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:- Infrared Camera (or other optical sensor)
- Infrared light
- Visual Feedback (projector or LCD)
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
http://sethsandler.com/multitouch/
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