Visual Studio Code - Serial Monitor not working

Hi so I just started with Visual Studio ( I used the Arduino IDE before),
and i have a problem that the Serial Monitor is not showing anything.
It just shows the baud rate I set and the USB port.
(btw Idk if its weird or not but the port is /dev/ttyACM0??)
i use a Teensy 3.5 board. It uploads just find but does not do anything in the Serial Monitor.

I already tried:
pio device monitor --encoding hexlify
pio device monitor --filter debug

but none of it works.

Weirdly it worked one time when I tried both and then Restarted the IDE. But second time i uploaded it, it stopped working again.

Can you open a shell, execute sudo dmesg -w, plugin in the Teensy and then post the newly created log lines?

Just in case anyone else hits the same issue I had with very similar symptoms which took me quite a while to work out…


  • all (native) units ran successfully
  • code uploaded to my Arduino Nano successfully
  • nothing output to the serial monitor

I had declared an array that was too large for the Nano. While there were no errors uploading, the code could not run.