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Every time that I open the Serial Monitor, my Arduino Uno, seems to go back to void setup(). Is it a normal thing?

marked as duplicate by Anonymous Penguin Sep 7 '14 at 12:57

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That is a normal feature of Arduinos, not an error. I find it mildly annoying sometimes, but it's nice for interactive programs that want some kind of menu message to be the first thing you see in the terminal.

If you want help disabling the auto reset, your options are detailed in Disabling Auto Reset On Serial Connection.

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