I’m sorry if I sound ignorant and naive, but I’m brand new to Arduino; very keen, but know very little.

I started with a Sainsmart Arduino Uno clone board. I downloaded the software, which opened OK (or at least seemed to), but the Serial Monitor kept telling me that there was a communication error, and a yellow light kept flashing on the Sainsmart board.

I got hold of a genuine Arduino (from Jameco), uninstalled everything Arduino, and started again from scratch.

Now I get the message:

Arduino: 1.6.5 (Mac OS X), Board: "Arduino/Genuino Uno"
Error opening serial port '/dev/cu.Bluetooth-Modem'. (Port busy)
  This report would have more information with
  "Show verbose output during compilation"
  enabled in File > Preferences.

And after enabling the verbose output, got:

Arduino: 1.6.5 (Mac OS X), Board: "Arduino/Genuino Uno"
Error opening serial port '/dev/cu.Bluetooth-Modem'. (Port busy)

Tried again, and:

Arduino: 1.6.5 (Mac OS X), Board: "Arduino/Genuino Uno"
Error opening serial port '/dev/cu.Bluetooth-Modem'. (Port busy)

I’m using a MacBook Pro, using Yosemite 10.10.5.

  • 1
    Try restarting your computer.
    – Avamander
    Commented Sep 5, 2015 at 16:52
  • Why are you trying to communicate with a bluetooth modem when the Arduino plugs in through USB?
    – Majenko
    Commented Sep 5, 2015 at 17:11
  • Is there a /dev/tty.Bluetooth-Modem? @Majenko that's an OSX thing. I have the same thing here on my Mac.
    – Gerben
    Commented Sep 5, 2015 at 19:03
  • @Gerben I know what it is - I am just wondering why the OP is trying to use it. It's the equivalent to /dev/rfcomm* on Linux.
    – Majenko
    Commented Sep 5, 2015 at 19:04
  • Sounds like the wrong port to me. It shouldn't be on the Bluetooth-Modem port.
    – Nick Gammon
    Commented Sep 5, 2015 at 21:20

1 Answer 1


You are not selecting the correct port to upload to - hence the strange message about the Bluetooth modem. Start by unplugging your Uno and running Arduino. Select Tools -> Port from the menu bar. You should see a list of options. Now plug in your Uno and do the same again. You should see an extra port listed now - this will be the Uno. Select it. You will need to check this every time you connect a board.

Also, before you click Upload, make sure you have Arduino Uno selected under Tools -> Board in the menu bar.

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