Hi,

My name is Sharath. I am planning to build a multi-touch surface as a part of a project for a school. I am facing several considerations before I can decide Whats the best suited solution for this situation.

* The use of Acrylic glass is causing some kind a panic due to its property of catching fire easily. Is there a possiblility of using a any alternative surface for registering the touch other than the silicone coated rubber.

* The other concern is about a compromise in the design of the IR LED along the surface. I was wondering whether the LED’s can be placed inclined on the top of the surface very close to the edge of the surface rather than being placed in the holes drilled onto the the sides of the suface. My concern is getting the Total Internal Reflection if the LED is placed a little away from the surface at an angle greater than 70 deg. The illustration is as shown ithe pic below..
[photobucket]http://i289.photobucket.com/albums/ll220/sharath_sridhar/altIRLEDPlacement.png[/photobucket]

Can anybody also educate me about any other types of arrangement of the display suface for a rear projection setup. Can I just use glass surface doubled up as a touch surface and as well as the display surface.
I will be really thankful if somebody could also illustrate the technical purpose of the Silicone Rubber.

Regards,
Sharath Sridhar

Hey Sharath,

The use of Acrylic glass is causing some kind a panic due to its property of catching fire easily. Is there a possiblility of using a any alternative surface for registering the touch other than the silicone coated rubber.

If you have FTIR in mind then you can use polycarbonate but that has the same properties as acrylic and is still flammable, you could use Glass but then you would have to change your setup from FTIR to DI. These are your 2 main choices.

As for not using silicone compliant surface the options you have are LLP and DI setups… LLP is still under development, and not a lot or resources are available in regards to tests performed and setup configuration.... you could look at these links Link 1, Link 2 and Link 3. As DI there is pleanty of information in regards to the setup and components used to create one for your slef easily…

* The other concern is about a compromise in the design of the IR LED along the surface. I was wondering whether the LED’s can be placed inclined on the top of the surface very close to the edge of the surface rather than being placed in the holes drilled onto the the sides of the suface. My concern is getting the Total Internal Reflection if the LED is placed a little away from the surface at an angle greater than 70 deg. The illustration is as shown ithe pic below..
[photobucket]http://i289.photobucket.com/albums/ll220/sharath_sridhar/altIRLEDPlacement.png[/photobucket]

This will not work for FTIR, TIR (total internal reflection) will not occur if you have the leds above the screen.

Can anybody also educate me about any other types of arrangement of the display suface for a rear projection setup. Can I just use glass surface doubled up as a touch surface and as well as the display surface.

You can check out this link for information regarding DI and FTIR setups…

I will be really thankful if somebody could also illustrate the technical purpose of the Silicone Rubber.

The use of silicone rubber is to achieve zero force input detection… essentially what happens is when you drag your fingers along acrylic your FITR effect is lost, with the use of silicone FTIR still occurs. this is pretty much the gist of why we use silicone.

hope i answered all your questions…

Taha

Thanks for the reply. I am sorry for the late response.  Really thanks for being so descriptive with your answers. I shall keep you posted with my progress with my decision. Thanks and regards,
Sharath