I'm rather disappointed because I just bought arduino and I am unable to upload any projects. The error I get is:

avrdude: ser_open(): can't open device "\\.\COM3": Časový limit semaforu vypršel.

Can be translated as:

avrdude: ser_open(): can't open device "\\.\COM3": Semaphore time out

Am I expected to brute-force all available ports to see which one is reserved for arduino? How can I, on Windows 7, quickly determine which port to use given that the IDE for some reason can't do that for me.

  • I'd look into the Device Manager.
    – Simon Richter
    Mar 13 '16 at 15:58
  • This has nothing to do with electronics design. You are best off searching on something like SuperUser or Arduino.SE to find out how to locate serial ports in windows and the Arduino IDE respectively. Mar 13 '16 at 15:59
  • @TomCarpenter I didn't know Arduino.SE has been resurrected again (how many times was it already...?). And many of those who said Arduino.SE should not be created argumented that all Arduino quesrions can be answered on Electronics.SE. Mar 13 '16 at 16:02
  • 1
    Looks like EE.SE doesn't agree with you. :) The IDE should detect which port the Arduino is on. I never have to brute-force search for mine. I just bought arduino - which Arduino? You may have to install a device driver. There is a "drivers" directory with some in it.
    – Nick Gammon
    Mar 13 '16 at 21:12
  • @NickGammon Do not misunderstand. I am supporting Arduino.SE! I just didn't know it's resurrected - I had all my questions from previous betas migrated. Although I see that I already have some question here. Maybe I forgot. And after installing drivers, the arduino now appears next to the correct port, though I still have to manually select it. Mar 13 '16 at 21:16

Start | Control Panel | System | Device Manager | Ports (COM & LTP).

Watch the list change as you plug / unplug the Arduino. The new port is the Arduino.


You may have to install a device driver. There is a "drivers" directory in the IDE download with some in it.


Windows drivers

According to the readme.txt file:

With this version of Arduino a new all-in-one driver (with security signature for Windows 8) is supplied.

The old (deprecated) drivers are still available in the Old_Arduino_Drivers.zip

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.