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Topic: Clarify USB Comms + External Power on UNO (Read 500 times) previous topic - next topic

DuaneB

Hi,
    I would be grateful if anyone who has tried it can confirm that a UNO can be simultaneously connected to USB for serial communication and an external source for power.

    I know that the UNO Automatically selects the power source, but which has priority and are they isolated once one is selected.

Thanks for any advice

Duane B
Read this
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
then watch this
http://rcarduino.blogspot.com/2012/04/servo-problems-part-2-demonstration.html

Rcarduino.blogspot.com

Grumpy_Mike

The external input is switched to power the unit if it is available. The two supplies are not isolated, that word implies the grounds are sepreate, they are not.

DuaneB

Hi,

Thanks for the quick response, I will rework my project to use this approach.

Thanks,
  Duane B
Read this
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
then watch this
http://rcarduino.blogspot.com/2012/04/servo-problems-part-2-demonstration.html

Rcarduino.blogspot.com

DuaneB

Hi,
   I have the UNO powered from an external LIPO battery and sending data to the PC through USB, its as simple as suggested. This kind of simplicity that makes Arduino a joy to work with.

   I am making a point of connecting the external power first, I am assuming that if I was to connect USB First, that would initially supply power, as soon as external power becomes available some sort of switch would take place. As I am unaware how this is managed and any of impact it may have I am avoiding it.

Thanks
     Duane.

Read this
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
then watch this
http://rcarduino.blogspot.com/2012/04/servo-problems-part-2-demonstration.html

Rcarduino.blogspot.com

Grumpy_Mike

Quote
As I am unaware how this is managed

On the board is a voltage comparator. It takes the USB voltage and a fraction of the external voltage, which ever is higher determines the output of the comparator. This is then fed to an FET to switch the appropriate voltage to the main board. I don't think there will be any issues doing this while the board is running.

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