New Arduino Uno, Arduino 1.6.3, MBP running 10.10.5.

The Arduino IDE is running, I connect to the laptop via usb. The green LED is on the amber light is on but it's not blinking.

I attempted to upload the blink file from File>Example>Basic>Blink. It compiles without issue but won't upload. I get the can't open device "/dev/cu.usbmodem1421" : No such file or directory...

I have attempted using the reset button, changing ports, cycling the IDE and the computer. The killer is that I've had an Arduino on this laptop before.

Any suggests for getting the Arduino linked and operational.

  • If the serial port is correct (it looks odd to me, check that /dev/cu.usbmodem1421 is the right port), then I think that the problem is the bootloader. Try flashing it again if you have a programmer or another working arduino (search for ArduinoISP tutorials)...
    – frarugi87
    Oct 28, 2015 at 11:00
  • Have you confirmed you have the right Arduino and Port selected in the IDE Tools menu?
    – linhartr22
    Oct 29, 2015 at 18:48

2 Answers 2


Sorry to dredge up an old thread (well, really only replying to one that got robo-dredged :), but maybe this will help someone someday.

A /dev/cu.<something> is a unix port designation. "cu." meant a port used for modems, back in the mists of time but probably isn't relevant today. But what we do learn from it is that the OP is probably using a Mac, and for sure, not Windows.

"/dev/cu.usbmodem1421" is a typical device name for an Arduino as seen by a Mac on a particular one of its USB ports - the numeric part varies according to which Mac USB port the Arduino is connected to each time.

Arduinos & FTDI devices do not need additional drivers on Mac OS (that may not be true for other, non-FTDI USB-to-serial devices).

In this case, the OS already reports seeing (what looks like) an Arduino. The suggestion already put forward, checking the board-type and port selections in the IDE's 'Tools' menu, is the place to start.


I think you may not install arduino hardware and ftd drivers, Follow the steps given here and then check,

  1. Download the latest version of Arduino software and install it.

  2. Open windows device manager - You can open windows device manager by right clicking on 'My Computer' and choosing Properties. In the new Window, Click on Device Manager

  3. Now Scroll Down the List of Devices in the Device Manager till you come to a Device or expand Ports (COMM).

  4. Now you should see Arduino hardware with warning icon or without.

  5. Now do right click on arduino hardware name. Now, Windows will provide you two options, Choose the one that says “Locate and install drivers manually from a specific Location.”

  6. By browsing locate arduino installed folder, then update.

If you previously done these procedure or now, then open arduino software

  1. Go to tools and choose board as what you have like (arduino uno, mega, due etc....)

  2. then in tools menu you should choose serial port (example comm 10, comm 21, comm 8 etc...) in which the arduino board connected, some time the board name displays with serial port otherwise you can observe from device manager ports list.

  3. now upload blink example and check.

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