Optical sensor simplifies heart rate monitoring

The small-footprint sensor module integrates an optical sensor, a green LED, LED drivers supporting up to two external LEDs, an ADC, control logic and an I2C digital interface.

According to Silicon Labs’ market estimates, 100m units of HRM-enabled devices will be sold per year by 2018, with the majority of those units being wrist-based wearables. Silicon Labs’ Si1144 HRM solution addresses this large and growing market across a wide range 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.

Heart rate monitoring is one of the most sought-after biometric sensing technologies available today for people of all fitness levels, from serious athletes looking to improve athletic performance to people simply seeking a healthier, more active lifestyle. Accurate HRM enables precise calculation of expended calories, making it easier to maintain dieting regimens.

Traditionally, heart rate measurement has been limited to the use of chest straps linked to an external device, such as a specialised fitness watch or a smartphone. These HRM solutions pose unique problems: chest straps are often inconvenient and uncomfortable to wear while smartphones can be difficult to monitor when running or cycling.

Wrist-based HRM technology changes the biometric monitoring game by providing a more convenient, comfortable way to measure heart rate rivalling the accuracy of chest-strap-based designs. The measured results vary widely and many of these HRM solutions are costly as well as power hungry, reducing battery life. Complex motion artifacts also combine to make wrist-based HRM a complicated design challenge.

Daniel Cooley, Vice President of Marketing, IoT products, Silicon Labs, commented: “Silicon Labs’ Si1144 HRM solution addresses the challenges of wrist-based heart rate measurement by providing an accurate, easy-to-implement and cost-efficient solution priced well below competitive offerings. Additional benefits of Silicon Labs’ HRM solution include industry-leading power consumption and a very small footprint, making the Si1144 module a very good fit for power-sensitive, space-constrained wearables.”

Supplied in a 10-lead 4.9x2.85x1.2mm LGA module package, samples and production quantities of the Si1144-AAGX HRM module are available now. The Si1144 module along with Silicon Labs’ HRM algorithm is priced at $2.82 in 10,000 unit quantities. The HRM44-GGG-PS development board, priced at $57.60, enables developers to jumpstart evaluation and development of wrist-based HRM applications.