When trying to upload the blink sketch to my (unofficial) Arduino Uno, I get the following error:

avrdude ser_open() can't set com-state for "\\.\COM3"

I have programmed this Arduino before using this same laptop, but not for quite some time. I have not changed anything in the Arduino IDE in this time.

I have tried the following:

None of the above fixed the issue and all gave the same error as shown above (except when trying different USB ports which showed the error just for different COM ports).

EDIT: Just tried both the Uno and Nano on another computer and both worked fine. This confirms that both the arduinos and cables I'm using are working properly.

up vote 2 down vote accepted

Maybe a Windows driver problem. Do your uno and nano use a ch340? (It is the component translating USB to uart (serial pins of atmega328). Windows has no software way to differenciate boards using this component. It is a common use on cheap clones to lower price. Official arduinos use a second atmega (atmega16u2 natively supporting usb) instead of the ch340. Allowing windows to identify the arduino model.

You should try to update your ch340 driver as you have the same problem with the 2 boards. here is the download page of the manufacturer (ch341ser.exe is the package you want)

You can also try to connect your board to an usb2 port as some problems (and solutions to try) are posted here (arduino forum) And even try to use an usb2 hub...

  • It was the driver. For reference, I uninstalled the driver using Device Manager, then plugged the Uno in again and it installed the correct CH430 driver for me automatically, which is exactly what it must have done on the other computer since there has never been an Arduino plugged in to it before. – rozzy Aug 14 at 20:29

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