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New video! The table is (almost) completed!

New video showcasing the final table at work. The software is all a work in progress and new releases will be coming soon of all applications as well as new ones. If you like the video, please pass it on. If you don’t like the video, please pass it on anyway. Enjoy!

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Projector Latency

Latency is a time delay between the moment something is initiated, and the moment one of its effects begins or becomes detectable. When it comes to projectors, latency refers to the time difference between the computer screen and projection from the projector. There will always be some latency (time difference) between the source image (computer) and the displayed image (projector).

Laurence Muller has a Beamer Latency Measurement Tool v0.2 that will measure the latency of the projector. Ideally anything under 20ms is really good. For multitouch, if the latency of the projector is high, there will be visible lag between finger movement of objects and the projection of these objects.
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Projection Screen tests…

I took some pictures of the projector projecting on 3 different types of materials. I’m using a Casio XJ-S30 Projector which has 2000 lumens and 1800:1 contrast.


The following images consist of Rosco Grey Projection Screen (left), tracing paper (middle), and Rosco Black Projection Screen (right).

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Rosco Projection Screen

Rosco Projection screen is an inexpensive projection screen that seems to give pretty good results. There’s a few places online you can buy it. I ended up purchasing it from rosebrand.com. All places sell by the yard and the the minimum size is 55″ by 1 yard. The price is $15 per yard at 55″ width. I ended up buying both the Rosco Black and Rosco Grey to see which would work best with my setup.
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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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Building the Table Frame

I went to home depot and picked out some wood that would be good enough for the inside framing of the table. I tried to get something light weight and sturdy. The main reasons for the frame is to keep the table sturdy and also make it so the walls of the table will be square, flush, and have something to screw into. I measured out all the pieces in google sketchup and then had someone at home depot cut the pieces to size.

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Building the Top Frame

From the Google sketchup file I created, I measured and fabricated the top frame that will hold the LEDs, acrylic, silicone (compliant surface), and projection layer. The top frame consists of two pieces; the top piece, which will fit the acrylic (in the center), along with the silicone rubber and projection material on top, and also the infrared LEDs alongside the acrylic and the bottom piece that will screw into the top piece and rest on top of the final box.

Top piece (left) and bottom piece (right)

View of the top and bottom pieces (with acrylic and LEDs sandwiched in between).

I bought two pieces of 4 foot x 8 foot x 1/2 inch thick hardboard at home depot

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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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Initial Multitouch Aesthetic Plans

My aim is to create a clean and simple table design. I don’t want the table aesthetics to outweigh or detract from the musical interface and interaction. I did a quick sketch of my initial Aesthetic thoughts using Google SketchUp. I will include pictures of the actual progress and SketchUp files once the building process begins. The following design is not set in stone, but will be the basis as I start the building.

top_bottom

top_bottom_together

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