Friday, 28th Nov 2014

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Jan 15 2007

Bluetooth Blues

While native serial ports have almost disappeared from modern laptops, COM port-mapped devices are very popular: USB ports, USB-to-serial adapters, Bluetooth devices, virtual devices, and so on… all of them are viewed as serial ports under Windows. Every time a new driver is installed, one or more COM devices are added and remapped to the first COM number available: this quickly causes the COM port number to shoot through the roof.

As for my laptop, there have been quite a few driver reinstallations, that caused the bluetooth port to be mapped to as high a number as 14. This behavior was quite puzzling: after some trials and Internet search, I was able to find a working solution which I’d like to share.

Disclaimer: the following procedure requires familiarity with manipulation of the Windows registry, and therefore I can’t be held liable for any damage/problem whatsoever. This modification applies to Windows 2000 and Windows XP: I can’t comment about other operating systems.

Here are the main steps:

  1. Perform a complete uninstall of the bluetooth dongle driver. Removing all other serial add-ons such as USB-to-serial adapters and virtual mappers may be also required.
  2. Reboot
  3. Reset the Windows COM port mapper by editing the registry (see below for details)
  4. Reboot again
  5. Reinstall the bluetooth dongle driver.

And here’s how to edit the registry (“close-up” of step 3 above):

  1. Open Regedit
  2. Navigate to the following key: “HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\COM Name Arbiter”
  3. Highlight “COM Name Arbiter”
  4. Write down the current value of the “ComDB” key. In case of problems, you can easily restore its original value.
  5. Right-click on “ComDB” and click “Modify”
  6. Now a dialog pops up in which you can edit the entry’s value (hexadecimal string). Please pay attention NOT to alter its overall length!
  7. Clear all of it hex byte values until it reads all “00″‘s.
  8. Click OK and close Regedit.

Please note that the COM port remapping does not take place until you trigger a “re-detection” by reinstalling the dongle driver.

If everything works out OK, the bluetooth serial port(s) will get mapped to “more reasonable” device numbers (in my case, COM4). Everything now works like a charm! :-)

Good luck!