This circuit board was designed as a fun project for a SAMD21E microcontroller based development board. The circuit design follows the recommended design from the SAMD Datasheet – including section 39. Schematic Checklist. The USB protection may be overkill, but it is complete. I made this just for fun – I am not going to provide any special support, but always welcome recommendations, suggestions, and ideas for improvements. You are free to take it and run with it, but do not sell this design.