To have a Raspberry Pi scan and automatically connect to different wireless networks:
sudo nano /etc/network/interfaces
Remove all extra entries so it only has the following:
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
Edit wpa_conf
sudo nano /etc/wpa_supplicant/wpa_supplicant.conf
Make sure it is exactly as shown below. Add the SSID and Secret Key for each network:
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
ssid=”SSID 1″
scan_ssid=1
proto=RSN
key_mgmt=WPA-PSK
pairwise=CCMP TKIP
group=CCMP TKIP
psk=”The encryption Key for this network goes here”
}
network={
ssid=”SSID 2″
scan_ssid=1
proto=RSN
key_mgmt=WPA-PSK
pairwise=CCMP TKIP
group=CCMP TKIP
psk=”The encryption key for this network goes here”
}
Reset the wireless network
(Can use --force with ifup and ifdown)
ifdown wlan0; ifup wlan0
ifconfig
You should now see an IP Address next to wlan0 if it has connected to the wireless network.
With hidden SSIDs you must include
bssid=mm:aa:cc:aa:dd:rr
(See https://www.raspberrypi.org/forums/viewtopic.php?t=66656&p=488120)
Enter the MAC address of the access point in the network={...} block in your supplicant config.