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Here's a funny thing... (Power and Duemilanove)
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Here's a funny thing... (Power and Duemilanove)

by shobley on Thu Mar 19, 2009 2:54 pm

I've just noticed that on my new shiny laser harp the 7805 regulator keeps going into thermal shutdown when I use a Duemilanove, but not when I use a Decimilia.

A little more info...

I've put together a shield for the Arduino that requires +6,-6 and +5v. So I use 3 regulators to provide this. They connect directly to the shield and connect the 5v to the Arduino underneath. Effectively bypassing the onboard regulator.

The shield is for a laser harp, and up until now I've been using this powering technique with no problems - with both Boarduinos and Arduino cores.

Anyone know if the "automatic power selection" feature of the Duemilanove would cause problems like this?

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Re: Here's a funny thing... (Power and Duemilanove)

by adafruit on Mon Mar 23, 2009 4:52 pm

im a little confused by the duemilanove power selection circuitry, to be honest. one day ill examine it in detail.

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Re: Here's a funny thing... (Power and Duemilanove)

by westfw on Mon Mar 23, 2009 9:38 pm

How much current does the arduino draw in through the +5V pin? And how does that compare to how much it draws through (say) the USB connector? Like Lady Ada, I'm not finding the duemilanove power selector "obvious", but it's definitely "upstream" of the +5V shield pin, and it wouldn't surprise me a lot if the resulting confusion caused odd behavior. I didn't analyze things in detail, but it looks like it might (for example) short together the USB and +5V supplies (which is what it wants, right? Since Vin is off?), which could cause power issues if you had the USB plugged into a computer as well as providing a not-quite-matched Vin via the +5V pin. ?? How did you have the power jumper placed on diecimila boards? Removed entirely? That would have been much safer. I think.

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Re: Here's a funny thing... (Power and Duemilanove)

by thatonekid on Tue Mar 31, 2009 7:53 am

i believe that with the duemilanov, when it is being powered by the USB port, it is bypassing the voltage regulator since the computer already regulates its 5volt output. i also believe that the voltage regulator on the duemilanov has a bad heat sink design(it needs a bigger one).
i don't have mine with me so i don't know if its possible, but you might be able to add a small heat sink. that would probably solve the problem.
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Please be positive and constructive with your questions and comments.