Smart solution :)
Note however that if Vdd varies dynamically only +/- 1% between A/D samplings, both the reference and interesting input converted values will vary that much, ending up in +/- 2% additional error after calculation.
/Morgan

Olin Lathrop 16:29 2004-11-17:
>Or you can feed the 2.5V reference into the A/D as another input, run the
>A/D reference off the Vdd supply, and do the correction in firmware.  This
>is what I did in the ProProg.  The 2.5V reference from a LM385 goes directly
>to an A/D input.  The reference voltage is still read with about 1 part in
>500 resolution, which is well beyond its accuracy.  Multiplying it up to a
>higher voltage would have introduced much more error than it would have
>given back in terms of A/D resolution.  Correcting the other readings to the
>measured reference is just a little math in the firmware, which costs
>nothing in parts and introduces virtually no additional error.

--
Morgan Olsson, Kivik, Sweden

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