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On 06/03/11 11:24, V G wrote:
> I've been looking into various types of filters (active, passive, digital=
),
> and wanted to give a digital filter a try.
>=20
> I have a 3 electrode (+, -, ref) ECG hooked up to an LT1168 instrumentati=
on
> amplifier. There is a lowpass passive filter on the breadboard blocking o=
ut
> all high frequency noise (can't remember the cutoff frequency I chose, bu=
t
> it was something reasonable, maybe 150 Hz or so). There is the problem of=
 a
> 60Hz signal going through the entire heartbeat signal. The output is
> beautiful, but I would like to clean it up to the best of my abilities. I
> COULD make an active filter (Butterworth or something), but I dislike the
> phase characteristics. Since I'm going to be using an ADC, feeding it int=
o a
> microcontroller, and transmitting it to a screen of some sort, I figured =
I
> could implement an FIR filter on the PIC32. I would think the PIC32 runni=
ng
> at 80 MHz is more than fast enough to filter a sub 200 Hz signal.
>=20
> The main purpose is to first eliminate the 60Hz signal, then test, then s=
ee
> what else I could get rid of.
>=20
> What do you guys think?

You may find an IIR filter is faster and not much more effort to design
for a simple notch filter. See
http://www.mathworks.com/help/toolbox/filterdesign/ref/iirnotch.html for
an example--using MatLab--which is basically exactly what you're doing.

See also:
http://www.dsprelated.com/showmessage/101952/1.php

Regards,
Brendan
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