Fingertip heart rate monitor

[Embedded lab] has a nice tutorial on building your own heart rate monitor. The monitor works by shining infrared light into the fingertip and looking at the changes in the reflected infrared signal caused by a heartbeat.  The IR detector produces a very small AC signal so a couple of op-amps are used to filter and amplify the signal. The output of the filter circuit is then read in by a PIC16F628A, which counts the beats and displays it on a seven segment display.  This might be a good project to try if you’ve got your microcontrollers down and you are looking to learn some analog electronics. Its noted at the end that the two main problems with building a circuit like this are going to be cross talk and adjusting the filters. The infrared diode and receiver should be close to each other to allow maximum reflection but you also need to make sure that you don’t allow the emitter to shine directly into the detector because the reflected light will be drowned out by the bright emitter.

[via make]

Comments

  1. st2000 says:

    You came this far, you might as well take the next step. I understand that if you also do the same w/visible light then look at the difference between the infrared and visible detectors you can infer blood oxygen levels. Anyone care to comment?

  2. zing says:

    Sure, you could easily do a relative oximeter. One was on HaD a year ago.

    http://hackaday.com/2010/01/06/pulse-oximeter/

  3. Jamie says:

    Nitpick: This will allow you to measure your pulse, not your heart rate. The two measurements will be about the same when your body is at rest, but can differ when cardiac stress is varied (such as during exercise).

    Neat hack, nonetheless. It could be used approximate your resting heart rate which is a good indication of your overall fitness level.

  4. Tom says:

    @Jamie: Your pulse and heart rate SHOULD be the same, unless you have some kind of arrythmia going on (Like premature contractions, which dont pump any blood out as the heart hasnt filled yet)….

  5. Nick says:

    I love the hand drawn schematics!

  6. Solidacid says:

    AWESOME, i am building a heart rate monitor at this very moment! great timing! :D

  7. Jamie says:
  8. blue carbuncle says:

    I remember my caretaker in the 90s had a Casio watch that could do this and take blood pressure…

  9. Whatnot says:

    It’s odd but they had circuits like this in the hack scene years before it became stock and trade in hospitals to have the finger clip monitoring.

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