Write back to PC using the USB connection?

I bought a Duemilanove board, because none of my computers have serial connections. Now, however, I realize that the ability to write data back out to the computer for debugging reasons could be critical.

Is it possible that the USB connection on the Duemilanove is just a usb-to-serial conversion and I can just "cat /dev/usb" on my computer while doing "serial.print" in my arduino code?

USB connection on the Duemilanove is just a usb-to-serial conversion

Yes

http://arduino.cc/en/Guide/HomePage

Since this is related and not wishing to start another thread (and I'm struggling to make headway with google). I'm wanting to pull information out of my Arduino into my home server. " cat /dev/ttyUSB0 " works fine (usually stick "|head -n 1" on the end to stop it running forever) on my desktop machine (Desktop Ubuntu 8.10), but when I use the same trick on my server (Server Ubuntu 8.10) it works but it resets the Arduino every time and loses all the information its been collecting.

Any clues / workarounds ?. Its a new 'genuine' Arduino Duemilanove with the 328 chip.

ok, I read the tutorial and now I can use the arduino serial monitor to read the serial output. But is there any way to just listen without using the Arduino program? Because my computer at home is 64bit and I may want to listen to the serial output. I was hoping I could possibly just plug in my Duemilanove to an arbitrary linux box, it would run its sketch, and I could read the output somehow with cat or something.

As long as the arbitrary Lunix box has the USB drivers for the FTDI chip, you can read data from the Arduino with a terminal emulator such as 'minicom' or 'PuTTY'. Or you can 'cat' the raw serial port /dev/ttyUSB0 (or similar), provided you have the right baud rate (see 'stty').

I got the answer to my problem by emailing tod of todbot.com, very helpful guy who knows this stuff inside out. My problem was that my server system was switching the DTR line which causes modern boards to reset ( the auto reset function ). He suggested a patch to make ardunio.serial.c work and I worked out the mods to the publicised 'linux and stty' to make it work.

This is how you read your arduino duemilanovo board using bash :

set your sketch to Serial.println your data out - just stick it in so it does it over and over in the void loop.

!/bin/bash

stty -F /dev/ttyUSB0 cs8 115200 ignbrk -brkint -icrnl -imaxbel -opost -onlcr -isig -icanon -iexten -echo -echoe -echok -echoctl -echoke noflsh -ixon -crtscts -clocal cat /dev/ttyUSB0|head -n 2|tail -n 1

the stty line is the same as : http://www.arduino.cc/playground/Interfacing/LinuxTTY with -clocal appended to get over the DTR problem. If your Arduino isn't on /dev/ttyUSB0 or your Serial.begin() isn't set to 115200 adjust to suit. The cat line reads it twice, and returns the second, because it sometimes misses part of the first read.

Or you can 'cat' the raw serial port /dev/ttyUSB0 (or similar), provided you have the right baud rate (see 'stty').

Thank you. I could not use cat before, because my baud rate was too high. I did not know about stty. I fixed the problem by running

stty ispeed 9600