Em 13/09/2015 19:08, Denny Esterline escreveu:
>> Thanks.   I am only looking for 5 bit accuracy.
>>
>>
> That might be asking a bit much - not from the PIC, that's easy enough -
> from the person.
> 5 bits =3D 32 position values. Typical pot has about 270 degrees of trave=
l.
> 270 / 32 =3D ~8.4 degrees.
>
> Very much depends on the scenario. Some scenarios the exact value isn't a=
s
> important
> as "a little bit" more or less, this would likely be fine. Any situation
> where you have
> some type of feedback to the user (LCD?, serial?) and they can see the
> actual value
> would likely be fine.
>
> I would also recommend a small cap between the analog and gnd. Most likel=
y
> you
> wouldn't need it on the bench... The real world is not the bench. :-)
>
> -Denny


I don't know if it can actually happen, but for a ratiometric conversion
the cap may keep the A/D input steady while the VDD fluctuates, and you
may get varying A/D readings, specially if the cap has a large value and
VDD is not stabilized. If the A/D input is allowed to fluctuate together
with VDD that won't happen.

If the acquisition time is long enough and the pot resistance is inside
the recommended range of input impedance for the PIC, the cap is
unnecessary.

Isaac



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