Multitouch is cool, but its also becoming cheaper and more accessible thanks to the work of folks like Jeff Han, and communities like the NUI Group. Of course, devices like the iPhone have made many of these ideas mainstream, but not everyone wants to do multitouch on a tiny display. Multitouch surfaces have great potential as intuitive, multi-user, social computing environments.
I wanted to build a small, portable touch table that can be used by one or two people. The display surface is the horizontal table top, and people "play" at opposite sides. Its a bit like those old-style sit-down arcade games, though for the life of me I can't remember any games that were simultaneous two-player. Both users can touch the surface, but also maintain face-to-face interactions across the table. The device is designed particularly with kids in mind, for play between two children, or between a child and parent.
One of the main motivations for building this was to come up with an aid for educating kids as young as 2 years old. Some children struggle to learn stuff that most of us pick up effortlessly, like how to talk and interact socially. Very early intervention can make a huge difference for kids with conditions like autism and other language disabilities. While therapies like ABA can be very effective, they can also be gruelling and intense for both the child and the therapist (usually, the parent). If we can simplify this process using engaging interactive games, and by sharing and building resources collaboratively on-line, this has to be a good thing. More on this later...
There are many ways to do multitouch sensing, but the basic idea used here is to measure pressure optically with a camera. A great place to get some background is this thread at NUI group. Since I wanted to do fiducial tracking, I chose an approach based on diffuse illumination. This means that the display does not rely on a very tight coupling with the surface to illuminate objects.
I wanted my table to be small, cheap and robust, so I chose to use an LCD rather than a projector. LCDs don't transmit diffuse IR very well, so the illumination is provided by the surface itself (Diffuse Surface Illumination, or "DSI"). A special type of acrylic (called "Endlighten" or "DLux", depending on the manufacturer) is used as the top surface of the display. This has embedded particles which reflect light out the surface when lit from the side. This material is often used in display signs.
- LG W2252TQ-PFT 22" LCD Monitor
- Unibrain Fire-i B/W Camera
- 2.5mm focal length lens
- Mac Mini
- Firewire 9-pin to 6-pin cable
- IR pass filter 850nm
- Acrylic panel, 10mm "Endlighten"
- IR LED strip illuminator
- Power supply, 12V for illuminator
- Misc hardware: MDF, wood screws, nut/bolts, square dowell, 1" aluminium angle, steel strip, T-nuts, hinge, construction adhesive, silicone sealant, magnetic catches, gaffa tape
I found a lot of useful information on-line, but much of it was fragmented. So here is an illustrated guide to how I built my system. Click on the images for higher resolution versions.
Continue reading ‘LCD Multitouch Table Mark 1’ »