I've trolled these forums for a while, made a projector but eventually gave it up and went w/a 48" LCD. I'm not a complete noob w/these ideas, but by no means an expert.

I had an idea the other day for a Microsoft Surface-type setup (table-top computer surface), since I need a project to keep me busy now:) I apologize in advance for the long post, but want to give some background so people don't just tell me to search:) So far I know the following:

1) I can use a Wiimote and infrared pen(s) along w/a free .Net library to track movement on the table surface (which would have to be a glass table-top on a custom stand). This lets me locate 2D screen points in real time on the surface that translate to screen coordinates and "mouse-clicks." The library also supports multi-touch for I-Phone like manipulation of screen objects (rotate, stretch, move, click, etc.). If interested, you can search Google or YouTube for "Wiimote VR" or "Wiimote whiteboard" for details on how this works, but in short the whole system costs about $60 and is very accurate in it's tracking on most surfaces.

2) I can use .Net 3.5 to create a WPF app that would host the widgets. I wrote a quick mock-up app that hosts a video player, picture viewer, and a front-end for a yahoo local-search web service I had already. This also was surprisingly easy (in .Net 3.5) with the wpf wrapper around the DirectX classes.

3) I'm at the point now of determining the actual display method.
a ) One possibility is a 27-30" LCD TV (I've recently found a few case-damaged sets on ebay & craigslist for $120-200). It would lay flat on the support structure just below the glass table-top (which contrary to popular opinion does NOT damage the LCD screen itself in any way). This means the Wiimote tracker would have to sit on one corner of the table-top and scan the table surface, which isn't an issue in itself but makes for a less attractive overall design.
b ) The other option is the method Microsoft uses, which is a rear-projection system from below. Overall this would be a better solution since the Wiimote could be placed in the support structure itself facing upwards to scan for an infrared light-source. This would actually let me use the 2nd method that the guy in the YouTube video discusses (reflective IR), eliminating the need for IR pens.

So, my question is, given the above long-winded explanation, does anyone have any suggestions on designing an extremely short-throw, small-output system using say a Lilliput or psone screen? This would be a normal coffee-table height (say 30-36" max from floor to projection surface) and a relatively small projection output (anything past 32" would make the table itself too big). From what I've read it would need to be a folded mirror setup, but what I'm looking for are some suggestions on if the optics to pull this off are going to be cost prohibitive and guidance on the geometry to make it work. One big advantage is that the system is completely enclosed so there's no need for an extremely bright light-source (although I have my old metal-halide setup around here somewhere if need be). Gracias in advance.

I think you're right about needing a folded design, that way you utilize all available space for the throw to get your image the right size.

Plugging some numbers into FocalCalc - 5 inch LCD (PS1 size?), 180mm triplet, 24" throw, check the screen size as your unknown - with that the projected size will be just under 12"

Play around from there and see what you get, with a 10 inch LCD the image will be just under 24"

Here's an idea...
Use the 27/30" LCD, but remove the backlight. Then make the whole bottom of the coffee table a big backlight using white acrylic or something (so the backlight chamber will be like a 2 ft. deep box). Put the tracker in the center of the box on the bottom. I would imagine you might need to use IR pens still since the LCD will probably absorb so much of the IR that you'll need your tracking points to be pretty bright.

Hirudin, I thought about doing that but was just worried about being able to move the TV boards out of the way enough to allow the backlight & Wiimote through unobstructed (just like w/the LCD monitors for proj's). If I can find a TV cheap enough I think I may go ahead and try it out though, worst comes to worst I just use it as is and track from the top surface of the table. I think it would be the easier route overall.

wwinder, from focalcalc: unsplit, 15" lcd, 180mm triplet, 1.8' triplet-to-screen distance gave me a 30" display screen, which is just about perfect. This doesn't seem right for a folded design though, no? Plans like I've seen HERE for example seem to use different math because of the folding. Am I interpreting focalcalc correctly? If so it seems like I could just use a straight-through design if I go big enough on the LCD. I'm thinking I can go low power & flat/thin as possible on the light source so not much extra distance behind the LCD.

Thanks again for the replies guys.

I don't know how well a non-flat-against-the-LCD backlight will look though, or how easily it could be made.

Flat/thin light source? Did someone say LEDs? But seriously, it might be worth a try (they're still pretty experimental now). Check out: http://www.lumenlab.com/forums/index.php?s...0435&st=900
If that looks like something you might want to try check out the group buy link in my signature.

Folding the light path wont do anything at all to the distances. The distances just get... folded. For instance, if you need the triplet to be 600 mm from the LCD and you stick a mirror 300 mm from the LCD the triplet will need to be 300 mm from the mirror.

If I fold it that will decrease the overall distance between the triplet and the floor though, correct? I'm trying to keep the overall height from the floor to the projection surface as low as possible, ideal would be 2' but that doesn't seem possible from what I've read so far. The best I've been able to do in focalcalc is: split frensel, 17" screen, 180mm triplet, 317mm frensel fl, 20mm frensel gap, 287.5 lcd to frensel, 1.56' frensel to projection surface for a 30" picture. With a straight through design that's already 2.5', without the lamp & ballast. I understand the "end-to-end" distance can't change, but was hoping a folded design could cut down on the "floor-to-screen" distance. I wonder if I were able to find a TV that would be "strippable," so far as I could move the control board out of the way enough to point a wiimote through, if I could just it's backlight from a further distance? Probably still wouldn't be bright enough, though, even in a fully enclosed box... There has to be a way to do this, I'll keep looking

You could make it like a rear projection TV, but laying on its back.

Even the "Traditional" Method will put the screen 19" or so off the ground.

Check out the Rear projection forum. Short throw is all they think about over there.

Wow I am SO glad I found this website and this forum. A friend and I were just talking about doing this earlier today and we have a lot of "free or donated" materials to use. My question at the moment is, how do I go about getting started? I realize that is a really lame question.

But after reading through a lot I have a fairly tangible idea of what I want to do. Id like to use some LCD screen's we have from older laptops and try and create a giant table top screen, with the IR Wii Remote functionality discussed. I understand the Wii Remote part.

What I am thinking of though.. is what would I use for the actual table top? To capture the light and display it so it doesn't just pass through and shine on the ceiling?

Eventually I would like to hook this up to something like a mac mini and make the whole table enclosed underneath with one of those new apple aluminum keyboards or something laying flush with a smooth black surface :-D

Found the wii project here. http://www.cs.cmu.edu/~johnny/projects/wii/

If your using a 30" LCD do you really need a point source for your light? A row of bulbs with some sort of diffuser might do the trick.

wow... nice. Other people have the exact same idea! using the wii mote setup too! also it can be done using total internal reflection with IR through thinish transmission medium.
and using just a webcam with an IR thru filter (like the "black" plastic on the wiimote)

anyhow... im trying to work out the optics for this set up as a coffee table... it's tuff.
picked up a crazy but VERY nice short throw lens off ebay 12mm focal length.
Infocus shortthrow lens
got it for 3 bucks... ya went for 1500 new. not sure il get it to work as is... but compounded lenses are take apartable with tools.

(ebay is great resource if used wisely. waiting on a research grade VR visualiser i got for 450 shipped... costed $95000 @ 8 years ago!)

an even cooler use (what i want to build) is a reactable. Reactable

Will update with any progress I make.
got lots of projects going on... but want this one done soon so hopefully it doesn't hit the "time left till completion approaches infinity" pile.


new here so nice to meet all

cheers - mars

I'm planning on doing a multi-touch coffee/dinner table also. I found very useful info from TBeta. Once the RoGR gets here, I'll create a nice cabinet for it. I imagine some linear actuators to raise the table to become a dinner table with side extensions for more table area. Perhaps another actuator to tilt the table to some degree to use it more like a drafting table. I was thinking of using one of those micro projector on glass as the screen.