This water instrument looks like fun to play, doesn’t look like the easiest project to build but I might have to add it to the list.

“It is really very easy. I do not claim to be an electronics professional, or even know anything about anything. The laser shines through the water in the dish, and LDR’s on the other side respond to the position of the laser points (whether they are fully on the LDR or not).

By using a voltage divider for each laser (that is where the 100KΩ resistors come in), the physical interface can see changes in voltage (as opposed to just resistance, as caused by the LDR’s alone). The LDR connects between ground and the analog in channel. The 100KΩ (pot) or similar connects the analog in channel and +5V. That is it. Repeat for all five or six lasers.”