Tuesday, 23 March 2010

Building a FTIR Multi-touch Tabletop in Multimedia University, Malaysia

The project was started due to the limitation of a Wiimote-based multi-touch tabletop developed by previous final year project student of Faculty of Engineering, Multimedia University. The Wiimote-based multi-touch tabletop requires the use of infrared pens instead of direct finger touch. After gathering necessary information from the NUI forum, a FTIR multi-touch tabletop is decided to be built. FTIR refers to the Frustrated Total Internal Reflection effect of the infrared lights enclosed in an acrylic surface which is the crucial ingredients of the multi-touch sensing.

The wooden frame of the Wiimote-based Multi-touch Tabletop is being reused for the new FTIR Multi-touch Tabletop after some modifications including structural enhancements and paint spraying.

Firstly, the display/projection layout has to be designed. Based on the Projection Calculator Pro, the projector used in the project, the Dell 1409x projector, requires a throw distance of 1.43m for a projection with a diagonal size of 34 inches. Due to the limited space under the tabletop, there will be not enough distance for the projector. There two mirrors have to be added to virtually increase the throw distance. The design of the projector plus mirrors layout is based on this forum post in the NUI Forum which is mainly just folding papers. Google Sketchup is used to visualize the layout.

Tracing paper shown below is used as the projection screen.

For FTIR, a compliant surface is required. In my opinion, it is mainly to make the dragging of the finger's touch easier as dragging on the bare acrylic is not comfortable and depends on how wet is the finger tip which is highly unpredictable. The compliant surface selected is the textured silicone layer and is created using the Tinkermans Method. The Xylene which can only be found in large ACE Hardware store is used to dilute the silicone so that it can be easily rolled over the tracing paper.

The projection screen/compliant surface will be layered on top of a 8mm thick 22" x 27" acrylic and the acrylic will be surrounded by 60 infrared LEDs (SFH 485) bought from RS Components Malaysia. The LEDs will be held in LED holders in 4 sides of aluminium U-channels. The LED array layout is designed using LED series/parallel array wizard based on the specifications of 12V source voltage (from PC power supply), 1.5V LED forward voltage and 100mA forward current. For the number, the value being keyed in was not 60 directly as the design will not be suitable, 16 was keyed in for the long sides and 14 was keyed in for the short sides.

The infrared camera used to detect the infrared blob is a modified PS3 Eye Camera bought from Peau Productions.

Additional items are the CPU which runs Community Core Vision CCV 1.3 to process the video input from the IR camera, to run the multi-touch applications and to output the display to the projector, as well as to provide the power to LED arrays and a cooling fan for dissipating the heat from the projector.

The final look from above after a wooden frame is placed on top to protect the IR LED circuits.

The FTIR tabletop was showcased in Multimedia University Open Day 2010 and a lot of kids were having fun playing the MT4j demo on it.

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