Equipment has arrived

Hey everyone.  You've all probably been thinking that the multitouch project was dead due to the 2 month delay since the last post. But never fear, the project is very much alive!  We've been patiently waiting for the equipment to arrive so that we can begin construction, and the acrylic finally arrived Thursday! So without further ado, I present to you the equipment we have to get the touchscreen prototype working:

The infrared LED strip lighting connects to the 100 watt power supply and is inserted into the aluminum channel that lines the edge of the acrylic screen.  The Neoprene setting block is cut into small pieces and placed in the aluminum channel to prevent the acrylic from smashing the LEDs.  We will add a layer of silicone rubber on top of the acrylic so that touching the screen will scatter more infrared light downward toward the infrared camera.

It's really unfortunate that the equipment showed up this close to winter break when all of us are finishing projects and studying for exams.  Seeing how long this equipment order took to get here, I'll probably be ordering the computer and the materials for the touchscreen case soon.

To any Miami students, let me know if you're still interested in helping next semester or have any suggestions on what materials to use for the touchscreen enclosure!

Project dimensions

Since we've decided on a projector to use with the project, we now have concrete measurements on the projector size, the throw distance of the projector, and the screen size.  These dimensions are illustrated in this diagram:

The surface of the table will be about 3 feet off the ground, around waist level.  This should be a comfortable height for people to interact with the table while standing.  It should also be low enough for people to be able to interact with it sitting down and for shorter users to interact with it.

I used an online tool from Projector Central to calculate what screen sizes we can use with the given throw distance. The screen size (33" x 24.75") is one of the smallest screen sizes possible with the given projector, but is still relatively large (imagine a 40" TV).  The screen size also represents the projector's native aspect ratio of 4:3.  Finally, I made sure that the camera we buy can still see the entire screen from underneath for infrared blob tracking purposes.  The M12 Infrared Web Cam from EnvironmentalLights.com can easily see the entire surface with a 73 degree lens even if the camera is mounted 12" above the bottom of the touchscreen case.

Please let me know if you see any problems with this design, as I will be ordering the first round of hardware very soon!  I'm really excited to start the physical construction!

The projector has been chosen

Ultimately, we were able to limit number of projector choices down to four by looking only at short throw projectors that provided the required screen size.  Many of the high-end ultra short throw projectors actually produced a screen size that was far too large.  This eliminated many of the super heavy duty projectors to reveal smaller and cheaper models with great resolutions.


After making sure that the projector had a short enough throw and a small enough screen, we evaluated them on the quality of the image.


Brightness
Because the multitouch screen will likely be placed in a relatively brightly lit lobby, we needed to look at high-lumen projectors.  The lumens of the projectors we considered ranged from 2000 - 3000 ANSI.


Resolution
In order to choose a projector with a crisp, sharp picture, we evaluated each projector on resolution.  All of the projectors that we considered supported a resolution of at least 1080i, while only one projector supported 1080p.  However, since our particular project was not intended for action movies or fast-paced games, the difference between 1080i and 1080p was rather insignificant.


Lamp life
In order to ensure that our touchscreen is affordable in the long run, we had to look at the rated life of each projector's lamp.  Lamp life ranged from 2000 to 6000 hours (a 3x difference!).


Other considerations
We also considered other projector properties, such as contrast ratio (higher is better), inputs (preferably HDMI, DVI, or VGA), price, and whether it was 3D ready (could we combine 3D and multitouch?).


The Winner
Ultimately, the winning projector was the ViewSonic PJD7382 DLP Projector.

This projector had a brightness of 3000 ANSI, a 1080i resolution, a lamp life of 4000-6000 hours, a static contrast ratio of 2600:1, a dynamic contrast ratio of 3000:1, two VGA inputs, and is 3D ready.


With this projector in mind, we can now begin to finalize our dimensions!

What projector / display size should we use?

Alright everyone, time to help out!  We need to decide on which projector we want and how big our table-top display should be.  If you haven't already checked it out, take a look at these diagrams to understand how our multitouch display will work.  The only change I would make to those designs would be to use an ultra short throw projector pointing straight up instead of a projector and a mirror.  Rather than commenting on this post, head over to the multitouch forum topic and give your input!


Edit: The previous forum didn't allow guest posts, so I switched to a different host: http://mumultitouch.forum-motion.net/hardware-f2/help-decide-what-projector-screen-size-we-want-t1.htm.  Click on the link to give your input!

Hardware Influences

Before I go into the details of what our multitouch display will look like, I want to take the time to credit all the hardware designs online that have influenced the final specifications.


Probably the most influential project I found was from Charless Fowlkes on instructables.com describing step by step how to build an FTIR multitouch display (see next paragraph).  Fowlkes not only showed a simple proof of concept, but demonstrated that the costs of building such a display were not much at all.  After seeing a cheap, simple, functional multitouch display, I was encouraged to bring the technology to the School of Engineering and Applied Science at Miami University.


Thanks to Fowlkes, I managed to learn about the concept of frustrated total internal reflection (FTIR) and how it can be used to create multitouch displays.  You can shine infrared light through a piece of acrylic and due to the angle that the infrared light hits the surface of the acrylic, it will remain entirely inside the acrylic.  Only after someone touches the acrylic and scatters the infrared light downward does the light break the surface of the acrylic.  When this happens, you can detect where the touch is located by using a camera with an infrared filter. See J. Y. Han's original research for more details.  Also, Christian Moore has some amazing diagrams that really help illustrate the process.


After seeing Charless Fowlkes and J. Y. Han's research, I discovered a number of other great and interesting multitouch projects built using FTIR - particularly among those in the Natural User Interface (NUI) Group.  I thought that building a multitouch table would be straight-forward enough until I saw the brilliance and creativity of other groups.  Instead of using a projector as many multitouch systems do, Alex Tan showed how you could disassemble and use an LCD display instead.  Also, user jbolton built a huge multitouch sphere, and Hiep Truong built a portable LLP display that can fit in a suitcase!


Finally, TouchFactors demonstrated even quicker and cheaper methods of building a FTIR display by using infrared LED strips, a single piece of polished acrylic, and Rosco Grey.  The results they got were incredible and among the most promising designs for our particular multitouch project.


So, from all these influences, we can pick and choose what features make it into our final design.  In the next post, I'll discuss the specifics of our hardware design!