On Fri, 19 May 2000, Spehro Pefhany wrote:

> At 02:01 PM 5/19/00 +0200, Quentin wrote:
> >My A/D input signal is such that I will always have a +/- 10 fluctuation
> >in my register value. Can somebody tell me how to get an average reading
> >over say 5 A/D samples?
>
> If your readings are periodic, one method is to pick a constant 'a'
>
> and do  value = (1-a) * value + a*reading
>
> (you might also use a flag to preload value=reading the first time.
>
> This forms a low pass filter, and more recent values have a higher weight
> than previous values. It has the advantage that it only uses one ram
> location and you get a value every A/D conversion.
>
> If you just want to take a bunch of readings in succession and average
> them, just add n values together and then divide by n. Obviously you
> need to avoid overflow during the add, so you might use 16 bit math
> for an 8/10/12 bit A/D reading with 256/64/16 values or less being
> averaged.


I guess this is a record for repeated thread frequency. Quentin, look at the
archives from just a few days back when we were talking about this exact issue
and proposed the exact solutions you've seen posted today.

Scott