The main problem with the acoustic option that I can see is that it relies
on nice clean heart sounds. A heart murmur or diminished heart sounds (e.g.
due to a pericardial effusion) would result in a poor signal. Then again, if
you had either of the above, you you would want to know more than your
exercising pulse rate!!!
Normally you'll get two noises per heart beat. Sometimes the second heart
sound can be split into two distinct peaks. This can vary with breathing. So
the second heart sound would need an acoustic debounce if that makes any
sense... Other than that it should be fairly straightforward...
Ben

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