Uno Stand-alone boot problem - looking for long term solution

I found a work-around by searching the forums, but I'm looking for a better solution.

The problem. My Uno R3 won't boot in stand-alone mode using only a 1000ma wall wart power supply.

The Uno will boot fine from USB or 9V battery (w/adapter cable). I did a search and it appears to be an issue with the voltage levels coming from the wall wart.

My work-around it to boot from USB power, then plug in wall wart, then disconnect USB.

Anyone have a solution on how to boot from the wall wart PS only?

Thanks, Jake

What's the voltage output from the wall wart?


Hi Jim,

I just measured it. 5.24V

Thanks, Jake

Too low. Needs to be 7VDC or greater for a 5V board.


Darn. OK, thanks Jim

Or connect the wallwart to the 5V/Gnd pins on the header. That bypasses the Reverse Polarity protection diode, and the 5V regulator, make sure the polarity is correct.