For the Nissan CAS trigger (360 pulses) 3 possible solutions (one working, one should be easy and one hard)
Current solution is a 24+1 slot trigger wheel as described here: VehicleFitment/Nissan
We have a number of cars running on these trigger disks.
Leaving the 360 impulse disk - we can also implement this if someone writes pattern info here.
TODO: find out if the exact pattern of the 4 sync pulses (from a reliable source or measurement).
Fill in this form: signal is normally 5V (is it?), but 0V in the small slots:
- ... - ... deg BTDC cyl1
- ... - ... deg BTDC cyl3
- ... - ... deg BTDC cyl4
- ... - ... deg BTDC cyl2
Geek notes
A hardware divby4 divider can help. We have divby4 / 8 implemented with HCF4024 circuit (under PCB manufacturing, originally for high toothcount ABS wheels). Since this circuit has (active-high) reset input, this can be useful to make a precise 180, 90 or 45 pulsetrain from the 360 tooth.
- Please help to find this out so our stimulated pattern is exact, and we can recommend good ignition trimming values if necessary ! - Gunni : Please find the patent information for the nissan trigger here (http://www.freepatentsonline.com/RE34257.pdf)
- because the sync pulse is mostly 0 (and high for only a short time), the active-high reset input of the HCF4024 seems suitable
- is the sync pulse falling edge not racing with (the rising or falling edge of) one of the 360 pulses ? (I assume not, because that would be very stupid. This would make a counter-type implementation impossible, but a helper "assistant CPU" could still help)
- configuring sectrig input=both edges and firmware modification is necessary with the 4-window sync pulsetrain
- by blocking 3 of the 4 windows, (and using a HW divider) firmware mod would not be needed (good for experiments, but this should not be needed finally)
- TODO: actually try the resettable divby4 counter (on bench, and on engine)
- with divby4 (360 => 90 pulses).firmware could (should) be configured to divby3 or even divby15 (via divby-ANY setting)
- divby8 (360 => 45 pulses) for 4 cyl engines requires a small trick of 4 crankdegrees ignition trimming (because delaying by 23 teeth is not exactly the same as the required 22.5 teeth)
- according to MembersPage/JannoKusman/NissanTrigger both sectrig edges must be sensed because of the 4 slot syncpulse
Besides any necessary HW, suitable config will be provided (configlet to be able to upload to suitable firmware with 1 click).
Alternative solution would be (without HW divider) a software divide by the main processor. The processor is definitely capable (up to at least 17000 RPM). But unfortunately we have some tasks in interrupt that would need to be rewritten. (not the trigger input capture interrupt, but other interrupts that could interfere).
From auditrigger bench experiments that worked at 11000 RPM (pulse=2.66 crankdeg), we know that 8300 RPM (pulse=2 crankdeg) is possible without major rewrite. Going above the "all pulse always sensed" threshold could delay ignition by 1 tooth (2 crankdeg) or more (not advance that could blow engine). We speculated that without HW divider going above 9300 RPM could be too much work that would delay other developments unacceptably. So we will only implement fw mod that works well with HW divider.
- we think >9300 RPM is minimum reasonable goal to say that some trigger is supported (even though much lower than the 11k RPM of 135 tooth auditrigger with sufficient divbyANY config or 25k RPM of lower toothcount wheels)
See also