DIY LTCC or similar system for LT1s

[lionelhutz]

I will not discuss this any further until I need to.

Getting a plan together first is better than going off half cocked with a "solution". But, you've got it all figured out so go ahead.

Still, this isn't your thread so it's not really your place to be pissy about my posts...

Personally, I will just buy a replacement sensor if it fails, or do a 24X conversion if I really want a change. So, I have no real incentive to design anything myself. I'd try to help but you apparently don't need it.

Still. thinking about it more I probably would have investigated using the combined rising or falling edges of the high and low res signals combined to clock a shift register chain of 8 flip-flops. Decode one of the pulse combinations to inject a 1 into the shift register each revolution. Then, the bit just passes through the chain at each TDC so there's you cylinder identification done and done. None of the AND gate decoding required and no latch required since the flip flops hold their state until the next low res signal comes along.

[kur4o]

Here is how PCM interprets opti signal and what it counts.

High res signal is counted at every slot full or empty, totalling 720 counts.
Low res signal is trigger for high res counting. The cylinders are encoded 8 1 2 3 4 5 6 7 in the software.

The rotation could be backwards, not sure. TDC location on the disk is also not confirmed. Someone with dismantled opti could check rotor position and see where the disk is at #1 TDC.

All calculations in PCM are handled by a special third processor. Unfortunatelly I cant access rom section of the processor to make a dissasembly of the code.
If anyone knows how to read the third processor rom or have a dump of it, I will be more than happy to make a dissasembly.

[lionelhutz]

Here is how PCM interprets opti signal and what it counts.

High res signal is counted at every slot full or empty, totalling 720 counts.
Low res signal is trigger for high res counting. The cylinders are encoded 8 1 2 3 4 5 6 7 in the software.

The rotation could be backwards, not sure. TDC location on the disk is also not confirmed. Someone with dismantled opti could check rotor position and see where the disk is at #1 TDC.

All calculations in PCM are handled by a special third processor. Unfortunatelly I cant access rom section of the processor to make a dissasembly of the code.
If anyone knows how to read the third processor rom or have a dump of it, I will be more than happy to make a dissasembly.

Looking at your picture, you can take make a decent guess that TDC will be the leading edge of each low res notch since the leading edges are all equally spaced 45* around the disk and it would only make sense for 1 edge of the low res signal to represent TDC.

It's also possible that the PCM detects the low res notch and then does the detecting to know the next upcoming cylinder so it can then fire that cylinder at the proper BTDC advance. So, the notch everyone assumes represents #1 TDC could really be to tell the PCM it's 45 notches from cylinder #8 being at TDC.

[vilefly]

Lionel, I did consider the method you mentioned above before I drew up the current design. It would work, but it would take as much as 2 crank rotations to sync, meanwhile the injectors are firing long before then, and might allow flooding in colder climates. I suppose you could disable the injectors until the sync, but I am uncomfortable doing so. So I decided to sync as soon as possible so that it won't change how the engine starts. This is simply a personal preference, nothing more.

Nice research, kur4o. I had posted previously an optispark wheel labled for coil switching and TDC. All leading edges of the Lo-Res signal indicate TDC. I had a spare optispark unit to confirm with rotor position, also. It is correct.