BatteryUse – BeaconZone Blog

GATT Connections and Battery Life

Our battery use power testing uncovered some cases where the battery current use during advertising was such that the battery would last longer than manufacturer specification. What was going on?

After contacting the manufacturers, it turned out that some of them include a degree of configuration activity in their battery life estimates. If you only measure the current during advertising then you haven’t taken into account the extra current used during configuration. Configuration via manufacturer apps connects, rather than just listens, to the beacon via Bluetooth GATT. GATT connections consume significantly more power. For one off configuration this will be negligible but if you are in the habit of repeatedly changing the beacon configuration then the battery life will be impacted.

The same goes for platforms/apps that periodically connect to beacons to read, change or monitor beacon parameters. The battery won’t last as long. It’s also for this reason, it’s preferable to read sensor beacon sensor data in advertising data rather than via GATT when this is supported by the beacon and your scenario can cope will less frequently reported data.

Understanding the Impact of Settings on Bluetooth Beacon Battery Life

A common concern that frequently surfaces is the beacon’s battery life. It’s often overlooked that the device’s settings play a crucial role in battery consumption.

The Influence of Advertising Period on Battery Life

One of the most critical settings that impact a beacon’s battery life is the advertising period, also known as the advertising interval. This setting determines how frequently the beacon broadcasts its signal. The principle here is straightforward: the more often a beacon transmits, the more battery power it consumes.

For optimal battery performance, it is suggested to set the advertising period to around 600 milliseconds when the use is detection by smartphones. This interval strikes a balance between battery efficiency and effective communication with smartphones in the vicinity.

However, if the beacon is primarily detected by a gateway rather than smartphones, consider setting the advertising interval to one second or more. Gateways are not powered by batteries so are are scanning more intensively and so don’t require as frequent broadcasting as mobile devices do.

Tailoring Beacon Advertising for Specific Needs

Bluetooth beacons can support various types of advertising protocols, such as iBeacon, Eddystone, and others. A common mistake is to have multiple protocols enabled simultaneously, which can unnecessarily drain the battery. To optimise battery usage, it’s essential to configure your beacon to only advertise the type of protocol(s) needed for your specific application.

Reducing Power Consumption Through Transmission Power Settings

Another aspect to consider is the transmission power setting of your beacon. This setting determines the strength of the signal emitted by the beacon. A higher transmission power means a stronger signal and a longer physical range, but it also leads to quicker battery drainage.

Evaluate your use case to determine if a lower transmission power would suffice. For instance, in smaller indoor spaces, a lower power setting can be more than adequate, significantly extending the battery life of your beacon.

Conclusion

In summary, the longevity of your Bluetooth beacon’s battery is not solely dependent on the hardware but is significantly influenced by the right configuration settings. By understanding and optimising these settings, you can greatly enhance your beacon’s battery life. Using these tips, in some circumstances, beacon battery life can be extended to 10+ years which is longer than the useful life of some projects.

Powering Bluetooth Sensor Beacons via Micro-Energy Harvesting

Recent research A Comprehensive Study on the Internet of Things (IoT) and Micro-Energy Harvesting from Ambient Sources, from researchers in Spain, discusses the potential of micro-energy harvesting (MEH) as a sustainable power source for Internet of Things (IoT) devices, specifically Bluetooth sensors.

Micro-Energy Harvesting (MEH) is a technology that captures and converts small amounts of environmental energy such as like light, heat, or motion into electrical energy, which can power small electronic devices. The study suggests that MEH could be a sustainable solution for powering Internet of Things (IoT) devices, including Bluetooth sensors, due to their low power requirements.

The benefits of MEH include reducing the need for costly and environmentally harmful battery replacements and enabling the deployment of IoT devices in remote or hard-to-reach areas. The study also points out challenges, such as the small and variable amount of energy that can be harvested, which may not provide a reliable power supply for devices that need a steady source of energy. However, even with small temperature gradients between the environment and the cold side of the thermoelectric generator, it wass possible to make several communications per hour.

Sensor Beacons

Beacon Tx Power

A critical aspect of beacon setup is the transmission power (Tx power) setting, which determines the range of communication and the beacon battery consumption. The Tx power is measured in dBm (Decibel-milliwatt) and indicates the strength of the radio signal. The standard range of TX power settings typically falls within -30 dBm to +4 dBm, the ‘standard’ level being 0dBm.

Lower TX power settings, between less than 0 dBm, are used for short-range. Low power settings conserve battery life by minimizing energy consumption, making them ideal for battery-powered beacons. Higher power settings, above 0 dBm are used for long-range communications. However, it is important to note that higher power settings significantly impact battery life.

A change in ± 3dBm is a halving or doubling of power. An approximate rule of thumb is that this halving/doubling affects the battery in opposite way way. For example, going from 0dBm to -3dBm will approximately double the battery life. This is a very rough approximation because the beacon also uses a small amount of power when not transmitting, which is most of the time because the beacon only transmits for a few milliseconds (ms) every configurable 100ms to 10 sec.

A change in ± 3dBm doesn’t halve or double the range. Instead, the range approximately follows inverse square law with distance. Again this is approximate due to antenna characteristics, obstructions and interference. Signal processing at the receiver can also optimise performance and improve on the usable range.

Our recommendation is to start off with the ‘standard’ level of 0dBm. This will provide the battery life quoted by the manufacturer. If you really need more range then increase the power. If the range is further than you require then reduce the power to obtain a better battery life. You can test the range and received radio level using nRF Connect app on a smartphone.

Temperature Powered Bluetooth Beacons

Bluetooth Low Energy (BLE) beacons transmit a radio signal at regular intervals, powered by small batteries. The batteries need periodic replacement that can be time-consuming and costly when a large number of beacons are in use. There’s a new paper from Rzeszów University of Technology, Poland on Bluetooth Low Energy Beacon Powered by the Temperature Difference.

The paper proposes a power source that gathers energy through the Peltier effect. As temperature differences between two surfaces are present in most environments, the authors evaluated this energy source’s effectiveness in powering the beacons through measurements and simulations. They measured the beacon’s power supply demand in different modes and examined the Peltier module under different loads and temperature differences.

Based on the data gathered, they defined an energy conditioning system sufficient to power the beacon at a given temperature difference and developed a model of the proposed device. This solution eliminates the need for batteries, making the beacon maintenance-free.

Beacons Without Batteries

The batteries in the beacons we sell can last from months up to 7+ years depending on the beacon, battery size and type.

While the latest power efficient SoC beacons can make more of the available battery power you might want to consider not using batteries at all so as to ease maintenance.

USB powered beacons run from any USB socket and can be plugged into other hardware such as desktops or used with any inexpensive plug-in mains USB power supply available for a few pound/dollars/euros. However, the location of the antenna so close to the desktop or power supply can cause the range and Bluetooth radio signal spread to be compromised. Some USB beacons solve this problem by using an external dipole antenna.

The Bluetooth (Class 1) standard has a maximum output power of 20dBm. (Read our article for explanation of power). Many beacons don’t use this maximum as it would quickly flatten the battery. Most only allow up to +4dBm, +6dBm or +8dBm. In most cases battery beacons are set to operate at 0dBm. An advantage of USB powered beacons is that they can emit more power than is practical with a battery. For example, the the FSC-BP109 up to 4000m.

USB Beacons

Getting the AnkhMaway Battery Level from Advertising Data

One of the great things about AnkhMaway beacons is that they provide the battery level in the advertising data. This allows you to view or easily programmatically determine the battery level without connecting. For example, here’s the output from the Android iBeaconDetector app:

The last two useful hex characters of the advertising data, ‘5E’ in this case, gives the level out of 100. You can use an online Hex to decimal converter to see the value in decimal that’s 94% in this case.

Note that the battery level in the advertising data is only present for recent firmware versions which might not be the case if you haven’t purchased the beacons from BeaconZone.

Is There a Beacon That Works Without Bluetooth On?

We sometimes get asked if it’s possible that smartphones can detect beacons without Bluetooth being on. All beacons are based on Bluetooth LE that, in turn, relies on Bluetooth being switched on in the phone to scan for beacons. There’s no magic underling operating system mechanism on iOS nor Android that allows you to use Bluetooth without the user having Bluetooth on.

More users are leaving their Bluetooth on due to the proliferation of connecting with other devices such as cars, Bluetooth headphones and smart speakers. If you are writing an app you should take steps to detect if Bluetooth is on and prompt the user appropriately.

The phone and beacon industries need to better educate users that Bluetooth is no longer the heavy battery drainer it was in the early days of smartphones.

Beacon Battery Size, Type, Capacity and Life

After project rollout, human effort used in regularly replacing batteries can be significant and the human resource cost of doing so can dwarf the actual cost of the beacons. Hence, unless it’s a temporary scenario it’s best to specify beacons with as large a battery capacity as possible. Beacons with smaller capacity batteries are only suitable for short trials, temporary events or use during development.

While BeaconZone stocks a very large range of beacons, we purposely haven’t stocked any beacons with batteries smaller than CR2032 because the battery life of CR2025 and CR2016 beacons is usually too short. All our beacons use either CR2032, CR2450, CR2477 or AA batteries.

How long a battery lasts depends not just on the battery capacity but also the transmitted power, advertising interval and beacon processor chip type. This article only considers the battery itself.

Battery capacity is measured in mAh. The mA part (without the h) is the unit of current. As an example, a CR2477 battery typically has a capacity of 1000 mAh which means it can supply 1 mA for 1000 hours or, for example, 2mA for 500 hours. However, most beacons only use tens or hundreds of µA when transmitting, where 1 µA is 1000 times smaller than a 1 mA. Also Bluetooth beacons only transmit for a few milliseconds (1 ms = 1/1000 sec) at a time so you can see how a coin battery can last a long time.

Here are the main battery sizes and their typical mAh rating:

CR2032 = 250 mAh
CR2450 = 500 mAh
CR2477 = 1000 mAh
2 x AA = 2200mAh (Alkaline), 3000 mAh (Li)
4 x AA = 4400mAh (Alkaline) or 6000 mAh (Li)

A beacon such as the i3 containing 2 Lithium batteries can last 3x one with a CR2477 battery and 24x one with a CR2032 battery. This gives a battery life of up to 3 to 4 years depending on other configuration parameters.

Lithium AA batteries such as the Duracell Ultra Lithium and Energizer Ultimate don’t just last longer than Alkaline AA batteries. Their voltage also doesn’t vary so much with temperature which might be a consideration if your rollout is outdoors.

Beacon Battery Use Testing

One of the issues with using Bluetooth beacons is that it’s not easy to predict how long batteries are going to last. Battery life depends not just on the battery capacity but also the transmitted power, advertising interval, beacon processor chip type and whether the beacon has timed transmission. Also, beacons vary from model to model, sometimes even between revisions of the same model. In some scenarios it’s essential to know which beacon models are the most power efficient and how long batteries will last.

Over the years we have spent a considerable amount of time investigating actual battery use. It’s not as simple as you might think. You can’t use an ammeter because it can’t see the short pulses in peak power. The majority of the power is expended in very short, few millisecond (ms) transmit pulses, in between which the beacon goes into low power sleep.

Nordic Bluetooth Advertising Power Use

Testing needs to integrate the current used over multiple advertising periods. The test equipment needs to capture this data at sub 1ms precision in order to catch the pulses. The testing also needs to be flexible enough to work for advertising periods from 100ms to 10 sec.

We have custom in-house designed test equipment capable of real-time battery current testing. This enables us to compare different manufacturers’ beacons having the same configured settings and provide our consultancy clients with beacon battery use data based on their exact configuration settings.

As an example, an interesting test we did was was to compare the Sensoro AA transmitting just iBeacon vs iBeacon at the same time as the 3x Eddystone advertising packets. With only ibeacon @ 760ms, 0dBm advertising, 4 typical alkaline batteries would last 7.7 years. Transmitting all 4 iBeacon and Eddystone frames reduces the battery life to 2.9 years.

Another interesting observation has been that the beacons that have the strongest signals aren’t necessarily the ones using the most battery power. Design of aspects, such as the antenna, contribute to power efficiency.

We also offer ad-hoc beacon battery use testing.