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Old 08-26-2010, 01:30 PM   #21
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i shed a tear of joy just now
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Old 08-26-2010, 01:46 PM   #22
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i shed a tear of joy just now
It start to sound like a VVT race engine (12:1 comp etc) would be a nice project next year.
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Old 08-26-2010, 02:51 PM   #23
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Ken, give me more clues like:

1) Pins to make it easy to attach oscilloscope probes for the CKP/CMP signals
2) Prefererences on how to hook up the megasquirt on my stim: DB37, etc...?
3) I'll add a 2x16 LCD to it, do you want any other data on the LCD?
4) Currently my stim is not using timers to generate the pulses, so above about 3000rpm, the MS is losing sync. Is 3000rpm ok, or do you need to go higher? I'm thinking that 3000rpm should be ok.
5) Pullups for the CKP/CMP signals on the stim or on the MS?
6) Something else that I can't think of right now?

Dimitris
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Old 08-26-2010, 06:03 PM   #24
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Ken, give me more clues like:

1) Pins to make it easy to attach oscilloscope probes for the CKP/CMP signals
Sure, that'd be nice, but usually I just connect them on the MS side.

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2) Prefererences on how to hook up the megasquirt on my stim: DB37, etc...?
Sorry, just assumed that's what you'd do. Just use the standard pins for everything on the bottom DB37. I need the cam to be a flying wire so I can just wire it wherever I want.

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3) I'll add a 2x16 LCD to it, do you want any other data on the LCD?
No not really, just the timing it thinks it's doing.

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4) Currently my stim is not using timers to generate the pulses, so above about 3000rpm, the MS is losing sync. Is 3000rpm ok, or do you need to go higher? I'm thinking that 3000rpm should be ok.
That should be a good start in any case. I will want to try it through the whole rev range at some point though. I'm probably going to have to rewrite the sync code for that wheel to handle the cam wheel moving relative to the crank wheel, so I'll want to try that through the whole rev range at some point.

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5) Pullups for the CKP/CMP signals on the stim or on the MS?
The "crank" signal should be +12v and hooked to pin 24 on the db37... the cam signal would be fine as a +5v signal.

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6) Something else that I can't think of right now?
I can't think of anything but if I do I'll let you know.

Don't rush getting it b/c I have plenty to get through before I get to VVT. I just wanted to make sure it's known that this will happen in 1.1.

Ken
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Old 08-27-2010, 12:35 AM   #25
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On an NA engine that doesn't accelerate very quick and doesn't have that much torque 12+1 is plenty. Going to 36-1 or 60-2 doesn't really help during steady state or during light acceleration or deceleration... Where it helps is under very heavy acceleration.
Actually the worst crank acceleration is not during vehicle acceleration. It's during misfire, full power shift clutch-drops, and acceleration in neutral. Especially at low RPM because the sampling rate of the crank is slowest.

When the RPM is rising, the crank angle prediction tends to lag (retard), when it's dropping, it is advanced. So the worst from a timing error point of view would be a full-power clutch drop shift.
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Old 08-27-2010, 11:11 AM   #26
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Aside from that one example, the amount of inaccuracy with a 12+1 is going to be negligible.

I think on the scope during events like those I measured at most a few degrees off. I mean you have to REALLY try hard to get it to be off significantly with a toothed wheel that has more than 8 teeth.

My main concern is that with a turbo engine that's in gear, it starts to hurt power in first and second gear if you have a wheel with too few teeth b/c of the ignition timing retarding.

Also, your examples cover "heavy acceleration" but I was mainly concerned by "heavy acceleration under heavy load," which only the clutch drop covers.

Ken
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Old 08-27-2010, 01:53 PM   #27
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fwiw with the AEM reading only 2 teeth, revving in neutral from idle, I saw 4* of retardation, very briefly at low RPM. It very quickly diminished to 2 then 1 degree.

Remember it's worse at low RPM. And I have a 12 lb flywheel, so engine acceleration in neutral will be way quicker than most any car in 1st gear.

With the AEM now reading 6 teeth, the worst I could see was 2*, and it diminished quickly to <1*.

J_Man reading 12 teeth barely sees half a degree.

He and I did another test, idling then turning one injector off to force a misfire. I could see 1* of error on one cylinder, he could see none. And he barely has any flywheel at all.

Based on this, I reckon 12+1 will be plenty - provided the crank position prediction algorithm is robust - barring a full power clutch drop shift example - but then again, that's at high RPM where errors are lower.
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Old 08-27-2010, 02:21 PM   #28
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Yeah, you're saying basically what I was trying to say. most prediction algorithms hurt steady-state jitter though, so may affect how smooth the engine runs.

Ken
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Old 08-27-2010, 04:32 PM   #29
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What do you mean by steady state jitter?
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Old 08-30-2010, 01:07 PM   #30
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I mean if the engine is at steady state, no load or RPM changes, there's always a little jitter in RPM due to mechanical factors, etc...

That's why you rarely see RPM perfectly flat, there's always some fluctuation in the 10's of RPMs even when cruising at steady RPM. That little bit of fluctuation can be magnified by a prediction algorithm depending on how it's done. At idle, the 1st deriv option in ms3/ms2-extra causes a tiny bit of jitter. I've seen similar things on other manufacturers' EMS's too.

We're porting over the ms2 standard firmware's "alpha-beta-gamma" prediction algorithm in ms3 1.1 though which is supposed to be much better all around than simple 1st or 2nd derivative prediction.

I usually turn off prediction for anything with 12 or more teeth.

Ken
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Old 08-30-2010, 07:03 PM   #31
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Link to alpha/beta/gamma algorithm pls.
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Old 08-30-2010, 07:05 PM   #32
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3) I'll add a 2x16 LCD to it, do you want any other data on the LCD? What type of displays should I use?
What is the simplest way to interface an Arduino board to 2 3-digit displays?

I want to hack my instrument panel, and replace my factory water temp gauge, with a dual digital water/oil temp gauge.

Ideally they'll be backlit LCD.

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Old 08-31-2010, 02:27 AM   #33
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A 2-3 digit LCD is not something readily available, standardized, etc. If you have the space, go for a 2x16. If you don't, get 3 7-segment led displays. You will drive them at high frequency, one at a time. So for 3 7-segment displays, you need 7 pins for the leds of the segment and 3 selection pins.

This is what I did to my own dash, sometime ago: AFR instead of the dummy oil temp gauge, connected to my LM-1:

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Old 08-31-2010, 02:58 AM   #34
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Hrmph, are there no displays with a standard serial comm scheme? 13 wires for 2 gauges is a PITA. How about using a 2.5 digit DVM and sending an analog voltage? Hmmmm
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Old 08-31-2010, 03:05 AM   #35
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Hrmph, are there no displays with a standard serial comm scheme? 13 wires for 2 gauges is a PITA. How about using a 2.5 digit DVM and sending an analog voltage? Hmmmm
That's why we use ribbon cables and 2xN connectors.

Yes, there are serial LCD displays, but I can't think of any off the top of my head, that would fit in there.

You can use any HD44780-based LCD in 4-bit mode, and get away with 10 wires: 2 for power/gnd, 1 for lcd contrast, 1 for backlight, 2 for control signals and 4 for the data (hence the term 4-bit mode), but you drop the speed to less than half.

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Old 08-31-2010, 11:24 AM   #36
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Old 08-31-2010, 12:27 PM   #37
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Yeah, but at $80 you don't call it cheap. The parts for the mod I did were probably less than $10.
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Old 08-31-2010, 03:37 PM   #38
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I spose the way around the hassle is to have a dedicated micro on a little PCB onto which the little 3 digit displays are mounted, so the only wires needed to go to said board are gnd, 12V, and the 2 temp senders.
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Old 08-31-2010, 06:09 PM   #39
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Yes, you would need to fabricate a two-layer pcb to help you with that, or two single sided board and join them via headers. I generally use veroboards and eurocards as much as possible, especially if I am doing anything that requires less than 20x of the same PCB.
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Old 09-01-2010, 02:56 AM   #40
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I've got access at work to PCB design software, and a 2-sided PCB milling machine.
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