Sunday, May 04, 2008

IR Beacon

This is the first finished beacon. It has 24 IR (infrared) LED's. The idea was that, since the tracking camera must have a wide angle in order to see the entire stage (which is about 6x6 meters, much smaller than I expected) from above, we needed an array big enough that would be easily tracked.

What I did not realize was that the angle of the LED's that I got was extremely narrow, so that when the performer lowers or tilts her head (the beacon is on top of her head) the LED's practically disappear. So we came up with the idea of using a diffusion dome to spread the light. That of course is half a ping-pong ball which happened to have the exact required diameter.

The ball was too thick and did not let enough light through, so I sanded it until it felt like a turtle egg, if you ever touched one. The solution worked, however there was still a considerable loss of light.

So I started to look for new LED's. This time I made sure that the lens of the LED would be wide enough to allow the free movement of the performer's head. This is what I found:

Ultra Wide Angle IR 850nm

These LED's are awesome. We could not believe how wide they emit light and how bright they are. You can almost turn the away from the camera and you can still see them!. So they will definitely do the trick without the need for a diffuser. We will use a set of ten which has the added benefit of resulting in a much smaller device and, because it is IR, it will be invisible to the audience.

I bought them form the guys at NaturalPoint which have a wide (yes, intended) variety of optical devices, mostly for motion-tracking. A set of ten cost me US$ 15 which is about half of the price of "cheap" LED's at RadioCrap.

So now we will design and burn another circuit and probably use a coin battery instead, to make everything really compact and unobtrusive to wear.

As soon as the UI (user interface) is ready for the tracking and motion-assigning program I will post pics of the UI and the tracking screen which is a lot of fun to see in operation.

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