27-09-2012, 12:19 PM
Microcontroller based heart rate measuring device
Microcontroller based heart.docx (Size: 97.21 KB / Downloads: 87)
Introduction
Heart rate is an important health parameter that is directly related to the fitness of the human body. It can be measured at various spots on body where the pulse can be felt. This article describes a digital method for measuring the heart rate through fingertip using a microcontroller and optical sensors. The result is displayed on a 3-digit seven segment LED module.
Theory
The principle of measuring the heart rate through fingertip is simple. The volume of blood inside the finger artery changes during heartbeats as the heart is pumping blood in to the arteries. If an infrared light is transmitted through the finger, the amount of light absorbed (and hence reflected back) by the blood inside the finger is altered by the changing blood volume. A photodiode with a proper signal conditioning circuit can detect this little variation in the reflected infrared from the blood cells. The circuit shown above is a 2-stage active low pass filter that amplifies the weak signal across the photo diode to appropriate level so that it could be fed to a PIC microcontroller. The PIC16F628A microcontroller counts the output pulses using Timer0 module and displays the heart rate on 3-digit seven segment displays.