Wandering through the MAKE Flickr pool the other day, I saw what appeared to be custom-made game controlling guitars. Taking a closer look, I saw that they were actually using Scratch Sensor Board controllers. The Scratch Board is a neat device with four inputs for custom built sensors. On the board itself are a potentiometer, light sensor, sound sensor and a push button. Your program can look for user generated input on each of these, which can change your program or game based on the sensor input.

Chris, whose photostream the picture was in told me a bit about the project:

Last year at Make Day at the Science Museum of Minnesota someone had created a scratch controller using a wet sponge. The PicoBoard measured the resistance across the sponge, which was varied by squishing the sponge, and the Scratch program used the resistance value to control a musical output. It was messy & didn’t work particularly well, but it was a clever idea that got me thinking about what other materials could be used in unexpected ways in a Scratch controller.

At the same time, I was volunteering at Expo Elementary in St. Paul, helping kids learn programming with Scratch and was thinking of ways to pique the kids interest in bringing the physical world into their Scratch projects via some PicoBoards the school had recently purchased.

Thus was born the idea of the Scratch guitar controllers.

I experimented with a bunch of materials trying to find a resistor with the properties I needed, including VHS tape, tin foil, nichrome wire and conductive thread, to name a few, before I stumbled on conductive foam. The foam is normally used to ship delicate electronics & ICs because it prevents the buildup of static electricity. It costs just a few dollars per sheet. I used the 1/4″ thick variety and paid about $7 for enough to make more than a dozen guitars. Other materials include scrap MDF, old futon slats, empty plastic film canisters (free from any place that still develops film), metallic tape (from any hardware store) and speaker wire.

The mechanism is simple: one lead is attached to one end of the neck of the guitar, which is covered in the conductive foam. The other lead is attached to the film canister which is covered in metallic tape. The player puts the film canister on her finger & places the canister on the guitar neck. The position on the neck determines how much
resistance is measured by the PicoBoard. Any Scratch program can then use that resistance value (which is normalized to between 0 and 100) to control whatever they want.

And of course, they had to look good, so I made them in the shape of the iconic Gibson Flying V and the Gibson Explorer. I cut the bodies with a jig saw based on a template I made in InkScape & printed out on paper. I’ve uploaded the SVG files to Thingiverse.

Wondering about Scratch and how to get started? You can check out the article in MAKE Volume 21, you can browse the support section of the Scratch website, or you can just download the free software and mess around with it.