[En-Nut-Discussion] AD conversion resolution?

[Lars Andersson]

Another 2c thing maybe worth looking at.
If the A/D power supply decoupling is not stiff enough,
this can show up as A/D comparator disturbances when a lot of 
internal register bits change state, e.g. 011111 -> 100000.
This is entirely inside the chip.

// Lars H. Andersson

> -----Original Message-----
> From: en-nut-discussion-bounces at egnite.de 
> [mailto:en-nut-discussion-bounces at egnite.de] On Behalf Of Nic 
> Cave-Lynch
> Sent: Thursday, 15 December, 2005 20:27
> To: Ethernut User Chat (English)
> 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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> >>
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> > 
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