The serial UART is a common interface used by many chips and devices. Ginpb designed a USB-to-UART adapter that works with 3.3V and 5V UART signals. The device is based around the FTDI FT232BL USB-to-UART IC with an added 3.3V power supply. The different interface levels are selected by an on-board jumper.
Simple USB to UART adapter that works with 3.3V and 5V UART signals - [Link]