The Bluetooth wireless data protocol has been in use for over ten years, and in recent time the new low energy standard has been introduced. This gives designers another option for wireless connectivity between devices with an extremely low power consumption. In the following we examine what it is, the benefits and implementation examples.
Bluetooth LE (for “low energy”) is aimed at novel applications of short-range wireless communication in connected Internet-of-Things devices for medical, fitness, sports, security and home entertainment applications, and was merged into the main Bluetooth specification as part of the Bluetooth Core Specification v4.0 in 2010.
Also known as “Bluetooth Smart”, it enables new applications of Bluetooth networking in small, power-efficient Internet-of-Things devices that can operate for months or even years on tiny coin cell batteries or other small-scale energy sources. Bluetooth LE devices offer ultra-low power consumption, particularly in idle or sleep modes, multi-vendor interoperability and low cost, whilst maintaining radio link range that is sufficiently long enough for the intended applications.
The Bluetooth LE protocol is not backwards-compatible with the “classic” Bluetooth – however, the Bluetooth 4.0 specification does allow for dual-mode Bluetooth implementations – where the device can communicate using both classic Bluetooth and Bluetooth LE. Whilst Bluetooth Low Energy uses a simpler modulation system than classic Bluetooth, it employs the same 2.4 GHz ISM band, allowing dual-mode devices to share a common antenna and RF electronics for both Classic and Bluetooth LE communication.
Small, power-efficient devices like wearable athletic and medical sensors are typically based on a single-mode Bluetooth LE system in order to minimise power consumption, size and cost. In devices like notebooks and smart phones, though, dual-mode Bluetooth is typically implemented, allowing communication with both Bluetooth LE and classic Bluetooth devices. When operated in Bluetooth LE mode, the Bluetooth LE stack is used whilst the RF hardware and antenna is usually the same set of hardware as used for classic Bluetooth operation.
Devices using Bluetooth LE typically have a power consumption, for Bluetooth communication, which is a fraction of that of classic Bluetooth devices. In many cases, devices can operate for a year or more on a single coin cell. This potentially makes Bluetooth LE very attractive for Internet-of-Things networks, telemetry and data logging from environmental sensor networks, for example.
Since many modern consumer devices such as mobile phones and notebooks have built-in Bluetooth LE support, data can be delivered directly to the user’s fingertips from the Bluetooth sensor network with no need for an intermediary gateway or router as would be required for an Internet-of-Things network employing other technologies such as 802.15.4 ZigBee. This direct interoperability with a large installed base of smart phones, tablets and notebooks could potentially be a very significant attraction of Bluetooth LE networks in wireless sensor network and Internet-of-Things applications.
An active Bluetooth radio has a peak current consumption on the order of about 10 milliamps, reduced to about 10 nanoamps (ideally) in sleep mode. In a Bluetooth LE system, the objective is to operate the radio with a very low duty cycle on the order of about 0.1-0.5%, resulting in average current consumption on the order of 10 microamps. At an average current consumption of 20 microamps, such a system could be operated off a typical CR2032 lithium coin cell (with a charge capacity of 230 milliamp-hours) for 1.3 years without battery replacement.
The lower power consumption of Bluetooth LE is not achieved by the nature of the radio transceiver itself (since the same RF hardware is typically used, in dual-mode Bluetooth devices), but by the design of the Bluetooth LE stack to allow low duty cycles for the radio and optimisation for transmission in small bursts – a Bluetooth LE device used for continuous data transfer would not have a lower power consumption than a classic Bluetooth device transmitting the same amount of data.
The Bluetooth specifications define many different profiles for Bluetooth LE devices – specifications for how a device works in particular families of applications. Manufacturers are expected to implement the appropriate profiles for their device in order to ensure compatibility between different devices from different vendors. A particular device may implement more than one profile – for example one device may contain both a heart rate monitor and a temperature sensor. Here is a non-exhaustive list of a few different Bluetooth LE profiles in use:
- Health Thermometer Profile, for medical temperature measurement devices.
- Glucose Monitor Profile, for medical blood glucose measurement and logging.
- Proximity Profile, which allows one device to detect whether another device is within proximity, using RF signal strength to provide a rough range estimate. This is intended for security applications as an “electronic leash”, allowing the detection of devices being moved outside a controlled area.
- Running Speed and Cadence profile, for monitoring and logging athletic performance.
- Heart Rate Profile, for heart-rate measurement in medical and athletic applications.
- Phone Alert Status Profile, which allows a client device to receive notifications (such as an incoming call or email message) from a smart phone. As an example, this is employed in the Pebble smart watch.
The Bluetooth LE shows a lot of promise, and with a minimal chip set cost gives the designer another cost-effective wireless protocol. And if this meets your needs but you’re not sure how to progress with a reliable implementation, we can partner with you to take care of this either in revisions of existing products or as part of new designs. With our experience in retail and commercial products we have the ability to target your product’s design to the required end-user market and all the steps required to make it happen.
We can create or tailor just about anything from a wireless temperature sensor to a complete Internet-enabled system for you – within your required time-frame and your budget. For more information or a confidential discussion about your ideas and how we can help bring them to life – click here to contact us, or telephone 1800 810 124.
LX is an award-winning electronics design company based in Sydney, Australia. LX services include full turnkey design, electronics, hardware, software and firmware design. LX specialises in embedded systems and wireless technologies design. https://lx-group.com.au
