SSTC Interrupter

[blahaj]

My journey into making a SSTC continues with the interrupter!
I have built the interrupter in Steve Ward's SSTC 5, and I wanted to know if my results looked okay
I have placed a 2.2uF ceramic in the spot labeled "cap sub point", and no resistor in the resistor sub point.
Here are some scope captures, with the first one being both pots at maximum, and the second one with both at minimum. The third is a capture of the minimum with a smaller time scale.
I have noted that one pot controls the on time, with the other controlling off time, is this desired?

[ZakW]

Hello Blahaj,

I created a simple simulation of the interrupter using Falstad. It is good for simple things.

Use this tiny URL https://tinyurl.com/ysstjgjg or the download and open the text file to run the simulation. To use the text file go to Falstad, select  Open file -> SSTC 5 Mini Interrupter.txt



Play around with R5 & R6 to see what they do to the output. You can also adjust the cap sup point to see how it impacts the output.

Does the simulation match what you are seeing on your scope?

[blahaj]

I haven’t checked, I will tomorrow morning.
But, did you mean 2.2uF instead of 220nF? I am using a 2.2uF cap in place at the sub point. Don’t worry about updating the simulation, I have used falstad before, quite a neat tool it is.
I’m also mainly curious about what on times/duty cycles and frequencies i should aim for in the interrupter, I have built a simple sketch for an arduino that gives me a bit more customization, but it is likely more susceptible to emissions from the coil.

[ZakW]

But, did you mean 2.2uF instead of 220nF?

I used that value since the time step in the simulation was set so low, I wanted to the output to be visible in the scope window.

I’m also mainly curious about what on times/duty cycles and frequencies i should aim for in the interrupter

• R5 & Cap sub point together determine the pulse width (PW or On-time), how long the coil will be on for.
• R6 controls beats per second (BPS or frequency), how many times the coil triggers and has an output

Remembering back when I built the coil and switched the cap to larger values (a couple uF) the output was almost like continuous wave/bushy plasma, long on-times. Smaller cap values resulted in less bushy lower power arcs.

Regarding the BPS, a wide variety works for the coil. It is not crucial and can be adjusted as the coil is running. Generally, higher BPS will result in more heating and stress on the components. Although, when I built this coil it seemed fine when turned to the highest BPS achievable with the potentiometers. 

I have built a simple sketch for an arduino that gives me a bit more customization, but it is likely more susceptible to emissions from the coil.

I have used an Arduino before in a SSTC and I didn't have any issues with EMI. I did have other issues like clock instability causing what should have been a fixed output to jitter but you should not have that issue if you are using it as a simple interrupter.

This coil is really stable and robust, as long as you follow the schematic it should be fine. Good luck!

[blahaj]

Alright thanks!
I remade my sketch to use a hardware timer, pretty darn stable now, I think I will use that for testing, as I dont have the components for the 555 to get low BPS, Ill attach it if anyone else would like to use it. The sketch works great on my Uno R3, and should be able to be combined with other sketches as long as they dont use Timer1. Be wary of the duty cycle, its set to 50% max.