oneTesla was invited to the tech fair at Thayer School of Engineering, and our demo was a smashing success. (See an article about the tech fair in The Dartmouth.) There were several other Tesla coils on display, as well as some demonstrations explaining AC vs. DC and the concept of wireless power transfer. Since we brought a keyboard and our setup was interactive, we attracted quite a significant crowd around our table!

In the meantime, we've been busy sourcing parts, while trying not to get swamped by schoolwork. We've had an interesting experience ordering parts by the thousands. Some of the packages have been wonderful to open (such as the dozens of freshly-wound secondaries); others, not so great (such as the surprisingly heavy boxes of one thousand power cords). We've also had some head-scratching moments, like when one of our suppliers sent us a hundred thousand 0402 2.61K 1% chip resistors instead of the thousand fiber transmitters we ordered.

Why hello there, 2000 meters of fiber cable (and Heidi)

On the technical side of things, we've been putting the final touches on the main driver board (mostly silkscreen changes), and testing the international (220V) version of the board. We've also been adding more feature support to the interrupter; the current version supports sustain, pitch bend, and velocity control, making the coil much more playable on keyboards. The interrupter hardware has been changed significantly - there are now frequency and pulsewidth knobs, to allow for classic fixed-frequency operation as well as MIDI operation.

The latest interrupter revision. Don't worry, the final revision will have a black board.

If you're waiting for kits to come back in stock, expect to wait until the beginning of summer. We'll be busy fulfilling the first 600 Kickstarter orders until then - our last round of Kickstarter kits should ship out at the end of May. Until then, add your names to the waiting list, and stay tuned for more updates!

This is crazy! We launched a Kickstarter campaign to get a critical round of pre-orders and also get a bit of publicity, but we expected to have trouble generating serious interest. We reached our $20K goal on day 2, and now (the start of day 4) we've got 230% of that. And we thought we'd be lucky to reach the goal by the end of the 27-day campaign.

It's been interesting to watch where people find out about the campaign. Kickstarter lets you see your referrers in the back end, and about half have come from external sites. That means that half of our backers have found us through Kickstarter, so a whole lot of people must check the site regularly. One interesting referrer has been Mashable, which made a video about the project within only 15 hours of the launch. Another one is Synthtopia, an electronic music portal frequented by MIDI geeks. We were even contacted by a BBC podcaster, and the next day I was called up to do a brief interview for the show Outriders (the podcast should appear on New Year's day). We've gotten so many pledges that had to cap the number of coils we could deliver by February to 150, and we're only promising the next batch by March.

Here's a snapshot from the Kickstarter dashboard of the progress at this point:

Just for fun, I did a little gender analysis of our backers so far, based on usernames and pictures. A total of nine backers so far with women's names, three of which contributed because they know us personally and wanted wanted to be supportive. Unsurprisingly, but regrettably, I need to ask: female coilers, where are you?!

The first iteration of oneTesla was designed and laid out over the course of three days in February, backed by copious amounts of bad pop music and caffeine. It used a BNC jack for interrupter input, FGH40N60SMDF IGBT's, a hand-wound current transformer, and couldn't play music.

The first (hand-etched) board wasn't tested until mid-April. Version 0.8 suffered from the disastrous problem of not having a high enough CT turns ratio. As soon as the primary current rang up high enough, the feedback CT would force tens of amps through the feedback resistor, burning it up.

Version 0.85 fixed this by sourcing a commercially available 300:1 CT from Triad Magnetics, and also replaced the 1/4W feedback resistor with a 5W wirewound resistor. This fixed the critical flaws of the prior revision, and resulted in a working Tesla coil. The old design paradigm was "efficiency first", which meant running very low duty cycles and pulsewidths, resulting in ~7" long sparks at about 50W into the coil.

Version 0.9 came next:

At this point, Kramnik re-designed the board to use an optocoupled interrupter, and etched a variant of the coil. This coil was used as a testbed for the development of the firmware that eventually became the oneTesla MIDI controller. At some point, we also realized that grounding the secondary to mains ground was actually more reliable than using a big foil counterpoise, and also significantly improved streamer performance. However, this revision was still somewhat noise-prone.

Shortly thereafter, the kinks in the MIDI code were finally ironed out, a low-pass filter was added at a key location, and the board was respun for commercial fabrication. The original idea was to send out for 50 boards from MyroPCB to take advantage of the price break, build a few coils, and peddle the rest on eBay in the form of simple kits to help recoup development costs.

At this point, I went on vacation to visit Heidi (who was interning at an accelerator in Germany). She pointed out that we would seem much more legit (and also be much more profitable) if we had a real web store and a good manual. Soon we had a nice website, and I wrote the first revision of the manual, which was done in LaTeX and looked like a math paper. Meanwhile, Kramnik added polyphony and figured out the limits of the driver design.

The manual was deemed stylistically unacceptable, so Heidi began re-writing it to read less like a technical paper and more like a manual. We also decided to scale up the operation and cater more towards the general "maker" community, as opposed to only experienced HV hobbyists. This turned into plans for a Kickstarter campaign (which is still in the works), and a massive and ongoing effort to streamline the supply chain, revamp the manual, improve safety, and simplify the assembly process. On the technical side of things, the board was respun with a few critical features (such as a fuse), the interrupter was improved, and we designed a nice acrylic case and primary supports for the coil.

So there you have it - the history of oneTesla. The design has come a long way from the day it was conceived; we've tripled our spark lengths and made the coil infinitely more reliable. It plays music, it's portable, it's consistent, and it even comes with a fancy lasercut case! At least internally, we can now go from zero to Tesla coil in a few hours. Hopefully, we can bring this simplicity and ease of assembly to you as well!