I have two Arduino Nano Every and a sensor connected to each of them. Here is what's happening:

  • I upload the sketch to the first Arduino on Com4 and see its output is correct via the Serial Monitor

  • I open a new instance of the Arduino-software, upload the same sketch to the second Arduino on Com6 and see its output is correct. However, in the meantime the Arduino on Com4 has stopped sending or receiving data

  • If I close the second IDE-instance and re-upload the sketch to the first Arduino on Com4, it starts working again.

So, essentially I have two Arduinos which I can't read out at the same time.

The sensors are not connected, so I don't know where the problem is. Shouldn't the Com-Ports be independent?


Shouldn't the Com-Ports be independent?

Not in the Arduino IDE, no. Basically the IDE is [expletive deleted] when it comes to using more than one board at a time.

You're better off using a proper serial terminal program, not the "serial monitor" in the IDE. Something like Teraterm or Putty, where you can have multiple instances on different ports at once.

  • Interestingly, the same happens with Putty.. – Christian Mar 12 '20 at 15:22
  • you could write a monitoring sketch in Processing ... processing.org – jsotola Mar 12 '20 at 15:23
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    It is kind of ironic that the chip they chose to implement the USB interface is far more powerful than the chip that you as a user get to program. – Majenko Mar 12 '20 at 16:08
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    @Majenko, it is ATmega4809 20 MHz, 48kB flash, 6 kB SRAM; SAMD11 48 MHz, 16 kB flash, 4kB SRAM – Juraj Mar 12 '20 at 16:57
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    Yes. Like I said. A slow 8 bit vs a faster 32 bit. More power in the USB interface. – Majenko Mar 12 '20 at 17:21

UPDATE, self answer:

It was a broken USB cable.

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