How to build a multi touch display

Ok, this is my way of giving back to my readers. I guess you might want to know how to build a Multi Touch display. Well first you need time because this stuff doesn’t come over night. It takes time to get all the parts and setting them up. So if you want to build a multi touch table over night forget it. Well at lest not your first one. So with that out of the way. What you need is to get some materials together I made a list for you.

1. Plexiglas
2. IR Leds
3. Power supply
4. Projector
5. Wire
6. Soldering iron
7. Screws
8. MDF board
9. Malar, tracing paper, rear projection screen ect..
10. Tape
11. Webcam
12. Computer
13. Mirror
14. Screw gun
15. Jig saw or Skill saw

After you get all the stuff you need together. Find some space to build your project. Basements and garages work great for this kind of work. Also remember to take notice of the doorways if you plan on building a one time deal. I used screws so I could take apart my multi touch table when I was traveling. This works nice.

Here is a drawing of the DI multi touch table.

This is just a rough idea of how it will go together. The projector can be pointed up if you have a short throw projector. I do not so I have mine pointing down towards a First Surface Mirror. You can use a reg mirror you can find at a local hardware store, but you might have a screen door effect on the display. FS mirror takes care of that. I found mine in a dumpster at a local TV repair shop. You can look on eBay for one. I saw some listed there.

The first thing I did was build my box. I used 1/4 inch MDF boards for the sides and bottom. Also 1×1 for the frame. My box is 37 inches tall. This works good because my screen size is 30 x 36 inches. My projector needs about 6-7 feet to make the size of the screen. I used screws in 1×1’s to frame it. The top of the box is lose so I can’t open and shut it. This helps me get to the projector. Once you have the box built you can start on the IR LEDs. I used 80 940nm IR LEDs. I have them powered by a 12v wallwart(power supply) They are in strips of 20. To build your own strips you can go to this website

http://ledcalc.com or http://led.linear1.org/led.wiz

They have a online calculator that will help you with your LED set up. Once you get your strips made they need to be placed on the bottom of the box on all four side. They need to be faceing up at the screen. You might want to use more. The way I have mine set up right now I can only use it in the dark. I think about 60 more should do it. It would be nice to have them on a day time on off switch.

After you get the LEDs set up. You should set up the web cam and place that also on the bottom of the box, but this time in the middle. Now you need to address the Plexiglas. You need some paper or rosco grey. I use vellum. You can get it at you local art store. I placed the vellum under the Plexiglas. This way you don’t get hot spots. Now it’s time to test out the computer program to set the calibration. You will have to move the web cam until you get it in the right spot. Also you will need to get a wide angle lens for the cam to see the whole screen. Well if you are using the Fire-i web cam like me. If all goes well you can mount the projector. I have mine facing down at the FS mirror. This will take some time to set up.

Once you get the projector set up. You can test it out again on the computer to see if it has worked. If all goes well you should have a MT08 NICEMINDS Multi Touch Display.
more to come…

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