Wireless Body Sensor Solution

Wireless body sensors are part of countless medical and fitness devices, from wireless ECG sensor units to fitness vital signs monitors.

TI has announced a free sample kit you can order that contains an almost out-of-the-box solution for a Bluetooth wireless body sensor system. The kit consists of 4 chips:

• Bluetooth ® low energy radio
  •  50% less board space
• Step-down converter with bypass mode
  • Works with radio to further reduce power consumption
• Precision sensor AFE (Analog Front-End)
  •  200 pA Ibias and 335 uW/channel power consumption
• Micro-power MCU
  •  5 low-power modes optimized to extend battery life

Let's take a look at each component in the sample kit.

Bluetooth low energy radio

The radio front end in this solution is provided by TI's CC2541 2.4GHz low-power Bluetooth SOC. This chip has an 8051 core, either 128kB or 256kB on board flash memory, 8K of ram and many other features and peripherals. This is a true system-on-chip, implementing a Bluetooth network node basically out of the box.

It also has a hardware I2C interface for communication with the MCU. This chip has plenty of flash and ram for applications, plus 23 I/O, a 12-bit ADC and a UART. The low power requirement and small format make this radio front end ideal for use in applications that demand an un-intrusive battery-powered device for measuring vital signs.

Step-down Converter with Bypass Mode

The next building block in the kit is the TPS62730 ultra low-power dc/dc converter for battery applications. This device uses a high-frequency dc/dc converter for low ripple, even with a small output capacitor. The TPS62730 is suitable for use with a variety of Li-primary battery chemistries as well as 2 AA alkaline cells. It also features an ultra low-power bypass mode that can be used when the processor or SOC is in sleep mode. Typical current consumption in bypass mode is 30nA.

This device could be used in any low-power battery-operated design to reduce battery usage while providing reliable power to your circuit. The bypass mode allows you to get maximum life out of the batteries used. Due to its battery-stretching characteristics this chip would be ideal for wearable body sensing applications.

Precision Sensor AFE

The ADS1292 low-power, 2-channel, 24-bit analog front end was designed specifically for medical and sports/fitness applications. It incorporates two low-noise PGAs and two high-resolution ADCs.

Power consumption is only 335 uW/channel. Data rates can range from 125 SPS to 8 kSPS. Gain is programmable to 1,2,3,4,6,8 or 12. The ADS1292 includes a built-in oscillator and reference. It features flexible power-down with a standby mode for when the processor is asleep. Communications with the MCU is accomplished via a SPI compatible serial interface.

This unit's low noise characteristics and high accuracy make this chip well suited for medical body sensing device design.

Micro-power MCU

The MCU chosen for this solution is TI's MSP430F5308, an ultra-low-power microcontroller with 16KB flash and 6KB SRAM. It features a 3.3V LDO, four 16-bit timers, two universal serial communication interfaces (USCI), hardware multiplier, DMA, and real-time clock module with alarm capability.

The MSP430F5308 also has 47 GPIO pins, providing plenty of IO to interface to control and display circuitry. Maximum clock frequency is 25MHz and the MCU features a watchdog timer, real-time clock and brownout reset. It also features a temp sensor and a 10-bit,12 channel ADC. The low power requirements and superior processing capability of this MCU make it a natural complement to round out this near out-of-the-box wireless body sensing solution.

Design advantages

The 4-chip solution you can test in this sample kit provides some major advantages to designers and software developers of medical devices using body sensors:

• Ultra-low-power operation and small size ideal for wearable wireless body sensors
• Already optimized for use as a biopotential sensor
• Ease of software development due to the architecture and the many tools and software routines provided by TI
• Can be used to implement a highly-accurate system with less design and development time

In short, this solution can save wireless body sensor designers countless hours in design and development time without sacrificing low PCB real estate, low power operation or accuracy. You can follow this link to get the sample kit.

For more information about Bluetooth® low energy: www.ti.com/ble