Multi-touch Table

Ive looked around for a good in depth instructable on how to make a muti-touch table and I didnt find any I liked. I hope you enjoy making your very own multi-touch table and that my instructions are clear to you. This uses the FTIR (Frustrated Total Internal Reflection) system to track fingers on a screen.

Here is an important list of materials you will need to construct a multi-touch table.

• Projector (Ebay $70)
• Clear 100% silicon (Homedepot $5 )
• Paint thinner (Homedepot $5 )
• Foam paint roller (Homedepot $2 )
• Vellum drafting paper (Art supply store $10)
• Infrared LEDs (Futurlec $15 for 150)
• Plexiglas (Surplus store $2.25 sq-ft)
• Angle Aluminum (Homedepot $13)
• Computer (Had one laying around Free)
• Web cam (Thrift store $7)
• Mirror ($5), I used a first surface mirror. This will make it so there isnt any extra reflection in the mirror.  

You need to get a projector with a fairly short throw distance. I got mine off of ebay for about $70 with 130 hours on it. If you already have a projector ready go to projectorcentral and find your projector and use the throw calculator to find the size of your screen and how far away it needs to be. This will be the measurements you will use for the screen size.

The Plexiglas will need to be fairly thick for the LEDs to fit into(around 3/8 in). I accidentally got blue tinted Plexiglas but it turned out not to be a problem. I cut my Plexiglas with about a 1/2 in extra on each side to give room for the LEDs and angle aluminum to go around. To cut the Plexiglas I used a table saw which worked great. Make sure to leave the plastic wrap on it until the very last moment!

Measure your aluminum to the length of the Plexi and add about 1/8in to it. Mine was 30in by 24in. Cut the aluminum to length using a hacksaw. Now with your aluminum measure and mark every inch along every piece of aluminum. Find the center of your Plexi and add a 1/8in to it for the thickness of the aluminum. Draw a line that high along the aluminum. Where the two lines meet is where you will drill. I used a 3/16in drill bit with a drill press to make the holes for the LEDs. After you drill the holes they will probably have large burrs on the bottom. Use a file or a Dremel with a grinder bit to grind the burrs off.

The LEDs light up where your finger presses down on the Plexiglas. Now that you have the angle aluminum drilled its time to make the holes in the Plexiglas. Clap the frame together and set up a drill press so you can drill approx 1/4 in down into the Plexiglas. Just make sure the LEDs go all the way in. Once the holes are drilled on all four sides put the LEDs in the holes and solder them together in the schematic you have here is a LED calculator to help with the schematic and power supply. I used a series parallel circuit with 7 1ohm resistors and 1 68 ohm resistor for a 12v power supply. You can test the LED frame by plugging it in and looking at it with the modified webcam from step 3.

To make the silicon paper I used the Tinkerman method which is mixing paint thinner and silicon and rolling it on the paper. I did about three layers but you can do more. This creates a better connection with the Plexiglas so the infrared light can reflect off the spot you are pressing down on.

This part can be done many different ways. I made a frame that was about two in bigger than the LED frame on each side allowing a half in to cover the aluminum and 1 1/2 in for the wires. I used a router to cut a line a half in from the inside for the aluminum sticking above the Plexiglas to go on.

Set up the projector and the mirror so it lines up with the screen above. Download ccv for the calibrating and setup for the touch screen. Once its calibrated go to Tuio and find the right software for the computer you have. Tuio allows other programs to use the input of your fingers to move the mouse.I mounted the webcam on the top of the projector at first but there was some weird reflections so i angled it on the side of the box. Depending on the calibration of ccv you can have it very sensitive (tracks very light touches) or less (makes it so you have to push harder).

This is a fun toy to mess around with and a great way to show off your to all of your friends. I hope you were successful in your project. I hope to see how all of yours turned out, Thank you.