Hi,
I eventually found some of the reference code and the responces, thankyou, have pointed out a bit more. In my application its the temperature of the die that I'm after including the heating effects of sinking current on the digital pins!
When in use this particular 'box of magic' of a uno and ethernet shield inside will live in a pretty hot enviroment so I'm probably going to need to turn on a cooling fan or a peltier cell from time to time to stop it from getting cooked. Hence consistency is more important than absolute accuracy . I want to do this with out sacrificing any of the analog inputs to a separate temperature sensor. Trouble is those other inputs need an external Vref. I read that you cant turn on the internal reference voltage if an external one is connected. I suppose using an external reference 1.2V from a potential divider accross the 5V rail and ground will alter the maths a bit. Any body know if the internal reference is also just a potential divider?
Another of my projects, see separate post, has a tendancy to die unexpectedly. That is probably due to RF interferance but it could be heat as well.