The second multi-touch table, that I have built is called The Virttable, which stands for Versatile Illumination Research Touch Table.
This table is the property of the department for Design, Computer Science and Media (DCSM) of the Wiesbaden University of Applied Sciences, which provided me with the money for the components of the Virttable. (Actually, we had student fees for a short time in Hessen/Germany. From a part of these student fees the Virttable has been built. Thank you, dear students!!! There’s no cent of public money in the Virttable.) Amongst others those parts include:
- a Panasonic PT AX 200 projector
a Unibrain Fire-i Firewire camera
- a Pointgrey Firefly MV firewire (mono version) camera
- a B+W infrared filter 092 (low-pass, lets transmit 90% of infrared light above 730 nm)
lots of Osram SFH 485P infrared LEDs
- 162 Osram SFH 4550 infrared LEDs for FTIR illumination Their min. radiant intensity is 400 mW/sr at 100mA while the min. radiant intensity of a SFH 485P LED is 4.5 mW/Sr at 100mA. Taken the LED’s half angles into consideration (3 for the SFH 4550 resp. 40 for the SFH 485P) this means that the SFH 4550 has around 6.5 times more light than the SFH 485P.
- Six high power infrared LEDs with 4 led’s on one dye (Aculed VHL IR 4-chip High Power LEDs) for Diffuse Illumination
two panes of acrylic glass(I burned the surface of the second pane, a Plexiglass EndLighten pane, while trying to apply a Lexel/Toluene dilution on top of it)
- A standard acrylic glass
- MDF boards for the box
The computer that I have used in the Virttable is my Mac Mini.
The main goals for the Virttable have been…
- a cheap setup
- It can be put into a closet when it is not needed
- It should be easily transportable in order to be able to exhibit the Virttable and innovative multi-touch software on it on fairs
- All parts should be easily accessable in order to test different illumination techniques and to make the Virttable maintainable.
- It should be usable with multi-touch and object input
The first point has been achieved: The whole setup did cost around 2000 Euro.
The second point has been achieved as well:
The third point has been enabled by the small form factor of the Virttable: the Virttable is 70 cm high, 74 cm wide and 54 cm deep. The wheels underneath the Virttable’s body make it rollable. The handles to the sides make it easy to carry and to attach tension belts in the trunk of a car.
The fourth point is provided by the lid and the hatch: The LEDs and the acrylic glass can be accessed via the lid and the projector, the computer and the camera can be accessed via the hatch.
The fifth point has been more complicated: A DI setup would have been easiest to support as well multi-touch as object interaction. However, DI is not as efficient as FTIR and thus we decided to make a hybrid approach by applying a mixture of DI and FTIR:
On the left there is no illumination. On the second photo the Virttable is FTIR illuminated. The third photo shows only DI illumination. The right photo shows the hybrid mixture of FTIR and DI: Touches are bright and precise and the fiducials of the objects are evenly lit.
We have also tried the DSI technology like it has been described by Tim Roth by using a Plexiglas EndLighten acrylic glass pane but the results have not been satisfying for us. Anyway, now our EndLighten has been burned on the surface by the application of a Lexel/Toluene dilution. However, we sawed some fiducial props out of it ;)
In the Virttable DI is provided by
a few aluminum bars equipped with Osram SFH 485P LEDs six high power infrared LEDs glued to star-shaped heat-sinks directly underneath the tabletop (see images above). The bars are diagonally emitting their light onto the underside of the acrylic glass. Each LED is covered with a piece of masking tape to disperse its light evenly and to prevent hotspots. The high-power LEDs are emitting their light to the side of the Virttable’s body, which diffuses their light to prevent hotspots. With this DI technique fiducials like those from the reactable can be used in this setup.
FTIR is provided by Osram SFH
485P 4550 LEDs in aluminum pre-soldered bars, which emit their light into the polished edges of the acrylic glass.
You can see some pictures of the LED setup here:
Some pictures of the whole setup:
Read this article about our Rear-Projection Mirror Fixture System for Multi-Touch Tabletops