On 20/02/13 02:23, Bob Camp wrote:
Hi
The first layer to the onion is that the ECG signal is a bit complex. There's
also likely to be a bit of this and that on it.
How about taking the output of the instrument amp into the A/D port on a cheap
PIC? That would let you do some AGC and dynamic filtering. At even a modest
sample rate (say 10 KHz) the heart rate could be worked out in software. I
think I'd run a PWM out and drive an analog meter with it.
Exactly which platform you choose isn't as important, but I was thinking
essentially the same.
Frequency measurement using time between suitable trigger-point on the
waveform would allow simple conversion into BPM scaled frequency. A
suitable exponential lag filter can then average the values, and allow
for a few suitable smoothing filter bandwidths.
AGC and trigger detector, possibly some pre-filtering, should be the
main things to look at, the remaining is relatively trivial.
There are Agilent function generators (33120A or 33250A if I recall
correctly) with heart-wave shapes which would be good to use for testing.
The nice thing about keeping it simple is being able to run it off a 9 volt
battery. That takes care of a *lot* of issues.
Oh yes. Unless the monitoring system being tapped isn't handling most of
the isolation/loop issues.
Cheers,
Magnus
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