Picture of Interactive Multitouch Display
Between the Apple iPhone and Microsoft's interactive table, multi-touch displays are all the rage. This instructable will show you how to turn your lcd projector into an interactive multi-touch display table using a few cheap components readily available from the hardware store.

Here is a video of my display in action:

Step 1: Theory of operation

This multitouch display screen design is based on the description in Jeff Han's paper,

Han, J. Y. 2005. Low-Cost Multi-Touch Sensing through Frustrated Total Internal Reflection. In Proceedings of the 18th Annual ACM Symposium on User Interface Software and Technology

The figure below comes from his web site.

An acrylic panel is edge lit with infrared leds. When your finger comes in contact with the acrylic, it scatters infrared light out the back where it is visible via infrared camera. As long as nothing is touching the acrylic, very little of the light escapes, instead just reflecting around inside. Image processing takes care of detecting tips of fingers and relaying their location to application software. Since the camera "reads" the whole display in parallel, it is easy to detect multiple fingertips at once, even those belonging to multiple users. All this sensing goes on in the infrared spectrum, leaving us free to utilize the visible spectrum to display interactive software.

Since most hobbyists can't afford multiple projectors (i don't even own one, just borrowed it from dr.eel), my design uses a ceiling mount that swivels so that the projector can be used either in standard mode (say for watching movies) or can be aimed downwards, bouncing off a reflector and onto the multitouch display screen.

The screen itself can be constructed from hardware store materials and hand tools. Excluding the projector and modified webcam (commodity items these days), the only thing complicated is the software. Halfway through this project, I was happy to discover that there is thriving DIY community which has already undertaken the task of writing the image processing code and several cool open source demos which can be found here:


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sunnycanuck2 years ago
so it is now a few years later, do you still use this system? Any changes?
tcarr23 years ago
can you use this for surfing the internet?
rwhite183 years ago
you could make a cheap projector yourself by using an old lcd screen and an overhead projector. made one my self and works as good as a sony.
repurpose the LCD as you only need the screen itself. not the lighting that came with it. the overhead projector supplies the lighting and can be adjusted for short range use. you would have to look it up on the web for details of the build.
Well I found an actual projector on craigslist for $150. I am also using LLP (http://www.instructables.com/id/How-To-Build-An-Optical-Multitouch-Setup-FTIR-Re/step3/Laser-Light-Plane-LLP/). What kind of acrylic is used for front projection?
redinc5 years ago
Is there a maximum number of fingers that can be used on a multi touch screen?
squiggy2 redinc5 years ago

no there is no limit to the amount of fingers you can use with a FTIR screen. the limits are

1. how many fingers you have - the average is 10

2. how many your computer can handle - the smoke demo especially uses a lot of processing power and the more fingers the computer needs to track and create effects for, the harder it will be.

Sorry, but the amount of finger cant be average as 10, because that means, more or less, that for everyone that have a missing finger, there must be one with 11 fingers, and if someone have missed 3 fingers, you will have someone with 13 fingers. the stabdar number of fingers is 10, but is not the average
It's true, 10 is the mode, but it was still a pretty funny response.
k fine my bad.
**'how many fingers you have - your average joe will have 10'
cheers copiesofcopies :)
Well... Since a much larger number of people tend to have 10 fingers that would bring the average up. No need for someone with 11 fingers. If you have 20 people with 10 fingers and 1 person with 9, the average is 9.95 fingers. Close enough to 10 in my opinion.
well, technically modally everyone has 10 digits, but only 8 fingers. Two Thumbs are quite common I hear...
jadronx 90mp113 years ago
i thought everyone had 20 digits.....just sayin
would a set up like this work?
yes but you need a short-range projector. . which are more expensive.
what if i made a serese of magnifying glasses to shorten the projection?
My thought was using some form of modified LCD/OHP setup... that way, you run most of it gutting an old laptop, and just using the lenses to project the screen directly...

I'd love to see this as a modified gaming table
I had roughly that idea, just jazzed up a bit. My idea was to use an old table or build one from wood, then give it a touchscreen and LCD. I would then put computer hardware into the base of the table, I would try to make it like the touchscreen table out of Quantum of Solace:

touchscreen table.png
M0HIZ M0HIZ3 years ago
One question, though: is there general rule of thumb for how many LEDs should be used per inch or perimeter or something, I mean, how do you decide how many to ue? Thanks!
I was thinking as a workshop table, but using the gutted laptop is a good idea and then creating a custom interface or something, that would be epic!!!!
You'd have to elaborate on what you meant by workshop table - all I can think of is like an actual work bench, covered with sawdust and small tools.. hahaha

I was thinking for running paper and pencil type games - being able to use an interactive table map that was solid enough to play on. There are a lot of programs out there that can be used (not in this intended way of course) to handle map generation and cloud of war effects.. but it would be awesome to do it with a table
Interactive project layouts, autocad renders, that kind of stuff, not like a wood shop table or anything.
that sounds brilliant.

I wonder how additional surface pressures/noise would impact that? like paper or white board markers, or rulers for example..

or, in my case, dice on the table surface...
Though my understanding Is minimal of how this works I believe that the only problem would be drawing on the surface with dry erase markers because you would be pushing on the "screen" maybe a program that creates a button in the corner that can turn off it's sensitivity on all but te button. I'm not sure how papers and things lying on the surface would react but it would depend on the weight of the object and the sensitivity of the system...it would have to be experimented with, unfortunantly I have neither the time or money to do so, with school starting it makes it impossible for me to tinker or in some cases think straight :-(
aagrlp6403 years ago
Before nothing thanks for this web page, its awesome, i have a question does it have to be of a specific size or it doesnt matter? for example of 32" or even 60", obviusly with a good projector and more leds on the sides
epicnoobpwn3 years ago
Could I use a large tv (rear projection/flatscreen) instead of the projector. I would have the transparent acrylic touch panel on top of the screen.

By the way, where did you put the ir camera? I never saw you mention where to mount it.
eluna33 years ago
How much are the thicknesses of the 2 acrylic?
Tarzan883 years ago
¿que tan separados están los LED's? ¿son 2 acrílicos verdad?
lshoesmith3 years ago
Hi there.

Im just wondering how this method of input acts in 'normal' computing e.g what can be achieved with a mouse pointer.
Basically, does it play well with programs that are not designed for touch or multi touch like word or Opera internet browser?

Thanks muchly :)
hi :) i am thinking of making this. i was just wondering how thick you reccomend the acrylic to be? thanks
zack2474 years ago
hey, i was wondering, could this work with a LCD screen?
i have a 15" one and i want to repurpose it, is there any way i can convert this to work with a LCD?

the only problem i can think of is the webcam being able to see the infrared light, especially since the LCD would need lighting too. (obviously not the original backlighting system, of course)

any help would be great, thanks!
dancmarsh4 years ago
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.
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
psalanoa4 years ago
how do you press the holes into theextruded aluminum c-channel?
Tangoforce4 years ago
Nice music man, what is it?

Oh great project too.
10fellowsd4 years ago
not the acer x110 its the best
softlux4 years ago
Sound’s good. Just one question for you. Can your multitouch recognize an object such as a glass resting on the surface? Thank you!
abadfart4 years ago
couldn't you just set the projector to rear project and put it under the desk
JamCat5 years ago
  I used to work in a plastics shop, and I guarantee the best options for nice clear edges are flame-polishing or clothwheel-wax buffing (but as buffing is pretty straightforward, and similar to other media I won't go into any tips)...
Flame polishing is really the best, and potentially fastest, but you should really practice on a similar thickness scrap first because you risk burning if you move the flame too slowly. I recommend using an oscillating power sander with 200 grit, then 600 grit til the edges are silky smooth. Then use a MAPP or hotter (for best results, we even used to use oxy-propane smallllll tip) torch to *QUICKLY* run the furthest tip of the feather of the flame around the edges at a backwards angle (so the cone is pointed opposite the direction you are moving) - after all dust and masking is cleared from the edges. You'll see the hazy sanded area turn clear and reflective very quickly if you are looking at the right angle.
If you miss a spot, or if some deeper sanding scratches remain, you can retouch with quick swipes keeping the flame even further back; if you burn it (and its VERY easy to do if you don't keep it moving) just resand the edge with 600 grit, and use some soap and water with a cotton (or preferably microfiber) rag to remove any scuz from the faces of the acrylic sheet. NEVER USE PAPER TOWELS ON ACRYLIC - they have wood pulp and will scratch it, eventually turning it cloudy...
This will give you nice crystal clear (acrylic is of course clearer than glass...) edges that will transmit wayyy more of your IR light!
Good luck!
Would a soldering iron be able to do the trick? According to wikipedia acrylic melts at ~160c, and soldering irons tend to be able to break 200.
Hossein JamCat4 years ago
Dear JamCat
i know what i wanted to ask is out of line but believe me i wouldn't ask if this was not my last chance .
I really really need to have the PDF version of this multi-touch screen here coz i took it as my major project and i have to build it in a week time and to be honest i don't have the money to be a pro member and since i'm a student i don't have any visa card as well.
I was wondering to ask if possible can you downloaded it for me and send it to my mail i would mean a lot to me .
THANK you so much
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