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Topic: Serial port 'COM19' already in use (Read 19829 times) previous topic - next topic


Hi all,

Would appreciate if anyone can share how to solve the problem of com port in use when trying to upload sketches.  I realized that I can only upload new sketches to the board by rebooting with the serial port disabled and enabling it after the system restarted.  All this is done with the board plugged in (to force the assignment of port to the board? doesn't seem right either...). It didn't work when I reboot without disabling the serial port.

Strange strange strange.

Anyone has any solution or has encountered this problem?



Your workaround continues to point to other software on your computer that is blocking the serial port.  It could be anti-virus, blue-tooth, or a range of other programs that are causing the conflict.


Anyway to find out which program or device is also using the same com port?  Can't find the information in Device Manager.

The strange thing is, regardless of what com port I changed to, the same problem occurred, giving me the impression that Arduino is preventing itself from using the com port (different threads of same program using the com port and blocking the other?).

I tried disabling norton AV, bluetooth, and other programs visible to me without avail.

Any suggestion to test?


Feb 07, 2009, 03:35 am Last Edit: Feb 07, 2009, 03:37 am by madworm Reason: 1
How about using a different OS ?
Windoze for gaming, something useful for the rest.

Can't comment on Vista. It's on my laptop, but only for purpose of reselling it sometime. Never used it, too many colors, ugly explorer.

I know this doesn't help much, but I've long given up thinking about the other OS, expect for running games. XP had become a decent flavour of windoze with SP2, Vista doesn't really exist, the W7 may be better, maybe not.


I've posted it in another thread but realized that the problem I encountered is different from the thread starter.  Pardon me transferring it here.  Hope someone can help.

I realised one thing while trying to figure out the port already in use problem.  After getting it to work following the cumbersome way of disabling, rebooting and enabling the serial port, I realised that it may be the ide refusing to release it hold on the port (pardon me if I am technically incorrect with terms and jargons here).

When I quite the IDE and started it again, the uploading works ok.  Once I plugged out the USB cable and plug it back again, the problem starts.  This occurs regardless of whether I unplug the usb cable with IDE running or after I shutdown the IDE.

So it seems to me that the device still hanging on to the serial port is the IDE than any other program.

Anyone has any solution or things I can try with?



Did you solve the problem? I had exactly the same problem on Vista Home Premium. I started to suspect a problem with Vista because I have the same error when trying to synchromize a Palm pilot using bluetooth over a USB connection. Then I loaded the program on an XP machine and worked at the first try.


Nope.  Unfortunately.  I don't have a XP machine right now.  Not enough space to do a dual boot.  I'm trying to repair my good old P3 which has some popped caps on its MB and graphic card.  If it can be revived, I can do a test.

If anyone has a solution with Vista, please share with me.... thanks.


Finally managed to salvage my dead-for-a-long-time P3 box after replacing mainboard and DVD/CDROM.  Quite a bit of trouble as parts are not easily available locally.

Installed the IDE and tried some codes with removal of the USB cable in between each upload.  The problem of com port in use didn't occur anymorel  ;)

How I wish the problem can be solved on my notebook running Vista so that I can move around with it.  Dual boot is out as I am already running low on disk space on my notebook.  Too bad...

If anyone has any solution or idea with the use of Vista, do share.

Thanks for all the comments, suggestions, and attemps to help.



Check your port activity with


If you have bluetooth you can try replacing the RXTX Serial Communication Library used by Arduino IDE with my patched one:

Good luck
My website: http://ried.cl


Thanks for the links.

Portmon also said that the port is in use and cannot connect to it.  Replaced the 2 files didn't solve the problem.  I got a feeling that the port wasn't "released" by arduino after I removed the USB cable and was still "marked" as being held till I disabled it and do a reboot.


Can you change the port number on the Device manager, Ports ? the ftdi driver has a bunch of options to play with
My website: http://ried.cl


I changed port number via device manager. Didn't help.

How do I explore the options available with the ftdi driver?


With properties, over that com port, in advanced.

Its very strange your problem, maybe with portmon you can see what thing is capturing your port. First disconnect the arduino, then disable the ftdi driver, then enable it and change the com port number, then connect arduino, checking portmon for misterius port activity
My website: http://ried.cl


Thanks for your patience with this problem my mine.

I'm not able to disable the com port with arduino disconnected despite  unhidden it from view using "show hidden devices".  I can only disable it with the arduino connected.

One thing I realized is that the work-around didn't work anymore with the 2 files replaced - with the same sequence of disable and unabling the port with a reboot, com port still show as being in use.

Portmon also couldn't monitor the port.

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