Thanks Rupurt- that is the sort of reference I am looking for- I was just hoping some more people that had tried it would come forth and give experiences. That design is certainly simple enough to
put together in an evening. I may try it. I have studied the RCM design a few years back- I can't remember at the time what kept me from wanting to try it. I'll take another look at it.
Carlosponti- you say you are using a design based on the RCM one? Any thoughts or pointers on it?

More than anything, like Carlosponti said- I like to tinker- and I also get a thrill out of doing it myself. I am just fiddling around with chainsaw and trimmer conversions with very inexpensive
airframes- just looking for a way to keep the cost of an ignition somewhat in line with the rest of my gear. If I can figure out the technology, I can then work on getting some of the cost out of it.
Maybe I can, maybe I can't- but I'll learn something along the way. Thanks for the input guys- anyone else tried any circuits and had good luck with them?