Ah, that all too familiar smell of burnt ozone permeates the air signaling the nearby presence of a tesla coil. However, that familiar drone of the discharge isn't anywhere to be found. Instead I'm hearing a rather buzzy sounding rendition of the theme from the video game Super Mario Brothers.
After squeezing through the crowd at the Maker Faire in New York City this past weekend, I managed to see what was making the noise. It was, in fact, a tesla coil but it was being used as a speaker. Through carefully pulsing the coil at the right frequencies, you can make a coil produce sounds. This makes perfect sense, but now they've made this into an easy-to-assemble kit that anyone can buy and play MIDI files through, via a USB connection to a computer.
The OneTesla team is actually three MIT students: Baley Wang, who you see in the video above, Heidi Baumgartner, and Daniel Kramnik. The three are devoted to open source, so the musical coil is completely open. The libraries, schematics, layouts, etc., are all available for download if you wish. However, if you're like me, you're really interested in their kit.
The $329 kit includes everything you need to build the singing coil:
All components for the coil itself
All components for the MIDI interrupter (which allows it to play music)
A laser-cut chassis for both the coil and interrupter
A 62-page manual
An optical link between the coil and interrupter so you don't burn up your laptop!
One particularly interesting bit about the OneTesla that makes it stand out is the fact that it is polyphonic. Most musical tesla coils I've seen (yes, I've seen a few), are only capable of playing a single note at a time. The ability to play multiple notes at once really adds to the audio experience. This isn't immediately evident in the video above, so take a peek at this promotional video taken from their site.
You're probably wondering about the tech specs of the kit at this point. Here they are from the kit's sales page.
Primary: 6 turns of 14 AWG wire, 3.5" OD acrylic former
Secondary: 2.5x10" of 34 AWG magnet wire
Tank capacitor: CDE 940C30S68K, 0.068 μF@3000V
Topload: 8"x2" stamped aluminum toroid
Resonant frequency: ~230 KHz.
Inverter: half-bridge of FGA60N65SMD IGBT's running at 340 V
Driver: Primary current feedback driver
Peak primary current: ~300 A
Pulse-widths: adjustable from 0 to maximum pulse-width. The maximum pulse-width ranges from 50 μS (at 1 KHz) to 150 μS (at 50 Hz) with a maximum duty cycle of 5 percent
Maximum recorded spark length: 23"
I can absolutely attest to the fact that seeing one of these in operation so much more impressive than the videos can show. I will most likely be buying one to build with my kids in the near future.