Hardware Overview
Updated March 10, 2009 - Click here or scroll to bottom for links to older versions of this page.
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. The multi-touch surface will be built in to the desk. 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 Wiki - Hardware Page, 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run into more budget constraints than purely software projects, my goal is to make use of otherwise-unwanted surplus, outdated, or damaged electronics that can still serve the desired function in this specific custom use. Nevertheless, ease of assembly and polish of the final product are important considerations in hardware costs. Reducing required assembly work, as well as possible openings for error, are being considered when making decisions.
Desk and Computer Workstation
Two desks are available -- one taller and heavier one, and a smaller, foldable one, originally used as a sewing machine desk. The sewing machine desk will be modified to include wheels, and will serve as portable multi-touch device for presentations and demos. As such, hardware assembly will first take place in this desk, but it will be designed so that it can be moved to the larger, heavier desk to make the second-generation hardware portal desk.
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. If possible the tower will be integrated with the desk, especially in the case of the portable, sewing machine desk.
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.
Hardware Revision 1 - Projected Rear DI
This technique involves flooding the back of an acrylic sheet with diffuse IR light. The computer display is also projected on the rear of the sheet. As a finger approaches and touches the acrylic panel, a moment of IR light being reflected back to the camera beneath the surface increases. The camera used is a modified webcam with the IR filter removed, and is mounted beneath the sheet so that it can see entire surface. An image from the camera is processed by software to extract the location of touches -- called blobs.
- Projector (640x480, InFocus LitePro 570 - or other repaired projector) set up to rear-project on acrylic surface - in hand and functional - needs focus distance adjustment to lens mechanism
- Mirror to reduce necessary depth for projector below table - one in hand, should work if above adjustment works.
- Acrylic sheet, thick enough to support touches as well as possible conversion to FTIR (8-10mm) - still needed - will seek at local sign shops or online - Roughly 2' x 3', clear if considering conversion/reuse for version 2, otherwise clear or extruded frosted (as a diffusing surface and/or projection surface)
- Projection surface and diffuser - in hand - cheap interfacing material from Joann Fabrics, tested to work - click for image of quick and dirty test of rear projection
- Infrared illumination for rear of acrylic sheet - Ordered from DealExtreme - Selected illuminators are preassembled and prewired
- Webcam (QuickCam Pro 4000) with IR filter removed, and a removable visible light filter installed - in hand, IR filter removed, needs visible filter installed
Hardware Revision 2 - LCD LLP (Laser Light Plane) or Projected FTIR
Based on an evaluation of a number of factors, I have selected two options for the second revision of the hardware: one using a projector, and one using an LCD screen. The projected option is an FTIR -- frustrated total internal reflection -- multi-touch device, likely reusing the acrylic panel from the version 1 and rear DI device. If a suitable LCD screen is found, I will construct an LLP (laser light plane) device using a deconstructed LCD, a thin sheet of acrylic for protection, and IR line lasers. In both cases, the second revision hardware is generally more polished and of a higher quality, though if materials and budget allow, I will maintain both versions of the hardware for the computer science department to use in the future.
LCD LLP
- LCD screen, burnt out backlight okay - have a lead, but larger/more sought - if backlight is burnt out, we'll need to purchase white LED clusters for backlight.
- Infrared lasers and line lens - a few sources known (ebay, DealExtreme)
- One or two thinner acrylic sheets, for LCD support and panel protection - still needed - will seek at local sign shops, Menards, or online - much cheaper than the thicker sheet used for DI and FTIR - ideally two sheets, either the size of the screen (cannot know now because I don't have it yet) or 2' x 3' (to fit maximum desk hole size), thinner (4-6mm, or even thinner for top sheet), and either both clear or topsheet clear, bottom extruded frosted.
- Marine proxy putty to mount line lasers - still needed - inexpensive, source known
- Webcam (QuickCam Pro 4000) with IR filter removed, and a removable visible light filter installed - in hand, IR filter removed, needs visible filter installed
Projected FTIR
- Projector (640x480, InFocus LitePro 570 - or other repaired projector) set up to rear-project on acrylic surface - in hand and functional - needs focus distance adjustment to lens mechanism
- Mirror to reduce necessary depth for projector below table - one in hand, should work if above adjustment works.
- Acrylic sheet - either reused from revision 1 or additional sheet needed - roughly 2' x 3', clear, 8-10mm thickness
- Projection surface and diffuser - one idea in hand - cheap interfacing material from Joann Fabrics
- Compliant surface (rolled diluted silicone) - still needed - using Tinkerman's method, generally acknowledged as the most successful/reliable
- Infrared illumination for edge of acrylic sheet - prewired LED strips from environmental lights needed - I could wire my own LEDs, but this seems like perhaps too much trouble for too little savings. These prewired strips make acrylic illumination a "solved problem".
- Webcam (QuickCam Pro 4000) with IR filter removed, and a removable visible light filter installed - in hand, IR filter removed, needs visible filter installed