Install TP-LINK TL-WN821N v2 on Raspberry Pi

Download firmware like this:

$sudo apt-get install firmware-linux-free

Modify the file /etc/network/interfaces :

$ sudo nano /etc/network/interfaces

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
auto wlan0
iface wlan0 inet dhcp
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp

Setup wifi by editing /etc/wpa_supplicant/wpa_supplicant.conf, insert at the of the file your wireless ssid and password

$sudo nano /etc/wpa_supplicant/wpa_supplicant.conf

network={
    ssid="YOUR_SSID"
    psk="YOUR_PASSWORD"
}

$ sudo ifup wlan0

$ sudo reboot

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