Michael sez:

> > 5.  Consider some kind of software noise immunity.  The technique I
> > used was a median filter.  I would clear out a section of RAM, take a
> > measurement, sort it into the RAM array, take another measurement,
> > sort it into the array, until I had an array of 10 or 12 measurements
> > all in sorted order.  The middle one is the median, and that is the
> > result.
> >
> If this better than just using a circular buffer and calculating the
> average?

YES.  Consider the following data points:

1000
5
5
5
5
2

The average is 170, the median is 5.  Which is more representative of
the data?   I also found BIG problems with errors due to the lack of
floating point math.  Calculating an average always results in a
division.  In a simple PIC, without floating point math you introduce
tiny rounding errors that add up after a while.  I don't want to
belabor this extensively, because it was all hashed out here about
six months ago.   Once you have the basics worked out, median filters
are easy to code and they are very noise immune.

Since I haven't gotten around to posting it I'll email you some code
for median filters privately.




-- Lawrence Lile

     "An Engineer is simply a machine for
      turning coffee into assembler code."

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