Sean,

My A/D application isn't too time sensitive since I'm only
measuring the air temperature.  To stabalize the readings, I
don't pass the results back to the main program until the value
has stayed the same for twenty consecutive readings.  I chose
that number after experimenting with higher and lower values.
It produces a smooth change in temperature even when I suddenly
heat or chill the sensor.  Of course, you'll have to choose a
number based on your own criteria; speed, accuracy, etc.

Andrew


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---- On    , Dave Dilatush (dilatush@COMCAST.NET) wrote:

> Sean wrote...
>
> >I am just about to tackle the A/D convertor. Can anybody
give me an
> idea of
> >how many times you should check the A/D for a single
reading? Is simply
> >taking one reading good enough or is it preferred to take
multiple
> readings
> >and average them. What is considered "enough" samples for a
single
> reading?
>
> It depends on what you're doing, and the application's
sensitivity to
> measurement errors.
>
> Even with a well-regulated and filtered Vcc, careful board
layout, very
> light loading on all of the PIC's outputs, and a noise-free
input
> signal, you can figure on the A/D results bouncing around by
1 to 2 LSBs
> from reading to reading with the 10-bit converters, and more
than that
> on the 12-bit ADCs such as on the PIC16C774.
>
> And with non-ideal conditions, the readings are going to
bounce around
> more than that.
>
> If this is too much for your application, you'll have to
filter the
> readings, either by averaging a number of readings or by
using some sort
> of recursive filter algorithm, such as the one Olin Lathrop
has
> described.
>
> Dave D.
>
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