Arduino UNO Serial port already in use

Hi guys,

i keep getting the "Serial port 'COM3' already in use" error when I try to upload a sketch to my Arduino UNO or when I click on the "Serial Monitor". I've tried all kinds of stuff I could find on the internet but nothing seems to work. It's really frustrating.

This happends on my PC (windows 7 64bit) as well as on my Macbook Pro (on my mac the error is "Serial Port '/dev/tty.usbmodemfd121' already in use" of course).

Only option I think I have left is flashing my Arduino UNO and try to upgrade to a newer firmware, but I'm affraid it would brick/ruin my board (I already tried on my win7 machine but got stuck when I got a weird usbdriver related error in the FLIP program).

Does this sound familiar to anyone, or does anyone have an idea what can cause this? Or does anyone now how to fix this?

This has been frustrating me for days! Hope someone can help!

Thanks in advance!

Kind regards,
G

COM3 on a Windows computer is almost always a built-in modem. What have you done to ensure the Uno really is COM3?

I plugged it into a free usb port and installed the driver. Please note: the error also occurs when I try it on my mac...

Disconnect the Uno.

On the Windows computer, start Device Manager. Expand the Ports node. Connect the Uno. Wait a few seconds. Which serial port is added?

Disconnect the Uno. Which serial port disappears?

Connect: COM3
Disappears: COM3

But I think it's got something to do with the board itself since it also occurs on my Mac. Do you think updating the firmware will solve this?

Updating the bootloader will make no difference for this error. I suspect this...

I already tried on my win7 machine but got stuck when I got a weird usbdriver related error in the FLIP program

...is the the reason for the "already in use" error. But only you know if the "already in use" error started before or after you tried to update the firmware.

Do you think updating the firmware will solve this?

Seems like a good theory...