[En-Nut-Discussion] AD conversion resolution?

[Nic Cave-Lynch]

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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