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Wearable Technologies Meet Bluetooth Low Energy

By Dave Bursky, Semiconductor Technology Editor

The low-power Bluetooth® operating mode gives wearable technologies the endurance they need.

Wearable technologies come in many forms – fabrics with integrated wiring and sensors; medical devices for in-hospital use such as heart-rate monitors, RFID wristbands, etc.; smart watches and fitness bands to keep track of your health as you exercise, smart glasses such as Google Glass, and even electronic jewelry with Bluetooth links, and clothing with embedded LEDS to display custom messages or artwork. Many of these wearable devices communicate wirelessly with a smartphone, tablet or a custom basestation, and in almost every case one form of Bluetooth is used to provide the connection.

All eyes are on the wearable electronics portion of the market – indisputably a market of billions of dollars and becoming tens of billions of dollars in the next decade, stated Dr. Peter Harrop, Chairman of IDTechEx, a market research company. A big challenge in selling the body-mounted devices, from headwear to footwear, Harrop explained, is a lack of available real estate. We only have one head and we will rarely put more than one electronic device on that head. Additionally, we behave as if we only have one wrist, so it is a challenge to get us to remove our existing bracelet, watch etc. and replace it with an electronic device because we are unlikely to have something functional on each wrist or several things on one wrist.

At the recently held Wearables DevCon in Burlingame, Calif., and an upcoming Smart Fabrics Conference in San Francisco, many of the issues relating to hardware and software implementation were and will be discussed. For example, several sessions at the Wearables DevCon examined the implementation challenges for Bluetooth-enabled hardware using Android, looking at the development of the Pebble smart watch and still other aspects of hardware development.

Next week’s Smart Fabrics event includes companies such as BodiTrak who will show off smart body sensors that can be embedded in stretchable/breathable smart fabrics, and even sensors embedded in smart beds that sense and then adjust the bed to meet the sleeper’s needs through the night. Another company, Heapsylon, will be showing its Sensoria Fitness smart clothing products, including a Fitness T-shirt and Sports Bra that supplement its previously released Sensoria Fitness Socks (Figure 1). The clothing is powered by proprietary textile sensors and Bluetooth-enabled detachable devices.

Beyond fitness, the Sensoria wearables are geared to enhance the overall wellness of its user by tracking how much sleep he is getting, and how “good” the sleep is. The ComfTech textile sensor offers an electrocardiogram (ECG) signal through virtually any electronic device that is able to provide information such as: Heart Rate, Breathing Rate, and Calorie Burn.

Figure 1: The Sensoria Fitness T-shirt incorporates proprietary textile sensors and can connect to Bluetooth enabled detachable devices such as from Polar or Garmin.

Additional companies showing off smart fabrics include Clothing+, and EEONYX Corp., While Shimmer will be highlighting a wearable sensor platform, the Shimmer3, that measures just 51 x 34 x 14 mm. The platform is based around an ultra-low-power Texas Instruments MSP430 16-bit microcontroller (Figure 2). The MCU consumes less than 100 microamps/MHz, and just 100 nanoamps is needed in its stop mode to retain data in the MCU’s RAM. Also included in the sensor platform are accelerometers, magnetometers, gyroscopes, a pressure sensor, and a Bluetooth radio for wireless connectivity.

Figure 2: The wearable sensor platform offered by Shimmer is based around a TI MSP430 16-bit microcontroller and packs accelerometers, gyroscopes, magnetometers, pressure sensors as well as a Bluetooth radio.

Bluetooth–taking over the connectivity challenge

Bluetooth devices have evolved to meet the increasing demand for low-power solutions. Today there are three mainstream standards for Bluetooth in use – Bluetooth 2.0 (often referred to as Bluetooth Classic), Bluetooth 4.0, which offers both a standard high-speed mode and a low-energy mode with limited data rate referred to Bluetooth LE; and a single-mode Bluetooth LE standard that keeps power consumption to a minimum.  A recent addition to the Bluetooth offerings is an enhanced version of Bluetooth LE, dubbed Bluetooth Smart, that uses the GATT (Generic Attribute Profile), which is built on top of the Attribute Protocol (ATT). The GATT profile establishes common operations and a framework for the data transported and stored by the ATT. The use of GATT simplifies the task of connecting a wide variety of Bluetooth devices to a platform.

Almost all vendors offering Bluetooth chips are adding Bluetooth Smart to their portfolios.  At the recent Bluetooth World Conference held in San Jose, Calif., Broadcom, CSR, Dialog Semiconductor, EM Microelectronic, Nordic Semiconductor, Texas Instruments all highlighted their BT Smart solutions.  One of the newest solutions, the DA14580 from Dialog is a highly-integrated Bluetooth chip that incorporates an ARM® Cortex®-M0 32-bit processor core to handle both control operations as well as executing the Bluetooth software stack, thus eliminating the need for a second microcontroller.

Housed in a tiny 2.5 by 2.5 mm chip-scale package (or standard 5 by 5 or 6 by 6 mm QFN packages, the chip and the surrounding components needed to deliver a complete BT subsystem require little additional board space. Multichip modules from Murata and Panasonic provide complete BT LE subsystems in an area of less than 11.2 mm2. The BT Smart chip has a deep-sleep mode that consumes just 500 nA with data only maintained in the retention memory. When powered by a 3-V supply, the chip’s transmit power consumption is 4.8 mA while the receive power is 5.1 mA.

Also leveraging the ARM Cortex M0 core the nRF51 Bluetooth system-on-chip from Nordic Semiconductor provides a multiprotocol BT Smart solution that also handles the ANT/ANT+ standard as well as proprietary 2.4 GHz protocol stacks.

Also offering a single-chip solution, the CSR101x single-chip device from CSR delivers a full BT LE radio with an on-board 16-bit processor, as well as many I/O support features. The CSR1010, CSR1011 and CSR1012 provide 64kbytes of on-chip ROM for Bluetooth4.0 single-mode software stack and up to 64kbytes for customer applications and data storage. Thus the chip packs everything required to create a Bluetooth LE product with RF, baseband, MCU, qualified Bluetooth v4.1 specification stack and customer application software running on a single IC.

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