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SSTC 5 mini questions

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James

Mon Apr 18 2011, 01:40AM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

I etched one the other day along with a half dozen other layouts that had accumulated, so I'll be able to let you know sometime soon if it works. I ended up altering it to use some different film capacitors but the circuit itself is unchanged.

ZakWolf

Mon Apr 18 2011, 01:48AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

OK, let me know how it turns out, I just scored some sweet heat sinks from an old tv for the lm7812

ZakWolf

Mon Apr 18 2011, 04:07PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

I made several changes of placement and I changed out the lm7805 to the lm7812 footprint. I moved the board edge out, added another filter cap, rearranged the bridge rectifier, and moved the coil output.

Do I need to fill the board with a ground connection because I see a lot of people fill the empty spots with ground.

thanks for the PCB, I am having some trouble with the people I am ordering the board from so it will be like a week before I can get started.

James

Mon Apr 18 2011, 05:21PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

I fill some PCBs with copper zones as power and ground planes and some not. I'm pretty sure it's not necessary here as Steve's prototype was built on perfboard, but you can add it if you desire. I tend to avoid it when I can because I fab my boards at home and a large copper area is just that much more opportunity for pitting or other etching defects.

Useful tip, especially if you're having the board made by a service is to print it out yourself and test fit the parts on paper. More than once I've etched a PCB that looked good only to discover that some parts wouldn't fit. Either the spacing between them was too close or I had made an error drawing the footprint.

On this board, I did install almost all of the parts last night, so I know everything fits the way I had it.

ZakWolf

Tue Apr 19 2011, 04:11AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

what are you doing for the sub points? I really want VTTC arcs, the quietest buzzing sword like arcs what would be best?

James

Tue Apr 19 2011, 05:15AM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

I dunno, your best bet would be to refer to Steve's chart.

I just did a quick lashup tonight to test the board. I used a 1uF cap and 10k pots and connected it to the secondary I wound for the VTTC. Found a 12.6V radio shack transformer in the garage to power the low voltage section and then ramped up the AC with a variac and it sprang to life, that was almost too easy. I'm guessing I can wind another secondary closer in size to the one Steve used and get better performance but this proves that it does work.

Interruptor coils are awful sounding though! I may eventually disable the interruptor completely and see what happens. As it stands the heatsink barely gets warm.

ZakWolf

Tue Apr 19 2011, 06:52AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

very nice, that is good news that the PCB works. I watched this video

and right at 17-19 seconds the arcs become sword like and only have a slight hum to them, thats what I want for an output. The video description says it runs off of unfiltered mains, I read somewhere that the 60hz hum had something to do with the VVTC arc appearance; please correct me if i am wrong.

Side note: The smile button doesn't work with Google chrome

Wolfram

Tue Apr 19 2011, 01:00PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

For sword-like sparks, you don't need an interrupter. You need to operate the coil CW and feed the bridge with half-wave rectified mains, and no smoothing capacitors. You will also need a startup-oscillator, this can be something simple like an oscillator made out of one of the gates in the 74HC14 or just a 555, running at a few hundred kilohertz, connected to the antenna through a high-value resistor. This is in fact exactly how my coil is built up.

ZakWolf

Tue Apr 19 2011, 02:28PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

Anders M. wrote ...

For sword-like sparks, you don't need an interrupter. You need to operate the coil CW and feed the bridge with half-wave rectified mains, and no smoothing capacitors. You will also need a startup-oscillator, this can be something simple like an oscillator made out of one of the gates in the 74HC14 or just a 555, running at a few hundred kilohertz, connected to the antenna through a high-value resistor. This is in fact exactly how my coil is built up.

Steve says on his documentation of the sstc 5 mini "I made another change to the circuit that improves some things. It seems the coil will work fine without U1 (the 555) even installed! Basically, when the driver chips are enabled, the inverting chip will send a short pulse to the MOSFETs causing the oscillation to start without any problem. "

this is located right under the value table. This is my first SSTC so I might just build it as is, unless it would be easy to get rid on the interrupter.

Wolfram

Tue Apr 19 2011, 03:00PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

Yes, with an interrupter, it will self-start. Without an interrupter, there is no pulse to start the oscillation. With an interrupter, you won't get proper sword sparks. Disabling the interrupter is easy, if you decide to do this.

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