The projector will shine on the chalk paper and the acrylic plate, it is important that only the ‘blob’ is identifiable and there may not be disturbance like the image of the projector. Therefore, there has to be a filter that only flows the signal from the infrared signal and blocks everything else. For this, I have searched for old photographic negatives that are actually failed. Usually there is a small piece of black at the end of a photo film. It’s a small piece of failed negative and that’s exactly what is needed for this filter. I have put 4 or 5 pieces on top of each other and so attached it on the lens of my webcam. This way you get a total black image (even if you put a spotlight of 100watts on it) and it passes only the infrared light or ‘blob’.

Before I began with the construction of my table, I have tested the basic elements of the FTIR technology with my (old)webcam and a simple TV remote control, which is equipped with a basic infra-red led. First I had to know whether my webcam could detect infrared light because usually webcams have built in a filter that’s blocking this light. Fortunately, I had found an old webcam who still wasn’t applied with such a filter (later-on I discovered that it still had one and I had to break this filter before I could use it). The set-up was pretty simple. I had the webcam image of my remote stream while I was running Touchlib on my computer. This program calculates the ‘blob’ activity and calculates the presence on the x and y-axis. Actually, this is the engine behind this technology. Through a small script, these signals are transmitted via a localhost to flash.

Later on I discovered that the blobs with my fingers on an acrylic weren’t visible, so I decided to remove the IR-filter from my webcam with a positive result. I had to open this webcam and had to break al small piece of glass that consists the IR-film, just in front of the CCD-ship. Very tricky, but it worked.

The most known tabletop at the moment is the Microsoft Surface. This device was launched in late 2007 and has a price tag of €5000. (watch the promoclip here) I would like to had this device on loan but this was unfortunately not possible. So I decided to build an own prototype which I can use for my interfaces and testing purposes. As a ‘newby’ in this technical field, it was a big challenge for me to build this. After research, I decided to go for the FTIR technique (Frequently Total Internal Reflection) whereby an infrared light is horizontally sent true the acrylic plate and scatters trough the plate. A camera in the box below, which is equipped with an infrared filter, captures the image of the acrylic plate, and therefore sees touches with the finger on the plate, so-called ‘blobs’. A projector puts a screen on a chalk-paper underneath the acrylic.

Before I began, I first calculated and measured out everything to prevent surprises. I used the following ingredients for my tabletop:

- Acrylic glass 60cmx45cmx0,8cm ordered at a company called BAG www.bag.be
- OSRAM SFH485 leds ordered at Conrad www.conrad.be
- Plastic halve rails bought at BRICO and glued together with TEC7
- Gridpaper with a grid from 400 to 1200 bought at a local car distribution center
- Electronic wires and resistors bought at a local electronics parts shop
- An old webcam
- Old photo-negatives who are not properly developed and have a black look
- A computer-source with a 12v AT-connector found in an old basement
- Wood, glue and a lot of screws
- Mirror found on my attic
- Beamer which I had at home

In recent weeks I have been working on my first prototype for my masterthesis. It consists 2 stages: First, the building of an interactive table prototype and secondly, creating an appropriate interface on a pre-school level. After a big research on interactive tables, I started building a personal tabletop with a FTIR-technology. The following days I will explain here with text and pictures how I came step by step to my current prototype that’s still under construction. If you want more information about my masterthesis or my motivation for this project, please check out the “about-page” in the upper-right corner. Stay tuned!