You mean i should use a DC level shifter in hardware so that signal will be 
positive all the time,But im preferring not to use it,instead i want to make 
some changings in software so that it can read negative values too.

> Date: Fri, 13 Aug 2010 13:38:07 -0600
> From: sc...@santafe.edu
> To: hmitvoms...@hotmail.com
> CC: tinyos-help@millennium.berkeley.edu
> Subject: Re: [Tinyos-help] (no subject)
> 
> If it's bipolar maybe it needs a shrink?
> sorry....couldn't resist.
> 
> You'll need to bias the signal up such that it never
> goes below 0v or above the nominal 3.3v supply voltage.
> It might be as easy as using a couple of resistors, one
> to the signal and one to the supply. I'd start with
> around 10Kohms and see what ratio was needed to mix
> the signals together correctly. I think, but will not
> guarantee, that most micro-controller's can take
> very low current input that is out of their supply
> voltage range without damage while you are experimenting.
> 
> MS
> 
> 
> Naila Munaf wrote:
> > Im using imote2.And I want to read a bipolar signal from ADC
> > Generically, tinyos-2.x/tos/sensorboards/im2sb/examples/TestMax136 can 
> > read only unipolar value of a battery voltage.How should i edit it to 
> > read bipolar signal using ADC.
> > 
> > 
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