Hello,

I’m new around here, and I was hoping to be part of this fine community. I decided to make my own multi-touch project; I’d like to start by making a LCD FTIR setup.

I wanted to ask about the compliant surfaces for FTIR setups. As I looked around the forum, different Silicon applying technics are mentioned. Could someone list and give a short explanation of these “techniques”? Also, what would be the proper layering for my specific setup. Being a LCD FTIR, I need a perfectly transparent FTIR compliant surface.

As of now, I’m thinking

no diffuser needed here
---------------------------- 120gr sketch paper (See this thread)
................................... 1mm thick silicone rubber - shor 40
================ acrylic surface

I’m hoping those layers will not distort the image what’s so ever.

Thanks for the help, very much appreciated.

Hi Sniperchang ,
check this post about rollover technique

sketch paper and rosco , both works but i would say that you have to go for one or the other ,
sketching paper + rosco fade the image .
about the “ perfectly transparent FTIR compliant surface “
silicone sheet with mylar on top or a sheet of lee filter 226 (or a sheet of transparent plastic )

Ok, so I get some sort of nice clear plastic that’s flexible enough to press on the silicone but rigid enough to glide fingers on easily. I apply the silicone to the plastic via rollover technique described in the other thread and simply throw that ontop of the Acrylic?

About that Lee filter. It looks like the 226 cuts out in the visible purple color range. Is that a problem or not since LCD are basically giving off red-green-blue?

One more thing, should I apply the silicone on the acrylic surface, or the Mylar Surface?

Applying it on the Mylar should theoretically give you brighter blobs.

GFantini - 06 September 2008 03:54 PM

Applying it on the Mylar should theoretically give you brighter blobs.

Is that because the Silicon will not be bonded with the acrylic? Would that also avoid the tracing effect?

i guess isilicone will dry faster on the mylar
also if you ( eventually) failed it will be easier to remove from the Mylar

In addition to what Jimi said, yes, the silicone not being bonded to the acrylic results in better blobs, because when the silicone is bonded to the acrylic, it changes its refraction angle, thus causing some light to escape without any touches. This should be especially true if the compliant surface is textured.

But again, this is all in theory. Anyway, in practice I could confirm these results, and other people in the forums have reported likewise. And if you take a closer look at Jeff Han’s patent request, you’ll notice that he’s also using the same principle. So, you can’t go wrong with it.

Furthermore, some thinners could actually damage the acrylic. Good luck.

Thank you guys, this information is very much appreciated.

So I’m curious how the Mylar has worked for you Sniperchang or others who have info?

I found something that might do the trick. I was browsing at staples when I notice they were selling this clear Desktop pad. The material seem to be transparent, flexible but with a good thickness to it. I noted the manufacter, and I found out (here) that it is a PVC material. Do you guys think this will be ok for applying silicon to? It’s seems like a perfect material, but I’m not sure if it’s worth the 25$?

EDIT: Hmm, the website has a footnote that says: “* Not recommended for use on lacquer, acrylic or urethane finishes as material may mar surface"…

Ok, I found a website supplying Plastic films for very reasonable prices. (Click here.)

They offer:
Mylar Polyester Film
Lexan Polycarbonate Film
Vinyl Sheet
Acetate Film

I’d like to set-up a table to compare these materials so I can order the best one for my project. Keep in mind I’m looking for something flexible but still rigid for clear tracking but with no “dragging” effect, minimal friction for finger dragging, optically clear and a good scratch resistant surface - The most ideal Touch surface.

I’d like to find out the following properties: flexibility, clarity, friction and abrasion/scratch resistance.

----------|-Flexibility-|-Clarity-|-Friction-|-Resistance
Mylar---|---Good-----|--Good--|------------|-Excellent
Lexan--|----Bad?-----|----------|------------|--Excellent
Vinyl---|---Good------|--poor--|---poor----|----fine
Acetate|---Good?----|-Good---|---fine?---|---good?

Is the Acetate the same material they use for overhead projectors in schools? I don’t think vinyl is good for my application if it’s what I think it is. Mylar seems really good, but I don’t know much about Lexan.

Any info to help fill out my table is very much appreciated!

Sniperchang-
I was having the same question as you about FTIR LCD compliant surfaces, and Johannes.Schoening told me that I actually don’t need a compliant surface at all for an LCD setup; he gave me a few links to some papers about it: http://nuigroup.com/forums/viewthread/3161/

Anyways, I picked up a piece of Lexan polycarbonate from Home Depot today, and even though I’m not going to use a compliant surface for my FTIR LCD setup (for now, anyways...), I’ll try applying some silicone. I’ll let you know what my results are...probably going to do it this weekend.

What did you finally decide on using?

-rbedi100

I was able to order some samples of clear plastic films that Ridout Plastics offer. I will receive various thicknesses of Mylar Polyester Film, Lexan Polycarbonate Film,Vinyl Sheet, and Acetate Film. I’ll post my comparisons once I receive them, and get a chance to test em out.

Link to Ridout Plastics

Maybe your right about compliant surface, I was so focused on doing a FTIR, I haven’t considered it might be easier just to stick with DI for LCDs. I guess I can try both and see what happens. I’ll still try out the sample and stuff, could be quite usefull for the forum. And I’ll eventually make a comparison guide for the NUI group with LCD once I get my hands dirty.

Looking forward for your test results!

Hi!  Does anyone know the suitable brand of LCD monitor to use in LCD FTIR setup?  Dell?  How about Samsung or LG?  Will a 15” do just fine or do I need to have a 17”?  Thanks.

The brand doesn’t really matter - the only issue is if there are any “FFC issues”. FFC issues occur when the cabling for the LCD components are not long enough to take them away from the LCD matrix and they are too compressed and folded up in the casing. There is a database to check for FFC issues; here: http://www.baseportal.com/cgi-bin/baseportal.pl?htx=/Lumenlab/main

“No FFC” indicates that there are no problems, and the monitor will work fine. The LumenLab database link I mentioned earlier only has LCD models upto 19”.

good luck
rbedi100