[email protected] hath wroth:
Hi i realized the heart rate monitor that is showed in this page:
http://www.emant.com/694006.page
But it is not reliable: the signal is not so clean and it is affected
by my arm's movements.
Do you have any idea? thanks
Try not moving. Whenever I get my BP/pulse measured, I'm required to
keep rather still.
If you're trying to measure pulse rate while exercising, you'll
probably need to do it accoustically or by directly measuring
pressure, rather than optically. The change in IR density through the
finger is rather small and movement will create substantial "noise".
You can't tightly clamp the device to the finger as you'll restrict
blood flow.
However, there is one place where you can clamp it down and not wreck
the waveform with movement. The ear lobes. This is where some
bicycle like exercise machines do their sensing. A contivance similar
to a clothes pin is used. IR emitter on one side of the ear lobe. IR
detector on the other.
The trick is to get the clamping pressure just right. Too much and
you restrict circulation. Too little and it falls off. However,
since you're now measuring the expansion of a thin capillary instead
of a large valve, the amplitude of the pulse will be MUCH less. You'll
probably find it difficult to even see a resting pulse, but it works
well once the heart starts pumping.
I strongly suggest you concentrate on sensor construction and
optimization rather than trying to clean up the waveforms (and mess)
produced by a non-optimized sensor construction. That turns this from
an electronics design exercise into a mechanical design exercise.
For example, you'll need to make sure your optics doesn't pickup stray
light from the side as the ear lobes are quite translucent to IR.
Burying both the IR emitter and IR detector down a small hole inside
the clamp arms, is usually sufficient. See various patent drawings
at:
<
http://www.google.com/patents?q=ear+lobe+blood&btnG=Search+Patents>
This is one I've worked with:
<
http://www.google.com/patents?id=Y1A0AAAAEBAJ&dq=4334544>
I have some photos of the above (somewhere) but can't find them.
More, thanks to Google:
<
http://www.hobbyprojects.com/cosy_products/digital_heartbeat_monitor.html>
<
http://www.tunturi.com/fitness/heart_rate.cfm>
