Magnetic Casio

Magnetic Casio

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Hex Oscillator

Circuit_Bending29

In 2007, I found a huge pile of circuit boards covered in reed switches being sold at a criminally low price at my favorite upstate supplies haunt, P&T surplus. A reed switches is a wonderful little component nearing obsolescence in 2011. it’s a switch made out of two metal filaments sealed in a vaccuum tube. When you put a magnet over it, the filaments snap together and make a connection.

This action sounds like tiny grasshoppers when you listen to it. At first I was just excited to listen to the tiny clicking sound, but after having them in my life for a few months, I realized they could be used for as an expressive tool for circuit bending. A friend lent me his old Casio MT-240, a keyboard with a nasty reputation for circuit-bending. It even has primitive MDI capability!

Now, usually I kind of don’t like circuit bending, but that has more to do with the gestural limitations of tweaking knobs and switches than any electronics-geek elitism (which is, admittedly, a growing problem for me). But I thought that the idea of controlling the bends by gliding magnets through the air could be an interesting comment on normal bending. I liked the collision of a fluid gesture as it meets the switches, which only give you a YES or NO output. Essentially, I see this project as a magnetic prepared piano—I like to use magnets of different sizes and shapes to make different music.

There are two Magnetic Casios. The first keyboard uses the prexisting traces from the reed board (cut in half) and wired to a DB-25 connector, so you can plug in the bending matrix as an auxiliary tool. At the time I liked to open up data switches in order to harvest the connectors already wired up and everything… only later did I realize it’s a lot easier to just solder your own connectors if you have the right tools and parts. When I opened this keyboard up again in 2010, I was pretty stunned at my ugly soldering job. It’s a miracle I pulled it off. While bending it, I sort of blew up the piano sound—I think from accidentally pulling off a circuit trace while the power was still on. Okay… pretty bush league move, but it actually made for a beautiful, if unintentional, mod, in which the piano is replaced by a clicking sound, which registers syncopated artifacts when combined with other tones. Somehow the thing works, even though I made every bend without using low value “safety” resistors to protect a fatal short circuit. When I revisited the keyboard, rather than moving any of the bends around, I just went ahead and made a 15 ohm safety connector for the DB-25 connector as a little additional piece of protection. So far, so good.

The second keyboard uses a different method. I realized that my surplus reed boards were laid out in 11 columns and 4 rows—if I cut the PC traces, I could wire up my own 11×4 matrix, which would fit quite elegantly on a DB-15 connector. Cool. I went ahead and built the thing inside an oak frame, and this time made a test cable to explore for the hot points inside the MT-240. This was very useful for swapping out different resistor values (for many many many subtleties of sound!), and at the time I guess I hoped to be able to use the reed matrix for future projects.  While testing, I realized I had made a goof in the design. I thought I’d be getting 11 ins and 4 outs, which would be 44 possible connections made. But because of the way the reed switch works, the magnet actually connects point along the input bus as well as to the output. (eg, if two magnets are over 11A and 5A, points 11 and 5 are also connected.) This yields 15! [factorial] possible connections, or 1,307,674,368,000 unique short circuits made inside this keyboard. Oops. That’s what we call “bent-by-design”.

test_cable

Each keyboard also has a clock mod which was designed by Pete Edwards, who has also done some pretty exciting work with this machine. The keyboards can sync together without tempo drift by running off the same crystal.

Keep these magnets away from your hard drive.