GB2481210A

GB2481210A - Alarm device including a wireless transmitter powered by a capacitor

Info

Publication number: GB2481210A
Application number: GB1009959.6A
Authority: GB
Inventors: William Basil Harrold
Original assignee: APOIDEAS Ltd
Current assignee: APOIDEAS Ltd
Priority date: 2010-06-15
Filing date: 2010-06-15
Publication date: 2011-12-21
Also published as: GB201009959D0

Abstract

An wireless alarm device is disclosed comprising: one or more sensors 202; a controller 201; a power supply 200 which buffers energy from a power source into a capacitor 203; and a wireless module 204 powered from the capacitor 203 to send messages. The capacitor 203 is kept charged by the controller 201 periodically connecting it to the power source 200 so that when the sensor 202 wakes up the controller because an event has been detected, the controller 202 connects the capacitor 203 to the wireless module 204 and triggers it to send a message. The message may be an SMS message sent via a server to a mobile phone. The sensor may comprise a contact switch, temperature sensor, humidity sensor, gas detector, light sensor, passive infrared sensor or passive infrared motion detector.

Description

WIRELESS ALARM SYSTEM

TECHNICAL FIELD

This invention relates to an apparatus and a method for wireless sensing. In particular, the invention relates to an apparatus and method for low power wireless sensing and alarm applications.

BACKGROUND TO THE INVENTION

Optex provide a VX4O2R-GSM product which relays Passive Infrared (PIR) motion detection via a GSM link to alert a mobile phone. The device claims a 3 year battery life and works down to zero degrees centigrade. It is used for providing security in outdoor areas where mains power is not available. The device seems to have a large battery and questionable low temperature performance for outdoor operation.

Alarms for Farms and Parabeam provide systems whereby PIR motion detectors are used for protecting driveways. In their systems the detections are relayed back over a short range radio link to an alarm controller. From the controller it is possible to use auto diallers to provide the alert. This system requires extra hardware within a distance of around 250m to make it work.

Compared to solutions requiring an external power supply these systems are much easier to install in remote or outdoor locations and can be more easily moved from one location to another. Their internal power supplies are typically dimensioned to provide a few years life with a typical activity level. The VX4O2R-GSM solution above has no limits to the distance between the PIR sensor and the alerted device and does not need control boxes and auto diallers inside a nearby mains powered building.

Various suppliers add the ability to use the PIR to trigger cameras, lights, or other devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention are hereinafter described with reference to the accompanying diagrams where: Figure 1 is a schematic diagram of the GSM alarm system in accordance with an example of the invention; Figure 2 is a schematic diagram of the energy buffering power supply of the device in accordance with an example of the invention; Figure 3 is a time chart showing the operation of a GSM Alarm system in accordance with an example of the invention;

SUMMARY OF EXAMPLES OF THE INVENTION

An example of the invention is shown in figure 1. The device (101) has a PIR motion sensor detection area (102) which is triggered by a passing person or object. This causes the device to wake up and send a message using SMS (103) to an Internet Based Server (104). The server then passes a human readable alert message via SMS (107) to a specified mobile phone (106). The detailed behaviour of the device (101) and the Server (104) can be configured using the User Interface (105) to the Server.

Figure 2 shows some details of how the device (101) wakes up when the PIR motion sensor (202) triggers it. The sensor (202) applies an external interrupt to the controller (201) which wakes it up from a low power state. The Controller (201) then connects the Capacitor (203) to the GSM module (204) typically via a Boost Regulator (205). The Capacitor is kept charged from the Power Source (200) using periodic top ups. If the delay in sending the alarm is less of an issue then the Capacitor can be charged when needed, thus saving self-leakage losses in the Capacitor which occur if it is kept charged all the time.

With this approach to the power supply design the power source required is limited by the energy stored in it rather than the maximum power that it can produce -the peak power requirement is met by the Capacitor and boost regulator not the power source. The benefit of this is to allow energy harvesters such as solar panels to be used and smaller batteries at lower temperatures than would be needed without this energy buffering power supply. If the peak current drawn from a battery is reduced then this typically increases its capacity which compensates for some or all of the losses in the energy buffering power supply.

The messages from the device (101) may be relayed to a server (104) rather than directly to mobile phone (106). This has many benefits including a simpler to use user interface; the ability to record data and analyse before setting up the alert thresholds thus reducing false alarms; the ability to send alert messages repeatedly to more than one destination (for example user devices or enterprise applications) without requiring more energy from the device's power source. It also allows the data from more than one device to be easily compared.

Rather than reporting all alarms immediately the device might be configured to just record the detections and then report the times they occurred as a group. This data can be viewed perhaps on the server user interface and the user can decide how to configure the system so that only more useful alarms are reported. This might involve setting detection conditions for the PIR (and other) sensors and ignoring detections which happen outside specified times. Along the same lines the user might only wish to be alerted if there have been a certain number of detections in a specified time window.

A further example of the invention provides an apparatus for carrying out the method described above or in any of the appended claims.

A further example of the invention provides computer programs for carrying out the device and server related processes of the method of any of the appended method claims.

A further example of the invention provides a computer readable medium having the computer program described above stored thereon.

A further example of the invention provides a device substantially as described herein and as shown in Figures 1 to 3.

A further example of the invention provides a method substantially as described herein and as shown in Figures 1 to 3.

This summary provides examples of the invention which are not intended to be limiting on the scope of the invention. The features of the invention described above and recited in the claims may be combined in any suitable manner. The combinations described above and recited in the claims are not intended to limit the scope of the invention.

Further examples of features of the invention are described in the appended claims.

Features and advantages associated with the examples of the invention will be apparent from the following description of some examples of the invention.

DESCRIPTION OF EXAMPLES OF THE INVENTION

The Telit GE865 is a typical GSM module. It takes a 3.22-3.8V power supply and while active draws an average current of 40-5OmA but over 2 amps peak. Lithium rechargeable batteries have high self leakage (-20% per month) and would not last for years, Lithium primary cells are needed with typically 1% leakage per year at 250. Lithium primary cells such as a 3.6 V Tadiran LiSOCl2 D Cell can draw 6OmA at 25C while still keeping their voltage output high enough to drive the GSM module. In order to address the peak power requirement large decoupling capacitors can be used and it is also possible to limit the in rush current that such large capacitors take when first connected to the power source.

However, at low temperatures the same D Cell's current output drops dramatically for example it can only supply 6mA at -5C while maintaining 3.22V. So on a cold night no messages would be sent.

Instead, the present invention charges a low equivalent series resistance super capacitor with enough energy to send an entire SMS. As the super capacitor energy falls during the sending of the SMS the voltage is maintained by a boost regulator and this combination is also capable of supplying the 2 amps peak current due to the low ESR of the super capacitor.

Allowing for the inefficiency of this power supply in the system we have measured that sending or receiving a GSM SMS at full transmit power takes about 10 Joules from the power source including the overhead for registration and synchronisation.

An AA sized Omnicel 3.6V 2.4Ahr battery would therefore be able to send [no. of messages] = [Volts] * [Current] * [Time] / [Energy per message] = 3.6 * 2.4 * 3600 / = 3110 messages. At one message per day this corresponds to 8.5 years.

The charging of the super capacitor is achieved using a trickle charger whose resistance is chosen to match the preferred current output of the power source. For example for an LiSOCI2 battery this would be chosen so as to maximise capacity.

For an Omnicel 3.6V AA LiSOCI2 battery the current for rated capacity at 25C is met at 7niA. In this case the charge time to store 1OJ would be [Energy] / ([Voltage] * [Current]) = 10/(3.6 * 7.10) = 397 seconds or 6.6 minutes. Actually this calculation assumes a constant current which is not true of a trickle charger, so if a constant current source is not used we have to increase the charge times a bit. If this is all considered too long then it can be speeded up at the expense of battery capacity. At -30 Centigrade the capacitor will still charge, but in the current example the battery capacity of the AA cell would be reduced by a factor of 2.

Although the present example of the invention has been described in the context of a GSM module, other cellular systems such as WCDMA, LTE, CDMA, 802.1 6e etc and a plethora of non cellular wireless systems, could be used instead.

PIR motion sensor systems consist of a pyro-electric sensor, a Fresnel lens, an amplifier and a detection device. Off-the-shelf modules such as the Panasonic NaPiOn AMN 34111 have a continuous current consumption of 46uA. With the same AA battery this would last 5.95 years if used continuously.

So assuming that sending SMS messages and monitoring the PIR sensor are the dominant energy consumers in the device, then a life of around 3 years should be possible with a single AA LiSOCI2 battery.

Waiting several minutes for an alarm to be sent may not be acceptable. We may have to keep the capacitor charged so that alarm can be sent with low latency. We would typically be using a low ESR super capacitor and the leakage current from these capacitors is of the order of 80 micro amps. Keeping the capacitor charged would halve the battery life again to about 18 months due to this leakage current. It will be possible to mitigate this leakage current by configuring the device to only keep the capacitor charged when low latency alarms are needed.

The invention is not limited to the use of batteries as a power source. A variety of means to charge or replace the battery might be used. For example, a small solar cell could be used to charge the capacitor and a small rechargeable battery to keep the controller and PIR sensor running.

The procedure for communicating an alert to the server and the user's mobile phone will now be described in relation to figure 3. It is assumed that the controller may be recording sensor readings from other sensors. In figure 3 time is continuous from left to right and then from the Device line to the Server line and on to the User's Device line.

The Capacitor (203) is charged (300) at the "start of day" and periodically topped up (301) at intervals determined by the leakage rate from the Capacitor (203). A PIR motion sensor detection event occurs (302) and processing (303) is applied inside the device. The processing decides whether to report the event to the server and attach recorded sensor readings from the PIR and other sensors to the message. An SMS containing all the information (in efficient but non human readable format) is sent to the server (304). The server receives the SMS message and may timestamp it (305). There follows some processing (306) which depends on the system configuration but it will decide on whether to send a message to one or more User's Devices (or Phones, PDAs, PCs etc), and whether to add other information to the message from other sensor reports. The message sent to the user's device is in human readable format (307) the message could for example be an email or an SMS where the user is alerted (309) and the message can be displayed (310).

The applicant has realised that the power management of the combination of a triggering device and a GSM module can be configured into a low power system limited not by the peak power requirements of the GSM module, but the total energy requirements of the system. This leads to a smaller battery being required and much better tolerance to low power conditions where the battery chemistry reduces its output power.

It will be appreciated that each of these techniques may or may not be applied, and that these techniques may be applied in any combination.

Various modifications, changes, and/or alterations may be made to the above described examples to provide further examples which use the underlying inventive concept, falling within the spirit and/or scope of the invention. Any such further examples are intended to be encompassed by the appended claims.

ADVANTAGES OF THE INVENTION

The advantages of the energy buffering power supply and server are as follows: -Smaller / cheaper device for the same battery performance whilst still being able to report alarms quickly.

-Or for the same size / cost improved battery performance -Better low temperature operation -Improved false alarm rate / energy consumption by looking at triggers on the server and reconfiguring the alarm threshold / mechanism in the light of these -Server allows multiple users to be alerted without drawing more power from the device.

-Server allows more sophisticated alarm triggers to be set up e.g. based on average readings of a sensor.

Claims

Claims 1. An apparatus and method for a wireless alarm device comprising one or more sensors, a controller, a power supply which buffers energy from a power source into a capacitor and a wireless module powered from this capacitor to send messages and the capacitor is kept charged by the controller periodically connecting it to the power source so that when the sensor wakes up the controller because an event has been detected the controller connects the capacitor to the wireless module and triggers it to send a message.
2. An apparatus and method according to claim 1, but where the message is sent to a server which may pass it onto a user's device, such as a phone, or an application.
3. An apparatus and method according to claims 1 or 2, but where the capacitor is only charged or topped up after the sensor trigger has occurred.
4. A method and apparatus according to any of the above claims where the wake up comes from a contact switch closure or opening, or processing of recorded readings from other sensor types, for example temperature, humidity, gas detector or light level.
5. A method and apparatus according to any of the above claims where the device initially reports sensor readings to the server and these are processed in order to set appropriate alarm conditions and hence to reduce the false alarm rate or merely to choose the valid alarms which the user would like to be reported.
6. A method and apparatus according to any of the above claims where the sensor is a passive infrared sensor, a passive infrared motion detector, a contact switch or any sensor whose output conditionally generates the trigger.
7. A method and apparatus according to any of the above claims where the trigger condition is set on the server or elsewhere and downloaded to the device.
8. A method and apparatus according to any of the above claims where an indication of the remaining energy left in the battery and or the rate at which it is being consumed is communicated by the device to allow the user to reconfigure the device to save power.
9. A method and apparatus according to any of the above claims where the power source is a battery or a solar panel or other energy harvesting device.
10.A method and apparatus according to any of the above claims where the capacitor is replaced by a combination of a rechargeable battery and a capacitor or just a rechargeable battery.
11.A method and apparatus according to any of the above claims where the controller is woken up by a real time clock alarm.