Monday, January 13, 2014

Finally back into the flow of things!

Well, it's certainly been quite a while since I last posted on this blog.

The inconvenient combination of college application frenzy and subsequent senior slump followed by a hectic first semester at college is truly no excuse for such a long leave. Still I will endeavor to begin updating again, if for no other reason than to motivate more projects out of my lazy butt.

At any rate, the first small SSTC coil that graced the face of my last post was a resounding failure. Not because it didn't work, but rather because the project was abandoned due to a combination of bad planning and lack of resources.

However, time has passed, and I've learned from my previous mistakes, and thus out comes TraloCoil I


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 The layout and schematic were inspired by the oneTesla DRSSTC. As I didn't want to mess with the increased sensitivity of a DRSSTC, I simplified the design and adapted it to the basic SSTC. In exchange for smaller spark length, I get the benefit of increased reliability and not having to worry about 60+ amps flowing through the primary. Ultimately, it was a simple matter to replace the primary current feedback mechanism with antenna feedback, and voila! Tralocoil is born into this world.

SSTC's in a nutshell, operate off of hard switching a bust voltage at the resonance of the LC circuit that comprises the secondary and topload. The oscillations produced by the secondary during operation produces an E-field that oscillates at the resonance frequencies. This, then, is “picked up” by an antenna, which is then fed back into the logic that drives the half-bridge of transistors that performing the switching action.

At any rate, because spare oneTesla parts happened to be laying around MITERS, I decided to do the smart thing, and just use the same parts. And away goes the parts problem from earlier. This was particularly beneficial, as the optoreceivers and optotransmitters laying around allowed for optoisolation of the interrupter, thus preventing any derpy noise affecting the interrupter that would no doubt arise if they were electrically connected. The other rather wonderful effect of being able to scrounge up parts (other than the fact that crufting is free) is that I was able to gain access to a bunch of FGA60N65SMD IGBTs – great at handling large currents and voltages at high frequencies. Honestly a bit of an overkill for the low-current SSTCs, but nevertheless, they're good to have to any future projects that I may build.

I sent out the boards a few weeks back to OSHPark to be printed professionally, and only recently got them back!


One issue with the operation of an SSTC is that the feedback loop is fundamentally circular. Indeed, how can one half the feedback that starts the oscillations which in turn start the feedback?

The answer lies in the interrupter, which sends periodic signals to the logic side that essentially turns the coil on and off. The initial pulse can cause an initial “tickling” that gets the coil going. It also makes sure that the coil isn't running in continuous wave mode, which can easily burn out the transistors due to the strain.

That's not all though. The interrupter's periodic signal can be sent at a certain frequency, say 1kHz. This causes the streamers to pulse out at said frequency. This in turn creates a pressure wave that propogates at 1kHz, and thus plays that note – audio modulation!

I whipped up a simple interrupter in EagleCAD out of a 555 timer and an inverter that allows me to access 100% of the duty cycle at audible ranges. Not the most elegant thing I've designed, but it should be sufficient.



After printing... .

After populating... .

And after testing the signal on the optoreceiver end of things... .

Great Success!

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