[bobski]

Originally Posted by msc

Of course this would be a pointless exercise that adds two chips unless the second interrupt is put to good use.

I like to think the VSS is "good use", though I suppose it could be moved over to the new interrupt expander setup. Keeping the VSS and injector(s) on interrupts lets the non-time-critical code (such as variable calculations, display rendering, button handling and whatever else people come up with) run amok without affecting the accuracy of those core measurements.

Originally Posted by msc

Since you are working on a general re-rendering of the concept you might try and add DPFI support. It would be a significant contribution and you would be a hero to a number of people with throttle body injection.

I'll see what I can do.

Originally Posted by msc

Adding support for a second injector would require a second set of injector calibration values and summing the output of both injectors for total fuel flow.

Yeah, the software side seems pretty easy: A check-what-changed code snippet that triggers the appropriate chunk(s) of code in the interrupt. I've pretty much already written the chunk(s), I would just need a few additional variables to differentiate the two injectors.

Originally Posted by msc

On another topic. If you want to really keep the inductive kick of the injector away from the MCU you can give the input side of the opto it's own ground wire back to near where you pick up the injector signal, presumably at the ECU.

Yeah, I thought about that. The ground line you get on the Arduino's headers is uninterrupted back to the negative external power terminal, which would presumably be connected to a ground wire near the ECU. A second wire might help with noise rejection (not really a problem afaik), but I don't think the shared ground is going to cause problems protection-wise.