[En-Nut-Discussion] AD conversion resolution?

[Nic Cave-Lynch]

I was just referring to the situation described in the OP, which was definitely 
a pot, but you're absolutely right: if you're just measuring a voltage, then a 
nice stiff stable reference is essential.

I typically use an external reference diode, but I have also had good success 
with the internal one, provided it's well decoupled, and I always put a filter 
(either inductor or 10R resistor) on the AVcc, to isolate it from the noise on 
the main Vcc rail.

Nic C-L

Alexander Baranov wrote:
> 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 -----