I am really sorry about the delay. But, just before to publish the electronic schemes and the PCB layout I decided to make some changes. Now I published the first public version of the pHduino hardware scheme and PCB. I have a code example but I need clean it up.
One change was remove a gain adjust trimpot to a fixed value resistor. This change makes me know exactly the voltage of the glass electrode. In the beginning of the project, the trimpot did make me sense for a better use of ADC range. But, tests show me that the operation was a little bit complicated.
About the offset adjust trimpot, I decided to keep it, because each electrode will give an electrical potential different from zero at pH 7.00.
I changed the position of some components for a better layout and put the operational amplifier input near the connector terminal.
I am still feeding the project with documentation. So, I am sorry about the lack of information. I will really appreciate suggestion.