Open WiFi settings on raspberry Pi
If you are trying to connect to an open wifi router with your Pi, change the following settings in
/etc/network/interfaces. These settings worked with Raspbian 2012-09-18-wheezy-raspian.
# my wifi device
auto wlan0
iface wlan0 inet dhcp
wireless-essid [ESSID] # your router SSID
wireless-mode [MODE] # usually mode is "managed"