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The simplest ignition I can come up with besides points.
Just a quick update on the LS1 smart coil and driver board. I tested the coil a bit more and the required driver components. It will work with just a Hall-effect but it's not consistent. To correct this a PNP transistor is needed to drive the spark signal. The signal drives a transistor inside the coil so more current is needed. I went to a 1K ohm pullup resistor and I don't want to go below that because the Hall-effect or most of them can only handle 20ma of current. I could go down to 600ohms for 20ma. I did notice that just like older GM designs it needs to see a positive going pulse to trigger. The board is 17mm wide and 26mm long. C1 should be 0.01uf to 0.1uf ceramic depending on Hall-effect used. In the setup below the coil will fire after the magnet passes the Hall-effect or when the LED turns off. No dwell control or limiting resistors are needed because the coil handles all that. Just add a Hall-effect, 12 volt supply, and a LS1 smart coil. You don't have to use the 2N4403 (PNP), you can use something similar. I used it because I had them.

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I included a pdf below that can be used to turn a CD disk into a timing wheel. I have others to share with timing events. If there is enough interest I'll get extra boards made. Oh I also cleaned up the board design a bit, things like better pours and changed Q1 to a wide T092 pad.

Did you ever get anymore boards made? I'd be interested. Dave
You have already blown by my limited electronic knowledge. Years ago I started flying giant scale warbirds with available gas two strokes . Initially these all had mag ignitions and were non adjustable . In fact it was the prop location that made starting easier . Being curious I connected my race car clip on the wire timing light to find out timing . Testing a number of popular small lawn engine I found 24 degrees give or take was about average advance . Eventually I got a “ modern “ hot rod fed 2 stroke with mechanical adjustable advance . About all the thing did was complicate something simple then fall apart when it did work it really only allowed a high strung engine to idle a bit slower which was desirable but ver inconsistent . It was easier to just adjust the exhaust tuning and have a fixed timing . Later the onboard tach was very desirable we had two and located the displays in the top gun turret. Unfortunately both were destroyed in eventual crash . The single high strung performance engine did run very well but had finiky idle even the big props were not good flywheels and carbon fiber props were not common yet . Actual idle was a bit of compromise speed and vibration . Carb and exhaust worked together . The big Corsair flew for 13 years with it’s more or less standard for the era engine. I had only one dead stick landing that was due to not having clear runway and forced go around . Some of the more modern flat twins supposedly like slightly different timing between cylinders . I’d need to see this before jumping in . The big bomber twin engines ran very close to the same rpm all the way through the range with stock mag or after market electronic ignition once I got exhaust tuning adjusted

As for model radial engines well that’s beyond me at this age. Keep up the development it’s interesting to read about all this .