My MKR GSM 1400 works fine when connected to a computer (powered USB) and after opening a serial connection to it. It does not when I plug it into a power supply. My power supply is a 5V 3A with a USB adapter.

void setup() {
  // put your setup code here, to run once:
  while (!Serial);

void loop() {
  // put your main code here, to run repeatedly:
  • 1
    What means that it does not work? What does actually happen? Also show us your code and your circuit. Currently you don't give us enough information to help you.
    – chrisl
    Oct 4, 2019 at 23:27
  • @chrisl The sketch doesn't run = It does not work. Is my power supply sufficient? Is it ok to power it through the USB connection or do I need to power it somewhere else? I don't think my code is the issue.
    – Mike C.
    Oct 5, 2019 at 0:04
  • 2
    do you have while (!Serial); in the sketch?
    – Juraj
    Oct 5, 2019 at 4:49
  • 1
    It was the while(!serial)
    – Mike C.
    Oct 9, 2019 at 17:18
  • 1
    I've posted a question with more details since I am having the same issue at: arduino.stackexchange.com/questions/77324/…
    – Gineer
    Aug 5, 2020 at 21:25

1 Answer 1


If your sketch on an Arduino with native USB doesn't run if not connected to USB, always first check if you didn't forget to disable a dependence on Serial. A common error is a while (!Serial) {} endless loop in setup().

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