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Connecting USB while using other power sources
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Connecting USB while using other power sources

by Mnuckols on Fri Mar 19, 2021 10:17 am

I have a Metro M4 Express that will be enclosed and difficult to get to. I don't plan to power it using USB, but I would like to expose the USB port to flash new code periodically.

1) If I power it using 9V to the barrel jack, then plug in a USB cable connected to my laptop, will bad things happen to my Metro or laptop?
2) If I power it using 5V to the VIN pin, then plug in a USB cable connected to my laptop, will bad things happen to my Metro or laptop?

I'm hoping someone knows that answer because I don't want to try it and burn something up.

Mnuckols
 
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Re: Connecting USB while using other power sources

by dastels on Fri Mar 19, 2021 11:06 am

From what I read and see on the schematic, there shouldn't be a problem plugging USB while powered via the barrel jack. It states that it will switch automatically. That should also be the using the Vin pin (which is essentially the barrel connector voltage after the power switch).

About Vin. It's meant to be an output that is the higher of 5v (from the USB connection) and whatever is on the barrel connector. I.e. the voltage coming *in* to the board. Also, since it's the input to the 5v regulator, it should be higher than 5v. The recommendation for the barrel jack is 6-12v.

TL;DR power it internally through the barrel jack with between 6 and 12v. Freely use the USB connector to reprogram it.

Dave

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Re: Connecting USB while using other power sources

by Mnuckols on Fri Mar 19, 2021 11:39 am

That's great, thanks!

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Re: Connecting USB while using other power sources

by User_UMjT7KxnxP8YN8 on Fri Mar 19, 2021 7:52 pm

I can confirm that I do this regularly with my Metro M4.

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