Hi, everyone. I'm a newbie (though I've been following these forums for some time). I've never had to run the Arduino uno off an external power supply until now. So I connected the + ve terminal of the battery to the 2.1 mm barrel plug's centre connection and - ve to the outside connection. Nothing…

Uno external power supply problem

LarryD April 1, 2014, 4:23pm 2

When you attach external power to the power connector and not plugged into USB, measure the voltage on the 5 volt header pin.
What do you get?

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