Install TP-LINK TL-WN821N v2 on Raspberry Pi

Download firmware like this:

# apt-get install firmware-linux-free

source:
https://wiki.debian.org/it/carl9170

then configure network:
http://www.bufferoverflow.it/2013/06/10/tp-link-tl-wn725n-nano-wifi-adapter-v2-0-e-raspberry-pi/