USB Serial prints unreadable string from Arduino UNO board

Dear All...

Happy New 2013.. I'm entering 2013 with trying arduino UNO board.
I can send a string continously by Serial.println ("TEST"), and I could see Serial Monitor prints TEST continously. But when I was trying to connect Tx (pin 1) and GND to my Aten Usb Serial Rx (pin 2) and GND (pin 5) with same baud rate (9600), I could see my ATEN indicator LED was blinking (data received) but it's printing unreadable string on hyperterminal.
Here is my code :

void setup(){

void loop(){
Serial.println ("TEST");

Please let me know, why should I do??

Thank you.


If that device has a DB9 connector, it is almost certainly NOT a TTL level device. You MUST have a MAX232 or equivalent chip in between. You are risking destroying your Arduino.

Quite right. Apart from the voltage level difference the signal will be inverted (0 will be 1, and 1 will be 0).

Thanks Pauls,
I really don’t know what chip on my usb serial converter. But I do connect to my devices (scales) with this converter. What should I do if I still need to connect this arduino board to my device?
Please, I beg for explaination…

Please, I beg for explaination..

There are RS232 devices and TTL devices. TTL devices use 0 and 5V signals. RS232 devices use +12V and -12V. Connecting a RS232 device to an Arduino can damage the Arduino.

A MAX232 chip handles the conversion of TTL to RS232 and RS232 to TTL, allowing an RS232 device, like your scales, to be, indirectly, connected to an Arduino.

An FTDI cable does the TTL serial to USB conversion. You could use that instead.

You probably can make a simple signal inverter similar to below using a transistor and two resistors.