soulid:
Mhhh- a 360° stroke at 10.000RPM takes about 6mS. I am sure you agree that using interrupts is the best way to handle it not using IFTHEN loops. 1° of ignition is 17microseconds at 10.000RPM. The 328 is not as quick as that...I know I am naggy, but beside learning something about engines no one answered my question from my first post:
As the igntion timing is critical I need to pull the coil pin to low with an internal interrupt commandCan anyone help me with that?
I have worked with ignition systems, and I think you are glibly ignoring some fundamental problems which will prevent you from getting a solution that works as well as the original, let alone better. I suspect you'll find it difficult to get it to start at all.
But since you only want to ask about interrupts, you need a power transistor to pull the coil dopwn, and a driver circuit to drive that from the Arduino output. Remember that you will get some savage voltage transients back from the coil LT circuit and the supply voltage will also be all over the place - it will need quite a bit of work to prevent the Arduino being damaged or confused by the electrical transients. I assume you're also going to deal with dwell timing which means that as well as your firing point changing with speed the advance needed to charge the coil will also need to change with speed.
I think your best bet is to decide what ignition timing you want to start the engine. You [should] know what dwell time you're going for, and you should know the cranking speed, so you can calculate how far in advance of the firing point you need to start charging the coil. Position your crank position sensor there and start charging as soon as you see the trigger, this will give you the cranking spark at about the right place. This will probably be well retarded to get it to fire reliably at low speed.
Once you start getting consecutive crank triggers fast enough to show you are running you can start averaging these to produce an estimated speed and use that to decide how much to advance the ignition and control your dwell. Remember that in this scheme with a single crank position sensor your ignition timing and speed estimates will will be based on a pulse that is probably 300 degrees old so you won't get very accurate timing.