So I have this moped. It has a really shitty points-condenser ignition system that I want to improve. So here's what I'm thinking.

I want to build a 555 trigger circuit powered by the magneto. The magneto output would be rectified, regulated, and filtered. It would be used to pulse the primary of the ignition coil whenever a hall effect sensor picks up a rotation on the crankshaft.

I don't like points, cams, condensers, and all that bullshit. CDI kits are too expensive. Has anybody done something like this before? I googled, but didn't find much in the way of DIY ignition projects. I've built several 555-powered circuits in the past.

Help? Thanks.

..Should this be in gearheads or here?

I figure the people who would be able to contribute to this idea lurk in both forums (ahem, Argon).

If you do this, post pictures/slight instructions. I have a 1974 yamaha TY-250 that needs a condenser, and always has a bitchfit with the points/electrical.

So why exactly are you using a hall sensor on the crank and not on the magneto? How exactly do you figure you are going to detect cam phasing?

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Oh come on, you know what I meant. Hall sensor will go where the points are, small magnet glued to where the high spot on the flywheel cam is. I'd make it so that the dwell time is set by the 555, not by the magnet; the hall sensor would just trigger the 555 for one pulse. How long is a typical primary current pulse anyway?

Interesting idea...

How durable would this be...

"Primary" has quite a myriad of definitions...

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Alright Argon, if you want to step on toes, I want to know the average pulse duration seen at the the primary winding of a typical induction coil used on small engines with points-condenser ignition systems.

Does anyone have any helpful info or ideas on what I'm trying to do here?

I don;t mean to step on toes, but I am not completely familiar with your vernacular. Like I said, "primary" has many different definitions depending on what we are talking about.

From how I understand you, you are talking about finding the dwell, correct? You will need the arc magnitude of the cam where the points close and then open. Using this, one can figure out the time it takes to traverse this arc from engine speed, or, in this case, the magneto speed. (I assume this is a single cylinder?)

I think this is an interesting project, especially to not use microcontrollers. I think you can use a 555 timer to pulse a MOSFET that will drive the coil. Also be aware that the pulse width of dwell cannot remain constant due to how the ignition system at a fundamental level. Thus, you must be able decrease dwell time with increasing engine speed. However, this might not be that big an issue for a single cylinder engine since the RPM won't be that high and it's a single cylinder to drive.

If you need it, look into building a frequency to voltage converter. Using that voltage, you will drive a variable resistor in order to change the resistance in the pulse-width section.

I can't be much more specific at this time since I'm not extremely familiar with the operation of the 555.

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