On Sunday 17 July 2005 03:31 pm, Charles Linquist scribbled:
> I use a $1 quad National Semi Rail-Rail I/O Quad op amp to handle 4
> sensors.  They don't really have to be close to the Allegro parts, since
> I use an R/C filter ahead of each one to filter out any garbage.

In my app, the display unit is already done (a board/enclosure used for 
another project), and I want to add this functionality.  Keeping the same PCB 
is a *big* plus.  So I'd put the op-amp on the sensor end anyway.  But the 
Allegro chip requires 5V power, so I'd need a regulator for that anyway.


> > However, I'm now re-thinking that I could eliminate the op-amp and use a
> > 50% voltage divider for Vref-.  And Vref+ would be fed with Vdd directly.
> >  This would let my full-scale output (for a 100A sensor) be (2.0/2.5) *
> > 1024 = 819 steps, which is pretty good for my requirements.
>
> I'm sure this will work.  I couldn't do this in my application since I
> had to measure ground-referenced DC voltages with the other channels.

Couldn't you also switch A/D modes when sampling different channels?


BTW, would anyone here have an Eagle library already made for this, before I 
go create it?

Cheers,
-Neil.


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