I am developing an electronic gadget which monitor heart beat measurement using a low cost microcontroller. Optical sensors will measure the alteration of in blood volume at fingertip with each heartbeat.
The sensor unit consists of an infrared light-emitting-diode (IR LED)
and a light dependent resistors (LDR), placed side by side. The IR diode
transmits an infrared light into the fingertip (placed over the sensor
unit), and the LDR senses the portion of the light that is
reflected back. The intensity of reflected light depends upon the blood
volume inside the fingertip. So, each heart beat slightly alters the
amount of reflected infrared light that can be detected by the LDR.
With a proper signal conditioning, this little change in the
amplitude of the reflected light can be converted into a pulse. The
pulses can be later counted by the microcontroller to determine the
heart rate.
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