BPM DETECTOR
Heart rate is the number of heartbeats per unit of time and is usually expressed in beats per minute (bpm). In adults, a normal heart beats about 60 to 100 times a minute during resting condition.
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. The signal conditioning circuit consists of two identical active low pass filters with a cut-off frequency of about 2.5 Hz. This means the maximum measurable heart rate is about 150 bpm. An LED connected at the output blinks every time a heart beat is detected.
The firmware does all the control and computation operation. In order to save the power, the sensor module is not activated continuously. Instead, it is turned on for 15 sec only once the start button is pressed.
Turn the power on, and you will see all zeros on display for few seconds. Wait till the display goes off. Now place your forefinger tip on the sensor assembly, and press the start button. Just relaxed and donxe2x80x99t move your finger. You will see the LED blinking with heart beats, and after 15 sec, the result will be displayed.
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