Wednesday, October 21, 2009

math fail

So it turns out that if you want to like, play with electricity, you have to do some of that math crap. It also turns out that when you see numbers like "3.2V 25m" the "m" doesn't stand for milliamps, it means milliwatts... and using that math stuff, that works out like 7.8 mA.

P = V * C (power [watts] = voltage * current [amps])
V = I * R (voltage = current [amps] * resistance [ohms])

I was testing the lasers out by simply hooking the power leads up to my cell phone 5.5V cell phone battery, but later we rigged up something a little more stable with a 9V battery, and some alligator clips on a 270 ohm resistor. Turns out that's pushing 33 mA on 300 m.

Whups. It still worked, but apparently overclocking the lasers means you lose some of their life.

In other news, I snagged a Logitech Quickcam for Notebooks (yes, that whole thing is the product name... no version numbers or anything.. "for Notebooks) for around $40. The cam is way easy to disassemble as everything is screwed together, and driver support for Linux is in most current distros. IR filter popped out easily enough. For the regular light filter, I tried cutting out a square from an old floppy disk, but it severely dims the IR light at a distance of about 3 feet. Going to try an exposed negative next.

Still trying to figure out what I'm going to do about mounting the lasers on the acrylic. The diameter of the laser (including the casing) is about 1/2 an inch which is about 13mm, so just sitting the laser on top of the acrylic is going to be about 6mm above the surface (and it needs to be at one). Thinking about just getting the acrylic so that there's an extra inch on each side and cutting 4 1/4 inch wide slides at 45 degree angles in each corner. That should let me sit the laser so the beam is just right above the surface, make it easy to secure with some tape, and allow me to easily remove them from the board to make adjustments.

Now I just have to find a way to deal with the nightmare of cutting acrylic... :(

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