Reference pulse, how to extract it?

Then count you must, since you must also include "crank".

I did this in the '60's, for ignition systems, using integrators, but it wasn't "pretty" ;-)

...Jim Thompson

Low RPM during crank. In my day that was around 18RPM that had to be detected.

...Jim Thompson

Yes, I need to read the pulse at crank time, I need to inject fuel at proper time for the engine to start.

Bye Jacques

What IS your minimum crank RPM specification?

...Jim Thompson

A suitable method might be to phase-lock to the 36-tooth signal, and discriminate on the phase detector output (which will glitch at the extra tooth). Or, you could run your phase-locked loop at a higher frequency (5x) and only trigger when the midcount (from 2 to 3) coincides with a pulse output from the LM1815.

For a 300:1 frequency range??

...Jim Thompson

Would you please re-post this, but in a fixed-width font?

It looks like pulse "R" comes between pulse "36" and "1", but during the three quick ones, the pulses don't line up any more. Are you saying that 1-36 are one interval, then then 36-1 would be the same interval, with the "R" pulse nestled between them, or should I take your diagram at face value, and assume that each rotation is ~180 degrees out of phase with the last?

Thanks, Rich

Frequency to voltage converter (such as charging/discharging a capacitor) feeding a differentiator?

I really like the software method though - compare the most recent inter-pulse time to the average of the last 5 inter-pulse times. If it's less than say 70% of the average, consider it to be the extra tooth. Can also easily add things like disable below a certain RPM, etc, consistency checking by counting pulses since the last extra tooth detection (should equaly one revolution's worth of pulses regardless of speed), etc. Small OTP micros are pretty cheap. But I bet you could do it in your main processor with some care in programming.

Not sure, I will have to ask the engine expert guy.

In the mean time, we will try to do it by software at the beginning of next week. We are actually assembling a small prototype kit to test the method.

Bye Jacques

I don't think the bit heads are accounting for acceleration much, so this business about taking averages is just so much crap. You have the inter-tooth time varying over a 300:1 range, and if the engine is capable of accelerating over this range in a time on the order of a few seconds, then things become much more critical at the low RPM in so far as distinguishing the reference pulse from an ordinary tooth passing in front of the sensor early due to acceleration. You're not doing anything here that can't be quantified precisely, so this stuff about averaging over say...5 interpulse times...and declaring reference when an interpulse time is... oh say...70% of an average...is your typical pussy programmer crap that's going to get you in trouble.

And there should be a TDC pulse from which to run default timing until the engine is actually running.

...Jim Thompson

more

You could count clock pulses (from the micro's clock or whatever) from the start of one tooth to the start of another tooth. Store that number and then compare the next count to the stored number. When the index tooth comes along it should nearly cut the count in half. Set up some rules in your software to look for an abrupt change in the count. I don't think a typical gas engine could accelerate to 2x the RPM within a tooth or two, so what you are really looking for is a rapid change (2x) in the frequency of the teeth. Doing it this way would work at any RPM or range of RPM because you are comparing the rate from one tooth to the next.

What could possibly be simpler than ten lines of code in the cpu you are going to connect it to?

connect signal to timer capture pin, if captured period is half of previous period,

-Lasse

doesn't have to be, lots of engines run just fine with nothing but a

on e.g a inline 4 running with wasted spark not running real sequential injection you don't need to know

-Lasse

On the "crack"? That explains it ;-)

BTW, what good is 6° tooth spacing?

...Jim Thompson

Is it safe to assume that the duty cycle (high to low time) of each of the 36 teeth are the same and the 37th tooth has the same high time (same tooth width) but a shorter low time (smaller gap)?

Space between all tooth is constant (1 to 36 & 36 to 1), the 37th teeth is nested in the middle of the time between 36 and 1. My drawing is not really exact, using the characters to draw graphic is far than precise, sorry.

Bye Jacques

crank ;)

frequency in Hz equals speed in rpm? :p

regardless of number of teeth timing will be usually done by software as something like an edge plus a fraction of a previous period.

-Lasse