Hi! I want to ask you a question about Arduino rev 3. I've just read that in Ard.rev 3 the power DC in every pin is 3.3 v and not 5 like in the last version. Is it correct??? Thank
The Arduino UNO is a 5V device. If you are thinking about the Arduino ZERO, yes it is a 3.3V device. It WILL fry if you connect 5V to it.
The Zero and the Due are 3.3v devices, and cannot be used with 5v signals without level shifting (unlike some ARM boards you may have used, that run at 3.3v, but have 5v tolerant pins).
Just about every other arduino board is 5v, except for Lilypad and the 3.3v pro mini's (both of which use chips that could be run at 5v)
The Teensy is 3.3V and is 5V tolerant unless you get the Teensy LC.