GB2259390A - Vehicle alarm system - Google Patents

Abstract

In response to a disturbance, sensors 2 initiate an activating signal which may be interrupted and cancelled by appropriate means. Failure to cancel the signal causes, in addition to conventional audible and visible alarms, the transmission 10 of an encoded signal to a remote receiving and decoding apparatus 11-15. In an exemplary embodiment of the invention, information may be included in the signal corresponding to the registration number of the vehicle. Where a network of receiving points is utilised, analysis of the pattern of signal reception may also give an approximate indication of the location of the vehicle. <IMAGE>

Description

ImProvements in or relating to Alarm Systems This invention relates to alarm systems, mainly but by no means exclusively for fitting to vehicles.

It is well known to have electronic vehicle alarms in which a sensor, which may be for example, a switch which is activated by the opening of a door, or a proximity detector which is activated by human presence, provides a signal to electronic processing equipment which energises an audible and/or visible alarm. The processing equipment may include a means to delay the signal for a given number of seconds and cancel it if the alarm is correctly deactivated by the user.

There are a number of drawbacks to such an alarm system. For example, in many alarm systems the thief can stop the alarm ringing by cutting off its power supply. Also, only persons in close proximity are alerted at the time.

According to the present invention there is provided an electronic alarm system including a sensor, signal processing apparatus and a transmitter wherein the system, upon activation, encodes a pre-determined signal into a form suitable for transmission and transmits the encoded signal to receiving and decoding apparatus located at a remote site.

The system is particularly suitable for incorporation in a vehicle such as an automobile. The sensor, which may be a switch activated by the opening of a door of the vehicle, produces an activating signal which may be delayed for a pre-determined time by a first section of the signal processing apparatus.

During the delay period the user can cancel the activating signal by, for example both closing the door and placing a key in the ignition system of the vehicle. Should the activating signal not be cancelled then it may optionally set off an audible or visible alarm. In addition it will trigger a second section of the signal processing apparatus and the pre-determined signal stored therein, which may be for example, the car registration number, is output to a third section of the signal processing apparatus where is it encoded into a form suitable for transmission. Such a form may be, for example, serial post-position modulation encoding (serial PPM) although a variety of other forms known from signal processing literature may be suitable.The pre-determined signal may be combined with prefixes and suffixes prior to encoding and then it is fed to the transmitter, the aerial of which may be concealed for example in the frame of a window of the vehicle. Transmission may be direct to the receiving apparatus or indirectly to the nearest base station of a mobile phone network for further transmission to the receiving apparatus via the public switched telephone network.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, purely by way of example to the accompanying drawings in which: Figure 1 is a block diagram of an alarm system in accordance with the present invention for incorporation in a motor vehicle; Figure 2 is a gate level diagram of a part of the system shown in Figure 1; Figure 3 is a circuit diagram of a first stage of another part of the system of Figure 1; Figure 4 is a circuit diagram of a second stage of the part shown in Figure 3; Figure 5 is a circuit diagram of a third stage of the part shown in Figure 3; Figure 6 is a view of the rear of a car indicating the position of an aerial forming part of the alarm system of Figure 1, and Figure 7 is a circuit diagram of a further part of the system of Figure 1.

Referring to Figure 1, the alarm system includes a logic system 3 which evaluates signals from one or more sensors such as a door switch 2, from an alarm on-off indicator 1 and from an ignition switch 20 (shown in Figure 2) to decide whether to activate the rest of the alarm system or not.

In practice several door switches may be incorporated. For example in a car there may be a switch provided for the driver's door, one for each passenger door, one for the boot and perhaps one for the bonnet. Proximity sensors would also be suitable for the system.

If it is decided to activate the rest of the alarm system, then an EPROM memory unit 5 is switched on by clock and control logic 4 to output a pre-determined signal such as the car registration number. This signal is passed to a PPM encoder 7 where it is converted into serial PPM form and then it is modulated for transmission by an FM transmitter 10 at 99.9 MHz.

The reason PPM is chosen is its compatibility with FM broadcasting. FM broadcasting, as opposed to other wavebands, allows a smaller, less power-consuming transmitter to be utilised and is therefore preferable.

The encoded signal is received by a receiving apparatus comprising an FM receiver 11 which employs a phase locked loop circuit 12 to enable the receiver to lock on to the received frequency. A decoder 13 recovers the original signal as stored in the EPROM 5 and this is connected to input port 14 of a computer system.

Figure 2 will be used to explain the workings of the logic system 2.

The inputs to the logic system are the door switch 2, the alarm on/off indicator 1, the ignition switch 20 and a 1Hz clock 21 which provides overall timing control for the logic system 3. Typically, the car owner will deactivate the alarm before opening the door but, if he does not he has the duration of a pre-set time delay to deactivate the system using the ignition key.

The signals from the door switch 2 and the alarm on/off indicator 1 provide the inputs for a two input And gate 16. A High on the output of And gate 16 therefore indicates both that the alarm is on and the door has been opened. This signal feeds through to OR gate 17 whose output is passed to an And gate 22 where it is combined with the output of the 1Hz clock 21 to produce 1 second pulses at its output. These will continually be produced unless the OR gate 17 is deactivated by turning the ignition key. This produces a High signal at input 20 which is inverted at gate 19 and combined with the output of the OR gate 17 at And gate 18. Provided that either the alarm has been disabled or the door switch deactivated so that the output of gate 16 has gone low, the output of OR gate 17 goes low and thereby operation of the ignition disables the alarm.

If the alarm is not disabled then the output of gate 22 is fed to the count input of a four bit binary counter 23.

The one-second pulses are counted and bit 4, which is set on the eighth pulse, is used as the output.

This gives the user a delay of seven seconds in which to deactivate the alarm. A combination of bits 1 and 4 is used to reset the counter via And gate 25, which combination is set on the ninth pulse. The ignition switch 20 also resets the counter via OR-gate 24.

The output of the logic system is fed to the first stage of the encoder through input 27. The first stage consists of a transistor 29, a multivibrator NE 555, 36, a 12 bit binary counter 4040B, 40, a quad 2 input NOR, 74L502, 34, and a 2764 EPROM chip. The transistor 29 serves as a buffer between the logic system and the encoder in that the transistor 29 is switched on at its base by the output of the logic system and this causes its collector to go low. The output of the collector is connected to the trigger input of the 12-bit binary counter 40 via the inverter chip 34 so that a High at the input 27 results in a High at the trigger input of counter 40. The count input of the counter 40 is fed by pulses from the astable multivibrator 36 whose rate is set by the combination of resistors 37 and 38 and capacitor 39.The outputs of the counter 40 are connected to the address inputs of the memory chip 41 and this allows the successive addressing of bytes of memory so that the pre-determined signal previously stored in the memory, is accessed in a serial fashion.

The pre-determined signal can be made to include a header to allow it to be recognised by a receiving apparatus and routed correctly. As shown in Figure 3, only the first 7 count bits of counter 40 need be used due to the brevity of the signal and the eighth is connected to reset the counter. The pre-determined signal is output to the succeeding stages of the decoder via the date output pins (DO-D8) 44 of the memory chip 41.

The upper 4 bits, 44a, of the pre-determined signal are sent to stage 2 of the encoder, shown in Figure 4, which consists of a 4-16 converter 45, which is a 74 LS 154, and two buffered hex inverters 46 and 47, 74 LS 04. The operational details of these chips may be obtained from their respective manufacturers' data sheets.

Eight bits of the output of the 4-16 converter, 45, are used. Six of them are fed to the first hex inverter 46 and the remaining two to the second hex inverter 47.

The output 48 of the hex inverters 46 and 47 is fed to Encoder stage 3 together with the lower 4 bits of the output of stage 1. Encoder stage 3 as shown in Figure 5, consists of three quad analogue switches 50, 51 and 52, each accepting 4 of the 12 input bits of that stage, a frequency generator 53,54,55, and an asynchronous post-position modulated (PPM) encoding integrated circuit 57 for which the Plessey MV 500 chip is used.

A pin on the encoding chip 57 is connected to one of the inputs of each of the quad analogue switches whose operation may be determined from the relevant manufacturers data sheet. The outputs of the switches are connected to provide a 4 X 8 matrix 58 such that any one of the twelve data inputs to this stage may be connected to the encoding chip 57 by operation of the analogue switches 50, 51 and 52.

The frequency generator consists of a ceramic resonator 55 and two polystyrene capacitors 53 and 54.

It generates a frequency of 500 KHz which is applied between 2 inputs of the encoding chip 57.

The output of the PPM chip is serial PPM which is passed to a further analogue switch 9 where it is combined with a 10 KHz signal from an astable multivibrator (not shown). This produces an encoded signal of suitable form for transmission and this is output to an FM transmitter 10 tuned to 99.9 MHz.

The receiving apparatus consists of an FM receiver 11 combined with a phase-locked loop circuit 12 to maintain it at the received frequency. Tone decoding allows the PPM signal to be recovered and this is passed to a Hex inverter sq, for which, again a 74 LS 04 chip is followed by a PPM decoder chip 60 which is a Plessey MV 601. The decoder chip is connected to a frequency generator 61 62 63 corresponding to that connected to the encoder chip 57. This allows the original binary pre-determined signal to be recovered and this may be fed into a computer system 15 as desired.

If the public telephone network is used it will be apparent that the various parts of the receiving apparatus will be located at separate sites. For instance the FM receiver will be part of a base station of a mobile phone network whereas the computer may be at the offices of a security company. In such a set up a chip may be provided at the base station adding its own prefix or suffix to the message and hence indicating the approximate location of the vehicle.

A number of features have been incorporated so as to conceal from the thief the fact that the alarm is incorporated into the vehicle. Firstly, an independent power supply is used for the system so that there are no cables to the vehicle battery. The system may be attached to a standard vehicle alarm which the thief would deactivate by cutting the cables to the battery.

It is a particularly attractive feature of the invention that it would continue to work because of its independent power supply even though the thief thinks he has disabled the alarm. Once the battery cables are cut there is no remaining means of disabling the alarm.

Secondly, the aerial is concealed around the outline 65 of the rear window 64 of the vehicle as shown in Figure 6.

The security company, upon being alerted by the alarm, may attempt to verify whether the vehicle has been stolen, and alert the police or have the car logged as stolen by the Driver Vehicle Licensing Centre in Swansea.

In the event of accidental setting off of the alarm, vehicle owners could be provided with personal numbers to use in contacting the security company operating the system and telling them to disregard the signal.

Claims (12)

Claims:

1. An alarm system adapted for use in protecting vehicles including a signal processing means, a transmitter and a sensor adapted to produce a sensor signal in response to a disturbance, wherein upon activation of the system a predetermined signal is encoded by the signal-processing means and the encoded signal is transmitted by the transmitter to a remote receiving apparatus.

2. An alarm system according to claim 1, wherein the signal processing means includes a time delay mechanism.

3. An alarm system according to claim 1 or 2, and further including a cancelling means for interrupting the sensor signal.

4. An alarm system according to claim 1, 2 or 3, in which the sensor signal also triggers audible and/or visible alarms.

5. An alarm system according to any preceding claim, wherein the transmitter includes an aerial adapted to fit in the frame of a vehicle window.

6. An alarm system according to any preceding claim, wherein the signal-processing means generates serial post-position moduluation encoded signals.

7. An alarm system according to any preceding claim, wherein the remote receiving apparatus includes a mobile phone network base station.

8. An alarm system according to any preceding claim, in which the transmitter is an FM transmitter.

9. A vehicle including an alarm system according to any preceding claim.

10. A vehicle according to claim 9, wherein the sensor comprises a door switch or proximity sensor.

11. A vehicle according to claims 9 or 10, wherein the predetermined signal is an identification of the vehicle.

12. An alarm system substantially as described herein with reference to the accompanying drawings.