BeatSneaks I

BeatSneaks – Musical Shoes from Tom Hobson on Vimeo.

Like many people, I often find myself unconsciously tapping my feet, whether it’s along to a song or out of some nervous habit. As fun as that is though, I’ve always felt as if something has been missing. If only I could trigger the sounds of say, a rabid pack of furious jungle beasts instead of those boring old toe taps. Or, you know, drum sounds or something. I guess that’s cool too.

Well, now I can! I’ve put together a pair of shoes that, with a little help from an Arduino, will let me trigger MIDI signals. There are FSRs (Force Sensitive Resistors) in the heels and toes of the shoes, which serve as the tap sensors. Basically, an FSR, without any applied pressure, is like a break in a circuit (i.e. has infinite resistance), and as you apply more force, it becomes less and less resistive. So, if we hook up one end of an FSR to a voltage source and the other to the Arduino’s analog input, we can send a signal to the Arduino every time we apply pressure to the FSR. We can then take this signal, convert it into MIDI, and start making sounds. This can be accomplished most easily with a little program from spikenzielabs.com, Serial-MIDI Converter. It saves you the hassle of attaching a MIDI jack to the Arduino and using an external MIDI interface. Of course you can also use MAX/MSP/Jitter to interpret the signals as well, and in many ways this provides more flexibility, although it’s slightly more complex and MAX isn’t free, like the Serial-MIDI Converter.

Drum triggers have often been made before with piezoelectric transducers, but when I tried them out I found them to be fairly unreliable. Since piezos react to flexure, they often send a signal after initial impact, as they rebound. This may be less of a problem in a typical drum trigger setup, where the impacts are fairly brief, but in shoes there is always at least some pressure being applied to the sensors. Setting thresholds can mitigate the problem, but won’t solve it entirely. Piezos are also not as durable as FSRs, being much less flexible. Granted FSRs cost a little more, but are so much less of a headache that it’s easily worth it.

There isn’t a ton of hardware required for the BeatSneaks. All you need is:

• A pair of shoes
• An Arduino
• A project box
• An LED (optional)
• 6 10K resistors
• 10 1/8″ audio jacks (mono or stereo)
• 4-6 FSRs

I used the Serial-MIDI Converter from Spikenzie Labs. The serial-MIDI conversion could likely be performed in MAX or otherwise manually, but this does the trick and saved me some time. For the actual sounds I used Garageband, but you could use MAX, Ableton Live, etc.

…and don’t forget the Arduino sketch: midishoes.pde

The code works by setting both a lower and an upper threshold for the force exerted on the FSRs. This is known as hysteresis. When the force exceeds the upper threshold, the MIDI message is sent, and not until it sinks below the lower threshold is another message allowed. Adjusting the thresholds is essential to the effectiveness of the shoes. Thresholds will almost certainly vary with different users, dependent on a variety of factors such as weight distribution, strength, shoe material and design, tightness of laces, and foot-tapping style. Sensor placement is vital for the same reason. The sensors may have to be repositioned several times in order to find the optimal arrangement.

There’s an instructable. It’ll give you a bit more detail on the BeatSneaks’ construction.

Check out this fantastic project that Jason Hockman sent me! There’s video, too!

Send me an email if you make a pair of your own, or are interested in a kit. I might even make a pair for you!

BeatSneaks by Tom Hobson is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.