I am having an issue with external loads causing the computer I have my Arduino connected to to momentarily drop out, which causes the Arduino to lose USB power momentarily and the port drops out and won't reconnect unless I physically remove and reconnect the USB cable. Since I need the USB connected in order to send and receive serial data to/from the Arduino, I was wondering if I could physically open the USB cable, cut the 5V line, and supply it via and external regulated 5V supply. I wouldn't cut the ground wire, but would tie it to the external 5V supply. I have read conflicting information on this (something about handshaking) but was wondering if that applied to Arduino's specifically.

  • You probably could, but why not just get a powered USB hub?
    – Majenko
    May 2, 2018 at 15:41
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    A powered hub would be a more proper solution USB-wise. However it may be that whatever is causing "dropouts" would break the USB session as well. You might need to switch to using an actual serial connection (if still logic-level) and use a different serial port on the computer. Another thing to look at would be galvanic isolators for USB or serial. It really all depends on the cause and nature of the "dropouts". If these are being cause by other USB peripherals try putting them on their own powered hub, ideally connected to a different port or internal hub on the PC. May 2, 2018 at 16:24
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    The dropouts are being caused by external loads being powered on and off. The loads have pretty high starting current, which is causing power for the whole computer to fluctuate. I've tried using a UPS but the problem still persists. I'll try getting a powered hub and see if that helps.
    – joshua0823
    May 2, 2018 at 17:00
  • USB devices are only slaves. They cannot do anything without the host. When the power of your computer drops, it seems to close the usb sessions. So this is most likely not a problem with the Arduinos USB, but with your computer. It has to reestablish the connections after a voltage drop. Using a powered USB hub will only ensure, that the Arduinos power isn't cut of, but it will not ensure, that the computer reestablishes the connection, that you need for data transer.
    – chrisl
    May 3, 2018 at 12:18
  • I solved this problem by using a laptop instead. It is immune to these power fluctuations
    – joshua0823
    Jun 5, 2018 at 15:39

2 Answers 2


I solved this problem by using a laptop instead. It is immune to these power fluctuations


If you are drawing more than 500mA from your PC then that is why it is happening.

I suggest, rather than butchering a cable, you get yourself a "wallwart" (Mobile phone charger) and use that to power the board. You really should work out how much current you are pulling before deciding on what PSU to use.

A problem with wall warts is earthing, you need to make sure that your PC and wall wart are connected to the same earth connection, so that they share a common ground.

If the current being drawn us only for a very short time then it might be possible to provide additional power using a capacitor in the power line. But plugging a charger in is much easier.

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