Photoplethysmography (PPG) and Pulse Oximetry (SpO2) are carried out by a single sensor which is used to measure reflectance of three LEDs of different wavelengths. SpO2 is found by measuring the reflectance of 650 nm light in comparison with 940 nm light. Heart rate is measured by PPG wherein the change in blood volume is found by measuring reflectance of 850 nm light. The measurement of vital signs by placing sensors and LEDs behind the earlobe has been validated by previous work.

The Si1143 I2C light sensor was chosen for its small size and cost. The presence of an integrated amplifier and Analog to Digital Converter (ADC) has resulted in a lesser Bill of Materials (BOM). The Si1143 light sensor also has inbuilt LED drives which allow easy control over three LEDs. I'm currently toying with the MAX30100, Will post the results here shortly.

Here is the heart rate data for 3 mins.


Here is the SpO2 data for 3 mins