Laser trip wire

New project! and completely different from the previous ones...although, as usual, it also includes a JeeNode...

So here is the problem to solve: I have a garage, where I have to park a rather large van, that fits in tightly. Once it is properly parked inside, I have 20 or 30 cm of play, divides between the front and the back. So when I park it, I usually do a few iterations of leaving the van to check if the door can already close, get back in, reverse a bit more, check again, and by the time it fits the parking sensors are already beeping that I hit the back a long time ago.
So, to address this problem, I am sure there are plenty of analog solutions, ranging from balls hanging from the ceiling to god knows what, passing by my backup solution: a brick on the floor where the rear wheel hits.
But an analog solution would be no fun, so here is the action movie solution: a laser trip wire.

I wired a laser and a LDR in a small enclosure, and connected all this to a JeeNode, which reads the value of the LDR and turns on and off large red and green LEDs! Place this right at the foremost point where the van is fully inside, and problem solved!

I even thought of reflecting the laser all around the van to make a virtual box where the van would have to fit inside...maybe in the future.

So, I hear you all thinking, this is a bit of overkill, to use a JeeNode for this that would easily be done in analog electronics with a couple of transistors, but here are the advantages of a radio enabled micro controller:

1) I can connect a door sensor to it, and broadcast the status, effectively using it as an alarm.
2) (the truly amazing one) I can send the status (inside/outside) at a high refresh rate over the air, and build me a small receiver to have inside the van giving me an aural and visual warning!

This receiver is not yet there, but it is in the plans...so it is still vaporware...sorry for that, but here are some pictures of the laser trip wire:

 This is the emitter unit that will be located at the foremost point that the van is in and is connected by a cable to the main unit (below) which is located at eye level.

The main unit, with the 2 large LEDs, I have put it in a box, and I'll show some pictures once it is in place. The unit allows for reading a second analog input, which I intend to use to read a pair of limit switches, indicating that the door is open enough for the van not to hit it, and to alarm the house when the door is opened.