Maxim has created a module for sensing human heart-rate and oxygen saturation that includes photodiodes, an analogue front-end and a Arm Cortex-M4 microcontroller with embedded algorithms, in a thin (0.88mm) 4.5 x 4.1mm 38pin OLGA package.

MAXM86146-health-sensor-app

However, it does external component to operate: four LEDs, a multiplexer and an accelerometer chip.

“MAXM86146 uses accelerometer data to compensate for periodic motion artifacts and is optimised for two simultaneous green pulse signals,” said the company. “These two green signals can be achieved by either two photodiodes and one LED or one photodiode and two LEDs. Oxygen saturation requires the use of two different LED wavelengths, namely red and IR. They need to share the same photodiode and separation distance.”

MAXM86146-health-sensorThe module consists of a MAX86141 dual-channel analogue front end chip plus a MAX32664C MCU and a pair of 3.8mm2 PIN photodiodes.

In the front-end chip, twin 19bit ADCs read the photodiodes and, although the LEDs are external, three LED drivers are included (needing their own supply rail). The external multiplexer is required for the LEDs if all possible functions are to be implemented.

Power needs for the module is a single 1.8V supply (plus the LED supply), and the module supports I2C communication to a host processor. “The integrated algorithms adjust the optical analogue front-end settings to maximise signal to noise ratio while minimising power consumption based on activity classification” – the latter done by one of the algorithms.