This project uses a bright infrared (IR) LED and a phototransistor to detect the finger pulse; a red LED flashes with each pulse.
The pulse monitor works as follows: LED is the light side of the finger and the phototransistor on the other side of the finger, phototransistor used to obtain the emitted flux, when the blood pressure is pulse of the finger when the resistance of the phototransistor is increased. light changed.
We chose a very high resistance resistor R1, because most of the light passing through the finger is absorbed, it is desirable that the phototransistor is sensitive enough. The resistor can be selected experimentally to obtain the best results.
The most important thing is to keep the stray light from the shield into the phototransistor. For home lighting this is especially important because home lights rely mostly on 50Hz or 60Hz, so weak heartbeats produce considerable noise.
