I had a German exchange student living with me last year who was a musician and I was trying to get him interested in electronics so we decided that a laser harp would be a good project to build.
Instead of totally reinventing the wheel, I did some searches online and came across a few designs like
Jean Michel Jarre's framless laser harp but this looked to be too costly with the laser used and the galvanometer mirror set up.
And then I found and was impressed with Chris Ball's Laser Harp Mark iii design on Youtube:
http://www.youtube.com/watch?v=FKAZhhargLg
I contacted Chris and have been creating some documentation on how to build one for < $300.
Mine is very similar to the one that you see in the link provided except I chose not to use the lighted buttons and my frame is made of PVC pipe instead of the fabricated wood frame that he uses. This was to keep the costs down and to make it easy to build. Also, using a PVC frame keeps it light enough that I added a brad hole nut on the bottom of the case so that it can be mounted to a camera tripod...
Also, I did layout a PCB for this with through hole parts to make it easy to build and salvaged the lasers out of some laser cat toys that I bought at Walmart...
I hope to wrap up this documentation up in a few weeks once my harp is totally operational.
Because this is Chris's design, you will need to contact him for more info as I respect his work on this. I will leave it up to him if he wants to share the documentation that I am preparing for this device, but he mentioned that he wanted to take my documentation and maybe turn it into an instructible...
Cheers
BTW: I figured that the harp would be connected to the keyboard MIDI-IN, just wasn't sure if there was anything special I needed to do to set up the keyboard to accept the MIDI input... thanks