Use a USB WiFi adapter with your RMSv2 board
Sometimes it may be inconvenient to run an ethernet cable to the location where your RMSv2 board is installed. This is a tutorial on how to setup a USB WiFi adapter so you can access your remote monitoring board over a WPA/WPA2 wireless connection.
We tested with two different USB WiFi adapters, the Linksys AE6000 (MT761003 chipset), and the Panda PAU03 (RT5370 chipset).
Both adapters performed well and have decent range for their small size.
Many other USB WiFi adapters that use the same chipsets are available and will also work with this tutorial, some of them
even come with antennas that give extended range.
How to connect to a WPA/WPA2 WiFi network using the Linux command line
This tutorial assumes that:
- The RMSv2 board has the latest firmware installed.
- The end user has a basic knowledge of networking.
- The end user has an SSH client such as Putty installed on their host computer.
- The end user has a basic knowledge of using the Linux command line.
- The end user has a network cable plugged in between the RMSv2 board and the host computer.
- The RMSv2 board can be accessed via SSH from the host computer.
- There is a WiFi access point in range that is setup for WPA/WPA2 and the SSID and passphrase are known.
The pre-installed tools on the RMSv2 board that we need to use are:
- wpa_supplicant - the wireless tool for connecting to a WPA/WPA2 network.
- wpa_passphrase - a tool for pre-computing PSK entries for network configuration.
- iw - the basic tool for WiFi network-related tasks, such as finding the WiFi device name, and scanning access points.
- ip - the basic tool for enabling/disabling devices, and finding out general network interface information.
The steps for connecting to a WPA/WPA2 network are:
- Log into your RMSv2 board with SSH.
- Plug in the USB WiFi adapter into your RMSv2 board.
- Type out dmesg. You should see output at the end similar to what is shown below.
[root@RMS-100v2: /# dmesg
... snip ...
ieee80211 phy0: rt2x00_set_rt: Info - RT chipset 5390, rev 0502 detected
ieee80211 phy0: rt2x00_set_rf: Info - RF chipset 5370 detected
ieee80211 phy0: Selected rate control algorithm 'minstrel_ht'
usbcore: registered new interface driver rt2800usb
This shows that the RMSv2 board has recognized that a new USB device has been plugged in.
-
Find out the wireless interface name by typing out iw dev as shown below.
[root@RMS-100v2: /# iw dev
phy#0
Interface wlan0
ifindex 4
wdev 0x1
addr 9c:ef:d5:f8:60:bd
type managed
txpower 0.00 dBm
The above output shows that the system has 1 physical WiFi interface, designated as phy#0. The interface name is wlan0. The type specifies the operation mode of the wireless device, managed means the device is a WiFi station or client that connects to an access point.
- Next, check that the wireless device is up.
[root@RMS-100v2: /# ip link show wlan0
4: wlan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
link/ether 9c:ef:d5:f8:60:bd brd ff:ff:ff:ff:ff:ff
Look for the word "UP" inside the < > brackets in the first line of the output.
In the above example, wlan0 is not UP.
Execute the following command to bring it up:
[root@RMS-100v2: /# ip link set wlan0 up
If you run the show link command again, you can tell that wlan0 is now UP.
[root@RMS-100v2: /# ip link show wlan0
4: wlan0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000
link/ether 9c:ef:d5:f8:60:bd brd ff:ff:ff:ff:ff:ff
-
Scan to find out what WiFi networks are detected. Pipe to the grep command to only search for SSID's.
[root@RMS-100v2: /# iw wlan0 scan | grep SSID
SSID: SD-AP
SSID: sd58wireless
SSID: WiFiPlus7128-2.4G
SSID: TELUS0220
SSID: TELUS2714
SSID: TELUS5615
SSID: TELUS6004
To get more detailed informaion about each access point in range, use the iw command without grep. In our case, the list is quite long, so we will only look at one access point's detailed information.
[root@RMS-100v2: /# iw wlan0 scan
BSS 74:4d:28:f6:07:2d(on wlan0)
freq: 2412
beacon interval: 100 TUs
capability: ESS Privacy ShortPreamble ShortSlotTime (0x0431)
signal: -63.00 dBm
SSID: SD-AP
Supported rates: 1.0* 2.0* 5.5* 11.0* 6.0 9.0 12.0 18.0
DS Parameter set: channel 1
ERP:
HT capabilities:
Capabilities: 0x102c
HT20
SM Power Save disabled
RX HT20 SGI
No RX STBC
Max AMSDU length: 3839 bytes
DSSS/CCK HT40
Maximum RX AMPDU length 65535 bytes (exponent: 0x003)
Minimum RX AMPDU time spacing: No restriction (0x00)
HT RX MCS rate indexes supported: 0-15
HT TX MCS rate indexes are undefined
RSN: * Version: 1
* Group cipher: CCMP
* Pairwise ciphers: CCMP
* Authentication suites: PSK
* Capabilities: 1-PTKSA-RC 1-GTKSA-RC (0x0000)
Some important pieces of information from the above are the SSID and the security protocol (WPA/WPA2 vs WEP). The SSID from the above example is SD-AP, this is the access point that we will attempt to connect to. The security protocol is RSN, also commonly referred to as WPA2. The security protocol is important because it determines what tool you use to connect to the network. The signal strength shown is -63 db which is adequate for decent performance. The channel is shown as 2412 MHz which equates to channel 1.
-
Connect to the WPA/WPA2 WiFi network.
This is a 2 step process.
Step 1: you must generate a configuration file for wpa_supplicant that contains the pre-shared key ("passphrase") for the WiFi network. After you type out the command below and hit enter, the SSH session will pause waiting for you to type out the passphrase for the WiFi network.
[root@RMS-100v2: /# wpa_passphrase SD-AP >> /etc/wpa_supplicant.conf
...type in the passphrase and hit enter...
The wpa_passphrase program takes the SSID as the single argument, SD-AP in our case. Using that information, the wpa_passphrase program will output the necessary configuration statements to the standard output. Those statements are then appended >> to the wpa_supplicant configuration file located at /etc/wpa_supplicant.conf.
Next you can optionally check out the wpa_supplicant.conf file to see what the wpa_passphrase program added to it.
[root@RMS-100v2: /# cat /etc/wpa_supplicant.conf
network={
ssid="SD-AP"
#psk="SuperSecretPassword"
psk=b214ccd321dae124080f6bdd520473978d0e1e115090b8b6fea45a1c0e67e96b
}
Step 2: you must run wpa_supplicant using the new configuration file that you created in step 1.
[root@RMS-100v2: /# wpa_supplicant -B -D nl80211 -i wlan0 -c /etc/wpa_supplicant.conf
-B means run wpa_supplicant in the background.
-D specifies the wireless driver. We are using nl80211.
-i specifies the interface name discovered in step 4.
-c specifies the path for the configuration file.
Once the above command is run, use the iw command to verify that you are indeed connected to the SSID.
[root@RMS-100v2: /# iw wlan0 link
Connected to 74:4d:28:f6:07:2d (on wlan0)
SSID: SD-AP
freq: 2412
RX: 77264 bytes (528 packets)
TX: 1363 bytes (15 packets)
signal: -63 dBm
rx bitrate: 1.0 MBit/s
tx bitrate: 21.7 MBit/s MCS 2 short GI
bss flags: short-preamble short-slot-time
dtim period: 1
beacon int: 100
-
Obtain IP address by DHCP
[root@RMS-100v2: /root# udhcpc -i wlan0
udhcpc: started, v1.35.0
udhcpc: broadcasting discover
udhcpc: broadcasting select for 10.0.0.59, server 10.0.0.1
udhcpc: lease of 10.0.0.59 obtained from 10.0.0.1, lease time 600
deleting routers
adding dns 8.8.8.8
adding dns 1.1.1.1
Use the ip command to verify the IP address assigned by DHCP. The IP address is 10.0.0.59 from above.
[root@RMS-100v2: /root# ip addr show wlan0
4: wlan0:
link/ether 9c:ef:d5:f8:60:bd brd ff:ff:ff:ff:ff:ff
inet 10.0.0.59/24 brd 10.0.0.255 scope global wlan0
valid_lft forever preferred_lft forever
inet6 fe80::9eef:d5ff:fef8:60bd/64 scope link
valid_lft forever preferred_lft forever
-
Check the default route.
[root@RMS-100v2: /root# ip route show
default via 10.0.0.1 dev wlan0
default via 10.10.10.1 dev eth0
10.0.0.0/24 dev wlan0 proto kernel scope link src 10.0.0.59
10.10.10.0/24 dev eth0 proto kernel scope link src 10.10.10.13
As you can see from the output above, there are now two default routes, one for the eth0 interface and one for the wlan0 interface.
-
Connect to the RMSv2 board via WiFi
Unplug the ethernet cable from the RMSv2 board, and in a new web browser tab try to connect using the ip address obtained by DHCP and confirmed with the ip addr show wlan0 command. In our case we use 10.0.0.59. Success!
The above series of steps is a very verbose explanation of how to connect your RMSv2 board to a WPA/WPA2 WiFi network.
Some steps can be skipped if you connect to the same access point for a second time.
For instance, if you already know the WiFi device name, and if you know the wpa_supplicant configuration file is already set up
for the network. The process needs to be tailored according to your situation.
If the RMSv2 board is rebooted or power cycled, it will not automatically connect to the access point again.
In the next section we will discuss how to make the RMSv2 board automatically connect to the access point on boot.
Automatically enable WiFi settings when the RMSv2 board boots
In order to make the RMSv2 board boot up with the wireless settings intact so it will automatically connect to the
access point that was configured in the wpa_supplicant.conf file, you must edit two files on the RMSv2 board.
FOR DHCP IP
From the RMSv2 web interface, use the built-in file explorer to edit the /etc/startup.sh file.
Add the two lines marked in red and then save the file.
#!/bin/sh
. /etc/functions.sh
########### Insert you own stuff for bootup here ###############
#information "Starting my App 1" #edit this with your app name
wpa_supplicant -B -D nl80211 -i wlan0 -c /etc/wpa_supplicant.conf
ifup -i /etc/network/wireless wlan0
################################################################
exit 0
The second file to edit is the /etc/network/wireless file.
The lines that are preceeded with a pound sign (#)
are only comments, the important lines are colored red. When you are finished editing the file, save it.
# Configure Wireless
# Configure wlan0
auto wlan0
iface wlan0 inet dhcp
It is now time to reboot or power cycle the RMSv2 board. If you entered everything correctly the RMSv2 board will automatically connect to your WPA/WPA2 WiFi network and use DHCP to obtain an ip address and DNS from your router on every boot.
NOTE:
There is good and sometimes not so good about using DHCP to obtain an IP address automatically. The good is that there is virtually no network configuration. The DHCP client on the RMSv2 board will grab a free ip address that is offered from the router's DHCP pool. The DHCP client on the RMSv2 board will also add the default route and will use the DNS numbers obtained from the router.
The possibly not so good part is if the router gets rebooted or power cycled, there is no guarantee that the router will offer the same ip address as it did before, they usually do, but not always. The RMSv2 board may get offered a different ip address so that you have to look in the router's DHCP leases table to determine what ip address the RMSv2 board obtained. Some routers circumvent this by allowing you to statically assign the same ip address from the DHCP pool to make sure that the RMSv2 board always gets the same ip address even over router reboots.
FOR STATIC IP
From the RMSv2 web interface, use the built-in file explorer to edit the /etc/startup.sh file.
Add the three lines marked in red and make sure to edit the third line marked in red to match your wireless gateway ip and
then save the file.
#!/bin/sh
. /etc/functions.sh
########### Insert you own stuff for bootup here ###############
#information "Starting my App 1" #edit this with your app name
wpa_supplicant -B -D nl80211 -i wlan0 -c /etc/wpa_supplicant.conf
ifup -i /etc/network/wireless wlan0
route add default gw 10.10.11.1
################################################################
exit 0
The second file to edit is the /etc/network/wireless file.
The lines that are preceeded with a pound sign (#) are only comments, the important lines are colored red.
Change the iface wlan0 inet line to have static at the end instead of dhcp. Edit the address line to have the ip address
you want the RMSv2 board to have. You must also put correct information in the network, netmask, broadcast, and gateway lines.
If you need help to determine what the network and broadcast ip addresses should be, you can use our online broadcast address
calculator.
Broadcast Address Calculator.
The broadcast address calculator will also compute the network address.
When you are finished editing the file, save it.
# Configure Wireless
# Configure wlan0
auto wlan0
iface wlan0 inet static
address 10.10.11.11
network 10.10.11.0
netmask 255.255.255.0
broadcast 10.10.11.255
gateway 10.10.11.1
It is now time to reboot or power cycle the RMSv2 board. If you entered everything correctly the RMSv2 board will automatically connect to your WPA/WPA2 WiFi network and use the statically assigned ip address on every boot.
This concludes the WiFi project. We can now access our RMSv2 remote voltage monitoring board via WiFi and leave the
network cables unplugged. "In a wireless world, there sure are a lot of wires."
