I am trying to interface a PH probe to a pic 18F458. The amplifier and buffer circuit for the probe puts out 0 - 14 volts correlating to the ph scale. I tried using the on board AD converter but the resolution is not good enough. I ran the signal threw a voltage divider so that I could scale down my 0 - 14 Volt ph reading. And calibrating the probe could be a problem because Vref+ is 5v. Calibration is at 4, 7, and 10. 10v / 2 = 5 which would be at the top of my vref with no room for error. I've looked all over the internet for an ad converter to fit my purpose but can't find one. This is what I am looking for and why. I want a 14 bit AD chip that is I2C bus capable, its Vref+ needs to be able to goto at least 16.384 volts and vref- needs to be 0v.The 16.384 v is so that I would have a resolution of 1mV. The I2C bus is needed because it is easy. I would try SPI but I am not very good at the protocol. Is there an AD chip thats Vref+ goes that hi. Does anyone know where to look for a chip like this. I looked at MC and Maxim but did not see anything close. They both had chips but nothing that has a Vref+ that hi.
Thanks
Shawn