I have a circuit which I now plan to use an allegro ACS711 current=20
sensor.  This puts out voltage based on current, where zero current is=20
referenced to VCC/2.   As I only care about current in one direction,=20
I'd really like to remove this offset and then be able to amplify this=20
to a range based on my expected current range.

Vcc is 3.3V.  The  full scale output is from 1.65 to 3.3V.  The current=20
range I am working with is probably more like 1.65V to 2.5V. I'd like to=20
move this to where this is scaled to a range of around 0 to 3.3V.

The obvious way to do this is to feed this output into a difference=20
amplifier made out of an opamp and four resistors.  Wire the positive=20
input to the ACS711, and wire the negative input from a VCC/2 voltage=20
source made from another opamp in unity gain mode and with a voltage=20
divider on the input.  But that seems like a bit of overkill since I'm=20
pretty certain I should be able to do this all with one opamp and skip=20
the unity gain amp- unfortunately I'm not seeming to have much luck=20
doing the correct analysis to make this work.

So, I'd appreciate any opamp wizards which could either just point me=20
towards the solution, or even better help me figure out where my 'mental=20
model' of opamp operations is falling down in this case, so I don't have=20
to ask a similar question again.

Thanks,

-forrest
--=20
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