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After reading this Instructable, I have built a nice multitouch display during my spare time as a hobby. In this article, I will share plans and explain how to construct a 56 inch multitouch screen that looks like a TV. It's totaly homemade, it's not made from an old tv but you could do so. This article is for people who already have basis in this kind of thing. It's not an easy setup and it's not suitable to be commercialized but for personal use it's fine for testing new softs.You can look my website at: www.Softmt.com
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Signing UpStep 1Basic principle
Basic Principle
The principle is to modify a webcam to allow it to capture only IR light and point it to your screen. Then the software analyzes the images and detects press where there is a blob. A blob is the light projected back of your screen when you press onto it (Scattered Light on the schema).
Multitouch technology grows at a lighting speed during those years. There are many different methods for sensing the touch on the screen. As far as I know there's electronically and optically based setup. Iphone and Ipod touch are multitouch devices and use electronic circuit for sensing touches.
Optical systems are the simplest to build for home users. Those systems require a low light environment and may not be as stable as electronical systems. There's two big principle in multitouch optical system, the first Is FTIR (Frustrated total internal reflection) like I use and DI (Diffuse illumination) like Microsoft surface uses.
Frustrated Total Internal Reflection
When light encounters an interface to a medium with a lower index of refraction (e.g. glass to air), the light becomes refracted.
The extent of refraction depends on the angle of incidence, and beyond a certain critical angle, it undergoes total internal reflection (TIR).
Fiber Optic cable is a common technology that employs TIR.
However, another material at the interface can frustrate this TIR, causing the light to escape the waveguide there instead. Ref : http://www.cs.nyu.edu/~jhan/ftirtouch/
Under "ordinary conditions" it is true that the creation of an evanescent wave does not affect the conservation of energy, i.e. the evanescent wave transmits zero net energy. However, if a third medium with a higher refractive index than the second medium is placed within less than several wavelengths distance from the interface between the first medium and the second medium, the evanescent wave will be different from the one under "ordinary conditions" and it will pass energy across the second into the third medium. (See evanescent wave coupling.)
A transparent, low refractive index material is sandwiched between two prisms of another material. This allows the beam to "tunnel" through from one prism to the next in a process very similar to quantum tunneling while at the same time altering the direction of the incoming ray. Ref: Wikipedia
Diffuse illumination
In DI system, The IR light isn't inside the acrylic but projected onto it by the top or the bottom. The acrylic should be evenly projected onto the screen to be reliable.
+ Simplest construction
+ DI don't require a compliant surface (Rubber)
+DI don't require acrylic, it can be made out of any transparent material
+ Allow tracking of Fiducial
-Blobs are not as clear and sharp compared to ftir blobs
The principle is to modify a webcam to allow it to capture only IR light and point it to your screen. Then the software analyzes the images and detects press where there is a blob. A blob is the light projected back of your screen when you press onto it (Scattered Light on the schema).
Multitouch technology grows at a lighting speed during those years. There are many different methods for sensing the touch on the screen. As far as I know there's electronically and optically based setup. Iphone and Ipod touch are multitouch devices and use electronic circuit for sensing touches.
Optical systems are the simplest to build for home users. Those systems require a low light environment and may not be as stable as electronical systems. There's two big principle in multitouch optical system, the first Is FTIR (Frustrated total internal reflection) like I use and DI (Diffuse illumination) like Microsoft surface uses.
Frustrated Total Internal Reflection
When light encounters an interface to a medium with a lower index of refraction (e.g. glass to air), the light becomes refracted.
The extent of refraction depends on the angle of incidence, and beyond a certain critical angle, it undergoes total internal reflection (TIR).
Fiber Optic cable is a common technology that employs TIR.
However, another material at the interface can frustrate this TIR, causing the light to escape the waveguide there instead. Ref : http://www.cs.nyu.edu/~jhan/ftirtouch/
Under "ordinary conditions" it is true that the creation of an evanescent wave does not affect the conservation of energy, i.e. the evanescent wave transmits zero net energy. However, if a third medium with a higher refractive index than the second medium is placed within less than several wavelengths distance from the interface between the first medium and the second medium, the evanescent wave will be different from the one under "ordinary conditions" and it will pass energy across the second into the third medium. (See evanescent wave coupling.)
A transparent, low refractive index material is sandwiched between two prisms of another material. This allows the beam to "tunnel" through from one prism to the next in a process very similar to quantum tunneling while at the same time altering the direction of the incoming ray. Ref: Wikipedia
Diffuse illumination
In DI system, The IR light isn't inside the acrylic but projected onto it by the top or the bottom. The acrylic should be evenly projected onto the screen to be reliable.
+ Simplest construction
+ DI don't require a compliant surface (Rubber)
+DI don't require acrylic, it can be made out of any transparent material
+ Allow tracking of Fiducial
-Blobs are not as clear and sharp compared to ftir blobs
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its just a computer with a projector and webcam installed
would this work if i used a LCD screen?
is there any way to make something like this with a lcd screen?
please post back and let me know!
This project and NuiGroup inspired me to make somehting similar to this. I am changing a couple things from your design as a basis.
1. Screen will be glass and sit 30-45 degrees for a more ergonomic approach for extended use. Like a drafting desk.
2. I think I will go with a 1/4 inch tempered glass (clear no tint and without manufacturer bug engraved)
Seems everyone is migrating to lasers over the surface for touch(less) interface. Would you considering doing an updated project with IR lasers?