[time-nuts] Off topic project sort of heart rate monitor NEED BEATS PRE MINUTE TO ANALOG VOLTAGE

Magnus Danielson magnus at rubidium.dyndns.org
Wed Feb 20 17:49:05 EST 2013


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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