Well you can configure a bare ATtiny85 to connect to a USB port using zener diodes and resistors like that guy did. The most common way to do that is to just buy a digispark or trinket, which already have those parts with the ATtiny85 on the board. Then you could search on the Internet for making Trinket or Digispark act like a keyboard. Pro Trinket can also be a keyboard, and that is your ATmega328P.
Please enter a valid email to subscribe
We need to confirm your email address.
To complete the subscription, please click the link in the
email we just sent you.
Thank you for subscribing!
via Egeo 16