Interactive Multitouch Display

Step 6: Screen sandwich assembly

Once the frame, rails and acrylic are prepared you are ready for the final assembly. Clamp the layers together for easy drilling and bolt them in place. Once the sandwich is assembled, it is necessary to caulk along the edge of the aluminum in order to block any light that might spill out thru the crack. We want it all nicely ducting along the inside of the acrylic instead.

In order for the projector to display on the surface it is necessary to also introduce a diffuser (not shown here). A sheet of thin drafting paper was included in the sandwich supported by a second thin layer of plexiglass.

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dancmarsh says: Mar 5, 2011. 3:20 PM

I know someone asked before, but there was no answer, so i wonder if anyone has tried it.

Has anyone tried mounting the projector under the table yet and setting the screen to rear projection?

I'd like to know if it works, would make for a neater and more portable install.

ridekrooked in reply to dancmarshApr 14, 2011. 4:03 PM

it works but the focus length tends to be longer than the distance between projector and the screen, you then also have the reciever in the way of the projector leaving a dark patch on your screen.
you can have the projector in the top corner near your screen and reflect it off a mirror at the bottom of your case. that works too

Hypernoob says: May 31, 2009. 7:18 PM

did you drill through the acrylic? or are there gaps provided by the spacer blocks so you are actually drilling through an empty space.

turkey tek (author) in reply to HypernoobJun 1, 2009. 12:37 AM

i didn't drill thru the acrylic. it is just floated inside the frame.

ydeardorff in reply to turkey tekNov 9, 2009. 1:15 PM

Im wondering how this could be made into a large desktop for working with cad/photoshop and other programs.
Also, I noticed you were having just a tad difficulty playing with those picture files. Is that a problem with the web cam used?
Please contact me on this. Id like to know more. about making my own.

Rjessick in reply to ydeardorffNov 9, 2009. 9:21 PM

part of it could be the webcam used. With some webcams there is actually a IR diffuser inside of it over the lens and they can sometimes mess with the IR sensing. Another problem could be the paper that Turkey Tek uses. Normal paper may be too thick and not let quite enough light through. The last problem could be the number of LED's that he has installed. More would obviously be better but require a hell of a lot more soldering and what he already did probly sucked! lol

Rjessick in reply to RjessickNov 9, 2009. 9:23 PM

a nice substitute for the paper is anything like drafting vellum or trace paper or the like...

UniBot in reply to RjessickSep 26, 2010. 8:57 PM

above this comment I posted a solution on the LED amount problem by eliminating the need of resistors, as for the diffuser issue, the besto soution I know is to put vegetal paper (white / translucent) under the acryllic, it provides the best visibility for the projector's image and touch capability (that last part, im not very sure):
pros:
-good visibility
-easy installation, it sticks to acryllic thanks to static electricity

cons:
-limited size availability. maximum size I know of: mercury format (110 x 77 cm)
-critical installation. if theres an air bubble between the acryllic and the paper, the IR refraction of the finger will turn too blurred and inaccurate.
-environment. the vegetal paper is EXTREMELY sensitive to changes in temerature and moisture, too much moisture... and the paper bends on itself, causing air bubbles where we dont want them.

housewright30 says: Apr 20, 2009. 1:43 PM

i don't know if this is a dumb question or not but how well dose the IR pass though the paper? i mean i would think that it would be blocked by the paper.

Pyshotic Wards in reply to housewright30Apr 30, 2009. 3:44 PM

well technically the paper is underneath the acrylic sheet or Plexiglass it is used as a projection surface so the image ur putting on the screen wont pass right through Note: drafting vellum and three+ coats of silicon sealant will work equally well if not better b/c it could possibly be more durable (and you can always add more sealant using a dense foam paint roller to spread the silicon evenly across the vellum and when you mount the vellum, make sure the side with the sealant touches the acrylic sheet or Plexiglass)

cba20k says: Jun 17, 2008. 2:10 PM

This instructable is great! Quick question though. I am not sure how you are attaching the channel to the acrylic. I see that the wood frame sections are bolted to channel, but that would not keep the four pieces attached to one another....would it? Sorry if I'm missing something obvious here.

Zero-Vision says: Apr 9, 2008. 10:48 PM

You used drafting paper in your setup, and this part is not critism...the image quality would be super low when compared to say a rigid rear projection screen. Of course no one wants to spend 500 on a rigid frame, in adition to the possibility that it would effect the ir refraction. So my question is, this. I have, for my company a transluscent material. Under normal lighting a person can SEE fingers shapes ect. It is meant for rear projection. So it works for that. When I take my IR cam, and loook at the material and put a remote control behind it, the ir is very clear, meaning it doesn't block ir at all or disperse it like it does lower band visible light. In theory would this effect "bouncing" of ir waves inside? or does it take actual Preasure to do so? I'm asking this now so i can better design the final product in advance.

turkey tek (author) in reply to Zero-VisionApr 10, 2008. 11:03 AM

If you put the diffuser behind a sheet of acrylic, then i don't think there would be any problem. If you want to use the diffuser as both diffuser and the touch surface, you'll definitely want to experiment to see how well the internal reflection works in the diffuser.