Hi all - newbie warning! OK, so brand new Uno being played with for the first time, and I almost fried it. All I wanted to do was measure the pd/voltage from my bench power supply using the example code. Supply on 3.5 V, polarity correct, but spurious values and a very hot processor! Quickly disconnected and tried measuring the 5v and 3.3v outputs - no problem. So, is there something silly I have done? I'm running the board on USB power from my laptop with the charger plugged in, and trying to measure a confirmed 3.5V output from a bench power supply. I'm guessing there is an unintended current route I have missed.
Thanks for any ideas.