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Old 09-30-2011, 06:31 PM   #1
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Default Microcontroller - Automotive Timing Resolution Needed

How much precision in mS or uS does a micro-controller need to properly control timing +/- .5deg. I'm trying to use a micro to delay the charge time on my Toyota COP's. But, according to my scope I'm firing the coils (going low) late by about .02mS.
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Old 09-30-2011, 07:04 PM   #2
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0.5* at 7200 RPM is 12 us.
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Old 09-30-2011, 07:07 PM   #3
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Simple math, really.

7,000 RPM is 117 revolutions per second, or put another way, 42,000 of crank rotation per second.

So one degree of crank rotation is 1/42000 of a second, or about 0.024 milliseconds.

Thus, your 0.02ms error is slightly less than one degree. That's pretty trivial.


edit: Jason beats me to it.
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Old 09-30-2011, 08:42 PM   #4
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And Now I Know

So, being off .5deg at 7200rpm is probably ok?

Thanks Guys
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Old 09-30-2011, 09:00 PM   #5
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Quote:
Originally Posted by kingofl337 View Post
And Now I Know

So, being off .5deg at 7200rpm is probably ok?

Thanks Guys
If it's late, probably fine because you can tune around that. If there's added jitter, then do not want.
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Old 10-04-2011, 10:19 AM   #6
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If it's ALWAYS 0.02 ms too late, you might be able to build some compensation factor into the software.
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