I came across this project on YouTube and am trying to build basically the same thing, but I can't seem to find a code or schematic for it anywhere. I'm using this for a school project, so if anyone could help me out I would really appreciate it.
The display is a DMD by freetronics. There is a library and examples on their site:
The laser sensor is just a photodiode which acts pretty much like any other switch. The only thing that is left is the stopwatch code itself
http://forum.freetronics.com/viewtopic.php?f=6&t=710