USB-TTL Serial Module - 5V and 3.3V
This USB to TTL serial module from PMD Way is a great value way to connect your Raspberry Pi, Beaglebone or microcontroller's serial console to a PC via USB. Please note that these are not for uploading sketches to Arduino Pro Mini-compatible boards, instead you need an FTDI adaptor.
Monitoring activity is simple with power, TX and RX LEDs, and you can easily switch between 5V and 3.3V operation with a hardware jumper - as shown in the image below:
Click here for USB drivers.