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Sunday, June 10, 2007

DIY FTIR interface UPDATE

(What's an FTIR interface? read this)
I've been collecting parts to build a budget FTIR multi-touch interface:

$25.00 Picture frame from IKEA
$50.00 vintage briefcase-style overhead projector
$50.00 Polaroid PolaView 3000 lcd overhead panel
free misc wire, power supply, and electronic bits
$25.00 19x19 plexiglass sheet, 1/4" thick w/ edges polished
-------
$150.00

Need to get:

- 20 infrared LEDs
- led pcbs (or just hand-wire them?)
- Fire-i™ Digital Board Camera firewire w/ IR and changeable lenses
- 4 telescoping legs
- diffuser layer / compliant surface (tbd)



So I'm thrilled with my eBay purchases. I skipped the modern projectors (LCD projector = too expensive, new o-head projectors = too flimsy) and found an old brief-case style by Buhl that looks like it was made in the 60's or 70's. $30 plus $20 shipping - such a deal. It folds up cleverly into a textured red and black tolex case, has dual bulbs, temp sensitive fan, everything is made of metal and it works beautifully. I found an inexpensive lcd overhead panel display that sits on top, making a very nice big monitor image on the wall. For the FTIR I'll need to get the reflector close enough to project a small (19" wide) image that will fit inside the frame yet still be in focus. It might require lengthening the head adjuster track but not by much.

The plan is to add 4 adjustable legs to the picture frame to make it into a tall tabletop. The projector and lcd will lie "on it's back" pointing up through the picture frame and plexi, at a distance of around 3 feet (tbd). The plexiglass will be covered by a piece of translucent material (tbd) to catch the image. Around the edges of the plexiglass will run 4 rows of infrared leds, shielded so as to only allow IR (infrared) to enter the edge of the plexi. Next to the projector lens, also pointing up, will be a firewire camera that has been modified to see only IR light. Fingers or objects placed against the tabletop, by "frustrating" the internal reflective properties of the plexiglass, will reflect blobs of IR downwards towards the camera. The camera will be hooked up to blob-tracking software (lots of openSource code/tools available on the web). The blobs will control a music interface (tbd). The resulting image is projected up through the plexi in normal (non-IR) light to display against the diffusor.

Right now it seems like the biggest challenge will be sourcing/making the correct material to use as a diffusor, see: How to create a Zero-Force Compliant Surface for FTIR Based Multi-touch on a Back Projected Table

Updates:

1) It seems someone on the NUIgroup forum has discovered that the bottom of a stock Dance Dance Revolution pad makes a good translucent/compliant surface. Hm, we have one of those in the closet!

2) I am also exploring the possibility of using the IR projection method instead of ftir. MS Surface uses this method. Basically, instead of using internal reflection of the plexi, they simply shoot ir up from underneath and catch the reflections of things that are touching the table. Not as precise as ftir but it seems to avoid a lot of the trickier requirements, especially the compliant surface issue. Also you can use regular glass, and off-the-shelf IR beamers are readily available (in fact they sell several "night vision" cameras that have built in IR beamers).

Lots o' links on the subject here: My Delicious FTIR DIY



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