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Wiring the LEDs for FTIR

I contemplated making my own PCB boards for the LEDs, but after doing some searching I found some boards online that would be more cost effective and work better than making my own boards. I decided to buy the following board from futurlec.com It’s possible to get 4 individual strips from each board for making individual LED PCBs. I needed a total of 10 strips for the two sides of my acrylic so I purchased 3 boards for $9.50. The strips are good because they will allow for 4-8 LEDs per strip. I chose to do 5 LEDs with a 1ohm resistor per strip (@ 7.5v), making a total of 25 LEDs per side of my acrylic.

The LEDs I’m

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FTIR or DI, my final multitouch decision…

After spending a large amount of time focusing on Diffused Illumination ( Rear DI), I’ve switched my concentration back to FTIR. I had great results with DI and was happy with the ease of use and setup, but one issue I had was the constant calibration I would have to go through every time I tested. This most likely had to do with an incomplete setup and open box where the IR light, shinning at the acrylic, would easily change as the environment changed. Although with some fixing it is possible to have a great DI setup, I’ve chosen to go with FTIR.

There are a couple main reasons for this decision:

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FTIR and DI. How they work and what they mean for multitouch.

FTIR and DI are the two main technologies used in NUIGroup (I will be posting information on alternative techniques at another time):

FTIR = Frustrated Total Internal Reflection (a phenomenon) – This is currently the most popular method, possibly due to the wide internet distribution of Jeff Han’s videos. IR light is shined into the side of an acrylic panel (most often by shinning IR LEDs on the sides of the acrylic). This light is trapped inside the acrylic by internal reflection. When a finger touches the acrylic surface this light is “frustrated” causing the light to scatter downwards where it is picked up by a IR camera.

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