For discussion of Speeduino compatible boards designed / built by other members of the forum and for guidance around making such a board
By rcrpaul
#50605
pazi88 wrote: Mon May 24, 2021 8:40 am You can try it quite easily by plugging in ardustim directly to mega2560. It works higher than 9kHz. But including default speeduino crank filters, the limit is much lower.
Thanks for the responses. Ya, I'm going to try ardustim with my mega2560. I may also try 'ifdef'ing out some of the features I don't need to get the loop time down (flat-foot shifting, launch ctrl, baro, etc)

If the RPM goes above 7K, I assume I'll lose 'sync', but then what happens? Is there some sort of limp mode until it regains sync?
Also, if I set up a rev limit at 7K, does that actually help? I hope so, but if it loses sync, then maybe the rev limit doesn't function properly either.
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By pazi88
#50606
rcrpaul wrote: Fri May 28, 2021 11:37 am
Thanks for the responses. Ya, I'm going to try ardustim with my mega2560. I may also try 'ifdef'ing out some of the features I don't need to get the loop time down (flat-foot shifting, launch ctrl, baro, etc)

If the RPM goes above 7K, I assume I'll lose 'sync', but then what happens? Is there some sort of limp mode until it regains sync?
Also, if I set up a rev limit at 7K, does that actually help? I hope so, but if it loses sync, then maybe the rev limit doesn't function properly either.
In actual engine you will start to see some sync losses if/when RPM gets too high. It's not like sharp "hard" limit, because the trigger signal from engine isn't perfect. Anyways with the components in BOM for these bmw boards, 8k at least is perfectly fine. I have not yet finished my new trigger "simulator" that can rev higher. With ardustim, you can trigger all the way up to 16k, but it's bit different than actual trigger signal, because ardustim has push-pull output. BMW hall sensor and/or max9926 with vr-sensors is only pulling to ground and then there is pull-up using 1k resistor. So crank signal filter cap will dominate in max RPM limit when real trigger signal is used, instead of ardustim.
By rcrpaul
#50607
Thanks for that. But doesn't speeduino only trigger on the active edge--the other edge isn't really important, is it?
If it were, then couldn't we modify ardustim to mimic the open-drain behaviour by adjusting the pin control register, and adding a pullup between the boards?
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By pazi88
#50611
Max9926 isn't push-pull. There is separate 1k pull-up on speeduino vr-conditioner board because of that.

And the crank filter cap is charged through that 1k resistor but discharged by basically short to ground (bmw hall sensors and max9926 only pull to ground). So rise time is slow and fall time is short. The slow rise time is the reason why you start getting sync losses at high rpm, because the signal might not have enough time to rise above "high" thresold of the mcu input. That's where the max rpm limit of 5000-7000rpm of regular speeduino crank input becomes using 60-2. But by using smaller crank filter cap like I have in the bom, the rpm limit is much higher.

Here's a pic of how the slow rise time looks at high rpm.
Image
Last edited by pazi88 on Fri May 28, 2021 6:12 pm, edited 3 times in total.
By rcrpaul
#50612
I see you are right--page 7 of the datasheet shows that COUT1 and COUT2 are open-drain, and they recommend 10K pullup to 5V. I can mimic this on my Uno running Ardustim.
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