After cleaning up my power supply with the many capacitors and using a
better voltage source, the ADC cleaned itself up dramatically.  I
dropped my number of ADCs to average over to 10 instead of 100, and it's
now always right +/- 0.005g or so, which is all I can ask for.

-David

-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
Of Gerhard Fiedler
Sent: Friday, October 07, 2005 6:48 AM
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] Increasing ADC Accuracy

David de Regt wrote:

>> And I dunno the 322, but with the 311 the internal resistors are far
>> larger than the recommended (required?) source impedance for the F88
>> A/D (either 10k or 2k5, depends on the part of the datasheet you
take).

> Yesterday evening, I tried using a power supply to provide fixed
voltage,
> and the ADC stayed spot-on, so I'm thinking you might be right about
the
> source impedance of the 322. 
> 
> So what would be a way around that?  Use an opamp voltage follower?

That's what's usually done. While you're at it, you can also use the
opamp
also to scale and/or active low-pass filter the signal (if required).

Gerhard
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
------------------------------------------------------------
Mail was checked for spam by the Freeware Edition of No Spam Today!
The Freeware Edition is free for personal and non-commercial use.
You can remove this notice by purchasing a full license! To order
or to find out more please visit: http://www.no-spam-today.com

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist