External Power Uno

I have an Uno, and when I plug in a 9v, 1A supply, I don't get a power on. What am I doing wrong? And the USB power works fine, but i can't constantly have this connected to a computer. Thanks, Sam

Are you sure the 9V supply both fits the barrel jack right, and that it is functional... If you plug it into somthing else that takes 9V, does it work?

Yes. I know it works, but I don't know about the barrel... It fits snugly and seems to be the correct size...

slc2015: Yes. I know it works, but I don't know about the barrel... It fits snugly and seems to be the correct size...

Two things you can check. Polarity of your power supply, center pin socket sould be positive and barrel negative, if backwards the arduino won't work. Proper connector, outside barrel is 5.5mm which yours sounds ok because of snug fit, however there are two sizes of internal pin socket sizes, 2.1mm and 2.3mm. The Arduino board's power connector uses an internal 2.1mm pin and if your plug has a 2.3mm pin socket then no connection will be made for the positive voltage to the board. A multimeter is the best way to check all that out.

Lefty

A snug fit is not a guarantee of a good connection, I have a few connectors that appear to fit but need a good wiggle and holding your head just so to get them to connect. Try moving it in and out slowly and look at the on LED.

Wow. Really dumb mistake. Had it hooked up through the relay controlled to the Arduino.... :0

slc2015: Wow. Really dumb mistake. Had it hooked up through the relay controlled to the Arduino.... :0

:D

In the Air Force we called that kind of problem a "short between the headsets"

Lefty

LOL, Lefty. When my dad was in the TV business some 5 decades ago, we used to call that 'dead air' ...