Arduino ADC question...

[James Coplin]

Since I know there are some folks here doing Arduino and similar I thought
I’d ask since I’m not getting a satisfactory answer on the Arduino forums or
elsewhere.  I’m working on a module now that requires me to read a CV from
my modular that can be in the range of -5v to +5v.  The ADC on the Arduino
only reads positive voltage with a maximum input of 5v at 10 bits.  The
resolution is sufficient for this project So I’d rather not mess with
another ADC chip as looking over those they are expensive and I have no clue
how to hook one up anyhow.  So, I need to shift the input from +/-5v to
0v-10v and then attenuate it 50%.  The problem is that I need to be fairly
confident of where a 0v input would be after all this shifting.  I will have
+/-9v (also could have +/-12v or +/-15v)available on the module from an
external supply.  So:



1.)    Is the best way to go about this with a dual opamp and just add +5v
and then attenuate?  Anyone have a pet schematic?

2.)    What is the best way to ensure an accurate and stable 5v source for
the above?  My thought was to use this stable 5v as an analog ref input an
read/calibrate the Arduino to it on initialization.

3.)    If the ADC on the Arduino has a max read of +5v, is it better
practice to instead attenuate my range to a smaller value so as to not push
the limit on the inputs?

4.)    Or something different?  I’m kind of guessing/talking off the top of
my head so I’d love to hear better or more correct solutions from folks who
know more than I.



I’d really appreciate any help as I’m kind of at a wall after smooth
sailing.  Thanks!



James R. Coplin
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