000 and corresponding to 254 voltage levels between 4.0V and 1.5V. This procedure is repeated to provide a range of threshold valves for each sensor. When the actual threshold level is chosen during installation the table is stored in a set of memory addresses ascribed to that particular sensor of the security device and the potentiometer is used again to ascribe a particular threshold voltage for each sensor. This voltage is converted to an 8-bit word by the analogue-digital converter and is then located in the particular table of that sensor in the memory of the micro-controller. Then that particular 8-bit word is marked in the memory as the threshold level for that sensor. When an incoming signal from a sensor is digitised by the analogue - digital converter it is compared with the marked 8-bit word to decide whether the threshold level is exceeded.

The threshold levels of the ultrasonics, shock sensor and current sensor may be changed using the routine described by the flowchart of Figure 7 by adjusting the position of the potentiometer when the micro-controller has been placed in setting-mode by operation of a mode key described in more detail below. "Beep-noises" are used to denote when particular functions have been performed and when values have been stored etc. When re-setting a particular threshold level the previously stored level is indicated by a "Beep" when the potentiometer is adjusted to that value. This is to give the user an indication as to the potentiometer position corresponding to the previous threshold level so that he can know which way to turn the common connection. The user is able to make choices etc within the programme by pressing the radio remote control key (R key) where necessary whilst consulting the flowchart of Figure 7. The periods of the various sampling operations ie Tx, Ty etc are programmed into the read-only memory at the manufacturing stage and are not subsequently alterable by the installers or the users.

As an alternative to the simple "beep" indication provided by the device during the setting operation it is possible to include a speech synthesizer to indicate when the steps of the routine are complete (as shown in the flowchart of Figure 3) .

The EEPROM 25 of the device is also used to store information about any triggering of the device whilst the user has been absent. Once the device is activated the micro-controller continuously monitors the sensors and any stimulation of the sensors is recorded in the EEPROM.

Figure 8 shows, in schematic flowchart form, the routine which a user can perform to enable him to discover which, if any, sensors have been triggered since the last check. The routine is accessible when the micro¬ controller is in diagnostic mode. This mode is selected using the mode key described below.

The memory of the device informs the installer which sensors were triggered and how many times. Triggering of a particular sensor is remembered up to a maximum of seven times. For example, if the ultra-sonic detector repeatedly triggers then the diagnostic routine would give an indication of this. This enables a faulty sensor to be identified and replaced. Presently, the routine work on a system of beeps although a speech synthesizer could be fitted as an alternative, which would enable the user to interpret the stored information more easily. If, for example, a particular sensor is triggered regularly, the installer can quickly check the reliability of the particular sensor having been able to identify it immediately with the diagnostic routing.

Apart from the LED's located on the outside of the device, and the "beep" indication which takes place at various stages in the diagnostic and setting routines, the device is equipped with a diagnostic socket into which may be plugged a lead from a display such as a roll-printer. Once the lead from the roll-printer has been plugged into the diagnostic socket the micro-controller 10 of the device ceases to use "beeps" and sends any data on triggering etc to the printer where it may be printed out an a copy given to the user. This facility is particularly useful to the dealer network as it provides a quick an easy method of producing a hard copy of the diagnosis of the device.

In addition to the setting mode and diagnostic mode as well as the normal operating "alarm" mode the micro¬ controller has a check mode to enable a user to check that all or some of the sensors are working. A user, enters the check mode using the mode key and then he is free to stimulate each sensor of the device e.g. by opening a door (courtesy light sensor) or tapping the car (shock sensor) without triggering the full alarm routine. A simple beep indicator is provided by the micro-controller to indicate that a particular sensor is functioning. The check mode is de-selected using the mode key.

The mode key is an additional radio remote-control transmitter, also in the form of a keyfob which transmits a locked signal which is received by the security device and which enables the various modes to be entered into. A further problem with prior security devices arises from the requirement that the radio remote control transmitters should not be permitted to operate security devices of other vehicles (ie to perhaps gain unauthorized access to those vehicles) . Because of this the radio signals transmitted by the remote transmitters are coded and only the correct code will be recognized by the security device. In order that the security device may be "taught" to accept a new code, for example when the keyfob transmitter has been lost and a replacement is obtained having a different code, the security device has a "learn mode" which may be selected by throwing a switch located on the case of the security device. The replacement keyfob transmitter is then made to transmit its coded signal which the security device "learns" to recognize as acceptable. Unfortunately it is therefore possible for a person to re-code a security device without the permission of the owner of the vehicle simply by following the above procedure.

The embodiment of the present invention provides a "recode-mode" of the micro-controller in which the micro¬ controller may learn a new code and which mode can only be selected by a special recode-key transmitter. There is therefore a much limited scope for abuse of the recoding procedure since a person must be in possession of the recode-key transmitter to gain access to the recode mode. It is envisaged that certain persons in responsible positions of companies which are, for example, major installers of the security device should have access to such recode-key transmitters.

The micro-controller used in the above-described embodiments of the present invention comprises an NEC UPD 78C12 with 256 bytes of internal RAM, two eight-bit timers, one sixteen-bit timer-counter, an asynchronous serial interface and an eight-channel, sixteen-bit analogue-digital converter. It will be appreciated that other processing means could be used without departing from the scope of the present invention.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A security device for a vehicle, the security device comprising a sensor, processing means and alarm means, the processing means being arranged to process a signal from the sensor and to operate the alarm means according to a characteristic of the signal from the sensor.

2. A security device according to Claim 1, wherein the processing means operates the alarm means if the characteristic of the signal from the sensor is indicative of a hostile stimulation of the sensor.

3. A security device according to Claim 1 or Claim 2, wherein the processing means does not operate the alarm means if the characteristic of the signal from the sensor is indicative of a non-hostile stimulation of the sensor.

4. A security device according to any of the claims 1 to 3, wherein the processing means compares the characteristic of the signal with a predetermined value to determine whether the characteristic is indicative of a hostile or a non-hostile stimulation of the sensor.

5. A security device according to Claim 4, wherein the processing means operates the alarm means if the characteristic of the signal exceeds a predetermined value.

6. A security device according to Claim 4, wherein the processing means operates the alarm means if the characteristic is below a predetermined value.

7. A security device according to any of the claims l to

8. wherein the processing means converts an analogue signal from the sensor into a digital signal.

8. A security device according to any of the claims 1 to

7, wherein the characteristic is an amplitude of the signal.

9. A security device according to any of the claims 1 to

8, wherein the characteristic is a frequency of the signal.

10. A security device according to any of the claims 1 to 7, wherein the signal consists of a number of discrete pulses and the characteristic is the magnitude of the pulses.

11. A security device according to any of claims 1 to 7, wherein the signal consists of a number of discrete pulses and the characteristic is the number of the pulses present in a predetermined time period.

12. A security device according to any of the claims l to 11, wherein the processing means comprises a micro¬ processor.

13. A security device according to any of the claims 1 to

12, wherein there is provided a plurality of sensors.

14. A security device according to any of the claims 1 to

13, wherein the sensor comprises transmitting means arranged to transmit a transmission signal, receiving means arranged to receive a reception signal and detector means arranged to detect differences between the transmission signal and the reception signal to produce a difference signal, in which the signal supplied to the processing means is the difference signal.

15. A security device according to Claim 14, wherein the sensor comprises an ultrasonic sensor arranged to transmit and receive ultrasonic signals.

16. A security device according to claim 13 wherein one of said sensors comprises a voltage sensor arranged to sense a change in voltage of a voltage source.

17. A security device according to claim 13 wherein one of the sensors comprises a shock sensor.

18. A security device according to any of the claims 1 to 17, wherein the alarm means comprises a siren.

19. A security device substantially as herein described with reference to the accompanying drawings.

20. Control means for controlling an electrical door- locking circuit of a vehicle, the control means comprising processing means, a memory and switching means, the memory being arranged to store information about an operating characteristic of the electrical door-locking circuit, the processing means being arranged to operate the switching means in accordance with the stored information in the memory.

21. Control means according to Claim 20 wherein the memory is arranged to store information about a plurality of operating characteristics of the electrical door- locking circuit.

22. Control means according to Claim 20 or Claim 21 wherein the memory is arranged to store sets of information about the operating characteristics of electrical door-locking circuits of different vehicles.

23. Control means according to any of the claims 20 to 22 wherein the stored information includes information about the type of electrical signal required to operate the door-locking circuit.

24. Control means according to any of the claims 20 to 23 wherein the stored information includes information about the duration of the electrical signal required to operate the door-locking circuit.

25. Control means according to any of the claims 20 to 24 which is arranged to control the locking and the unlocking of a door of a vehicle.

26. Control means according to any of the claims 20 to 25 arranged to control an indicator lamp of a vehicle.

27. Control means according to any of the claims 20 to 26 wherein the switching means comprises a relay.

28. Control means according to any of the claims 20 to 27 having only two electrical connections to the door-locking circuit, one to provide a lock signal to the locking circuit and one to provide an unlock signal to the locking circuit.

29. Control means according to any of the claims 20 to 27 arranged to control the closure of a window of a vehicle.

30. Control means substantially as herein described with reference to the accompanying drawings.

31. A method of operating a security device for a vehicle, the security device comprising alarm means, a sensor and processing means, the method comprising converting an analogue signal from the sensor into a digital signal, processing the digital signal and operating the alarm means if a characteristic of the digital signal is indicative of hostile stimulation of the sensor.

32. A method according to Claim 31 comprising comparing the characteristic of the digital signal with a pre¬ determined, stored value.

33. A method of according to Claim 32 in which the characteristic compared is a frequency of the digital signal.

34. A method according to claim 32 or claim 33 in which the characteristic compared is an amplitude of the digital signal.

35. A method according to any of the claims 32 to 34 in which the characteristic compared is a pulse-height of the digital signal.

36. A method according to any of the claims 32 to 35 in which the characteristic compared is a number of pulses in a sample of the digital signal.

37. A method according to any of the claims 31 to 36 comprising transmitting a transmitted signal and monitoring a received signal from a sensor and identifying whether the received signal is indicative of a hostile stimulation of the sensor by temporarily ceasing transmission of the transmitted signal and monitoring any received signal, the persistence of a received signal being an indication that the received signal is not indicative of a hostile stimulation of the sensor.

38. A method of operating a security device substantially as herein described with reference to the accompanying drawings.

39. A method of recording the activity of a security device for a vehicle, the method comprising storing in a memory of the security device information about hostile stimulation of a sensor of the security device.

40. A method of recording the activity of a security device substantially as herein described with reference to the accompanying drawings.

41. A vehicle incorporating a security device as claimed in any of the claims 1 to 19, or control means as claimed in any of the claims 20 to 30 or employing a method as claimed in any of the claims 31 to 40.

42. A security device as claimed in any of the claims 1 to 19 when used with a method as claimed in any of claims 31 to 40.

43. A security device as claimed in any of claims 1 to 19 or 42 which includes control means as claimed in any of claims 20 to 30.