Photoplethysmography (PPG) sometimes called pulse oximetry is on of the easiest ways to get heart rate information. With a little more analyze and signal processing it is possible to extract even more information related to your heart condition like arrhythmia. But first lets focus on how to acquire PPG signals with the things you might have lying around. SteveQuinn have built a PPG device around Arduino Mega2560, 128×160 TFT LCD, and several passives.
The measuring of PPG lies on blood perfusion to the dermis and subcutaneous tissue of the skin. Every cardiac cycle pumps blood to peripheral organs and this flow change can be measured with simple optical method – LED and photo diode. There are two ways of measuring PPG waveform – transmissive and reflective. Transmissive method seems to give better results this is why it was selected for this project. He built a simple finger clamp out of coat hanger where he fixed LED and photo diode. There are many small things to take care of, because signals are very small and susceptible to noise. For instance LED driving current has to be constant, power supply has to be clean, proper component selection plays also a significant role.