/etc/wpa_supplicant/wpa_supplicant.conf for Edimax EW-7811Un on Raspberry Pi

wpa_supplicant.conf

/etc/network/interfaces
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auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
iface wlan0 inet dhcp
pre-up wpa_supplicant -Dwext -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf -B

iface default inet dhcp


/etc/wpa_supplicant/wpa_supplicant.conf
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ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1

network={
        ssid="SSID"
        psk="PASSWORD"
        scan_ssid=1
        key_mgmt=WPA-PSK
        proto=RSN
        pairwise=CCMP
}