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January 14, 2008 2:45 AM CST by psilord in category Useless Ideas

Black Box Fun

Five or six months ago, an acquaintence of mine and I were talking on the long bus ride home. He is getting a PhD in polymers and was building a device to measure the coefficient of friction of polymers by some method where a period of oscillation of the polymer was directly proportional to its coefficient of friction.

He was lamenting about how he'd wish to have some sort of a device that would use an infrared beam and could send beam break/resume events to a computer to time the period. I told him that something like that could be made pretty easily, even by an idiot.

He looked at me with a pair of eyes that said what his mouth confirmed, "Hey, uh, could you build something like that for me?" I looked at him long and hard, remembering all of the free time I didn't have. So, I threw the Hail Mary pass, which always works in situation like this where I can politely decline when I don't think I have enough free time to do something even though I very much wanted to build this thing for him. "It'll cost you X dollars in parts and labor", I slid in under my breath. He sat in repose.

A few days later, having thought I was free from his request and greatly saddened since I really did want to build it, I had thought about it in greater depth than an OCD patient aligning 5 months worth of finger nail clippings just so on his bathroom floor. Luckily, that day he called me up and said "Ok, I'll pay you X dollars.".

Damn, I thought--here I am, ready to get into electronics and an application with funding shows up at my feet. You bet I took the job. :)

So, here is the picture of the device as I had finished it. My drill slipped a bit for one of the holes on the cover, but other than that it looks fine.
[The Finished Box]

Here is a picture of the inside of the device.
[Inside Layout]

Here is a picture of the device plugged in and working. The digital camera picked up the IR light and it is displayed as a lightish purple in the emitter jig. The lit red LED on the box indicates the beam is present. Also, I might add that it is not on fire.
[The Functioning Box]

And here is the thing which most people leave out when they put some do it yourself project on the web--Theory of Operations Document. I get so pissed off when someone has really cool pictures of some hot shit thing they made and don't have theory documents explaining them.

For projects that I make which I don't patent or don't think from which I'll make any serious money, there will be pictures and full theory/construction docs to explain them.

End of Line.

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