For less than $3 you can get old usb-r232 mobile phone data cables that don't include a level shifter so they're compatible with TTL serial ports directly. You just need to guess the pinouts.
It's somewhat dumb to first shift levels from TTL to real RS232 and then have them shifted again in the USB serial converter, which you usually need to use if your other computer is a laptop. I've used loads of said data cables to interface microcontrollers etc. They're usually cheaper than a level shifter and DE-9 jack, and often the computers I want to interface with don't have real RS-232 ports anyway. -- Jussi Peltola
