alan smith wrote:
> figured I didnt have to use a neg supply.

You just "figured" you didn't need a negative supply instead of looking in
the datasheet to see what the opamp really needs.  Duh!

Remember, opamps don't really know whether a supply is negative or not.  But
they do have a common mode range they work correctly over, which is usually
closely related to the supply voltage range.  Dave Tweed pointed out that
this is not a rail to rail opamp, so needs some headroom from either supply.
If your inputs are closer to the negative supply (whether you think of it as
ground or not) than this headroom specified in the datasheet, then of course
it should be no surprise the opamp isn't working as you expected.

As always, READ THE DATASHEET.  If you don't understand something it says,
ask about that.  But don't just ignore it and then wonder why your circuit
doesn't work.


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