Hello guys and thanx for sharing your ideas. I am really new to this subject and i would like to build my own multitouch display using FTIR. My question is if this surface will do the job:
ST-Professional-D, rear projection, grey, 3 mm from http://www.screen-tech.de
For more details, i think this is the product’s page: http://www.webmart.de/wmshop.cfm?ID=44918&ProductID=358608&CID=71165&do=detail
I know that i normally need plexiglass and some kind of projection surface put ontop, and that the plexiglass needs to be thicker than the LED’s but i was wondering if i can make this work, as we have a large piece of this material (which is in fact a plexiglass surface from what i can tell) left over in the lab and it would be a shame to waste it.
for FTIR you may have trouble since the leds them selfs are around 5mm in thickness unless you go for SMT pakaging or somthing thing else another thing i can think of is that you can have this screen behind a regular acrylic where you project on this screen and the FTIR input is done on the regular acrylic sheet… but there is one thing you need to know FTIR requires a compliant surface so you always have to have the projection material on top so you dont damage the compliant surface.
I suggest you look into either DI or LLP if you want to use this screen… they will be better options than FTIR
Thanx a lot for your reply..Which of these methods is the easiest and which has the best results?Any links to instructions on how to build a screen based on one of these methods?
Thanx a lot, really usefull stuff in these threads. I measured the thickness of the surface, and its the 5mm, not the 3mm. Maybe FTIR will work with 3mm or even 5mm LED’s on this surface? Another thing that went through my mind, what if i place 2 sheets of this stuff on top of each other, to make it 10mm? Well i will test it anyway with a few LED’s on one side, nothing to loose i think
you could try it out i dont think there will be a problem in FTIR but you have have ghosting issues when you project… and if the thickness is 5mm then you may just get away with FTIR
but there is one thing you need to know FTIR requires a compliant surface so you always have to have the projection material on top so you dont damage the compliant surface.
Hey Taha. I have fixed the Tracing Paper (Projection Material) between 2 sheets of Acrylic and it works really good, as you can see in my Thread. It’s nearly like bare acrylic! So it works if it’s not on the Top too!!
Ok this is the thing, what you are doing will work… but you dont have a compliant surface on top… form my understanding, you have your layering similar to this
-------------------- FTIR (acrylic sheet)
-------------------- Tracing Paper (used for projection)
--------------------(acrylic sheet)
since you dont have a compliant surface you work on the acrylic sheet itself, the use of having a projection screen on top is manly because you dont want to interact with the silicone layer, because its really delicate and doesnt feel good.
Secondly the MelCy acrlyic is very different its more like the holoscreen it diffuses light in the surface itself so the acrylic is like a projection material as well
The acrylic itself is meant to be used as a rear projection screen. What worries me though is the FTIR effect, because the material is not clear and im not sure the IR light will spread through it. Taha, if i use it i will still need a compliant surface on top unless i want to press really hard on it right? But then if i use the compliant surface as well, what should i cover it with?
LLP is easy, but at the moment cheap lasers are not easy to find. If you don’t mind the price get some of AlexP’s, otherwise wait until other people clear the road with the Aixiz ones.
So i modified my webcam and did a little test just to see what the image is if i place my surface on two chairs over the webcam, with lights on and windows open during the day. I noticed that it gives a white image, which means that it diffused a lot of ambient infrared light right? That makes it impossible to use FTIR with it(unless we’re in a really dark room, or if its in a box)?If i place my fingers on top then i get black blobs, which reminded me of Front DI blobs, am i right? So maybe Front DI would be ok with this material?
I have attached a snapshot of the test, your comments are very welcome
xelapond: if it’s operating in the IR range, then it IS front DI.
MelCy: If you modified your camera and put an visible light filter over the lens, then you’re all setup for front DI. It’s hard to know, but FTIR/LLP might still work with that amount of light in the room. It doesn’t look too bad.
Yeah i put 2 small pieces of exposed film where the infrared filter used to be, as advised in some blogs that i’ve read, the good thing is that it works..So i got more curious today and headed on to a more serious experiment We have a small VR lab equipped with a back projection wall made of the same material as mine, mirror and projector, trackers and the like. So i set up the camera on top of the mirror pointing to the back of the screen, opened up some windows and touched the wall from its front side. I was expecting Front DI shadows, instead i got white blobs,not very clear but noticable. So there you go, a big Rear DI wall, i think(if only i could get it to work) I tried configuring touchlib to get it to recognise the blobs but that didnt go all well. What impressed me was the fact that plain ambient IR light coming from the back of the wall was able to create this effect. I will try again and post some snapshots of my effort.
So here’s what i get from the config app. I know its not really good, but i guess i can adjust those sliders a little more to make it better. I have tried a little calibration but my camera is not ideally located so it cant see the whole screen. The smoke demo was ok i guess, some false blobs, some offset between my fingers and the tracked blobs but i guess its a matter of correct calibration. There are also many false blobs when i stand close to the wall but it was ok as a first test. Can anyone help with the configuration(sliders values, maybe add or remove some filters to make it better)?
..So i got more curious today and headed on to a more serious experiment
