Bounce detector


I would like to make a bounce juggling piano like in this video: - YouTube, I think this is fake.
I would like for it to be just some thin sensors or something I can lay on the ground and bounce the balls on? I cannot use wood or cardboard because that will ruin the bounce. So I am looking for some good sensors I can use for this that is easy to read from the arduino. I have been thinking about piezo-elements, but I am not sure how to separate them unless I have separate blocks for the separate keys, but then the balls will fly away if they hit the area between the different keys. Do you have any ideas for sensors for this, the keys have to be quite a bit larger than the balls.

I am thinking about using the new Music shield from Sparkfun to generate the different sounds.

Could it be that the notes are pre-programmed and the 'piano' only detects a knock and triggers the next note?

I guess it only detects knocks, but I want to create a "real" keyboard that requires you to hit the correct keys. Ideally I would like some thin plastic I can lay on the ground and read with a digital pin if it is triggered or not, but I guess that is hard.

One of the touch-screen technologies sold by 3M uses a piezo sensor in each corner to detect the arrival time of the deflection waves caused when the glass surface is pressed. Perhaps you could use two piezo sensors on the ends of a rigid 'keyboard' to sense where along the board a ball bounced.

The Arduino can sense pulse lengths in microseconds. The speed of sound in glass is 4540 meters per second. That's 4.54 millimeters per microsecond. Seems like good enough resolution to implement a piano keyboard. Sounds travels faster in aluminum so you'd get less resolution.

Good luck!