Can't connect PI with WIFI Dongle by configuring the PI in two different ways

Question

I used the Edimax wifi dongle on the Raspberry Pi, by using the sudo iwlist wlan0 scan, I can get a list of wireless networks, and I found my wireless network information, such as

Protocol: IEEE 802.11bgn Mode :Master Encryption key :on IE: IEEE 802.11I/WPA2 version 1 Group Cipher : CCMP Pairwise Ciphers : CCMP Authentication suites :PSK

Then I tried two ways to change the WLAN configuration, 1. go to interfaces

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
###iface wlan0 inet manual
###wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf

iface wlan0 inet dhcp
wpa-ssid **MYSSID**
wpa-psk  **MYPSK**

then I saved the file, and reboot, check the ifconfig, still can't find the IP on WLAN0
I tried the second way. go to interfaces

iface lo inet loopback
iface eth0 inet dhcp

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

then go to wpa_supplicant.conf

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
   ssid=**MYSSID**
   psk= **MYPSK**
   # Protocol type can be: RSN (for WP2) and WPA (for WPA1)
   proto=WPA
   key_mgmt=WPA-PSK 
   pairwise=CCMP
   group = CCMP
   auth_alg=OPEN
   scan_ssid=1
}

then save it , reboot it, ifconfig , still don't work

I can' t figure out what is wrong with it now

the WIFI dong only give blue light when I command : iwlist wlan0 scan

Answer 1

first ,check whether lsmod lists your 8192cu.ko module. If not compile it for the specific kernel version and insert it.

Apply a sudo dhclient wlan0 ( usually lack of ip address is because of the error in wpa_supplicant.conf file ) This usually fixes mine..