For some reason I decided today to make a system to drop me a text message when the door of my bedroom is opened. I started off thinking about how this could be done - I didn’t fancy hacking a mobile to send a text particularly, I wanted more of a computer controlled solution. While I was thinking about the more complicated aspects of my sudden unexplained desire to make my room high security I did the more boring task of laying 10 meters of alarm cable neatly and invisibly around the perimeter of my room.
With this done, I had formulated the solution in my head - here’s how it works:
The VM167 Prototype Experiment board created by the good people at Velleman has an ample number of digital inputs to do this. I basically hooked up the reed switch on my door (Read: a type of switch that closes when it’s placed in a magnetic field that is strong enough and opens when it isn’t) to the VM167 on the other side of the room. From there, I hooked the VM167 up to the lovely netbook I got as one of our teams prizes at the Microsoft UK Imagine Cup 2011 finals. I then wrote a quick application in C# that accesses the Mediaburst SMS API to send SMS messages for a nice low fee.
The little black taped-up thing in the picture above is just a small Lithium battery - the board doesn’t react to open/closed circuit as an alarm-geek like myself might expect, it actually expects a potential difference between 1 and 5 volts to set the input to high. A minute amount of current is drawn so this little Lithium cell placed in-line works a treat.
And the result? Works like a charm. The program I wrote is really simple - it just provides a 15 second timer to “escape” the room and get the door shut. Once the door is opened, a text message is dispatched instantly and the program waits for the user to reset it to avoid spamming hundreds of texts if the door is just blowing around or something).
I doubt I’ll ever have any use for it, but it got me using the VM167 prototype that Velleman sent me, and I might even develop something for iOS later down the line if Apple can stop people stealing my work.
Anyway, to finish off here’s a little preview of how silly my UI design is:
Stay tuned for some posts from NYC!