You may have noticed that digital cameras, including webcams, can detect infrared lights. If you point an TV remote controller to a recording camera, you can see a white spot of light coming from the remote.
My idea was to use this light to control the cursor on a computer screen, enabling me to draw on screen using the remote controller.
On the other end of the remote controller system, i.e. the remote received, we usually have a redish transluced piece of plastic. This plastic is a IR filter, that filters out all the other light sources, so the received behind it receives only the IR commands. So, I chopped a piece of this plastic, put in front of the webcam and... Voila! The camera became an infrared position detector!
Now, with a simple dedicated software, I can detect the position of the remote, related to the borders of the camera image. With a simple rule of three, I can detect where the user wants to draw.
The video below shows the result of this experience. Sorry, but it need to be seen on high resolution, to compensate the dirty-cheap ilumination i've used during recording.
The webcam I used was so old that I can't event find its drivers for Windows 7. I'm planning to teste again on a new - AND FASTER - camera.