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Author Topic: Arduino UNO external power not working  (Read 1391 times)
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I started tinkering with my new Arduino tonight and found that I cannot get it to accept any sort of external power.  When I connect through the usb input everything works fine; I opened the fade example sketch and wired a led between pin 9 and gnd, and when I uploaded the sketch the led faded in and out as it should.  But when I disconnect the usb and connect to an external power source I get nothing- no power led, no sketch function, nothing at all.

I'm using the 12v output from a spare computer power supply that I've used in the past and checked to be stable.  I've tried connecting a cannon plug to the supply and then into the power input as well as connecting the 12v directly into vin, all with the same result, which is nothing.

So what am I missing here?  Am I doing something wrong or is my board just broken out of the box?
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I'm using the 12v output from a spare computer power supply that I've used in the past and checked to be stable.  I've tried connecting a cannon plug to the supply and then into the power input as well as connecting the 12v directly into vin, all with the same result, which is nothing.

So what am I missing here?  Am I doing something wrong or is my board just broken out of the box?

Have you measured the external 12vdc power with a meter? If it measures good, then plug it into the arduino external power connector and then measure between the Vin pin and a ground pin with a meter, does it still measure good?


Lefty

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I get 11.52v across the source by itself, but when connected to vin and gnd it drops to 1.5v

...that got me thinking though, and it looks like I've resolved the problem.

I was using one of the smaller fan power connectors on the supply for the more convenient smaller gauge connector inputs.  It supplied 12v unloaded, but I think it had some sort of current limiting circuitry built in.  I switched inputs over to one of the main 12v lines that you would use for your disk drives and everything came up green  smiley
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Good for you. The meter is always your friend when troubleshooting power problems.

Lefty

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