USB Arduino Serial Com problems

Hello,

I bought an USB Arduino and develop some code with USB interface.
I use in my program Serial command.
It work nice, however through the USB interface.

When I connect PIN TX and RX directly to a rs232, with Arduino alimented via an external power and without USB connection, the COM port receive strange characters. I have tried all the baud rates… whatever, it should be the same than with USB interface.

So, what’s the problem?
My code:

Serial.begin(19200);
Serial.println( “hello” );

Nothing special!!! Have a clue???

Best regards… Pierre :o

RS232 works with different voltages than the 0 and 5 volts used by Arduino's pins. You'll need some extra hardware to use the Arduino board with RS232. See this tutorial for details (note that you don't have to use software serial; you can use the normal serial commands and the RX and TX pins with the same hardware setup): http://www.arduino.cc/en/Tutorial/ArduinoSoftwareRS232

yes, you right of course... badluck. I though the output was rs232 sinal but they are TTL. Nevertheless... I must find the component now... One important question:

How much meters of cable shall suporte the rs232 ?

I need around 25 meters between my PC and arduino board. Any clue?

Thank for your speedy answer!

Pierre. :P