The MAX30102 uses a method called photoplethysmography to measure the heart rate of someone. This method shines light on the skin and the perfusion of the blood is measured. One of the practical aspects of this approach is that it is possible to differentiate between the light reflected by the blood of an artery (produces an AC output) and other components of the body such as bones and tissues (produces a DC output).  The photo-diode in the sensor then converts the light to current that we can use as comprehensible data. 

To counter difficulties such as skin tone differences LEDs with different wavelengths are used. In the MAX30102 there is an extra green LED for this purpose. 

Another log will be posted later on to provide precision on how we calculate the SP02 and heart-rate from the AC output of the sensor.