Hi,

I guess keeping the last N values and simply averaging them is out of the
question (uses too much RAM?).

Another approach would be to do the following:
Add the first N samples.  Lets make it 16.  Since your values are all 0
to 15, this sum will fit into a byte - lets call it Sum.
The average at this point is then Avg ~= Sum div 16.  When you receive
the next byte, you calculate your new average by
NewAvg = ((Sum-PrevAvg)+NewSample) div 16.  You simply keep in applying
this formula for each new sample.  The only storage spave you need is
for the Sum.
This is of course not a true average, but it performs a low pass function
on your data and will thus minimize the effect of noise spikes.

Hope this helps.
Niki


> Anybody got a good averaging algorithm?
>
> I've got a stream of numbers from 0 to 15 coming out of a PIC '620
> comparator representing temperature of an appliance.  When I turn on
> the flourescent lamp on my bench, the program picks up a spike, and
> the relay in this thing fires momentarily, because it reads the
> noise.  "NO PROBLEM" I sez, and sat down to write an averaging
> algoritm.
>
> This ought to be so easy.  The first "Algorithm" anybody learns in
> kindy-garden Math 1 is how to average numbers.  I've been checking
> out verious ways of averaging a stream of data, though, and don't
> have one that satisfies on a PIC with Two byte arithmetic and no
> floating point math.
>
> Try this.  Make a spreadsheet with 300 or 400 random integers between
> 0 and 16.  Take the arithmetic average of all of 'em, probably
> around 8.   Then try to simulate a PIC program processing each number
> in succession that would get near the average, without floating point
> math.  I tried a half dozen ways this morning.
>
> One trick I worked out is that the average of N numbers, given the
> NTH piece of data is being processed now, is (N-1)*(old average)/N
> plus (Nth piece of data)/N.  If you pick 256 data points, given the
> old average AVG and the new data point DATA,
>
> NEWAVG = {(AVG*255)+DATA}/256
>
> That oughta work!  Not so fast.  Using only integer values,no
> floating point math,  the average climbs slowly toward zero and stays
> there.  PICs can probably do floating point math, but there's gotta
> be an easier way!
>
>
> Best Regards,
>
> Lawrence Lile
>