Heart Rate Measurement Using AVR Microcontroller: A Photoplethysmographic Approach

Heart rate measurement indicates the soundness of the human cardiovascular system. This book 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 a LED that transmits light through the fingertip of the subject. Each heart beat slightly alters the blood volume inside the fingertip which changes the intensity of illumination that can be detected by the LDR. The changing blood volume with heartbeat results in a train of pulses at the output of the LDR, 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.