book_woorm:
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.
That is true. If you have any voltage wired to the Aref pin and have any of the internal reference voltages selected (Avcc and 1.1vdc for a Uno) then there will be a direct conduction path between that external Aref voltage and the internal voltage, never a good idea. A higher value series resistor on the Aref applied voltage can mitigate against possible damage perhaps per the second warning here: analogReference() - Arduino ReferenceI 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?
No, it's a fixed 'band-gap' voltage developed across an internal semiconductor, so it's accuracy is not effected by any variation of the applied Vcc or Avcc voltages.
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.