Here is a picture of the signal from an Arduino Nano, that is programmed as an ignition simulator. In the development process a distributor simulator provides signals that would be available from a spinning engine. The simulator changes the RPM up and down. A logic analyzer captures the simulator signal and the ignition system control signals. Things like dwell and timing are accurately verified by measuring signal timings.
The tooth with notch is the reference tooth. It is decoded by the fact the narrow teeth are less than the normal tooth width. The micro measures rise and fall widths, and uses the information on a cycle basis to measure RPM. RPM is used in the process of generating the timing based on control tables. More will be written about that at a later time.
The tooth edges are used in the timing control. The leading edge is the is maximum advance, the trailing is base timing. The width of the controlled timing is 45 degrees, the based timing is added to that.
