pressure sensor

is there any way or arranjement using analogic reference(internal) for a pressure sensor? Vss= 5,0V vout+ = 2,40V , vout-= 2,38V when I am interested only reading the difference (2,40V - 2,38V = 20mV )between vout+ and v0ut-. I have tried putting resistors for bringing voltage (2,4V and 2,38V) down to 1.1V or less, but it seems not have worked because analog read remains showing the max 1023. Is there any way to get better resolution in pressure sensors (MPX family) without that problems?

Use an op-amp to convert your differential signal into a single-ended output.

A good starting point: http://www.allaboutcircuits.com/vol_3/chpt_8/9.html

You'll need to tweak the circuit a bit to provide a "fake" ground of 2.5V (simple resistor divider).

There is a device called a rail splitter that will give you an exact midpoint and +/- 20 mA of current. Here is the interesting spec from the attached data sheet:

Initial output tolerance for a single 5-V or 12-V system is better than 1% with 3.6% over the full 40-V input range.
Ripple rejection exceeds 12 bits of accuracy. Whether the application is for a data acquisition front end, analog
signal termination, or simply a precision voltage reference, the TLE2426 eliminates a major source of system
error.

Vout = Vin/2. This makes working with dual supply Op-Amps really easy. It provides a good virtual ground. The emphasis is mine.

Doc

TLE2426.pdf (670 KB)