Actually there is not much about microcontrollers but more about building cheap and dirty USB to TTL converter so it could be used with any microcontroller with USART interface. You can always find chips that will do the job, but usually they are pretty expensive and may require special drivers.
So it seems there is another solution – buy cheap USB to RS232 cable and you will find that it isn’t RS232 compliant – only 0/5V levels and only can handle -12/+12V. So 0/5V is what you need. A little tweak to plug PCB and you will have cheap USB that works. On the page also you’ll a proof with Atmega microcontroller that uses simple uart_putc() and uart_getc() commands. [via]
Embedds highly recommends EasyEDA for circuit and PCB design