I am looking in to converting an optispark to use as a trigger for an aftermarket engine management. i have disected one and the high res signal will work out fine, however the low res has me a little concerned. there are 8 optic trigger holes are spaced to start 45 degrees apart, here's the catch though, every other trigger is an equal pulse length the other 4 grow in length by a factor of 2. The added length of the optical trigger holes for the odd cylinders are exetended to the trailing edge of the signal.
Since a picture is worth a thousand words, go here-->
Optispark diagram

Ok the outer ring has 360 opticle trigger holes spaced equidistantly. This is the high resolution pulse. In actuality the PCM thinks there are 180 pulses per Crankshaft revolution. Next you have the inner 8 optical triggers. These are circled in Red and Blue . If you look closely you will notice they all start 45 degrees apart. the extra pulse comes from increasing the distance trailing edge of the RED hole. I think I have come up with a way to cover seven of the 8 inner holes without affecting the outer high res signal which will give me a can sync signal. I will try to buy some junk optis this week to test out my theory. My question is does anyone know which one of the low res optical trigger holes references cylinder 1? I will of course put it on the motor and index it to get a proper reference angle but knowing which seven holes to cover would help me get a lot closer a lot faster. Also if anyone had any other information on opti output signals such as output voltage on the high and low res output it would help a bunch. Sorry for the long windedness, and I would like to also note I stole and modified the picture from Mike Cheney's excellent opti disection page locatedhere.

 

I think the longest one is #2 cylinder. It sould be about 22 degrees long. If you get the book "corvette fuel injection", it has a page or so about the opti and it eplains the low res pluse..