This Instructable is the simple version of the MaKey MaKey Monome, an electronic music instrument designed to be easy for kids and beginners to reproduce (and iterate upon!). For more information, feel free to check out my website.
Get the Code
Open Scratch monome program.
Copper Tape Grid
Alternative: Conductive Paint Grid
It's possible to build this instrument using conductive paint following the same process. Make sure, however, that when the columns cross the rows, the paint from each doesn't touch.