Patent Description:
Battery power is often used in preference to other power supplies, such as networked "mains" power supply or an intermittent or unreliable one such as solar, wave or wind, where continuity of supply is required together with a freedom to locate the device being powered without the constraint of having a wired connection. For example, in security monitoring systems, such as domestic burglar alarms and the like, as e.g. disclosed by <CIT>, peripherals such as glass-break detectors, movement sensors, door/window sensors, video cameras, and microphones, are preferably battery-powered so they can be situated wherever is most appropriate or most convenient without the need to run an electrical supply line. A problem with battery power is that, unlike "mains" electricity, the amount of power available is limited - so that eventually the batteries need to be replaced before they completely exhausted, to avoid the peripheral from ceasing to operate. Obviously, the proper operation of a security monitoring system is critically dependent upon the proper functioning of the various peripherals of the system.

<CIT> discloses a use-adaptive fuel gauging for battery powered electronic devices.

Although at the design stage it is possible to plan for a certain battery lifetime, in practice the same device will flatten its batteries at different rates depending upon the activity of the device, which depends upon its location and other factors. So we want to know when the battery the device needs changing, before it needs changing, but we also want to avoid changing batteries too soon because there is an expense and an opportunity cost (e.g. fixing an appointment for a service engineer to visit, and ensuring the visit takes place) to changing batteries. It is known to monitor energy consumption in battery-powered devices, so that an "end of life" warning can be given before the battery power supply ceases to have enough power to run the device correctly. For example, it is known to provide what are known as "fuel gauges" which use a technique such as "Coulomb counting" to monitor the amount of energy consumed by device. When the fuel gauge determines that a battery power supply is sufficiently depleted, an alarm of some kind is raised. Unfortunately, such fuel gauges themselves consume power. In security monitoring systems the power constraints for peripheral devices are severe, because a design goal is to have an average battery life of more than two years for every peripheral, and in many cases the target battery life is as much as five years. Of course, most security monitoring systems fortunately see very few security events each year, although they may see a greater number of false alarms. This means that most of the energy in a battery power supply for such a peripheral is used running the peripheral in a sleep mode or an idle mode, rather than in dealing with an alarm event. Against this background, the use of a fuel gauge arrangement to monitor energy consumption is contrary to the ideal of reducing energy drain in the usual idle or sleep states.

Another problem which needs to be addressed is how to deal with the variability in the amount of energy provided by a new set of batteries, when the energy content of batteries that are externally essentially identical vary very significantly, being critically dependent both upon the battery chemistry and even the brand of the battery.

There therefore exists a need for a method of determining battery status in a battery powered device, and for a method of controlling a battery powered device based on an identification of a battery chemistry.

In a first aspect there is provided a battery powered electronic device comprising: a first part that includes an electronic controller to control the operation of the device; a second part, controlled by the controller, which uses battery power only when energised and which is energised only intermittently;.

Preferably the device is configured to identify the battery power supply by determining the battery chemistry of the battery power supply. Because batteries of the same external configuration - e.g. AA, AAA, D, typically have very different energy capacities, it is useful to be able to identify the chemistry of a battery so that use can be made.

Optionally, the device is configured to determine the battery chemistry by comparing battery voltage measurements made after a first interval from initial use of the battery power supply, and again after a second longer interval. Optionally, the first interval corresponds to a first predetermined quantity of energy used from the battery power supply, and the second interval corresponds to a second predetermined quantity of energy used from the battery power supply. Optionally, the first predetermined quantity of energy is between <NUM> and <NUM>% of the initial energy content of the battery power supply. Optionally, the second predetermined quantity of energy is greater than the first predetermined quantity of energy and is between <NUM> and <NUM>% of the initial energy content of the battery power supply.

Preferably, the device is also configured to identify the battery power supply by determining the type of battery in the battery power supply. The type may equate with a brand or product specification.

Optionally, the type of battery is determined based on a comparison of a measured voltage drop with a stored reference value for alkaline batteries.

Preferably the type of battery is determined based on a comparison of results of the comparison of battery voltage measurements with stored reference values for known types of batteries.

Preferably reference values are stored for known types of batteries of at least two different battery chemistries.

Preferably, the device is configured to identify at least alkaline and lithium battery chemistries.

Preferably the device of the first aspect is configured to estimate the amount of energy consumed by the main part of the device based on knowledge of the energy usage of the first part in each of a sleep state and one or more active states. Preferably, the one or more active states include a radio receiving state and a radio transmitting state. Preferably the device is configured to estimate the amount of energy consumed by the main part of the device based on knowledge of the energy usage of the first part in an idle state.

Preferably the device of the first aspect further comprises a store that stores a power usage value for the first part in each of the multiple activity states.

Optionally the device is an intelligent peripheral of a security monitoring system, for example a video camera for such a system. Preferably, the second part comprises an image sensor and a video processor, and optionally a Wi-Fi transceiver. Preferably, the first part comprises a transceiver for communicating with a controller of the security monitoring system, optionally a transceiver operating in ISM radio bands.

According to a second aspect, there is provided a method of determining battery status in a battery powered device having a main part that is always on and that includes an electronic controller to control the operation of the device, and a battery power supply, the method comprising:.

Preferably, estimating the amount of energy consumed by the main part of the device is based on knowledge of the energy usage of the first part in each of a sleep state and one or more active states. Preferably, the one or more active states include a radio receiving state and a radio transmitting state. Preferably, estimating the amount of energy consumed by the main part of the device is based on knowledge of the energy usage of the first part in an idle state.

Estimating the amount of energy consumed by the main part of the device may be based on power usage values for the first part in each of the multiple activity states.

Optionally, estimating the amount of energy consumed by the main part of the device in each of the multiple activity states is based on activity periods as short as <NUM> millisecond, and optionally as short as <NUM> millisecond.

Optionally, estimating the amount of energy consumed by the main part of the device in each of the multiple activity states is based on activity periods as short as the period of a system clock of the device. Although this is an extremely short period, the clock is already available and using a short period can help achieve high accuracy in power usage estimation.

Optionally, if the remaining energy capacity is determined to be less than a predetermined amount, generating a signal to indicate that the battery power supply needs to be replaced. Preferably such a signal is transmitted to the central unit of the security monitoring system, from where it may be onward transmitted to a central monitoring station so that a service engineer may be dispatched to change the battery pack. Alternatively or additionally, the device may include an audio output device to emit a signal indicative of the need to change the battery pack - in this way, the user of the system is also alerted of the need to change the battery pack. Depending upon the circumstances, a user may be permitted to change a battery pack when the system is disarmed.

Preferably, the method of the second aspect further comprises identify the battery power supply by determining the battery chemistry of the battery power supply. Although there are significant differences between the available energy capacity of different brands of alkaline cells, and likewise for lithium chemistry cells, there is generally a bigger difference between cells of the two chemistries.

Preferably, the device is configured to determine the battery chemistry by comparing battery voltage measurements made after a first interval from initial use of the battery power supply, and again after a second longer interval. In this way it may be possible to identify the battery type with high accuracy, meaning that a better estimate can be made of remaining battery life. In particular, we select the second longer interval on the basis that we want the expected voltage drop to be large if alkaline batteries are used, because there are some uncertainties like temperature and difference between brands.

Preferably, the first interval corresponds to a first predetermined quantity of energy used from the battery power supply, and the second interval corresponds to a second predetermined quantity of energy used from the battery power supply.

Optionally, the first predetermined quantity of energy is between <NUM> and <NUM>% of the initial energy content of the battery power supply. In this way, we can be sure that we have come past the initial voltage drop point for lithium chemistry batteries.

Optionally, the second predetermined quantity of energy is greater than the first predetermined quantity of energy and is between <NUM> and <NUM>% of the initial energy content of the battery power supply. After such a significant power usage, the reliability of determining battery type may be greatly increased, while the bulk of the initial energy quantity remains to be used - so that adjustment of operating parameters, such as frame rate and resolution can be performed over the bulk of the life of the battery pack, thereby helping to achieve good battery life irrespective of the type of battery installed.

Optionally, the battery power supply may be identified by determining the type of battery in the battery power supply. For example, by determining that the battery type is a recognised Energiser, Panasonic, or Duracell battery- although in practice the particular brands supported may all be different from these examples. The determination of battery type may, for example, be achieved by the setting of a switch or the like when a battery power supply is initially installed.

Optionally, determining the type of battery may be based on a comparison of a measured voltage drop with a stored reference value for alkaline batteries.

Optionally, the type of battery may be determined by comparing results of a comparison of battery voltage measurements with stored reference values for known types of batteries.

Optionally, in the method of the second aspect comprises comparing results of a comparison of battery voltage measurements with stored reference values for known types of batteries of at least two different battery chemistries.

Optionally, in the method of the second aspect further comprising determining whether the chemistry is an alkaline or a lithium chemistry.

<FIG> shows a battery-powered electronic device <NUM>. The device comprises a first part, that includes an electronic controller <NUM> to control the operation of the device, and the second part <NUM>, controlled by the controller <NUM>, which uses battery power only when energised and which is energised only intermittently. The second part <NUM> of the device has a power consumption that is greater than that of the first part. In the illustrated example the electronic device <NUM> is a peripheral of a security monitoring system, details of which will be described later with reference to <FIG>, specifically a video camera peripheral. As can be seen, the second part <NUM> includes a video sensor <NUM>, which is coupled to a video processor <NUM> which is in turn coupled to a Wi-Fi transceiver <NUM>. This second part <NUM> is off, drawing no power from the battery power supply <NUM>, when the peripheral is in standby mode - which is most of the time. Conversely, the first part of the device, which may be considered to be the main part, draws power from the battery power supply <NUM> all the time, even when the first part is in a sleep state. The second part <NUM> consumes a lot of energy when it is taking photos, streaming video or sending images over Wi-Fi. The video processor <NUM> is an image signal processor (ISP) used for photo capture and controlling the Wi-Fi module <NUM>. A suitable ISP device is the Omnivision OA7000. The Wi-Fi transceiver may conveniently be provided by an RAF module such as a Cypress Semiconductor CYW43012, which is an ultra-low-power Wi-Fi and Bluetooth device which is compliant with IEEE <NUM>. The battery power supply <NUM> is here illustrated as including six battery cells <NUM>, which are arranged in two pairs of three series-connected cells. For example, the battery cells <NUM> may each be AA batteries, arranged to provide a nominal battery power supply voltage of <NUM> V. Clearly, the number, type, voltage, and arrangement of batteries within the battery power supply is not constrained, and the invention is clearly applicable to any battery power supply configuration.

The device further comprises a battery fuel gauge <NUM>, coupled to the battery power supply <NUM> and the controller <NUM>. Conveniently, the battery fuel gauge is, for example, a BQ35100 device from Texas Instruments, although suitable alternatives may be obtained from other manufacturers. With the battery fuel gauge <NUM> makes accurate voltage, temperature, current, and Coulomb counter measurements that report battery health and service life. The BQ35100 has a state of health (SOH) algorithm for lithium manganese dioxide batteries, and an end of service (EOS) algorithm for LiSOCL2 batteries, as well as a Coulomb accumulation (ACC) algorithm for all battery types. Texas Instruments quote a current consumption of approximately <NUM> micro amps for the SOH algorithm, approximately <NUM> micro amps for the EOS algorithm, and approximately <NUM> micro amps for the ACC diagnostic update. Although these current figures are commendably low, peripheral devices for security monitoring systems are required to have very long battery lives - typically the battery lifetime of a peripheral is required to be at least two years, and more preferably three or more years, and it would be difficult if not impossible to achieve such battery lifetimes if the fuel gauge <NUM> were used to monitor all power consumption of the electronic device. Consequently, we propose using the fuel gauge to record the amount of energy consumed by the second part <NUM> the fuel gauge only being activated when the second part is activated. However, as previously mentioned, the peripheral device <NUM> is "always on", and hence we need to take account of the energy consumption of the main part if we are to keep track of the condition of the battery power supply <NUM>, so that we know in advance when it is necessary to replace the battery power supply. In order to address this need we provide a monitoring arrangement <NUM>, which is distinct from the fuel gauge <NUM>.

The monitoring arrangement <NUM> is shown schematically as a module within the controller <NUM> - although in practice the monitoring arrangement will typically be implemented as an algorithm or software routine run by the controller <NUM>, the algorithm or software routine being stored, for example on memory <NUM>. The monitoring arrangement <NUM> is arranged to monitor the amount of time that the controller <NUM> spends in each of multiple activity states. For example, the controller <NUM> will typically have a sleep state, and one or more active states. The active states may include an idle state, a radio receiving state, and a radio transmitting state. Other active states may also be recognised. The monitoring arrangement <NUM> is arranged to monitor the amount of time that the controller spends each of these states. The power consumption in each of these states is determined at the pre-production stage. The amount of current used in the identified states is measured in advance. Preferably the measurements are done at more than one supply voltage, e.g. one low-voltage and one high-voltage, to reflect the changes in battery supply voltage that occur over the lifetime of a set of batteries. The corresponding power consumption values for each of the states is stored in memory in the device. In determining how much energy is being used, the monitoring arrangement <NUM> identifies the relevant state and then interpolates between the stored current values for the high and low voltage, based on the current voltage. The estimation is then done by measuring the amount of time spent on each of the different states. This is preferably done to a good degree of accuracy for example based on activity periods as short as <NUM>, optionally as short as <NUM>. The real-time clock associated with the processor <NUM> can be used as the basis for the activity periods measured. Therefore, with knowledge of the amount of time that the controller has spent in each state, and the known power consumption values, it becomes possible to estimate the amount of energy consumed by the first part.

The controller/processor <NUM> is preferably provided as part of a system on chip (SoC) device such as one of Silicon Labs' EFR32FG13 family of devices, which have a <NUM>-bit Arm processor, sub-GHz radio transceivers, e.g. for ISM <NUM> and other frequencies, and which may be used with <NUM>. xKhz crystal for the RTC. Thus with such a device, or a comparable one, the measurement of states over the controller <NUM> may be as short as the clock cycle of the RTC.

In order to determine the amount of energy remaining in the battery power supply, it is necessary to know the initial energy capacity of the battery power supply. Although we may know the contents of the battery power supply in terms of the number and configuration of the cells that make up the power supply, for example in the illustrated example we have six AA cells, this is insufficient to tell us the initial energy capacity. This is because the energy content of AA batteries varies not just between competing chemistries, for example alkaline and lithium chemistries, but also between different brands of cells with nominally the same chemistry. So, for example the best alkaline AA batteries may contain up to <NUM>% more energy than the worst alkaline double a batteries. Likewise, there is a great disparity between the energy content of the best and worst lithium chemistry batteries. It is useful therefore to know what type of cells are included in the battery power supply. At a simple level, the type of cells could be captured, on installation, by the installer setting a selector <NUM> to indicate the chemistry, for example alkaline or lithium - perhaps by setting a switch accordingly. Preferably the device includes an additional selector to enable the installer to indicate the brand of battery that has been installed. Energy capacities for each of the brands of battery that can be indicated through the additional selector are stored in the device, for example in memory <NUM>, so that the controller <NUM> can determine an initial energy capacity of the battery power supply based on an identification of the battery power supply. The controller or processor <NUM> is then able to determine the remaining energy capacity of the battery power supply based on the determined initial energy capacity, the estimate of the amount of energy consumed by the first part, and the record from the fuel gauge <NUM> of the amount of energy consumed by the second part <NUM>.

Optionally, the controller <NUM> may then, if the remaining energy capacity is determined to be less than a predetermined amount, generates a signal to indicate that it is time to replace the battery power supply.

Although, as previously described, the device may include one or more battery type selector <NUM>, and installer may forget to reset the selector, or may set it incorrectly. Consequently, the device is preferably configured to perform the process by means of which it can identify the battery chemistry, and preferably also identify the type of battery - i.e. the brand or model of the battery, from amongst a selection of known battery brands for which energy storage data is stored in the device. To do this, the devices configured to compare battery voltage measurements made at two different times. The approach will now be described with reference to <FIG> which shows output voltage plotted against the amount of energy withdrawn from the battery, for three notional brands of lithium chemistry battery, A, B and C, and three notional brands of alkaline chemistry battery, D,E, and F. It will be recognised that the plot corresponds to the battery pack illustrated in <FIG>, that is a battery pack arranged to supply and nominal voltage of <NUM> V, using six AA batteries arranged in two parallel stacks of three batteries connected in series. It can be seen that initially the battery pack provides in excess of <NUM> V, with some of the brands of lithium batteries supplying up to around <NUM> V. Importantly the plots for the six battery types overlap very significantly at this stage where little power has been drawn from the battery pack. It will be seen that the plots for the two different chemistries start to diverge significantly after about <NUM>. 2Ah of energy has been consumed with a very striking difference in supply voltage appearing by the time <NUM> Ah has been consumed. It is from around this point that significant differences in the behaviour of the different alkaline brands emerges, whereas differences between the different lithium brands are discernible earlier. By keeping track of the amount of energy supplied to the device from the battery power supply <NUM>, the processor <NUM> can run a check of supplied battery voltage after sufficient energy has been supplied for the differences between the supply voltages of the different chemistries to become clearly discernible. After performing one such check, after for example <NUM> Ah has been supplied, the processor <NUM> should be able to determine whether the type selector <NUM> has been correctly set, at least in terms of chemistry. Performing a second such check later, for example when the amount of energy supplied is between <NUM> and <NUM> Ah, for example <NUM> Ah should enable the processor to be to identify the type of alkaline battery, or type of lithium chemistry battery, that has been installed, based for example on the voltage drop between the first check and the second check. At each stage, the processor can calculate the amount of energy remaining in the battery power supply.

It can be seen from <FIG> that lithium chemistry batteries are typically able to supply a voltage close to the nominal battery supply voltage of <NUM> V for much longer than are alkaline batteries. In fact, alkaline cells tend to be rather poor at delivering anything like their full rated capacity, which might be in the region of 2500mAh, unless they are supplying at very low currents. For an application such as a video camera peripheral for a security monitoring system the current demand is sufficiently great that alkaline cells may only deliver less than half their full rated capacity. So that a battery pack with <NUM> AA cells may only have an effective power rating of as little as 4200mAh. Conversely, lithium chemistry cells are much better able to supply near their full rated capacity even when supplying at quite high currents. With this in mind, a device such as the peripheral shown in <FIG>, which occasionally requires quite high supply currents, is preferably arranged to adjust its performance based on the chemistry of the cells fitted in the battery power supply. The energy requirement of the second part of the device, that in the <FIG> embodiment includes the image sensor, the camera video processor, and the RF microcontroller, depends to some extent and configurable settings such as frame rate, resolution, RF transmitter power and bandwidth. If lithium chemistry batteries are fitted it may be possible to stream video at <NUM> frames a second, at a resolution of 1080P, in full colour, using a wider bandwidth and hence high speed Wi-Fi connection - given that in practice the peripheral is rarely called upon to transmit video. All this may be achieved while still achieving the design battery lifetime. Conversely, if the battery power supply is fitted with alkaline cells it may be impossible to achieve the design battery lifetime unless the performance of the second part is reduced, for example by significantly reducing the frame rate, by reducing the resolution significantly, by sending monochrome rather than full-colour images, and by reducing the bandwidth and/or transmission power of the Wi-Fi transmitter. With this in mind, once the processor <NUM> has determined the battery chemistry, it preferably configures the second part, in particular the ISP and the RF microcontroller, etc. to reduce energy consumption and hence prolong useful battery life.

A further complication arises from the fact that the supply voltage of a battery, whether alkaline or lithium chemistry, may vary very significantly over the temperature range to which a peripheral of a security monitoring system may be exposed - especially if the peripheral is mounted outside. This is represented schematically in <FIG> which shows how the voltage supplied from a battery power supply such as that in <FIG> varies according to temperature for an example of an alkaline chemistry battery and an example of a lithium chemistry battery. Basically, if the battery is hot, i.e. at <NUM> or above, it can supply a significantly higher voltage for longer than it could if it were at <NUM>. Consequently, particularly if the peripheral is mounted outside or somewhere else where it may be exposed to extremes of temperature - a cold store, a factory, or processing plant, the device is preferably configured to take account of the temperature of the battery pack - or at least of the ambient temperature. Preferably therefore a temperature sensor <NUM> is provided as part of the battery power supply or as part of the device adjacent the battery power supply. Then, when estimating the amount of energy left in the battery power supply, the controller <NUM> deducts the estimate of the amount of energy consumed by the first part and the record from the fuel gauge of the amount of energy consumed by the second part from the initial energy capacity of the battery pack, and then adjusts its estimate of the remaining energy capacity based on its knowledge of the current temperature and the temperature performance of the battery chemistry/type known to be installed.

One of the benefits of the present invention is that the processor <NUM> is able to estimate fairly accurately the amount of available energy remaining in the battery power supply. As noted earlier, for many applications, including in particular for peripherals of a security monitoring system such as the video device shown in <FIG>, it is important not to let the battery power dropped so low that the device is no longer able to perform its function - which is to contribute to the proper functioning of the security monitoring system. In other words, we don't want the battery power to full so low that, in the event of an incident, the camera is no longer able to capture and share images or video with the controller of the security monitoring system. It is generally established that a peripheral in the security monitoring system should indicate the need for a battery change at least <NUM> days before the battery powerful so low that the peripheral cease working. For a device such as the video peripheral of <FIG> we want the batteries to have sufficient power not only to support an idle or sleep state for <NUM> days, but we also want to be able to capture a burglary attempt or a false alarm within this period. We therefore factory in the amount of energy required for the peripheral to handle the events associated with a burglary attempt or a false alarm and add this to what can be regarded as a safe margin on top of an average <NUM> days battery life: we treat the resulting energy total is the minimum before which the peripheral will report a low battery condition. Depending upon the logistics supporting battery replacement, which may involve a visit from a service engineer, it will generally be prudent to budget for at least a <NUM> day energy capacity in addition to the amount of energy required for handling the events associated with a burglary attempt or false alarm. Optionally, the amount is increased to cover a <NUM> day energy capacity, in addition to the amount of energy required for handling the events associated with burglary attempt or false alarm.

The device may also be configured to keep track of how much energy has been used per day for the last <NUM> days, and a sliding window basis. Based on this history, an average usage per day can be calculated. And based on that value, an estimate is produced of the number of days the device can continue to run, taking account of how much has been consumed so far, the energy required two handle one burglary attempt or force alarm, the full battery pack capacity, and adjusted for temperature. If the expected number of days is less than a target number of days, e.g. <NUM> days, <NUM> days, or <NUM> days, the device transmits a low battery alert signal to the controller of the security monitoring system. The alert signal may then be onwards transmitted to a central monitoring station that supports the security monitoring system, so that for example, a service engineer could be called out to replace the batteries.

<FIG> also shows a battery anti-tamper arrangement <NUM> which is designed to trigger the controller <NUM> into sending a tamper alert signal to the controller of the security monitoring system in the event that an attempt is made to remove the batteries from the device. A device anti-tamper arrangement <NUM> is also provided so that a tamper alert signal will also be sent to the controller of the security monitoring system in the event that an attempt is made to remove the device from its fixed position. Also shown in <FIG> are an ISM transceiver <NUM>, which may be part of the previously mentioned EFR SoC, and crystal oscillator <NUM> which is used by the RTC of the processor <NUM> (e.g. the EFR SoC).

Claim 1:
A battery powered electronic device comprising: a first part that includes an electronic controller to control the operation of the device;
a second part, controlled by the controller, which uses battery power only when energised and which is energised only intermittently;
wherein the power consumption of the second part is greater than that of the first part;
a battery power supply;
a fuel gauge to record the amount of energy consumed by the second part, optionally using coulomb counting, the fuel gauge only being activated when the second part is activated;
a monitoring arrangement, distinct from the fuel gauge, to monitor the amount of time that the controller spends in each of multiple activity states;
the device being configured to:
estimate the amount of energy consumed by the first part based on knowledge of the energy usage of the first part in each of the multiple activity states;
determine an initial energy capacity of the battery power supply based on an identification of the battery power supply; and
determine the remaining energy capacity of the battery power supply based on the determined initial energy capacity, the estimate of the amount of energy consumed by the first part, and
the record from the fuel gauge of the amount of energy consumed by the second part.