OK, so we saw and played a bit with the MaKey MaKey at the Bay Area Maker Faire and it’s a fun little piece to play with. I have a fifth-grade teacher in the family, so the plan is to enrich the class room a bit;-)
I always want to look a bit behind the scenes to understand how things work. So after a bit of google-ing, I found that it should not be too hard to implement a DIY MaKey MaKey with an Arduino Leonardo, some resistors and some alligator clip cables. I did have the Leonardo and some resistors (1 MΩ – a little bit smaller than the 22 MΩ suggested around the web) and found the cables at the local RadioShack. I found the original(?) sources in the sparkfun github (https://github.com/sparkfun/MaKeyMaKey) and tried to adapt it a bit. I pushed my changes to a fork: https://github.com/mw46d/MaKeyMaKey. Overall, the setup worked pretty well, I guess not as sensitive as the original, but OK for mostly parts-bin parts.
So, overall, I would suggest to buy the original MaKey MaKey when you’re interested in something like that or want to attract kids to electronics. I don’t think, the DIY version would save you anything. It’s just a way to see what’s `in the box’ 😉 It’s some thing to read specs but it’s a different thing to be able to create a working setup.
As always, have fun exploring;-)