Did'nt really know where to post this. 2 Questions.

If an Arduino is powered by an external power source, i.e. 7 Volts through the barrel connector, and the USB lead is connected for data transmission between the Arduino an the PC as normal....

  1. Is the 5V from the USB port still going in to the Arduino, or is it disconnected internally somehow?

  2. If I disconnect the 5V line from the USB and leave the 2 data lines and the Ground line and power the Arduino by an external power source, will data transmission still work, or does it need the 5V line to send and receive data?

Any advice would be greatly appreciated.


  • In a UNO, it is disconnected by the control FET when the barrel connector exceeds 6 Volts or so.
  • Data transmission will still work.

Wow Paul__B, that was fast.
Thanks very much for the help.