I have a nasty problem with arduino Uno finding a com port.
I have started to use arduino in my secondary school classes since September.
We use about eight laptops, (xp, vista and seven) with arduino Uno's. We mainly use the ardx experimentation kit. Very often a sketch cannot be uploaded (‘problem uploading to board’) because there is no com port available. I searched the forum, but could not find a real solution. Eventually it always works (after pulling out usb cable, changing to other usb port, restarting arduino ide, restarting laptop etc.) but it is very frustrating and time consuming for me and my students.
Does anyone have a solution for this?
The UNO has its own unique serial drivers which have to be loaded on to the pc. The below may have some more useful info.
I read this post but I did load the drivers and the problem also occurs with vista and windows seven.
That is probably the down side of moving from the FTDI serial chip to a DIY version.
zoomkat:
That is probably the down side of moving from the FTDI serial chip to a DIY version.
No, I have the same problem with Win7 over USB with my mega. I'm at COM28 right now, and have to go up 2 channels every time.
No, I have the same problem with Win7 over USB with my mega. I'm at COM28 right now, and have to go up 2 channels every time.
Then you probably need to follow the info on assigning a fixed com port to your boards.
Then you probably need to follow the info on assigning a fixed com port to your boards.
Where can I find this info?
StanR:
Then you probably need to follow the info on assigning a fixed com port to your boards.
Where can I find this info?
Ditto
magnethead794:
StanR:
Then you probably need to follow the info on assigning a fixed com port to your boards.
Where can I find this info?
Ditto
You follow the posted links until you see the words "advanced comport settings". 
zoomkat:
magnethead794:
StanR:
Then you probably need to follow the info on assigning a fixed com port to your boards.
Where can I find this info?
Ditto
You follow the posted links until you see the words "advanced comport settings".
Problem with arduino Uno finding a com port. - #2 by zoomkat - IDE 1.x - Arduino Forum
The fix for me was to go into the advanced comport settings in device manager and assign a com port to the adapter. If xp said com port 8 was already in service and I had nothing using com port 8, then I would assign comport 8 to the adapter. xp would say 8 was already in use by another device, but i would go ahead and assign 8 to the adapter. After that xp would always use com port 8 for that adapter with no further issues.
Doesn't work in Vista or 7. At least not on either of mine. works on server 2003 though.
Doesn't work in Vista or 7. At least not on either of mine. works on server 2003 though.
Bummer. I have xp and can reassign the com port numbers.
zoomkat:
Doesn't work in Vista or 7. At least not on either of mine. works on server 2003 though.
Bummer. I have xp and can reassign the com port numbers.
You can reassign them in vista/7, but they'll change when you unplug/replug. They don't latch to the device ID number like they should.