As i know the arduino has a chip that convert the usb to serial to program the arduino. Can i use them for a regular adapter.EX:for a UPS
The Arduino uses 5V TTL logic levels for serial. You can use the Arduino as a USB-to-TTL Serial converter but you can't use it to talk to an RS232 device. TTL use 0V for LOW and 5V for HIGH. RS232 uses 3V to 12V for LOW and -3V to -12V for HIGH.
There are TTL/RS232 adapter modules available, a couple of examples: http://www.nkcelectronics.com/RS232-to-TTL-converter-board-DTE-with-Male-DB9-33V-to-5V_p_369.html http://www.nkcelectronics.com/rs232-to-ttl-converter-board-33v232335.html
If you want to communicate with another USB device, that is harder- the Arduino is not a USB Master, and does not support Slave-Slave connections.
If going with discrete parts, than 5 0.1uF caps and 1 chip for $1.16 is pretty convenient for RS232 to serial. http://www.digikey.com/product-detail/en/MAX232IN/296-6940-5-ND/371562
ok i understand thanks for the replies :)