The Web Cam:

To read the IR hot spots off of the screen you need to hack a web cam to only "see" IR light. most CCD based web cams can see IR, however for privacy reasons (cameras that can pick up IR can see through certain types of cloth) an IR filter is usually put between the lens and the CCD chip.

An older Microsoft web cam was used, taking it apart was extremely easy, only a single screw was holding the entire thing together. Let it all fall apart, just remember how to put it back together again after the alteration.

This would be a good time to point out that from this point forward you want to be as clean as possible, generally the lens to CCD chip assembly is done at the factory in a clean room to keep dust off of the censor, since your likely not in a clean room you'll likely get dust in the assembly,.. how much depends on how careful you are. minimally I would recommend tying back your hair, and wearing a mask over your mouth before going forward. After removing two screws to either side of the lens assembly carefully lift the Lens away from the circuit board.

Some times the IR filter is in the lens assembly other times its a thin film on the CCD chip itself. Luckily this one was the first kind with a glass filter attached to the back of the lens. I carefully pried the filter out with an exact-o blade.

Now that the IR filter has been removed the camera can see IR light, however if left as-is it could also see visible light. To make the camera only see IR light we now have to add a visible light filter or "IR pass" filter. This filter will block all visible light and only capture our IR hot spots.

A visible light filter is actually easier to acquire than one might think. The "black" parts at the beginning or end of a processed role of color film will act as one if two layers are applied. You can get a bit of this throw away film scrap by asking for it from most 1-hour film processing joints. I cut two small squares the same size as the old glass IR filter and placed them into the lens and re-attached it to the CCD board.

LED Power:

We chose to use a total of 38 (940nm) LEDs, 8 on each of the short length and 11 on each of the two long sides. Not a lot of science was used to come by this number, it was just the number we came to based of off even spacing of an LED every 1.5 inches. this coverage meant that on a 2' x 3' screen (aprox 864 square inches) that each LED is roughly responsible for saturating ~23 square inches.

I chose to treat each side of the frame as individual circuit, so two 8 LED circuits and two 11 LED circuits. We decided to power the LEDs off of the computers power supply that would be running the screens software. We chose to set the resistance using the 5v portion of the computers supply. As each LED draws 20mah this meant that each 8 LED strand would draw 160 mah, and each 11 LED strand would draw 220mah, so a total of ((160*2)+(220*2)) = 760 mah to power the entire frame. In theory this means that the Screens LEDs could possibly be powered off of a 5v 1 amp USB connection. we will see how that goes, worst case we will simply power it of its own 5v supply.

We put a small circuit board in two opposite corners each board heald the resistors for one short and one long length. Since the operating voltage of the IR LEDs that we purchased is 1.2v and we where feeding them 5v we had to add resistance to the circuit to keep the LEDs from blowing out. The 8 LED strands use a 33 ohm 2 watt resistor, and the 11 LED lengths use an 18 ohm 3 watt resistor.

From there it was just a matter of soldering all 38 LEDs one at a time and then placing them into the channel. We also chose to put reflective tape along the inside of the frame where the plexi edges where, in this we hope to keep the IR light bouncing around inside the plastic as much as possible.

TO BE CONTINUED.