Powering Arduino - Wall wort selection, need some help/advice

I need to select/choose a wall wort to power an Arduino Duemilanove, and I went up to Radio Shack earlier today to find an appropriate power supply, by selecting one based on the criteria listed in this guide. The guide states for a 2.1mm plug, but Radio Shack had measurements for inner and outer diameter, so I was not sure what measurement this 2.1mm plug statement was referring to. :-l (inside maybe?)

Also, when I got home, I decide to look through my junk drawer. I discovered two possible candidates to power the Arduino. One is a Radio Shack power supply with a Cat No: 43-742/743/744/747 The output is listed as follows, OUTPUT AC 9V 780mA but there is no labeling on the power supply describing whether or not it is center positive or not. :-l

The second candidate is US Robotics P/N 1.015.1286 with an output as follows, OUTPUT: 9V AC 1000mA. As stated with the first power supply listed there is no markings on the power supply stating whether it is center positive or center negative. If you can shed some light on this situation I would appreciate it.

I was not sure what measurement this 2.1mm plug statement was referring to

Yes it is the inside pin, the other size you can get is 2.3mm but this will not fit.

The output is listed as follows, OUTPUT AC 9V 780mA but there is no labeling on the power supply describing whether or not it is center positive or not

It's AC it doesn't have a positive line!

Using an AC supply is not recommended and while it will not break the arduino due to a protection diode it will not work well either.

Grumpy_Mike: It's AC it doesn't have a positive line!

:astonished:

Thanks, I was hoping one of these would work but guess not.

You could get a bridge rectifier, some filtering caps, run that DC into the VIN pin. Or get a 5V supply like this one: http://www.mpja.com/prodinfo.asp?number=18520+PS I power my arduinos with this direct to the VCC (Promini) or5v (deumilanove) pin. Lots of current for LEDs & stuff without heating up the board with its regulator.

I would take my arduino to a surplus store and test out an adapter. There is always a chance the adapter is just a tid-bit loose and you're haunted by random power loss like I was once. Should be a couple of bucks at surplus stores. Just observe the polarity, has to be center-positive. Recycle and reuse! :grin: :grin: :grin:

Here is a blog spot:

http://liudr.wordpress.com/2011/02/08/power-your-arduino/

FWIW here's a picture of the finished power supply I assembled for the Arduino.

So you cut the end off and put on a 2.1mm/5.5mm, center positive connector? What's the output voltage of the adapter?

CrossRoads:
So you cut the end off and put on a 2.1mm/5.5mm, center positive connector?
What’s the output voltage of the adapter?

Yeah, I cut the end off of one power supply that I picked up from a computer shop in town, and hooked it up to another power supply. The output of the power supply above is:

Output: 12VDC 850mA

Yep, that'll work. Your regulator may run a little warm, but that will work.