Optical sensor monitors heart rate using green LEDs

The sensor is used for monitoring heart rate, by measuring the volume of blood passing through blood vessels. It works by shining light on the surface of the skin. Different amounts of this light are absorbed by blood and the surrounding tissue. The light not absorbed is reflected to the detector. With its green emission spectrum, the SFH 7051 is suitable for measuring pulse rate at the wrist.

The green emitter chips of the SFH 7051 are based on the latest high-efficiency UX:3 chip technology from Osram Opto Semiconductors. The sensor uses three of these chips so that they can be operated at the optimum current of 20mA. At this operating current, the efficiency of the emitters is particularly high. Overall, the SFH 7051 produces an optical output of 3 x 3.4mW at 20mA and 3.2V. The low power consumption of the component enables long battery life in the device, increasing reliability. With an area of only 1.7mm², the photodiode is small enough to enable the sensor to be compact, but sensitive enough to provide the required signal quality. Its low capacitance of only 11pF ensures short switching times and high measurement frequency.

The SFH 7051 is the second integrated optical sensor from Osram for fitness tracking applications. In 2014, the company launched the SFH 7050, a multifunction sensor for measuring heart rate and the oxygen content of blood. “We are keeping a very close watch on the trend for heart rate monitoring in the wearables and medical markets,” said Christoph Goeltner, Product Marketing Manager at Osram Opto Semiconductors. “Wearables are electronic devices that are worn on the body, such as smart watches and fitness wristbands. The SFH 7051 meets our customers’ need for a separate solution, specifically for heart rate monitoring.”

Users now have a choice between the multifunction SFH 7050 and the SFH 7051, which is optimised for pulse rate monitoring. The housing dimensions of the two sensors are identical.