I believe the circuit is relatively insensitive to voltage V+ (within reason) thus the output current (hence calibration procedure) shouldn't depend too much on whether you use 12V or 15V. What voltage source do you have?
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Thanks for the helpful reply. I have a 12V supply i saved from a scanner which died. It had the same connector as the Duemilanova used.
The gadget shield looks like a complete overkill for my application. I just want to be able to remotely monitor the temperature in my observatory from m,y house via a WiShield. Then I will turn on/off a heater remotely.