GB2467126A

GB2467126A - Separation alarm using mobile wireless devices.

Info

Publication number: GB2467126A
Application number: GB0900978A
Authority: GB
Inventors: Colin Anthony Stroud
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-01-21
Filing date: 2009-01-21
Publication date: 2010-07-28
Also published as: GB0900978D0

Abstract

A separation alarm system has multiple self-powered wireless transmitter devices 1 that transmit a radio signal to a sensing alarm device 2 carried by a responsible person. The transmitter may be attached to valuables mobile phones and laptops, or to people such as children. The alarm triggers when the RF communication between the two devices degrades due to weak signal strength as their separation range increases. Preferably, the alarm is only triggered when separation is detected for greater than a user-controlled time. This range is adjustable via emitting power settings or receiver sensitivity. The device preferably utilises ZigBee technology providing low power consumption and unique identification for multiple devices. An alarm on the transmitter device may be triggered to aid in locating the device.

Description

This invention relates to a wireless alarm system to avoid the loss or theft of valuables or of children from their guardians.

Background of Invention

The Pro b/em Valuables, such as mobile phones, cameras, briefcases and laptops, can all too often be accidentally left behind or are stolen whilst the owner is out and about. Similarly children may wander away from their guardian. Many will go unnoticed until it is too late. A reliable, small and lightweight system to avoid this is required.

The Solution This invention is for a wireless alarm system to solve and eliminate the above problem. The system presented comprises coupled RF transmitter and RF receiver devices, and is able to safeguard multiple possessions. It is suitable for small valuables as well as big; can be discreetly hidden, or openly displayed (eg. doubling as a fashion accessory) for deterrent purposes; draws low power for longevity; uses an internationally free RF licensing frequency for greatest freedom of use; uses a high frequency to minimise antenna and device size; and utilises the latest RF communication protocol to provide a secure communication even in the most noisy of RF backgrounds and almost eliminate false alarms. The presented patent offers a practical solution for commercial exploitation.

Description of Similar Patents

There seem to be a number of similar patents for wireless systems that alarm when valuables are lost when separation distances exceed a certain range. But they are different. They have not presented a technical solution to provide a small or reliable or completely RF-base system that can be used practically for outdoor use. One identified patent (CN101025846) offers a system that combines RE and ultrasound, arguably to provide a better estimate of range between devices. The patent presented here is new in that it solves the stated problem using a methodology and combination of technologies that has not been proposed and patented before.

This patent is not setting out to patent any of its sub-systems (ie. RF and ZigBee) as these are already protected.

Terminology Some specific terms are referred to throughout this patent, and a description of their meaning are summarised here for clarification and the benefit of the reader.

Receiver device, or Receiver A Receiver device is an electronic subsystem comprising an RF unit (ie. antenna and microchip) and embedded software. The software controls how RF messages are responded to. It will be listening for one or more specific Transmitter devices. It will be able to undergo an initial and final setting whereby Transmitter devices can be added and removed to its internal list of devices to listen out for. See Figures 2 and 3.

Transmitter device, or Transmitter A Transmitter device is an electronic subsystem comprising an RF unit (ie. antenna and microchip) and embedded software. The software controls what and when RF messages are sent. It will be sending out periodic messages that can be listened to by nearby Receiver devices. It will be able to undergo an initial and final setting whereby it can allow a Receiver device to add or remove it from its list of devices to listen out for. See Figures 2 and 3.

Coupling, Coupled, or Coupled Devices These tenns are used to describe a communication linking between a Receiver device and one or more Transmitter devices. More specifically, that the Receiver device is told to actively listen out for the unique RF signals from one of more Transmitter devices. Each Transmitter device will have a unique identification sent within its emitted signals. In this way, a Receiver device can choose to listen and respond to signals only from specific (ie. coupled) Transmitter devices, and ignore all others.

Alarm-range This is the nominal separation range between a Receiver device and a Transmitter device used to determine when the system will alarm. When the devices are within the Alarm-range, then no alarm will trigger, but when they exceed this range the system will trigger an alarm.

In reality, only an approximate nominal Alarm-range can be engineered into the system since the environment (eg. physical obstructions) can slightly affect it. Even so, due to the ability of RF to effectively pass through and around most objects, the Alarm-range will generally not be affected significantly from the intended one.

ZigBee ZigBee is a communication protocol (based on IEEE 802.15.4 standard). It is a mechanism to ensure a robust and secure RF communication within a network, and is able to operate within noisy RF environments. It achieves this, at least in part, by transmitting a unique identification within each message, which allows messages that do not have the right identification to be readily rejected and filtered from those that do.

UART

Universal asynchronous receiver and transmitter (UART) is a way that messages can be communicated. Tt is a mechanism that translates a parallel message into a serial message, necessary for digital communication. This is used on programmable microchips to communicate to external devices via wire or RF.

Details of Invention This invention is for a wireless alarm system to avoid the loss or theft of valuables or of children from their guardians; it will alarm when they are separated from the owner by more than a certain range (called the Alarm-range).

An RF Transmitter device would be attached to the valuables (or to children). An RF Receiver device is attached to the owner (or the guardian). The RF Receiver device contains an onboard alarm system; this will be an audible buzzer, a flashing LED and/or small vibrator. See Figures 1 to 3 for illustrations of the devices.

The Transmitter device sends out very short intermittent signals and then enters sleep mode.

It is recommended that a signal is sent every 0.1 to 0.5 seconds. The reason for this duration and in entering sleep mode is to help ensure low power usage. The interval between the signals will assist in ensuring low false alarm rates. This timing is further discussed later.

The Receiver device listens out for RF signals. The Receiver device will generally be in constant listening mode, though entering very brief sleep mode to save power is a possibility.

When it receives a regular stream of signals from a coupled Transmitter device no alarm is triggered. When that signal stream is interrupted the alarm will trigger. The alarm is triggered only when a number of signals do not arrive over a period of time, rather than when just the first one doesn't arrive. This helps to ensure a low false alarm rate, as an occasional minor interruption can then be effectively ignored. Between two and four seconds of lost signal is recommended. The reason for this is that the owner and valuables would be separated by only a few metres (at normal walking pace) before an alarm is triggered, thus allowing the owner to simply return to look for, and retrieve, their valuables.

As noted above, the alarm triggers when the signal stream is interrupted, which can occur from one of four causes. The principle cause (which is the one this system is primarily designed to capture) is when the coupled devices are separated beyond a certain range (the Alarm-range). This is caused because the apparent signal strength drops away with distance from the Transmitter device (more precisely, this would be a function of the square of that distance, as based on the theory of propagation). The signal strength received by a Receiver device thus gets weaker as separation distance increases. Therefore, when the devices are increasingly separated, the received signal strength eventually becomes either too weak to be interpreted correctly or falls below a chosen threshold, and the signal stream is effectively lost.

A second cause of signal interruption is when objects obstruct the direct line of sight and attenuate the signal (either from scatter or absorption). In enclosed areas every day obstacles such as tables, walls and people will attenuate the RF signal. A third cause is due to the orientation of the antenna, as most antennas do not radiate equally in all directions. Hence, there could be brief times when the signal strength sent out towards the Receiver device is reduced when the device randomly twists and turns. A fourth cause is when there are significant amounts of background RF, and the Receiver device is unable to filter out the signals from Coupled devices.

The latter three causes of interruption are not particularly desirable as they raise the possibility of false alarms. Nevertheless, they are not significant problems as the range that triggers an alarm need not be precise and the aforementioned provision for waiting for a successive loss of signal before alarming can counter these issues in many circumstances.

Alarm-range is dependent both on the signal strength from the Transmitter device and on the sensitivity of the Receiver device. With increased Transmitter signal strength and with increased Receiver sensitivity, the Alarm-range can be easily extended. The precise combination of signal strength and sensitivity can be decided during final design and manufacture. The user will also be offered switches on the devices themselves to further adjust them (eg. to short or long range).

So far, the term signal has been referred to, but not explicitly explained. The content of the signals and the mechanism used to transmit them are discussed in the following paragraphs.

The Transmitter device will send one of three possible signals. The content of the signals is not important (eg. they could represent single characters such as "a", "b" and "c", or short strings such as "hello"); but their meaning would be sent and interpreted in a very precise manner by the system. The meaning of the three signals will be: "connect me"; "disconnect me"; and "I'm still here". The Receiver device is constantly listening to all RF signals, and interpreting what kind of message is being sent. How it behaves to them depends on its current mode, which can be one of two: "ready" to connect or disconnect; and "listening" for those already connected.

To recap: Receiver device has two operating modes: "ready"; and "listening".

Transmitter device has three signal types: "connect me"; "disconnect me"; and "I'm still here".

The system allows for the Coupling and dc-Coupling of multiple Transmitter devices to a single Receiver device. When a Transmitter device is first turned on, it will send a "connect me" signal for a few seconds (which optionally could be extended via a button on the device).

Provided the Receiver device is in the "ready" mode and within communication range, it will Couple to this device. Receiver devices will ignore all signals except from Coupled devices (whether from another Transmitter device or other RF devices). The Receiver device can be placed in the "ready" mode by depressing a button on the device, which will be interpreted by the onboard software to switch to this mode temporarily. When the Transmitter device is left on, it begins, and then continues, to send an intermittent "I'm still here" signal. With the Receiving device reverting back to its default "listening" mode, it is now listening out for the "I'm still here" signal from all Coupled devices. Whilst it receives them it knows that the Transmitter devices are within range. The Transmitter device can be dc-Coupled from the Receiver device by depressing a button on the device, which can be interpreted by the onboard software to send a "disconnect me" signal for a few seconds. To avoid inadvertent or surreptitious disconnection by a third party, this de-Coupling can only be achieved if the Receiver device has been simultaneously placed into the "ready" mode.

The mechanism used to transmit the signals is next described. Though there are a number of RF communications possible (eg. with different RF wavebands, or protocols such as Bluetooth, etc), this system is nominally proposing to use the ZigBee communication protocol at 2.4 GHz. ZigBee was chosen for its simpler set of communication instructions which are ideal for this type of application, its ability to uniquely identify between devices, its particular support for low power usage, the fact that it can meet the necessary range requirements of the proposed system, and combined with the high RF frequency used can meet the small system and antenna size required.

System Hardware Figure 3 illustrates an example of the sub-systems of the system: the RF transceiver unit, microchip, antenna, rechargeable batteries, buzzer, LED and user interfaces (ie. button).

Various aspects of these components are discussed below.

The microchip and an RF transceiver could be separate electronic entities or combined within a single chip, as both are commercially available. This system is not reliant on either one, and could use either. For simplicity, the following description is an example based on the assumption that they are separate.

The microchip will be programmed (see the section titled System Software) to control the system. It will be physically connected to the RF transceiver unit, LED, buttons, and alarm system (eg. buzzer) via a simple circuit board, and powered by onboard batteries.

The antenna could be a whip or chip type (shown as a whip antenna in Figure 3). This system is not reliant on any particular one as long as it's small, which is primarily a function of the RF frequency used.

Depending on the final design, the microchip and RF transceiver may require different voltages. A single battery will be utilised, and with the optional aid of an appropriate DC voltage regulator could provide the two necessary voltages required.

Onboard power is essential to the system in order to allow mobile outdoor use. In order to minimise running costs and maximise longevity, it is desirable to use widely used and commercially available rechargeable batteries. Whatever is chosen in the final design, they will be required to provide sufficient power to sustain the system for at least one operation (eg. perhaps a few hours). Options include (but not restricted to) rechargeable and non-rechargeable AAA, coin batteries or one of the mobile phone type batteries.

The button on the Receiver device is used to place the system into "ready" mode when depressed. When not depressed, it is in "listen" mode. The button will also function to temporarily switch off an alarm if it has been triggered. The button on the Transmitter device is used to send the signal "disconnect me" when depressed. When not depressed, it sends the "Fm still here" signal. Both the Receiver and Transmitter devices will have onloff switches (which could optionally be tied into the same button for changing modes).

The LED on the Receiver device is used to indicate that the system is on. It could intermittently flash green when in "listening" mode, and flash amber briefly to signify when it successfully Couples or de-Couples a Transmitter device. The LED on the Transmitter device is used to indicate that the system is on. It could intermittently flash green when it sends an I'm still here" signal, and flash amber briefly to signify when sending a "connect me" or "disconnect me" signal.

The alarm system located on the Receiver device will use one or more indicators: buzzer, vibrator and/or LED components.

A requirement is to produce devices whose sizes are small and lightweight. Anticipated typical and maximum dimensions of the system proposed here are from 25x35x10mm to 50x35x15mm for the devices (which will depend on final battery choice), and to weigh less than a few tens-of-grams (when the batteries are not inserted).

System Software The software can be programmed in any form suitable to be placed on a microchip. From experimentation carried out by this inventor, prototype software was written and compiled into HEX and then installed onto a programmable microchip within prototype devices to prove the theory and demonstrate concept of use.

The two pieces of key functionality that must exist in the software are discussed below, but there's much software that isn't shown here. This was implemented on a PlC 16F628 microchip; but many other microchips would suffice. It is expected that just 2KB of flash memory is sufficient to store the software.

The Transmitter device needs to sends out intermittent and very short signals. Here, software is shown that will send a signal every 0.5 seconds.

AGAIN1 Call SIGSEND; Send signal Call DELAY P5S GoTo AGAIN1; Repeat Send signal SIGSEND movlw H161' ; in this case, just "a" movwf 19H; word will be transmitted as soon as it's possible to do so retlw 0 lOms delay DELAY 1 clrf TMRO; Start timer LOOP 1 movf TMRO,W; Read timer into W sublw.36; O.Olsec for a 32kHz clock btfss STATUS,2; Check if timer diff=0 GoTo LOOP 1 retlw 0 0.1 second delay DELAY P1S movlw.10 movwf TIMER1 LOOP 2 Call DELAY_i decfsz TIMER1 GoTo LOOP 2 retlw 0 0.5 second delay DELAY P5S Call DELAY Pis Call DELAY P1S Call DELAY P1S Call DELAY P1S Call DELAY P1S retiw 0 The Receiver device needs to be in constant listening mode and to respond appropriately to a regular stream of signals from a coupled Transmitter device. The example code below checks for the signal from one Transmitter and when that signal is lost for four seconds (or more precisely, 384 failed checks at approximately 1 Oms between each check) an alarm is triggered (or more precisely, executes bsf 6,3, which sets high an output on a port that leads to an LED or buzzer); otherwise it remains quiet.

Check if signal has been received SIGCHECK btfsc 24H,O; If alarm is already on, just skip looking and return GoTo SIGRETURN btfss OCH,5; If no new byte/signal received (ie. it's 0), jump straight to not found GoTo NOTFOUND movf 1AH,W; Get last word received (->W) bcf i8H,i; Clear the overrun flag (even if it doesn't happen), otherwise the transfer of RSS to RCREG is inhibited movwf RXWORD; Save last word received (W->) sublw H'6l' ; W(Word) -6lh btfsc 3,2; Check if result=0, ie. "a" GoTo FOUND. . . yes GoTo NOTFOUND. . . no FOUND flop; Check to see if last received signal was strong enough.

btfsc 1FH,6; Check strength of signal GoTo WEAK Call COUNTRESET Call COUNT2RESET GoTo SIGRETURN WEAK flOg NOTFOUND Call TIMEDOUT movwf 25H btfss 25H,O GoTo SIGALERT. . .didn't get good signal, but we haven't quite lost the signal long enough yet bsf 6,3. . .lost signal for too long, so alarm (and keep on) Call DELAY P5s bcf 6,3 Call COUNTRESET Call COUNT2RESET bsf 24H,O GoTo SIGRETURN SIGALERT flOg SIGRETURN Call DELAY_i; Introduce small delay retlw 0 TIMEDOUT decfsz COUNT; Returns 1 in W when timed out or 0 GoTo TIMEOK Call COUNTRESET decfsz COUNT2 GoTo TIMEOK TIMEISUP retlw 1 TIMEOK retlw 0 COUNTRESET movlw.128; Reset counters movwf COUNT retlw 0 COUNT2RESET movlw.3 movwf COUNT2 retlw 0 From experimentation carried out by this inventor, a ZigBee hardware implementation of this system was developed and successfully demonstrated. In this prototype, the key controlling parameters utilised to provide reliable and secure communication were channel, personal area network identifier and the device's serial number. These can be set or chosen to reduce RF interference from similar ZigBee devices and to ensure that only Coupled devices communicate with one another.

Example Technical Specifications

The expected Transmitter and Receiver device currents will be around 5OmA. The expected Transmitter and Receiver device voltages will be around 5V. The intermittent peak power consumption could be around a few hundred milli Watts.

The RF Transmitter device will enter sleep (or extremely low power) mode between transmissions (which will be in fact the majority of the time), only waking to send periodic signals. The expected Transmitter device current will be just a few microAmps during these times.

The Transmitter and Receiver devices will have batteries chosen that are nominally at around 1 000mAh. This could equate to tens of hours of continuous operation. Anticipating that the system would be in use for an average of a couple of hours at a time, this equates to about ten uses between recharges.

It is envisaged that the batteries will be charged using existing technology (eg. current chargers) and does not form part of the system being patented here. Any recharging will be undertaken by extricating the batteries and charging them externally, though a future version could have such a feature added (which would be expected to then increase the nominal weight and size).

The expected Transmitter device emitted power will be significantly less than 1mW. This is extremely low, and is precisely judged here to allow communication over just a few metres distance. This emitted power does not represent a health hazard, and is not expected to break health and safety laws in most countries.

The expected Receiver device sensitivity will be around 90 to 100dB (compared to the strength of the Transmitter device). Depending on the precise Alarm-range required, the sensitivity can be adjusted during final design and then fine-tuned by the user on the device.

The antenna will be careful chosen to have as near an omni-directional emission behaviour as possible.

The baud rate on microchips and RF transceivers affect the frequency and power consumption at which messaging can be passed between devices. A recommended baud rate used of nominally 9600bps offers a sufficient speed of messaging transfer whilst minimising power consumption (greater baud rates tend to increase power consumption).

Example Drawings

An example of the invention will now be described by referring to several drawings. The drawings represent just one example configuration; other configurations exist that could equally be derived from the patent presented here.

Figure 1 shows the Transmitter and Receiver devices in an example situation, where a Transmitter is attached to a valuable device (in this case a camcorder) and a Receiver device is located in the pocket of the user.

Figure 2 shows close up of Transmitter and Receiver devices; illustrating their compact size and their relatively simple (and hence user-friendly) facia.

Figure 3 shows an internal view of the Transmitter and Receiver devices; illustrating the contents of the RF units: microchip, antenna, batteries, buzzer and LED.

A Transmitter attaches to a valuable item 1 (or alternatively, is placed in the pocket of a parent's child). The Receiver sits in the pocket (or could attach to their belt, etc) of the owner 2; both devices are very compact in size, typically of a few centimetres. The Transmitter has a dual-purpose recessed switch 3 to turn the device on and off and for coupling to a Receiver, and an LED 4 to serve as onloff/status indicator. The Receiver also has a recessed switch 5 to turn the device on and off and for coupling to a Transmitter, and also an LED 6 and buzzer 7 to serve as alarm and status indicators. 8 represents a standard recessed hook for attaching one end of a strap onto (the other end attaching to valuables or a key ring). 9 represents an RF chip and antenna (for receiving and transmitting purposes), though the RF chip could as easily be integrated onto the microchip or circuit board 10, which is used to electrically connect the components together. A buzzer 11 serves as an alarm indicator. Coin batteries 12 will power the device (though with a little reconfiguration rechargeable AAA's or a phone battery could be alternatively used). A microchip controls the functioning of the device 13.

Claims

Claims 1. A mobile alarm system for preventing the loss or theft of small and large valuables, and of children from their parents or guardians, for both indoor and outdoor situations.
2. Based on RF wireless technology.
3. Based on communication protocol and technology such as ZigBee, Bluetooth, or similar, that support low power consumption, small size and unique identification capabilities required for anti-spoof communications.
4. A high radio frequency (nominally 2.4 GHz) to ensure small antenna and device sizes.
5. An Industrial, Scientific and Medical radio frequency to benefit from free RF licensing in the majority of countries (nominally 2.4 GHz, 5.8GHz and 24 GHz).
6. System to comprise one or more RF transmitters and one RF receiver.
7. A transmitter device to be attached to possessions or to children.
8. A receiver device to be attached to the owner or guardian.
9. The system to alarm when a coupled transmitter and receiver are separated by a distance greater than a user-controlled nominal range and for a time greater than a user-controlled duration.
10. The alarm to trigger when the RF signal strength received by the receiver from a transmitter device is below a user-controlled threshold.
11. The receiver device to contain an alarm system, nominally comprising an audible buzzer and a flashing LED, but possibly include other mechanisms too.
12. When triggered, the alarm will remain enabled until manually reset or turned off at the receiver.
13. The system to comprise the coupling of a transmitter with a receiver, so that the receiver can uniquely recognise the transmitter and avoid spoofing and RF background noise.
14. The system to allow multiple transmitter devices can be coupled to a single receiver device to allow for the security of multiple possessions.
15. The transmitter device to send out periodic transmissions at regular short time intervals (nominally between 0.1 and 0.5 seconds).
16. The receiver device to listen continuously for the signals of coupled transmitter devices.
17. Receiver and transmitter devices to have a switch for coupling devices together.
18. Receiver and transmitter devices to have a switch for facilitating alarm resets.
19. Transmitter device to have a switch for adjusting emitting RF power.
20. Receiver device to have a switch for adjusting RF signal sensitivity.
21. Receiver and transmitter devices to contain an LED for the purposes of indicating when device is on and what its current status is.
22. A micro-controller located within each device, with specific software loaded to ensure the devices operate in the manner described here.
23. Transmitter and receiver devices to have their own onboard power sources.
24. The devices to be designed in both covert and conspicuous forms to allow different levels of security discreetness.
25. For a version of this system to also have an alarm on the transmitter device to start when the alarm on the receiver starts, so that the owner will know precisely where the transmitter is located.