USB Communication trouble on Mac OSX Snow Leopard


I'm a new user of Arduino and it's really awesome but I have a huge problem with the usb communication on a mac.

I have Arduino Uno, Arduino Nano and Arduino Mega. When I use the Arduino environment everything works perfectly. I can see value with the serial monitor and upload code on every Arduino Board.

But, if I tried to use pyserial or matlab, even just a cat in the shell (such as cat /dev/tty.usbserial#### or tty.usbmodem), I lose the handle of the program, nothing appears AND I completely lose my USB port i.e. it becomes unusable, for exemple if i plug a mouse, it doesn't work. I have to reboot my computer to fix it.

Yet, I'm just doing Serial.println(0); ...

I tried on a linux and it works find but not on my OSX 10.6.

I don't understand why, I'm trying to fix it for hours and can't find an answer. I hope you will be able to help me.



I lose the handle of the program,

What program?

Yet, I’m just doing Serial.println(0);

When asking questions, it is very important to post the code you are having trouble with. It is impossible to reproduce the issue if you don’t.

Running “stty -a” in the terminal will tell you what baud rate the terminal is setup for, make sure that makes your Arduino.

You can also try using screen, which is what I use, to communicate with my Arduino.

screen /dev/tty.usbmodemXXX <baud_rate>

Note: To exit screen you press CTRL-A followed by CTRL-\
(then answer Y)

Thank you for helping me

All, matlab, python and Terminal. I have to kill them because they freeze.

int value=0;

// the setup routine runs once when you press reset:
void setup() {
  // initialize serial communication at 9600 bits per second:


I’m going to try it but I’m not sure it’s the problem because with matlab I specified the baudrate and I had the same trouble.

I would suggest putting SOME kind of delay() in your loop. even 10 or 50 ms could make a huge difference.

The baudrate is 9600 so it's OK.

I tried with 1000ms delay, but it did change the trouble.

With the arduino Uno, it doesn't work but I keep my usb bus usable without reboot.

Another important point: On matlab and python, the freeze appears when I launch the function fopen(port). I suppose that it's the same in the Terminal.

Maybe a problem with the driver ? I saw some post about this.

I had just installed a virtual machine Ubuntu and it works fine. It seems that the problem is really MacOS ...

It seems that the problem is really MacOS ...

Given the large number of people who do not have trouble, myself included, this seems unlikely.

Any chance you have a wireless broadband card or any other devices that might emulate modems or serial ports? Ever install software for one of those devices?

I installed PL2303 drivers maybe it's a problem for arduino. I will try to remove them and install last FTDI driver.

EDIT: I removed all usb2serial driver I had i.e. PL2303, FTDI, Profilic.

I installed first FTDI 2.2.16 ==> same problem
Then I installed FTDI 2.2.6 as describe in the how to ==> same problem

I don't understand what happens ... :frowning:

FTDI drivers would not cause a conflict. They create virtual serial port, not virtual modems.

You might make sure lock is setup correctly:
sudo mkdir /var/lock
sudo chmod 777 /var/lock

Thank again for your help

For the arduino Nano, it's a serial port

I did these two commande but still the problem with arduino Uno/nano :frowning: