Multitouch Technologies

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Main DIY Multi-touch Technologies

FTIR (Frustrated Total Internal Reflection)

FTIR is currently the most popular method, possibly due to the wide internet distribution of Jeff Han's videos.

IR light is shined into the side of an acrylic panel. This light is trapped inside by internal reflection. When a finger touches the acrylic surface this light is frustrated causing the light to scatter downwards where it is picked up by a IR camera.

Diffused Illumination (DI)

IR light is shined at the screen from either below or above the surface. Citywall, Touchlight, reactivision, and MS Surface use these methods.

IR light is mounted underneath a glass/acrylic sheet with a diffuser. When an object touches the surface it reflects more light than the diffuser or objects in the background, the extra light is sensed by a camera.

Depending on the diffuser this method can also detect hover, and objects placed on the surface.

LLP (Laser Light Plane)

A laser light plane is created by IR lasers, and your fingers are interpreted as blobs when they hit the plane.

DSI (Diffused Surface Illumination)

Diffused Surface Illumination.


Other Technologies

Capacitance Testing

This is currently how the iPhone does it sensing, see Fingerworks. This method is very costly due to the complex electronic grid needed. See: [1]

Gap Method

Unsure about the popular name of this technique, so we shall call it "Gap" for now. A wide baffle is placed around the edges and above the glass/acrylic surface. This baffle leaves a little gap (0.5mm) between itself and the acrylic surface. IR light is shone though this tiny gap creating a small very narrow beam of light over the acrylic surface. This beam is broken when the user touches the surface, and the IR light is detected by a camera mounted underneath. LEDs should be mounted on all 4 sides.

A sensor based technique

AMLCD Optical Touchscreen

FTIR Side Scanning matrix

detect multiple touches by analyzing the light emitted from the sides of the FTIR glass. http://nuigroup.com/forums/viewthread/3532/

Video Plane Triangulation

Using multiple line scanner video sources to triangulate multiple touches for 2D Plane http://nuigroup.com/forums/viewthread/3250/

Sonar Matrix

Using ultrasonic sensors strip on the x and y axis to find multiple touches http://nuigroup.com/forums/viewthread/3953/

LED Matrix Layer

Using a layer of LED Emitters and Detectors that what would bounce light off objects above them that was be found by the detectors. Detecting would analysis the amount of light to find multiple touches http://nuigroup.com/forums/viewthread/3952/ and http://nuigroup.com/forums/viewthread/2576/

Spacial Hand Detection

Using multiple video sources to triangulate multiple touches and hand position in 3D space http://lightbucket.org

See also