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Author Topic: External power supply usage?  (Read 375 times)
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The Hague, Netherlands
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Just a quick question,
For my garden automation project (can be found in the exhibition section) I'm thinking of powering the arduino constantly with a wall wart but sometimes put my laptop on it to check on the progress.
Now the question is: if I run it constantly on the wall wart and then plug the usb into my laptop, will the arduino freak out because at has 2 power sources and will it reset the board?

Thanks
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The Hague, Netherlands
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Alright, I'm using an UNO. The reset thing just has to do with the fact that I'm keeping time without an RTC. If there's a power failure setting the time again is no big deal, but I'd rather not have to set the time every single time i hook up my laptop.
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Alright, I'm using an UNO. The reset thing just has to do with the fact that I'm keeping time without an RTC. If there's a power failure setting the time again is no big deal, but I'd rather not have to set the time every single time i hook up my laptop.

There is no problem with having external power and USB power on at the same time. The boards that have an auto-voltage selector circuit will always utilize external power if it's avalible, that is it has priority over usb power. However having your arduino board reset or not is more a function of the PC software you are using and if it activates the DTR signal or not. Most arduino boards these days have the auto-reset on DTR function so if it's important that your running sketch is not reset then you might consider disabling that function and only enabling it when needing to upload a new sketch.

Lefty
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Sounds good, ill already try it with a simple led sketch. External power and then hook up the usb.
Thanks for the tips!
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