CrossRoads:
Use a single supply op amp, like the LM358 on the Arduino boards.
http://www.ti.com/lit/ds/symlink/lm158-n.pdfWant a 0-5V output when done to be compliant with Arduino ADC input.
Is the LM358 a rail to rail op-amp? I don't think it is and that would limit it's ability to get to 100% measurement range of the ADC, if the chip is powered with ground and +5vdc. And if powered with a higher Vcc then there is always a risk of overvolting the input pin?
Lefty