Serial Monitor Not Available

Official Hardware UNO Family UNO R4 Minima
1

I am using the Arduino IDE 2.3.6 on Windows 11 with the Arduino R4 Minima. The board will connect over COM for a moment then switch to DFU, which makes the Serial Monitor unavailable. I need to be able to use the serial communication for my project.

When using an example project such as AnalogReadSerial, the board will connect over COM once the sketch is uploaded, but if I try to use the serial monitor, it disconnects and switches back to DFU. The LED on the board also reverts to the boodloader mode i.e. slowly fading on and off.

2

I have discovered that if I use a different application to do the serial monitoring, the board will stay on the COM port. So the issue seems to be when using the Arduino IDE Monitor.

3

Hi @djanwt. I am able to reproduce the problem by selecting "1200 baud" from the menu at the top right corner of the Arduino IDE window. When the UNO R4 Minima board detects that its serial port has been opened at this specific baud rate, it automatically goes into a "boot mode" where it only produces the DFU port and has the pulsing LED. This special treatment of 1200 baud is an intentional design, since the upload process relies on it. However, it is problematic when it occurs via Serial Monitor instead of the uploader tool.

Unfortunately Serial Monitor only shows the baud rate menu when you have a serial port open, so we have a "catch-22" situation where the baud rate menu configuration causes the board to not produce a serial port, and we can't change the configuration due to the lack of a serial port :face_with_spiral_eyes:.

I'll provide instructions you can follow to reset the configuration of Serial Monitor to its defaults, where it will have 9600 baud selected from that menu:

  1. Select File > Quit from the Arduino IDE menus if it is running.
    All Arduino IDE windows will close.
  2. Start Windows "File Explorer".
  3. Navigate to the folder at the following path on your hard drive:
    C:\Users\<username>\.arduinoIDE
    (where <username> is your Windows username.
  4. Delete the pluggable-monitor-settings.json file from that folder.
    :warning: Please be careful when deleting things from your computer. When in doubt, back up!
  5. Start Arduino IDE.
  6. If the UNO R4 Minima board is still in the state where the LED is pulsing, press the reset button on the board to change it back to the normal operating mode where it runs the loaded sketch program.
  7. Make sure the COM port of the board is selected from Arduino IDE's Tools > Port menu.

Serial Monitor should now work as expected. Be careful to avoid selecting "1200 baud" from the baud rate menu. This baud rate has a similar effect on other Arduino board models (though not always with the same difficulty of recovery), so this is a good general rule, unless you have a reason for needing that specific baud rate.