The timing control of the stock ignition control module (ICM) is entirely different from Speeduino. The tooth is the maximum advance width, from rising to trailing edge. Like most of the era, the trigger leading edge is the first reference for max timing (wait - we're not there yet
).
The trailing edge is the initial low-speed firing reference point.
[The equivalent in Speeduino is Fix Timing to Trigger, and it fires instantly when it sees the trailing edge at cranking and low speeds.] There is no calculation or other magic required. Simple. As rpm increases, the ICM firing point moves towards the leading edge, as a simple
delay from the leading edge. At high-rpm, there is no delay and max timing is at the leading edge.
From this we can see that the original ICM only required a leading and trailing edge to function timing between them. Very limiting, but very simple. Speeduino is different, and uses multiple passing teeth to calculate current crank position, speed, etc, in order to calculate the timing of both dwell and firing at any point in the crankshaft rotation. The number of teeth during rotation increases the calculation accuracy for these timings, or 'resolution'. Much different and very useful for multiple-cylinder engines and advanced functions.
Virgilio Caio wrote: ↑Tue Apr 23, 2024 5:59 pm
Ok, just to clarify: I will setup it as a "dumb coil" and Trigger edge - Whether the primary signal triggers on the Rising or Falling edge.
– VR Conditioners require specific setting depending on model used:
* VR conditioners based on MAX9926 or LM ICs should use RISING. This includes Drop-
bear units
That is correct?
Mostly. VR sensors have a polarity, and the image you posted of the VR signal is correct polarity for our uses. See that it has a rising edge at the front, and a falling edge at the back, corresponding to the rising and falling physical tooth edges. Normally, we want to read the falling sensor signal edge as a more stable edge to read, then use that position to calculate the
next dwell and firing -
not the current one. Now we can see how calculating for future firings would benefit greatly from multiple teeth with more calculations and greater resolution for accuracy.
Once we have the signal to the ECM, then the VR conditioner will either be inverting output (reverse the signal edge from Falling to Rising) such as MAX and
some LM conditioners, or NON-inverting (passes signal edge without inverting, so Falling is Falling) such as the DSC, and many others. The polarity of the signal, and the inversion (or not) of the signal, will provide best timing reference and the ability to properly read signal gaps (missing teeth).
The combination of the two conditions (polarity and inversion) indicates the setting for
Trigger Edge to read these edges properly. I hope the differences in timing control, and the multiple factors in VR polarity, inversion and
Trigger Edge are helping differences of function and understanding.
. 
- By kettlekev