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I'm sure this has been asked before but I can't find it.  I heard that the ATmega328 chip uses about 10-20ma when idle.  My Uno is drawing 150ma.  Can I turn off the USB port if my Sketch doesn't use it?  I've read how to get it from 10 down to 3ma or less.  I know about powering down and sleep modes.  That is not my concern.  I want to get down from 150ma to 10-20ma.  How do I do it?
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What do you have hooked up to your Uno? Shields or other modules? It should not be drawing 150mA by itself unless something is wrong.

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No hardware is connected for this test.  But I was running a Sketch.  Let me run an empty one?
Using 8v battery pack with multimeter to measure current.
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With an empty sketch
void setup() {}
void loop() {}
it's still 150ma.  Nothing is connected.  What am I doing wrong?
At 12v the regulator gets hot.
At 8v it does not.
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I'm not sure if you're doing anything wrong or if your Uno is damaged. It should really only draw about 25mA or so. Is this a "name brand" Uno or something a bit more...sketchy? Are any other components on the board getting warm at 8V?

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My friend has 2 more that look exactly the same.  All Arduino brand Uno with socketed 328's.  The other 2 measure 50ma at 8v.  50 not 150.  So something is different about mine.  Still why 50ma?  How do I troubleshoot mine?
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Try removing the '328 from the socket. If the current changes by a lot, the '328 could be damaged. If it only changes by a little, something else on the board is bad.

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The 328 gets warm on mine.  Cold on the others.  Easy to replace.  Why 50ma when it should be 25?  Any guesses how I blew it?
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Are you measuring the current being input to the on board regulator from an external power source, or the current when inputting 5v directly into the 5v bus on the board? Also, does the board have a serial to USB chip on it?
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Easy to blow an output - one little short, damages an IO pin, part will seem to work in lots of areas and feel warm, or even quite warm to the touch.
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I'm measuring the external power source.  Yes, it has the USB on it.  
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I'm measuring the external power source.  Yes, it has the USB on it. 

Then you are measuring the power loss in the regulator chip (which may be more than half the loss) and and other gizmos plus the ATmega328 chip. You are not just measuring the ATmega328 chip current useage.
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So 50ma is about right.  At 12v the regulator is more than 1/2.
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