View Full Version : External power & usb connected at same time

02-02-2011, 03:08 PM
Before I blow things up... is it safe to have the arduino powered through the external connection (direct to the main Lipo in this case) *and* hook up the USB while watching the configurator?

I suspect it is, but figured I'd ask...


02-02-2011, 03:20 PM
Totally safe, I do it all the time!

02-02-2011, 03:27 PM
Totally safe, I do it all the time!

I didn't knew that, I always double check if Arduino 2.1mm connector is disconnected before plugging in the USB. Are you sure it will do no harm to Arduino if it is double powered with different voltages?

02-02-2011, 03:49 PM
They have a check and security for that!

Never tried on APM since I power it up by the ESC, but, my UNO and MEGA, I have done it a lot, 11.1 volt in vin/ground pin and USB connected! So, I'm able to have the configurator plug and motor turning to check how it behave!

The only thing I got issue with is the XBee, on the UNO mainly, can't upload the sketch if the XBee is connected!

02-02-2011, 03:51 PM
It's not the Arduino (I think you're referring to the Atmega processor) that'd take any harm. It would be the USB 5V "fighting" the on-board regulator 5V. However there seems to be a FET and an OP amp selecting between the two power sources on some boards. The duemilanove has it, the APM does not:

If you look in that schematic on that OP circuit, you'll see that when VIN is seeing battery voltage (after diode drop), the FET T1 will shut off USB 5V connection totally. So then it will be isolated.

02-02-2011, 04:11 PM
Never take the time to check the schematic! I'm no a schematic/micro-controller guy!

But, have done it with no problem!

02-02-2011, 05:03 PM
i do the same as kenny and have no issues. i can read the data on the configurator and watch how the motors respond as well.

02-02-2011, 05:22 PM
I thought this was a handy bit of info, so I added it to the Wiki. Please revise (or just PM me) if you have info that the entry is not 100% correct.

02-02-2011, 06:23 PM
Thank you Revywarguy. There should probably be a link to the Duemilanove schematic on the wiki where you wrote that, and maybe a link to this thread.

02-02-2011, 06:39 PM
Done. I thought a more generalized schematic pointer was a good idea.

02-02-2011, 06:54 PM
Very nice looking! Well done. You get the Medal of Honor in documentation :)