On Wed, 22 Jan 2003, Olin Lathrop wrote:

> > I have an a/d tied to a fuel level sender, and am
> > trying to smooth the resultant value so that any quick
> > fluctuations in fuel level are dampened out (tilting
> > the tank, bumps, etc.)  I've thought of a push/pop
> > stack scheme to average but am afraid that would
> > consume too much memory.  I've also thought of
> > sampling the a/d once a second and taking an average
> > over ten seconds...
>
> I like to sample the A/D as fast as possible and filter in software.  I've
> mentioned this many times, so see the archives for details.  An easy
> software single pole filter is:
>
>   FILT <-- FILT + (NEW - FILT) * FP

And everytime Olin mentions this a few suggestions pop out on how this can
be efficiently implemented. For example:

http://www.dattalo.com/technical/software/pic/twist.asm

implements this formula.

;;;    A*x + B*y
;;;  ------------
;;;     A  +  B
;;;
;;; Such that A+B = 2^N

Or re-writing:

 = (A*x + B*x-B*x + B*y)/(A+B)
 = x + (y-x) * B/(A+B)

x == FILT
y == NEW
B/(A+B) = FP

Scott

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