Upcoming Project: LED IP Status Indicator. How?

Hi Marc. :-)

Given a GPIO LED control program (of which there are millions because it's the "Hello world" of hardware interfacing ARM boards like Pi), it's very easy to do the network testing in a shell script.  Let's assume that you have a program called switch_led which takes two numeric arguments, the first a LED number and the second either 0 or 1 to switch that LED off or on.

A one-liner can then test the network target and control the LED accordingly, eg. for target some_host and LED number 5:

if ping -n -c 1 some_host >/dev/null 2>&1; then switch_led 5 1 ; else switch_led 5 0 ; fi

And then you can wrap that up in a loop to perform your operation at whatever intervals you desire, and you have yourself a simple network monitor with LED display.  For example, to check every 30 seconds:

while true; do some_task_to_be_repeated; sleep 30; done

So, putting it all in a file to avoid one-liners and with a few embellishments to check a list of targets and light up numerically ascending LEDs for them, we have something like:

#! /bin/sh

 

LED_CONTROL_CMD="switch_led"

LED_CONTROL_CMD="echo"

BASE_LED_NUMBER="5"

INTERVAL="30"

 

HOSTS="

        google.com

        slashdot.org

        no-such-host.net

"

 

while true

do

        LED_NO="$BASE_LED_NUMBER"

        for TARGET in $HOSTS

        do

                if ping -n -c 1 $TARGET  >/dev/null 2>&1

                then

                        "$LED_CONTROL_CMD" "$LED_NO" 1

                else

                        "$LED_CONTROL_CMD" "$LED_NO" 0

                fi

                LED_NO=$(($LED_NO + 1))

        done

        sleep "$INTERVAL"

done

Running the above script outputs every 30 seconds the text:

5 1

6 1

7 0

because I've overridden the setup of the "switch_led" command by "echo" so that you can see what it's doing.  Comment out the LED_CONTROL_CMD="echo" on line 4 and it'll work properly, calling "switch_led" to light up LEDs 5, 6, 7, ..... depending on the ping success for the targets in the ordered list.

You'll notice that no-such-host.net turns LED 7 off (because DNS lookup failed, but it would do the same if the domain name existed but the host were down), whereas LEDs 5 and 6 light up unless Google and Slashdot are having a bad day.

Now you just need to find something to do the "switch_led" operation, which can also be done in the shell or you might want to write a tiny C proggie to do it as an exercise. Some examples here.

'Hope this helps.

Morgaine.

This is just a repeat of the little shell script example but using Element 14's new GitHub Gist facility.  I poked the code into GitHub as gist: 4182524 and with a bit of luck it'll be displayed below as a gist source inclusion:

Thanks you, Morgaine Dinova!

You gave me a lot of helpful answers. I'm looking at embedding it as a service, so it will be transparent regardless which SD Card is using, with the exception of OpenELEC. I'm looking at encoding it into a binary (rather than a script) in Raspbian and Arch Linux ARM. For this project, at first, I just want to know who's using my WPA-encrypted Wi-Fi access point so I know when to turn off (when no humans are using my connection). I'm specifying "humans" because my Androids don't complain if the Wi-Fi vanishes.

Thanks for the input!

Marc Miranda

Thanks you, Morgaine Dinova!

You gave me a lot of helpful answers. I'm looking at embedding it as a service, so it will be transparent regardless which SD Card is using, with the exception of OpenELEC. I'm looking at encoding it into a binary (rather than a script) in Raspbian and Arch Linux ARM. For this project, at first, I just want to know who's using my WPA-encrypted Wi-Fi access point so I know when to turn off (when no humans are using my connection). I'm specifying "humans" because my Androids don't complain if the Wi-Fi vanishes.

Thanks for the input!

Marc Miranda

I just saw your post, sorry for my late reply.
How about you open your router's attached devices page and parse it for the MAC address you are checking for?

So, while I was playing dumb and pretended that we know the IP address of the device in question, you are now pretending/assuming we know the mac address.

But the problem remains a generic one. It seems we're looking for a specific device, how do we recognize that device?

You both are right. First we need to know the device which is connecting with Raspberry Pi. I made RPi access point following this guide. I think we need to check the log file to get the IP of the device first and using that IP we can turn ON the LED connected with GPIO but I don't know how to do that.

My ISC-DHCPD shows:

Jan 26 13:40:14 myserver dhcpd[6871]: DHCPACK on 192.168.xxx.yy to xx:yy:zz:49:62:08 via enp4s0

in the /var/log/syslog file when a DHCP lease is given out or extended.

So with

tail -f /var/log/syslog | awk  '/DHCPACK/ { system ("/home/pi/ip_given_out"  $8 );}'

you can have a script (/home/pi/ip_given_out) run with as an argument the IP address that was just given out. You can save that to a file

LASTIP_FILE=/home/pi/.lastip

echo $1 > $LASTIP_FILE

and then use

the_IP=`cat $LASTIP_FILE`

in the script I've typed (and not tested) above. (some merging/mangling still required. Left as an excercise for the reader).