The pH sensor is inspired from phDuino. It is composed by an amplifier and a 2nd order low-pass filter (Rauch) The amplifier is designed to span the input range of a typical pH probe (-400 -> 400 mV) ...

Check serial line using Arduino IDE. /dev/tty/USB0. In PuTTY client, set connection type to 'Serial'. Make sure 'Serial line' is set to correct 'Serial line' and 'speed' is set to '9600'.