I've been using Arduino UNO for quite sometime and brought a new Arduino Nano. When I connected it to my computer, the power usb lit up and the blink sketch started running ( as expected of course).

Now I opened up the IDE and switched boards. But when I try to upload code to my Nano I get an error-

avrdude: ser_open(): can't open device "\.\COM3": The system cannot find the file specified.

Clearly the IDE can't see my board. Uploading to my UNO goes fine. The serial port option is greyed out so I can't change it.

I have searched extensively online for a solution and have found none. This must be either a very unique issue or a very simple one.

  • Is it a genuine Arduino Nano or a cheap Chinese clone Nano?
    – Majenko
    Commented Aug 7, 2016 at 13:35
  • @Majenko most probably a clone. I don't see anything written on the board. And the same coloured power and pin13 LED further confirm the fact. Have I done a mistake??
    – YaddyVirus
    Commented Aug 7, 2016 at 13:47
  • No, but it will need different drivers. CH340G
    – Majenko
    Commented Aug 7, 2016 at 13:48
  • 1
    No sounds no devices in device manager. I installed the driver and it said pre-installed the drivers. Just nothing happened. is that bcz I'm on Win10.
    – YaddyVirus
    Commented Aug 7, 2016 at 14:11
  • 1
    @Majenko I don't know. Its a new cable I bought off at a local shop just half an hour ago. It powers up the Nano. But I'm not sure about how many wires are in it
    – YaddyVirus
    Commented Aug 7, 2016 at 14:15

4 Answers 4


Firstly, you have a clone not a genuine Arduino Nano. They use a different USB chip and require different drivers. Install the CH340 drivers.

Secondly your cable is bad. It sounds like one with no data wires in it used for powering or charging small low-powered devices like bluetooth headsets etc. Replace the cable with a proper one.


When using a cheap knockoff Nano, it seems that in the newer versions of the Arduino IDE (at least in 1.8.8), you may need to select "ATmega328P (Old bootloader)" from the Processor options under the Tools menu in order to upload sketches.

  • 1
    Phew. I never would have guessed this. Thanks!
    – bigjosh
    Commented Aug 23, 2019 at 16:40

I've seen this error a few times and renaming the serial port fixed the problem in my case. I documented the steps in detail in Tip #4 of this blog post: https://gyorgybalassy.wordpress.com/2020/10/16/cant-open-device-com-access-is-denied-arduino-upload/


I don't really see a question in the OP, but here is the immediate answer:

Go into Control Panel..Device manager. Open the Ports (COM & LPT) and see what you have. It should be listed.

If it is a CH340 port it will just give a COMx number.

If you have the genuine article then it will actually say so and give you the COMx number to use.

If no COM ports show then try switching out the cable. Power cycle the Arduino and try again.

There aren't that many moving parts in this, but sometimes, Windows gets confused and a Windows reboot might be necessary. That usually only happens if you unplug and replug the Arduino too many times for Windows to keep track of.

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