A new ignition circuit

Eccentric said:

I attempted to use an Arduiuo to control the timing advance of my model engine and could never get it working. the Electromagnetic Interference from the ingition system always (eventually) killed the micro controller. I went from a CDI to a TCI (transistor controlled ignition) which was supposed to be quiter from an EMI standpoint. I used resistor spark plugs, I used a ballast resistor, I isolated the microcontroller, I used lots of local decoupling caps and an inductor isolation circuit with an encolsed metal case, I used a seperate battery and opto isolators.... I spent way too much time trying to get it to work until I finally abandoned the project. If you can get the arduino working, you need to let me know what you did. I wrote some really neat code to control the spark advance, but to no avail. Good Luck.

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stevehuckss396 said:

Who cares who it offends! If thats what you want to do then thats what you do. I would love to see it completed. Better idea! Go with dual plugs and 10 coils! Hahahaha!!!!

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dbowes12 said:

Put a 10K carbon comp resistor in the HV wire to the spark plug as close to the plug as possible.

Dave Bowes

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peterl95124 said:

this has probably been noted before, but sometimes those of us with flakey memory need reminding...

the improved circuit with time-out requires a possibly non-obvious technique to properly set the timing,

if you turn the engine over by hand in the correct rotation then the spark occurs when the time-out circuit does its thing, long before you've reached the end of the dwell where the spark occurs when running at speed

instead you time the ignition at the point where the LED turns *off* because at speed the spark occurs at the end of the dwell, or

if you turn the engine *backwards* then the LED comes on (and the spark occurs if you're turning slowly enough) at the same point where it will fire in full speed forward rotation because that's where the dwell ends.

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dsage said:

Unless you have really excessive dwell (points closed - Hall active) then under normal operating conditions - even at cranking speeds - the spark for all intents and purposes happens when the light comes on. Yes it really happens when the light goes out, but as mentioned there shouldn't be much difference. You can do the math. The timeout is about 15ms after the LED comes on. It shouldn't be timing out unless you have excessive dwell.
The best way to time the engine is to turn it over by hand and watch the led come on and set your timing accordingly. Then use a timing light to fine tune it. It won't be far off when the engine is running.
That said - some folks with full sized hit-miss engines with crude contact points or wiper contacts (excessive dwell) will have issues with the timeout. The engine might kick back.
For those cases I suggest you adjust the mechanics to shorten the dwell to a minimum. Again, you can do the math. A coil only takes about 3ms to fully charge. If you have more dwell than that it's just a waste of battery to keep it energized any longer.

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dsage said:

Does this clarify the situation?

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dsage said:

Good. It's always harder to explain it (write it out) than it is to do it.
Also you'll notice I went back and corrected my error(s) for future readers. Not sure if it got any clearer

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DKGrimm said:

Your experience with Electromagnetic Interference (EMI) struck a resonance with me. Ignition systems generate an unbelievable amount of high-frequency energy that can couple into any circuit they happen to be near. Analyzing coupling between circuits is anything but intuitive. I spent a good part of a 40-year career dealing with EMI in aircraft avionics systems, and it can be done, but it's a humbling experience. H-field (magnetic) coupling is the culprit more often than not. Visualize the path the spark current takes and how it might couple to the control circuitry, either through common impedance (like a common ground path) or by H-field coupling (like between parallel wire runs). Try to assure a single-point ground reference between the spark stuff and the control stuff, and keep the control stuff away from the spark current path.

Experiment. You will probably be amazed at what actually works! Good luck.

Don

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