One of the issues with analogue measurements on the Arduino is that typically we assume an accurate 5V reference,
and need to add fudge factors for a calibrated reading.
Well, I borrowed some code and re-read the ADC part of the datasheet again, and there is a neat little trick for
using the 1.1V internal voltage reference to measure (thus calibrate) the supply voltage.
It works, but not without caveats - so although QI, I’m afraid the net result may not be much of an improvement!
As always, all notes, schematics and code are in the Little Electronics & Arduino Projects repo on GitHub
