*****NOTE: This is NOT a medical device.
The circuit uses a finger cuff with an integrated IR LED and photodiode. When light shines through the finger, the amount of light that hits the photodiode varies with the pulse. The photodiode produces a current that is converted to a voltage using a transimpedance amplifier (current-to-voltage converter). The signal is then high-pass filtered to remove the DC bias from the signal and then biased at Vdd/2 so that the wave is symmetrical about 2.5 V. We have a final gain stage that amplifies the AC part of the waveform (the actual pulse). The signal is outputted to an Arduino and the accompanying software (LabVIEW and Processing) plots the waveform.