I purchased a USB<->Serial adapter/cable from Buyapi.ca. It is based on the PL2303HX chipset. It uses 3.3v to drive the RX and TX lines which is compatible with the Raspberry Pi.
The connections are:
- Red - GPIO2 (5V)
- Black - GPIO6 (Ground)
- White (RX into USB) - GPIO8 (TXD from Raspberry Pi)
- Green (TX out of USB) - GPIO10 (RXD to Raspberry Pi)
My Raspberry Pi did not have the default Raspbian Linux console (the console that prints on a screen if you have one) broadcasting on the serial interface. To enable it you can run:
To use the console, fire up a terminal in Ubuntu and type:
sudo screen /dev/ttyUSB0 115200
The device "/dev/ttyUSB0" maybe different depending on your host kernel. Just look for something in "/dev" that looks similar. You can double check if it is correct by removing the PL2303HX device and see if the device you suspect disappears from the list in "/dev".