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Multitouch – How To

How To Make a Multitouch Surface

There are several ways to make a multitouch surface. There are capacitive, resistive, acoustic, and other non-traditional techniques. Our focus will be on optical techniques since they are the easiest and most cost effective for the average person to create. The most popular optical techniques are:

  • Frustrated Total Internal Reflection (ie. Perceptive Pixels)
  • Rear Diffused Illumination (ie. Microsoft Surface)
  • Front Diffused Illumination (ie. MTmini, MTbiggie)
  • Diffused Surface Illumination
  • Laser Light Plane
  • LED Light Plane

Optical Multitouch Techniques

Each technique utilizes 3 main components:

  1. Infrared Camera (or other optical sensor)
  2. Infrared light
  3. Visual Feedback (projector or LCD)

setup thumb1 Multitouch   How To An infrared camera is pointed at the touch surface and detects when fingers/objects touch the surface. Infrared light is used to distinguish between a visual image on the touch surface and the objects/fingers being tracked. Since most systems have a visual feedback system where an image from a projector or LCD is projected or placed below the touch surface (the MTmini does not), it is important that the camera does not see this image when tracking objects/fingers on the display. In order to separate the objects being tracked from the visual display, a camera can be modified to only see the infrared spectrum of light (by removing the infrared filter and replacing it with a visible light or bandpass filter); this cuts out the visual image from being seen by the camera and allows the camera to only see infrared light that illuminates the objects/fingers on the touch surface. The projector is connected to a computer in order to display the software on the touch surface. The camera is connected to a computer and a tracking application uses the camera image to track and create touch coordinates.

6 Optical Multitouch Techniques

Click the image or title to view a description, diagrams, images, and other resources about a particular technique.

Software

Resources

This page is still being developed. Stop by often to see updates and more information for building your own multitouch surface.

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  • Dimitris

    Hey Seth,

    Can you use a monitor instead of a projector in your illustrated setup?
    If so what else would we have to account for? My guess is that by using an LCD Monitor we have to have some sort of a light source to make the reflected image more luminous.

    What do you think?

    • http://sethsandler.com/blog Seth Sandler

      Using a LCD is very hard. You can search on http://nuigroup.com/forums about using a LCD. It’s not recommended for this camera based multitouch. Check out nuigroup for great information on different techniques.

  • http://www.kathyhinde.co.uk Kathy Hinde

    Hi Seth, Thanks for posting such a lot of useful information. I’m hoping to try a method to detect where droplets of water are on a surface. I was wondering which of the methods above might be the best one to start with? – My initial concern is that water is transparent, so it may be difficult to detect. Have you ever tried detecting water? I will, of course do some experiments, but any advice would be much appreciated, Thanks very much, Kathy

    • http://sethsandler.com/blog Seth Sandler

      Hi Kathy,

      I’m not sure if water would work. My feeling is probably not. You might want to try asking on the forum at http://nuigroup.com/forums.

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