Dilshan Jayakody published a new build, USB to 3.3V – 5V serial TTL adapter:
This post is about experimental USB to 3.3V/5V serial TTL adapter which we build recently to work with both 5V and 3.3V MCUs. This project is mainly based on CH340G seral-USB chip. CH340G is cheap and commonly available serial-USB convert IC and now it’s commonly found on Chinese versions of Arduino development boards.
FTDI’s FT232 is another possible alternative for this kind of project, but we drop it because of its famous device driver base chip locking issues. Also compare with FT232, CH340G is cheap, commonly available and simple to construct with minimum number of components.
In this module we incorporate 5V/3.3V voltage selector switch to avoid interface matching issues due to different voltage levels of main-board/MCU and serial TTL adapter.
Project files available at elect.wikispaces.com.