Been thinking about this, sorry to say that this board is not needed.

All that is needed is a changed interrupt handler (a define and a firmware compiled with my_make for this setup):

* primary trigger (acts eg. on rising edge): increase engine.trigcount (a 1-byte counter in SRAM). This would be very short, in the 3 usec range (30 usec available at 12000 RPM).

* secondary trigger

** rising edge: engine.trigcount=0 and enable primary_trigger interrupt

** falling edge: disable primary_trigger interrupt (this way we only burn clock cycles for counting the dense teeth, when it really makes sense, appr. 5% of the total time) and fire rpmcalc, set engine.igncount to the relevant cylinder

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This is my current table setup:

The chip is the AtTiny2313.

The (ugly) schematic:

(I didn't have a AtTiny2313 component for the schematic, thus the older AT902313 is pictured, but the pinlayout is the same.)

The code is [here].

It will light up the corresponding green LED. I've never seen the LED used for decoding errors light up.

I also need to output the trigger for the tachometer, but that's just copying the simple trigger output.

When removing the need for the extra tachometer functionality, I realized that I just had copied the InputTrigger/AudiTrigger, but without the two LM1815 chips.

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TODO:

* Change output to simple trigger + cam sync

* Create a real schematic

* Get input on the solution

* Make a real board

* ?????

* Profit!!!