If you have seen my first schematic, we need to connect the 5v Board ( Arduino ) power pin for produce the Vcc for opamp and voltage divider.
This is a little bit tricky for the connection, and i want to solve it.
I introduce the new schematic with Zener Diode!
You can play with this schematic at this link: http://tinyurl.com/ycsd9gva
In this configuration we don't need the 5v from the board, but it use the voltage of the battery in series.