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Multitouch Interactive Table

As part of a three-person team (two engineers and an interior designer), I designed a multitouch interactive table for Special Topics in Smart Design. We used frustrated total internal reflection techniques to detect interaction on a rear projected polycarbonate surface. The basic idea is to use high-quality polycarbonate with IR LEDs scattered around the edges pointing into the “glass.” The IR light is reflected internally until someone touches the surface, at which point the light is “frustrated” (caused by the index of refraction change) and thus escapes opposite the side your fingers are touching. Beneath the screen we had placed a Firewire webcam modified with a IR bandpass filter tuned to the exact frequency corresponding to the LEDs. The camera would detect the escaping IR as “blobs” and send to the attached computer. A projector and diffuser completed the hardware design, allowing almost arbitrary size multitouch displays. In our setup, we built a 42″ display into the center of an old table attached to the projector stand using 80/20 framing and two first-surface mirrors. We used freely available blob tracking software for retrieving coordinates corresponding to points of user interaction and provide basic user interaction functionality. We architected a software stack incorporating open-source components in such a way that non-multitouch aware applications could benefit from the use of multiple points of interaction. A modified version of X11 known as multipoint X11 (MPX) serializes input from multiple keyboards/mice into a single stream so that multiple people can work on a single workspace. We were developing a script to translate the output coordinates of the blob tracking software into MPX’s expected inputs and hook into the standard applications through this channel, but did not complete this software. Cody was responsible for the initial research into multitouch hardware, describing how the various systems worked and outlining the pros/cons of each. After deciding to move ahead with the system based on frustrated total internal reflection, the second engineer started specifying the exact materials, supplies, and parts we would need to build such a system, while I started researching open source multitouch software, but found that none existed that allowed easy use of existing applications; therefore, I turned to looking into how we might send user input directly to window managers, file browsers, etc, which is when I discovered MPX. The table itself was physically constructed by a second Drexel Smart House team following the completion of the course, as part of an outreach project with a local high school (Science Leadership Academy). Some of the students we worked with in this outreach research project now attend Drexel.

Posted in Ramblin' Thoughts.


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