Switching on a lightbulb from 360km away!

Yes, my friend Prasanna just did the same. He SSHed into my system from Chennai and switched on the CFL in my room
Feels like the Big Bang Theory, except that it isn’t from all over the world

I opened SSH access on my ADSL router. A lot of articles on the net helped me, but let me write this out, so that it is clear and in one place. And before any brilliant bruteforcers decide to track me down, yes, I have the openSSH fix and run Debian, which means all vulnerable keys have been eliminated.

Most routers support telnet:


[13:akarsh@PENGUIN$ www]$ telnet
telnet> o
(to) 192.168.1.1
Trying 192.168.1.1...
Connected to 192.168.1.1.
Escape character is '^]'.
BCM96338 ADSL Router
Login: admin
Password:


Once I login, I get this main menu on my router. Most routers have a very similar main menu if I amn’t mistaken.


Note: If you have problem with Backspace key, please make sure you configure your terminal emulator settings. For instance, from HyperTerminal you would need to use File->Properties->Setting->Back Space key sends.

Main Menu

1. ADSL Link State
2. LAN
3. WAN
4. DNS Server
5. Route Setup
6. NAT
7. Firewall
8. Quality Of Service
9. Management
10. Passwords
11. Reset to Default
12. Save and Reboot
13. Exit
->


If you want to setup a virtual server (which is like a proxy server running on the router that hands over all requests for a particular port on the router to a particular port on a particular system on the local subnet), choose option 6, Followed by 1.


Note: If you have problem with Backspace key, please make sure you configure your terminal emulator settings. For instance, from HyperTerminal you would need to use File->Properties->Setting->Back Space key sends.

Virtual Server Menu

1. Add
2. Remove
3. Show
4. Exit
/ NAT/Virtual Server ->


You can now setup virtual servers. This is my configuration (I hit option 3 to get this). The internal IP of my system on our local subnet is 192.168.1.5. The config basically tells the router to forward all requests on port 80 (http) and port 22 (ssh) to 192.168.1.5:80 and 192.168.1.5:22 respectively on the local subnet.


Virtual Server Show

Server Name Proto. External Start External End Internal Start Internal End Server
Port Port Port Port IP Address
http TCP 80 80 80 80 192.168.1.5
ssh TCP 22 22 22 22 192.168.1.5


You will also have to set up the firewall to allow incoming packets on these ports. That’s option 7 (Firewall) on my router’s main menu, followed by option 1 (IP Filtering), followed by option 2 (Incoming).

Prasanna and I also played ‘alsamixer’ on his system. It’s real fun to be able to do what we were once doing within the local intranet of the institute with a 360km gap in between!!

Computer controlled tubelights!

A few months back, I implemented an interface using the Parallel Port to control my room’s tubelight and bulb. Such circuits that interface electrical devices to the computer through parallel port are extremely popular on the internet. My version uses one optocoupler (MCT2E), one transistor, a pair of resistors and a relay for every device I wish to control. So I’ve got some two implementations of this as of now.

A simple C program can help control the bits on the parallel port (and thereby the devices). Again, there are examples all over the internet like this one, that help you do that. I wanted something more flexible and easy to use, so I wrote a rather long program (maybe it is an overkill). Forgive me for the unclean and dirty code. Here it is. You can kick me for writing dirty C++ – I hardly learnt any C++. (I learnt that it is dumb to use stdio.h, fprintf etc in C++ code, and that all C++ code must be encapsulated, but who cares! I wrote this for my own use, and am graciously releasing it, so take it if you must, and if you do write better and cleaner versions, please link them in the comments to this post! ). What this code does is to implement something that can toggle the state of a specified device.

In this code, I read a configfile that defines the values of the bits that need to be switched on to control each of the devices. I implemented this so that it remains extensible – I’m planning to extend this to control my fan as well . Once you’ve defined values in the configfile, you can then do things like:

sudo lpdevctl bulb

You can also specify a default device that’ll get toggled if you just say sudo lpdevctl (without an argument).

Once you have such a program, you can do lots of interesting things. The simplest of them would be to switch on your tubelight after 10 seconds delay, say:

sleep 10; sudo lpdevctl tubelight

Something slightly more interesting:

for i in `seq 1 5`; do sleep 0.5; sudo lpdevctl bulb; sleep 0.5; sudo lpdevctl bulb; done;

That flashes the lamp 5 times. Even more interesting – switching on your tubelight every day automatically at 1830 hours is like setting up a cronjob at 1830 hours to execute sudo lpdevctl tubelight.

I use a Jabber client called mcabber which has external action triggers, that can call an external action when something happens. So if somebody pings me on IM, I am notified of it through the flashing of my bulb (which I seldom use otherwise) instead of some ding sound that interrupts the beautiful music I’m playing. Besides, this alert is easy to switch off – because I can go and turn off the light bulb switch – and the relay is in series with that!

Once you get a command on your Linux system to do something, the ways in which you can extend it are infinite and are only (un)bounded by your creativity!

I like the idea of switching on my room light while sitting in my department computing facility using SSH