It seems when ever I start a new project I have a problem with the COM port. I get the following message "avrdude: ser_open(): can't open device "\.\COM4": The system cannot find the file specified." I have tried to go into Windows 8.1 and change the COM port of the Arduino Uno to COM4 but is says it's "in use" I am not sure how to fix.
That doesn't quite make sense; it implies that you manage to get it working till the next time that you start a new project.
Did it use to work before? Or is this the first time that you started with the Uno? Does COM4 disappear when from the IDE (and device manager) when you disconnect the board? If not, it's not the Uno.
I only have the problem some times. And, I am not sure what I do that fixes the problem. Com4 does disappear from both the ide and device manager when I disconnect the Uno board.
For what its worth, I've found that disconnecting the Arduino then reconnecting solves my "can't find Comx issues"
Tried that. I get the same error message and the device manager still indicates that COM 4 is "in use" so I can't set my uno board to COM 4.
I am very frustrated!
My last resort procedure is to download nirsoft's "USBDeview.exe"
nirsoft is a well known set of safe utilities.
I will uninstall everything that is not connected (file / uninstall), reboot and try again.
JohnRob I appreciate your suggestion but, I am not familiar enough with computer stuff to follow your directions. I downloaded the latest UBS drivers from "Driver support One" But I got the same result. Sorry for being so dense.
If you want I can provide more detailed instructions. This particular process is kinda benign and will not damage Windows. The worst you will loose you keyboard or mouse and have to reboot. Also, it does not install so no changes are made in Windows (except the ones you would make)
However if you only uninstall non connected devices you are very safe.
I have windows 8.1, not 10. I already installed it but didn't see anything like the file list you showed in your reply.
Hey JohnBob,
I think I found out how to fix my problem! In Device manager I clicked on show hidden devices and then I could see that there was a hidden uno was using COM4. I uninstalled it and then changed the correct uno to COM4. That still didn't work until I disconnected the uno and plugged it back in. Then the upload worked.
Thank you for your effort to help! At least for now I am not dead in the water.
Great, happy you got it going. I know the IDE and connection should just work and it can become frustrating if it doesn't.
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