Upload to Pro Mini fails: 'avrdude: ser_open(): can't open device "\\.\COM8": Access is denied.'

Development Tools Uploading
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Arduino IDE FTDI driver for arduino Mini-Pro interface can't open the serial port. I get an error message since the latest driver setup. The driver interface is FT232RL .
Found somebody the same problem? Can somebody help me?

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Hi @Amiki9.

Please add a reply here on this forum thread to tell us the exact text of the error message.

Please also provide a detailed description of exactly what you were doing when the error appeared.

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Hi Mr. ptillisch.
I received these message:
avrdude: ser_open(): can't open device "\.\COM8": A hozz�f�r�s megtagadva.
The last is in hungarian, in englisch: Access denied.
I checked the serial port with other devices, like arduino Mega2560: working.
I have 3 pcs of Pro-mini interface, all of them has the same problem.

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There is a known bug in Arduino IDE 2.x that can cause uploads to fail with this "Access is denied" error if you try uploading to a board using an FTDI FT232R USB chip while the Arduino IDE Serial Monitor or Serial Plotter is open.

A port can only be used by one process at a time, so Arduino IDE must automatically close the port in Serial Monitor and Serial Plotter during an upload, automatically opening it again after. For some reason, that juggling of the port control is not working with boards that have the FTDI USB chip.

If that bug is the cause of the problem you are having, the workaround will be to manually close the port in Serial Monitor/Serial Plotter before doing an upload. Please give that a try and then let me know if you still have the error while uploading:

Serial Monitor

  1. Click the X icon on the "Serial Monitor" tab in the bottom panel of the Arduino IDE window to close the tab:
    image
    image405×345 38 KB
  2. Upload the sketch.
  3. Open Serial Monitor again if needed (by clicking the icon on the IDE toolbar or the Tools > Serial Monitor menu item) after the upload is finished.

Serial Plotter

If you have the "Serial Plotter" window open, the procedure is a bit different from closing the Serial Monitor connection:

  1. Close the "Serial Plotter" window.
  2. If the "Serial Monitor" view is not already open, select Tools > Serial Monitor from the Arduino IDE menus to open it.
    ⓘ We must do an open/close cycle on Serial Monitor as a workaround for a bug in Serial Plotter
  3. Click the X icon on the "Serial Monitor" tab in the bottom panel of the Arduino IDE window to close the tab:
    image
    image405×345 38 KB
  4. Upload the sketch.
  5. Open Serial Monitor and/or Serial Plotter again if needed after the upload is finished.

Please let me know if you have any questions or problems while following those instructions.

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Dear Mr. Hr. ptillisch.
You are right and solved the problem.
I have to close the serial Monitor window completely - I haven't even used the serial plotter yet - and then uploading to the Ardoino Pro-Mini via the FT232RL interface works perfectly.
Many THX from Budapest.

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You are welcome. I'm glad it is working now.

Regards, Per

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