[En-Nut-Discussion] AD conversion resolution?

[Piotr]

Dear Gerwin,
Could you put your voltages range on the same axises?
I mean, that some pot meters have some "holes" in values. This could be a 
reason for "holes" in these graphs.
Cheers,
Piotr


----- Original Message ----- 
From: "Gerwin Voorsluijs" <g.m.voorsluijs at wanadoo.nl>
To: "Ethernut User Chat (English)" <en-nut-discussion at egnite.de>
Sent: Friday, December 16, 2005 12:11 PM
Subject: Re: [En-Nut-Discussion] AD conversion resolution?


> Been investigating it a bit further based on the same data and I found 
> that the two major gaps in my data show a "funny" symmetry:
> 255 - 304 and 719 - 768 both have a gap of 49 and 255+768 = 304+719 = 
> 1023.
> Been investigating the gaps in the data a bit more and to my surprise, 
> this symmetry occurs throughout the data: check out the plot of the gaps 
> versus the mean value of the two endpoints and the same data mirrored in 
> 1023/2 which I added to http://130.161.167.171/ethernut.zip
>
> Anyone?
>
>
> Gerwin Voorsluijs wrote:
>> Hi Nic,
>>
>> These conspicuous jumps are essentially what I'm getting at: I see jumps
>> that don't make sense and come back all the time. I've made a
>> log-file of the values that I get. If I plot them I clearly see white
>> lines in my data: those are steps that I don't think can be explained by
>> the data being noisy or my setup not being 100% grounded.
>> Both files can be downloaded from http://130.161.167.171/ethernut.zip 
>> (tried to attach them but then this msg didn't seem to get through)
>> Plus I see the same jumps as I saw yesterday, with a completely
>> different setup, actually the only thing that's the same is the Ethernut
>> and some of the wires I used to set it up.
>>
>> My setup: simple powersupply set at 4.5 V with a 100K pot meter (not
>> used in previous test). That's all!
>>
>> Hope someone can shed some light on this.
>>
>> Gerwin
>>
>> Nic Cave-Lynch wrote:
>>
>>> 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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