Lol. What just happened again?

So yeah... it's been quite a while without an update, so I guess I'll get right down to it.

Last semester of school pretty much consisted of me derping around in my room, eating hot cheetos, and doing PSets. As a result, not too much stuff got done. This semester, things kinda changed.

First of all, the Tesla Coil finally plays music! As a test of it's functionality and how not-blowing-up the IGBTs were, I played the entire Pokemon Trainer Battle theme on loop for a while on max power. Fortunately, the thing didn't explode! In fact, the heatsink didn't even get significantly hotter than it was before.

Ahh, the magic of low duty cycle interrupting. :)

On the more activity-oriented side of things...

I found a new home in Yale's Center for Engineering, Innovation, and Design. It's an incredibly versatile space that's open 24/7 to registered students. From writing out entire PSets on the walls to passing out at 5am working on an especially frustrating PSet, the CEID was the perfect place to be.

Oh the loveliness of wall-to-wall whiteboards.

Anywhoo, while at this magical space, I joined two endeavors, the Intelligent Ground Vehicle Competition team, for which I'm the electrician, as well as the Flying Bulldogs - a startup/big project that involves drone stuff.

Fun times will be had.

Also, yesterday, I went to MakeMIT with my friends Noel Hwang (http://hellobowtie.blogspot.com/) , Will Zhang, and Daniel Kramnik (http://xellers.wordpress.com/). We made top 10 by making a pure analog device - an active differential oscilloscope with a bandwidth of to 1 GHz. It also has the dubious title of being the most amazingly named creation of all time

The "1 Gigahertz 10X Attenuation Active Differential Warp Speed Super Oscilloscope Probe."

At any rate, new projects should be popping up soon. Three potential projects could be a motorized scooter, a quadrotor (preferably controlled wirelessly), a tube amp, or a theremin, or a LED cube, or a BIGGER Tesla coil, or a giant death-ray robot thing that kills on sight... .

Well.

Better get to work, I guess.

Quick Update - Also lightningz!

Got my hands on a variac. Unfortunately, the interrupter can't do the whole music thing because of a missing MIDI cable.

Oh well.

On the bright side, it does the bzzipity zap thing that we've been looking for for a few months!

Audio modulation to come soon.

Panicked Board Population and Low Power Testing

Chrome was derping, and for some reason, the Blogger editor failed to work correctly. Fortunately, Firefox was more reliable. So here I am, sitting at my desk, abandoning my choice browser and updating this page after a day of restful and theraputic panicked board population.

After several hours, the board was finally populated - witness TraloCoil, in all of it's purple silkscreened glory!

Added masking tape to the right picture because of a rather nasty shock acquired from brushing sweaty fingers over exposed bus caps. Bus caps are dangerous. -_-

Anywhoo, I decided to use the oneTesla interrupter for low-power testing, as it's more reliable than the one I used, and it's low 10% duty cycle makes it less likely for any catastrophic errors to blow the transistors. Also, I just wanted to be as safe as possible.

First, after turning on the interrupter, a nice buzzing noise was heard from the GDT. Scoping the gate drivers...

Nice waveform!

Hmm. In retrospect, that workspace is surprisingly disgustingly disturbingly horribly messy.

Anywhoo, scoping the IGBTs themselves displayed a lovely looking startup pulse.

By this point, I was ready for low power testing. Plugging the secondary and primary into the board and connecting the whole shebang up to a DC power supply, I slowly upped the voltage.

The buzzing from the GDT inexplicably stopped.

This implies something is going wrong. Popular troubleshooting techniques dictate that the first thing to do should be to switch the two gate drives, as the drivers could very well be 180 degrees off from the actualy waveform.

After the switch, the buzzing came back, and lo and behold, first light!!!

REALLY faint, but nevertheless discernible.

Full power testing and audio modulation to come. Perhaps some use of my personal interrupter. :P

Happy days!

Now time to find a variac... .

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

.

 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!

Boardmaking

Time constraints be iffed, it's time to print my first PCB!

It took a while, but I was finally able to print the schematic onto photopaper.

The PCB that I was using was really badly oxidized, with disgusting fingerprints all over it. But with a little help from a sanding block and some acetone, the board came out all right in the end.

The actual process of printing was minimally irritating. Aligning the photopaper on top of the board took a while, but soon, the laminating process started.

After washing the board, getting all of the paper off, and exposing the toner, the board looked quite nice, actually.

After a dunk in the Ferric Chloride, and a dab of acetone, the board was finished!

Now comes the wait while all of the parts get here so I can populate...

The Next Step

So it's been a rough 2nd semester of school. Thankfully, with college apps finally over, I can get back to work.

The project I've started on recently is the next step following the spark gap coil I constructed late last year. I'm going Solid State!

I've found a schematic for building a basic solid state coil on the internet, courtesy of Steve Ward. The name of this particular version is the MicroSSTC. A link to Ward's webpage and the schematic can be found below.

I had a few concerns about the schematic itself. The diodes on the full bridge rectifier seemed to be insufficient to handle the wall voltage, so I switched then out for more resilient MUR440RLs . Also, the schematic recommended using a TC4420 as a gate driver. However, due to the fact that I had the perfectly functional alternative of UCC37322's lying around, I decided to change that up in the schematic as well.

So the original schematic is:

All credit to Steve Ward.

I redrew the schematic with the edits in Eagle, and after some advice from a mentor, the final schematic turned out like this:

Which, when routed on the board in Eagle, turned out thus:

Hopefully, I will have this printed within a few days.

Final Version of SGTC

I made some changes to the coil before tuning and running it again.
First, I replaced the corroded spark gap with fresh pieces.
Second, the size of the coil did not match the tiny size of the previously used topload. I needed more capacitance. Previously, I was unable to find a toroid large enough. That problem has since been rectified. By using a slightly larger tire, I made a stacked toroid.

Final results of my first SGTC are significantly better than the original run.
Now, the streamers created are significantly longer and more visible than the previous version's
Furthermore, ground strikes are now nearly a foot long.