Improved accuracy with optical heart rate monitoring, claims Silicon Labs

January 08, 2016 // By Graham Prophet
Silicon Labs has introduced an optical heart rate sensing solution designed to reduce the cost and complexity of wrist-based heart rate monitoring (HRM) applications. The Si1144 HRM is an all-optical (transconductance) measurement device that integrates a single (green) LED – there is no resistivity measurement path – that Silicon Labs says can yield HRM results of comparable accuracy to a chest-strap-based monitor.

The device includes a low-power optical sensor module with an EFM32 Gecko microcontroller (MCU) running Silicon Labs’ own HRM algorithm. The small-footprint Si1144 sensor module integrates an optical sensor, green light-emitting diode (LED), LED drivers supporting up to two external LEDs, analogue-to-digital converter (ADC), control logic and an I²C digital interface. Target products include activity-tracking fitness bands, pedometers and smart watches, in addition to providing HRM capabilities for gym fitness equipment, bathroom scales and geriatric monitoring devices.

Features include;

• Accurate sensing of weak blood flow signals on the wrist with exceptional performance rivalling chest strap HRM designs

• Choice of two algorithms to support static HRM and optional dynamic (motion- compensated) HRM using data from an external accelerometer

• HRM solution pairs optical module with a Pearl Gecko MCU containing a DSP-enabled ARM Cortex-M4 core for low-power, high-performance designs or with a Cortex M3-based Jade Gecko MCU for simpler, cost-sensitive designs

• Fully integrated HRM IC with green LED lens, high-sensitivity photodiode, low-noise ADC, LED drivers, optical blocking and host communications/interrupts

• Two LED drivers to support up to two external LEDs • Ultra-low power consumption for long battery life in wearables: < 500 nA standby current with 1.71 V to 3.6 V supply voltage

• I ²C serial communications with up to 3.4 Mbps data rate

• 10-lead 4.9 x 2.85 x 1.2 mm LGA module package

The Si1144 module along with Silicon Labs’ HRM algorithm is priced at $2.82 (10,000). The HRM44-GGG-PS development board, priced at $57.60, enables developers to jumpstart evaluation and development of wrist-based HRM applications.

Silicon Labs;