Dchcaracter built a breakout board for the common FT232BL USB to UART IC. Most hardware sellers have one in the $10-$15 range. He released his design files in the forum. The board has the following features:
- Jumper-selected slave scheme voltage: 5V or 3,3V (50mA max)
- RTS is out (with a wire cut, can be changed to DTR)
- LEDs for Rx and Tx
- Three GPIO broken out (one has a pull-up)
Via the forum.