The Si1144 optical sensing module also runs Silicon Labs’ HRM (heart rate monitoring) algorithm.

The sensor module integrates an optical sensor, green LED, LED drivers supporting up to two external LEDs, ADC, control logic and an I2C digital interface operating at up to 3.4Mbit/s data rate. It can uses 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

According to the company, the module addresses this growing market of wearables including activity-tracking fitness bands, pedometers and smart watches, in addition to providing HRM capabilities for gym fitness equipment, bathroom scales and geriatric monitoring devices.

Wrist-based HRM technology, in comparison with chest-based devices, is a more ng a more convenient, comfortable way to measure heart rate. To date though, they have produced varying results, are costly as well as power hungry, reducing battery life. Complex motion artifacts also combine to make wrist-based HRM a complicated design challenge, adds the company.  

There is a choice of two algorithms to support static HRM and optional dynamic (motion- compensated) HRM using data from an external accelerometer. The module includes an integrated HRM IC with green LED lens, high-sensitivity photodiode, low-noise ADC, LED drivers, optical blocking and host communications/interrupts as well as  two LED drivers to support up to two external LEDs.

Power consumption of less than 500nA (standby current) with 1.71 to 3.6V supply voltage, maximises battery life.

The module is supplied in a 10-lead 4.9 x 2.85 x 1.2mm LGA module package.