[En-Nut-Discussion] AD conversion resolution?

[Alexander Baranov]

Of course if you have a sort of a bridge and you excitate it with the same
REF then it doesn't matter but what if it is not a pot? Just a voltage you
have to measure?
----- Original Message ----- 
From: "Nic Cave-Lynch" <nic at tymar.com>
To: "Ethernut User Chat (English)" <en-nut-discussion at egnite.de>
Sent: Thursday, December 15, 2005 2:27 PM
Subject: Re: [En-Nut-Discussion] AD conversion resolution?


> Have to ignorantly throw in my 2c worth here.
>
> First, if it's a pot and the internal ref, no calibration should be
needed,
> because the internal ref feeds the ADC as well as the pot: FSD == FSD no
mater
> what. (assuming that the internal ref _is_ feeding the ADC in this case.
>
> Second: that big jump around 256: maybe coincidence, but I hate
coincidences
> that are a power of 2. Could it be something to do with being interrupted
while
> reading the ADC? having to read the high and low bytes in the correct
order,
> with nothing else going on in between?
>
> I've used the ADC a lot in the Atmels, at times quite happily decimating
to 12
> bits resolution, and I've never had this sort of problem. These weren't
using
> NutOS, but it shouldn't make a difference if the ADC reading is done
properly.
>
>
> Nic C-L
>
> Alexander Baranov wrote:
> > I strongly support. Don't use internal Ref if you would like to avoid
> > calibration of each device.
> > ----- Original Message ----- 
> > From: "Kathy Quinlan" <katinkad at kaqelectronics.dyndns.org>
> > To: "Ethernut User Chat (English)" <en-nut-discussion at egnite.de>
> > Sent: Thursday, December 15, 2005 9:57 AM
> > Subject: Re: [En-Nut-Discussion] AD conversion resolution?
> >
> >
> >
> >>Gerwin Voorsluijs wrote:
> >>
> >>
> >>>Hi Kathy,
> >>>
> >>>You mean it could be noise? That would not explain why I don't see such
> >>>jumps on my voltmeter, nor does it explain why I see this behaviour
over
> >>>a number of sweeps. Btw I use the internal reference voltage on the
> >>>Ethernut.
> >>>
> >>>In the mailing list I saw that you are also using the ADC function of
> >>>the Ethernut and I was wondering if you could look at the results you
> >>>are getting to see if maybe I'm unlucky and my Ethernut is broken?
> >>>I know that on the total range of the 10bit ADC (1024 values) a jump of
> >>>50 is not that big (roughly 5% ), but for what I want to use it for, it
> >>>is vital.
> >>>
> >>>Cheers,
> >>>
> >>>Gerwin
> >>>
> >>
> >>You know that the internal ref is not accurate (or even close) a good
> >>external Vref is essential)
> >>
> >>I have had ALOT of problems with the internal ref, and now only use
> >>external ones.
> >>
> >>I would try to feed in an external Vref first.
> >>
> >>Regards,
> >>
> >>Kat.
> >>
> >>
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> > 14/12/2005
> >
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