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Thiskind of sensors can be used for heart rate sensing.
The TCRT5000(L) has a compact construction where
the emitting-light source and the detector are arranged
in the same direction to sense the presence of an object
by using the reflective IR beam from the object.
The operating wavelength is 950 mm. The detector
consists of a phototransistor.
Here is more.....................
**broken link removed**
Plenty of noninvasive methods exist for electronically sensing the human heartbeat.
The job can be done acoustically (stethoscope or Doppler), mechanically (sphygmomanometer),
electrically (EKG), and optically. One handy optical technique presented here exploits the
fact that tiny subcutaneous blood vessels (capillaries) in any patch of skin
(fingertip, ear lobe, etc.) furnished with a good blood supply, alternately expand and
contract in time with the heartbeat. An ordinary infrared LED/phototransistor pair can sense
this rhythmic change as small but detectable variations in skin contrast