Heart Rate Measurement From Fingertip

Abstract

Heart rate is the number of heartbeats per unit of time and is usually expressed in beats per minutes (bpm). Normal heartbeats for adults about 60 to 100 times a minute during resting condition and directly related to the health and fitness of a person. This project demonstrates a technique to measure the heart rate by sensing the changes in blood volume in a finger artery while the heart is pumping the blood. It consists of an infrared LED that transmits an IR signal through the fingertip, a part of which is reflected by the blood cells. The reflected signal is detected by a IR photo diode sensor. The changing blood volume with heartbeat results in train of pulses at the output of the IR photo diode, the magnitude of which is too small to be detected directly by a microcontroller. Therefore, we use pulse sensor to detact that small amount and amplify and ragulate the voltage to give an appropriate voltage level output, so that the pulses can be counted by a microcontroller. The heart rate is displayed on a 16x2 segment display. We can count the number of pulses within a certain interval (15 sec), and easily determine the heart rate in bpm.