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I need my Arduino Due to work only from external power supply, not from USB power. Is there any way to modify the circuit to allow this? I still need to keep USB communication, but it should happen only when external power is on. Thanks

Isso
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2 Answers2

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Disabling USB power is slightly tricky, as the incoming USB power is not only used for potentially powering the system, but it is also used by the various USB interfaces to indicate the presence of a connection.

The best way, looking at the schematics of the Due, would be to remove one or both MOSFETs that switch the USB power - that's T1 for the native port and T2 for the ATMega interface. That will isolate the USB power from the 5V system while keeping it connected to the VBUS pins of the relevant microcontrollers.

Majenko
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There is four ways I know of you can do to achieve exactly this :

  • You can remove the usb polyfuse from your board, which will make the usb behave exactly as you need it to. Between the 2 two usb connections in this picture is a smd component marked 501V. This is your polyfuse. Disabling this cuts the +5v line to the board from the usb but leaves the data lines open.
  • If you dont want to physically modify your board, then there is 2 other solutions you could use instead. You can buy a data-only usb cable, but they will probably be expensive and difficult to find.
  • Modify your usb cable. It has 4 pins used by the board, +5v, GND, and the 2 data comms pins. All you have to do here is cut out or block the +5v. The GND pin is still needed as the data pins still draw power off the board.
  • The arduino boards auto select a power source(the usb usually) if you have both usb and external power connected at the same time. A way to force the board into switching to the external power source instead, while supplying power to the data lines on the usb is to make sure the dc supply is greater than 6.6v.

Edit: That last one is for the 5v arduino boards, I just remebered the due works on 3.3v instead so this probably won't work on your board

javawocky
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