The Rhythm+ is an armband heart rate monitor that helps you measure your heart rate in real time through smartphones, tablets, sport watches and any other devices that support Bluetooth Smart or Ant+ heart rate data. The monitor is optimized for tracking heart rate when you are actively moving around with an elevated heart rate with a comfortable armband instead of a restrictive chest strap.
In order to detect motions in the skin precisely, Rhythm+ makes use of Silicon Labs' optical sensor placed on its back, to optically measure weak blood flow signals and enable highly accurate tracking of continuous heart rate even under intense exercise.. The sensor integrates an infrared photodiode, ambient light sensor, LED drivers and signal processing. Two green LEDs and 1 yellow LED are used to shine light into the skin. As the heart pumps, the light reflected from arterial blood changes and is detected by the optical sensor. Advanced signal processing extracts the heart rate and adjusts for motion and physiological artifacts that can cause inaccurate heart rate measurements. Green has been found to work well for people with light skin complexions. A yellow LED is added to provide better accuracy for people with dark pigmented skin.
The monolithic Si114x sensors integrate high sensitivity photodiodes, a low-noise analog-to-digital converter, analog filtering, up to 3-LED drivers and a digital I2C control interface into one tiny 2 x 2 mm package. Broad spectral sensitivity supports green through 940nm LEDs for wrist, ear, and finger-tip heart rate/SpO2 signals. This low-power sensing family enables long battery life with standby less than 500 nA.
Learn more about Silicon Labs' wearable sensors here: