[Alex] sent us this project he’s working on where he’s building a phototransistor based multitouch input system. Though many people have built systems with phototransistors, most of them are quite large and very sensitive light and dark variances. [Alex] has done some fancy background subtraction through software. He believes his is the first to do this. As you can see in the video after the break, it seems impervious to the lamp he is moving around, and still fairly sensitive to his hand. We’re curious to see where he takes this one.