V G wrote:
> The main purpose is to first eliminate the 60Hz signal, then test,
> then see what else I could get rid of.

Trying to get rid of 60Hz is probably not a good idea since your signal
contains valid frequencies in that range.  For example, if the fundamental
(the heart rate) was close to 60Hz, the result could be a very strange
waveform.

It is far better to eliminate as much of the 60Hz as possible as early in
the analog chain as possible.  Most will be common mode, and keeping it fro=
m
turning into differential mode will give you better results than trying to
get rid of it later.

Even if you do want to try removing 60Hz after the fact, a FIR filter is no=
t
appropriate for that.  FIR filters can do lots of cool things, all with the
same algorithm, just different kernel functions.  However, their required
width goes up with the frequency discrimination.  If you want to filter out
a narrow band around 60Hz, then you'll need a wide filter.

A better approach for 60Hz noise reduction is to use the fact that the nois=
e
is exactly 60Hz.  You could convolve the signal with a 60Hz sine and cosine
to determine the average 60Hz amplitude and phase over some segment of
signal, then subtract off a 60Hz sine with its phase and amplitude adjusted
accordingly.

As for a PIC 32, it probably can do meaningful FIR filters on 150Hz data.
However, a PIC 32 is not a DSP whereas a PIC 33 is.  A PIC 32 may run
faster, but probably uses more time per point in the end than a PIC 33 does
with it's multiply-accumulate capability meant for exactly this kind of
problem.  The PIC 33 can do successive points of a convolution in successiv=
e
cycles.  It does the multiply, add, updating pointers to the next data word=
s
with possible wrapping, and loop termination all in one instruction cycle.

A PIC 33 can run at up to 40MHz instruction rate.  Let's say your data
sample rate is 500Hz.  40MHz / 500Hz =3D 80K, which is the maximum width
convolution  it could perform every data point.  That's way more than you
need, and certainly more than you have storage for anyway.  You could do a
2000 point convolution at 500Hz and use up about 2.5% of the processor.


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