> You think a digital solution is the way to go, too?
> Maybe I'm being hard-headed tyring to do this in an analog way, but it
> seemed like it'd be somehow more elegant, since I had analog inputs and
> wanted an analog output.

Nothing says you can't have an analog output- you just need a DAC
stage, as well.  And perhaps you should assess that analog output
need as well- if the data is just going to be digitized later, can you
skip the middleman?

> And just to specify, the voltage difference between the Va (Vref+) and Vc
> (Vref-) will be pretty small sometimes (100mV or less worst-case) with a
> range easily within what the inputs of an ADC could handle (easily scaled to
> absolute values of <5v).  And you're correct, "slow moving" in this case
> meant sub-audio, mostly less than a few Hz.  Call it 20Hz worst-case.

As Spehro suggests elsewhere, can you use a PGA to ensure a larger
difference between the two?  Or a differential ADC?  He's right- a 10-bit
ADC with a 5V range will give you very few counts within a .1V range,
but a (say) 16-bit ADC would give you ~1300 counts in that range.

Mike H.

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