Unlike anything you built before, this cool device uses infra red LED to detect the changes in the volume of your blood cells, and therefore it very precisely measures your heart rate with minimum extra hardware involved. Perfect for quick and painless operation. Code is written in mikroC PRO for PIC and is under 2K of program words in size, which means it can fit in the compiler's demo limit boundaries, so you can compile it with a free demo version! Cool, isn't it?
Heart rate measurement indicates the soundness of the human cardiovascular system. This project demonstrates a technique to measure the heart rate by sensing the change 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 of the subject, a part of which is reflected by the blood cells. The reflected signal is detected by a photo diode sensor. The changing blood volume with heartbeat results in a train of pulses at the output of the photo diode, the magnitude of which is too small to be detected directly by a microcontroller. Therefore, a two-stage high gain, active low pass filter is designed using two Operational Amplifiers (OpAmps) to filter and amplify the signal to appropriate voltage level so that the pulses can be counted by a microcontroller. The heart rate is displayed on a 3 digit seven segment display. The microcontroller used in this project is PIC16F628A.