Hardware Overview

Old Version! - Updated February 18, 2009 - Click here for the latest version

Synopsis: To the user, the final product will look like a regular desktop computer, but with the addition of a multi-touch display on the same level (and horizontal) as the desk surface, located conveniently near the keyboard. This display will be used only to run the software I am developing to permit users to easily manipulate applications and windows.

For an overview of these device techniques: NUI Group: FTIR Summary, or a more complete and comprehensive summary of touchscreen technologies can be found here - both of those are external links.

Because projects involving hardware construction naturally run into more budget constraints than purely software projects, my goal is to make use of otherwise-unwanted surplus, outdated, or damaged electronics that can still serve the desired function in this specific custom use. That is, the hardware side of my work sometimes feels like the world's most remarkable scavenger hunt.

Computer-vision Multi-touch Technologies

This phrase refers to input technologies that rely primarily on computer processing of optical images from some sort of live image source. Specifically, computer vision multi-touch devices can be affordable and easy for a hobbyist to build, since the only part connected to the computer, a minimally-modified USB or Firewire webcam, can be purchased cheaply and set up easily and without risk to the computer system. Most such systems work using infrared illumination to permit a display to be integrated into the tablet. Please see an introduction to IR and my webcam modification work for more information.

Multi-touch Input Device - Decision Process

Two hardware technologies are described below. However, I am not sure which of those two, or two alternate methods, I will be pursuing. The four new options to decide between are:

  • Projected FTIR (Frustrated Total Internal Reflection)
  • Projected DI (Diffuse Illumination)
  • LCD FTIR (Frustrated Total Internal Reflection)
  • LCD LED-LP (LED Light Plane, also known as "Side-DI" or "The Gap Method")

Historically, Projected FTIR is the technology that initiated this recent renaissance of computer-vision-based multi-touch devices, so it has received a lot of attention and many people have built devices using that technique. These techniques all vary in their image source (a projector or a possibly-deconstructed LCD display panel).

To be able to compare these techniques easily, I have created two documents:

  • Technology Comparison (PDF, Printable) - Summarizes the various techniques of construction, relative merits and drawbacks, and the work required to convert a given type of device into one using another technology. Also contains a subjective, relative ranking of each technology on several aspects and an unweighted sum total ranking - in both cases, lower is better. My sources for these ratings take into account the hardware I already have, the collective experiences of the members of the NUI Group forums in the posts that I have read, and the ease with which I can acquire the hardware I lack.
  • Price Comparison (PDF, Printable) - Based on equipment provided by the CS department and prices I've found at local stores and on eBay, I've summarized the price to construct each of the methods. Two notes: 1 - The given price does not include the actual computer or standard input/output device (regular monitor, keyboard, mouse), but that cost (or borrowing) should be equal for all methods. 2 - The price of each device considers building it entirely on its own as the first device - for conversion costs, use these charts in conjunction with the tech comparison above to find the specific components that have to change. Generally, the largest contributors to the cost are the acrylic panel (required for all but LCD LED-LP) and the LCD panel if purchased for both LCD techniques.

I have left the existing content below on this page intact - when I determine what my construction plans will include, I will update them to match the technique(s) I select.

Multi-touch Input Device: Projector and FTIR (Frustrated Total Internal Reflection)

  • Projector (640x480, InFocus LitePro 570) set up to rear-project on acrylic surface - in hand and functional
  • Mirrors to reduce necessary depth for projector below table - still needed
  • Surface for total internal reflection, touch sensing, and projection: I have a piece of glass (?) from an old add-on anti-glare filter which I hope will work. If it doesn't (too small or FTIR image not clear) I will need to purchase an acrylic (Plexiglass/Lexan) sheet) - testing required, acrylic sheet possibly still needed
  • LED's for internal illumination of touch surface, and associated minimal circuitry to drive them at a constant brightness. The department has visible light LED's (for demo purposes), IR (infrared) LEDs - salvaged from broken remotes - still needed.
  • Webcam (QuickCam Pro 4000) with IR filter removed, and a removable visible light filter installed - in hand, must verify functioning and remove filter

Alternate (Optional) Input Device: Deconstructed LCD Panel and FTIR or LED-LP(LED Light Plane)/"Side DI" (Diffuse Illumination)

Researcher's Note: I will not construct this optional device unless I manage to get an LCD I can deconstruct. To the computer system, the devices look the same, so if any time between now and the "pencils-down" date I get the resources to make this update, I can do so. The benefits include a clearer, higher resolution image, elimination of fan noise, greatly reduced weight, simplified mounting, and improved longevity (no bulb to replace every 50 hours). Most of this device is identical to the projection-based one, but the mirrors are eliminated, the deconstructed panel is mounted directly to the illumination system with the camera mounted behind it (LCD panels are transparent to infrared), and the acrylic is potentially removed (this is the primary difference between the FTIR and LED-LP implementation: I have read accounts of both methods working well). Hopefully someone has an LCD with a burnt-out backlight that they're willing to part with - as long as I have to deconstruct it to add touch capability, I may as well replace the burnt-out fluorescent backlight with a white LED one.

Desk and Computer Workstation

A standard Linux-capable computer with the ability to drive the navigation display as well as the standard one will be the target of my work: I will do much of my development on a virtual machine that I can move from system to system, and when it comes time to integrate a computer with the desk a decision will be made then. If need be, I can put my own personal machine on the multi-touch desk.

  • Desk with hole cut for touch surface and mounting constructed for projector, camera, and mirrors - located, modifications to be planned and completed.