Optical sensor screens out IR, cuts power in wearable heart rate monitors

February 22, 2017 // By Graham Prophet
Featuring low power consumption and high detection accuracy Rohm Semiconductor's BH1790GLC is an optical sensor for heart rate monitoring optimized for wearable devices such as sports bands and smart watches. Improved sensitivity allows pulse waves to be detected with high accuracy, even with low LED brightness, for lowest power consumption and extended battery life.

Optimized for wearables that meets market needs for low power consumption and high accuracy, the device features a specialized optical filter to enable high accuracy detection, extending battery life while reducing the effects of infra-red rays by 10-times vs conventional products. This makes it possible to acquire high quality pulse signals even in environments with strong IR presence, such as outdoors, or under intense movements (i.e. sports), contributing to increased performance and further evolution in the wearable device market.

 

An optical heart rate monitor expansion board (BH1790GLC-EVK-001) is available for purchase online that can collect and process sensor information by connecting to an open platform (general MCU board) such as Arduino Uno.

 

A photodiode matched to the green wavelength ideal for pulse detection is used, along with a filter structure optimized for pulse detection that integrates green and IR-cut filters in the receiver block. The BH1790GLC is capable of detecting high quality pulse signals using low VF low brightness LED elements, eliminating the need for DC/DC circuits for LED power supply conventionally required. This decreases mounting area by 30%.

 



Parameter

Specifications

Current Consumption (LED OFF)

200μA

Power Down Current

0.8μA

VCC1 Supply Voltage Range

2.5V3.6V

VCC2 Supply Voltage Range

1.7V3.6V

Operating Temp. Range

-20+85

Package Size (W x D x H)

2.8 x 2.8 x 0.9 mm

 

Rohm; www.rohm.com/web/global/sensor-shield-support/heart-rate-sensor