Arduino ADC question...

[Tony Hardie-Bick]

Just off thetop of my head:

I'd probably use a LM4041ADJ voltage reference, then sum the two with some kind 
of resistor network feeding into a voltage follower (op-amp). All the design is 
then just resistors. Depending on the op-amp, you'll probably need a couple of 
preset pots to trim everything and maybe set the correct balance. 18 or 27 turn 
cermets will give you the required precision.

Something like that ;)

Tony (HB)

On 18/10/11 15:21, James Coplin wrote:
> 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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