Arduino USB to serial UART interface is the the essential tool for establishing communication
between PC and MCU.
Operating Voltage: 5V (Compatible with 3.3V-5V)
Compatability: USB 2.0 Full Speed, Xbee
Indicators: TX RX PWR
Power Supply: 3.3V-5V DC
Dimensions: 53mm x 28mm x 0.8mm
*Note: This is not an original Arduino brand product.
I bought this as a replacement for the quite expensive 3DR-store XBee shields and they work wonderfully.
If you want to use the Serial Header as Input, it seems that you have to remove (or cut the PCB-wire) of the two Resistors nearest to the FT232RL chip (above the Resistor row, above the LEDs). I just resoldered them at an angle so that they won't get lost if I'd decide to use the USB-port again.