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]

12 thoughts on “Fingertip Heart Rate Monitor

  1. 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. 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.

  3. @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)….

  4. I believe they are measuring the amount of oxygen in your blood using the same principal. I always thought the little red light clip they put on your finger in the hospital is for pulse measurements, turns out – it’s an oxygen monitor. And I believe someone had mentioned to me that they do not actually measure heartrate with it, although, apparently, they could. Not accurate enough?

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