Abe & JasonC's NB Cam & Crank input circuits - Page 3 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 11-20-2008, 05:43 PM   #41
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I built Abe's circuit around the TL082 instead. It fits in the VR area as well.
Edited my post #38 above so there's no confusion.
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Old 11-22-2008, 01:47 AM   #42
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I built Jason's circuit and just fired it up for the first time tonight. I'm having hardware issues so I never went beyond idle but it synced up and ran no problem.

I'm running in parallel so no pull up.
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Old 12-27-2008, 09:03 PM   #43
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Hi, Im fairly new to MS.

Im planning to fit a MSIIextra v3 to a 1992 eunos roadster. I've just built the opto isolater circuit as described in the MSII extra manual and then just read this thread (or a few other similar threads on here) and found that I may have trouble with the circuit ive just built. Im not very technical (electrical engineering wise so don't understand the system design aspectsnor have the tools to do extensive testing) Im after the simplest and most reliable way to get my roadster running on the megasquirt.

Which option would you say best suits my needs,
a) switch to msI?
b) stick with the opto-isolater circuit,
c) build this,

d) switch to fords edis system?
e) any other suggestions?

Im planning to run standalone and also plan to fit a greddy turbo kit in the near future.

Im also struggling to see how to wire up the CMP/CKP wires to the db37 as I only see one CAS wire labelled? Am I missing something obvious?


Thanks in advance for your help,

Rob
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Old 12-27-2008, 09:33 PM   #44
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I don't think there's really much reason to run an MSII in a 1.6L
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Old 12-28-2008, 08:45 AM   #45
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Offline, it's the shielded grey wire that's the other CAS wire.

N3v, explain. MSII is a more powerful processor, with more accurate injection timing it's irrelevant what size the engine is. it'll run better once the MSII is going properly and tuned.
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Old 01-08-2009, 08:21 PM   #46
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Quote:
Originally Posted by JasonC SBB View Post
Oh they're using LM358's as comparators? Those buggers are slow. Hmmm... I wonder if they'll insert a significant delay...

You could maybe use LM393 comparators if they have the same pinout, but they'll need 1k pullups on their outputs.
Jason,
Most of the noise rejection (well, half?) comes from it being slow. You want it to be slow. The software will take care of subtracting a fixed gate delay,this is trivial. What isn't is digitially filtering out the noise spikes longer than one gate delay - hence using nice slow comparators. :-)

Huh, I really looked at reworking the opto part of the board to do this circuit, and decided it was more trouble than it was worth - but I think your part has a different pinout which might make it work.

Ah, well, I'm just about to run off some of my adapter boards, then it should be a moot point.



As far as running the MS-II - really... you have to be realistic about your goals. MS-II is the obvious choice for someone on OEM 99+ sensors, since the software is there. Yes they have better timing, but only marginally, and the code is so terrible you might be worse off. Either way, the slop in the cam belt driven CAS sensor is far and away the leading factor - so unless you want to run a crank trigger, give it up, do what everyone else is doing, and go drive your MS-I powered, CAS based car. It'll be fine. If you want to go win races or be a dyno queen, then look at questions of 1* timing accuracy. The ease of having something everyone knows works is better.
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Old 01-08-2009, 08:35 PM   #47
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Quote:
Originally Posted by JasonC SBB View Post
Ah yes, that circuit was designed for my setup which is a parallel install - the factory ECU is installed. I don't know if the NB sensors by themselves have pulldown outputs if the factory ECU is not there.

You can add a pullup to the left of R1 and then just get rid of R2.
Ok, skimmed the rest of the thread. Yes, you can leave off the caps - I haven't run them. For a while, the version floating around had 10x the capacitence of facotry, which (I built for fun) limits you to about 6,200 RPM. I cna't see Joe's picture, I should post one of my own, I guess.


And here's what i'm using for my boards:

Though it's quite old and I'm tempted to check it for mistakes. EDIT: It shows a 10 nf, and you want to use 1 nf. Or nothing at all.


Two points, Jason, not to pick on you...

1) Very minor, but in parallel with the OEM, you'll be seeing some of it's capacitence. Ok, past their resistor, but still, it's there.
2) The op-amp has a fair amount of hysterisis. Aside from the time delay, the biggest part is when in the 0V state, you need to see signal over 3.8V to switch, when in the 5V state, you need to see a voltage under 1.2V, or there abouts. All selectable with resistors. The one I run is just a bit wider than the factory's. This cleans up all sorts of noise.

Last edited by AbeFM; 01-09-2009 at 02:02 PM.
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Old 01-09-2009, 04:05 AM   #48
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Abe, I wonder why nobody ever answered your question in post #65 here, but a cap with 102 on it is 1nF not 10nF.

Here's a pic of your circuit in the VR area (the caps are not installed yet cause I'm having trouble finding NPO's overhere).
Yellow wires and resistors on the back of the PCB are for the circuit.



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Old 01-09-2009, 02:05 PM   #49
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Thanks! I'm certainly one to appreciate having mistakes pointed out over doing something wrong!

BTW, if you're losing sync ever, try pulling out the caps (you'll want to adjust the time delay in software down), and you can use 12 kohms, it actually gives you a bit wider noise rejection as I recall. Somewhere I did all the math.
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Old 01-11-2009, 07:14 AM   #50
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I'll give it a try once the car gets back from the UK. Might be a while though :(
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Old 01-11-2009, 12:56 PM   #51
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"If it ain't broke, don't fix it"... You'll just have to see how it runs, my guess is it's not a big enough deal to make it worth going back into surgery for. In fact, as I said, I don't even run caps.
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Old 01-11-2009, 04:15 PM   #52
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Quote:
Originally Posted by AbeFM View Post

Two points, Jason, not to pick on you...

1) Very minor, but in parallel with the OEM, you'll be seeing some of it's capacitence. Ok, past their resistor, but still, it's there.
The capacitance in the OEM circuit appears after its internal resistor - it doesn't load the resistor in my circuit, therefore it doesn't insert a large delay[quote]

Quote:
2) The op-amp <circuit> has a fair amount of hysterisis.
I know it does. I'm saying the chip I'm suggesting implements hysteresis internally, i.e. without needing a bunch of resistors.
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Old 01-11-2009, 07:07 PM   #53
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I thought so, but then earlier when you were talking about it, you kept mentioning "the" switch point.

Does it temporally filter to, or does an arbitrarily short spike show up (delayed) on the output as the same spike?
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Old 01-12-2009, 01:54 AM   #54
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Short spikes will get filtered out.
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Old 01-12-2009, 05:44 PM   #55
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Q1: Without this circuit, MegaTune will not register any RPM while cranking, right? And the engine will turn but not catch due to the MS not syncing, so it doesn't run at all, not just that it runs rough or anything, right?

Jim
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Old 01-12-2009, 08:52 PM   #56
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Indeed. You'll see "NOT SYNCED" in the display.
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Old 01-13-2009, 12:35 PM   #57
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I almost forgot, you do NOT do the DIY mods (+12v pullup on CKP, +5V pullup on CMP), right?

Jim
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Old 01-13-2009, 12:49 PM   #58
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Quote:
Originally Posted by Reverant View Post
I almost forgot, you do NOT do the DIY mods (+12v pullup on CKP, +5V pullup on CMP), right?
The circuits being discussed here are alternatives to the one which you refer to. In addition to not doing the pullup mods you listed, the CKP portion entirely replaces the whole Tach Input circuit described on page 3 of the schematic, including the optoisolator U3. Its input comes direct from the sensor, and its output goes straight to the CPU.

They can be constructed with an internal pullup circuit for standalone operation (as shown in my modified version of Jason's circuit in post 30, Abe's diagram in post 47, and drytoast's diagram in post 33) or built without a pullup, for parallel operation where the stock ECU provides one (as shown in Jason's original diagram in post 14)

I agree that this is all getting a bit confusing. Does anybody have a suggestion for how we can come up with a definitive schematic? I'd really like to be able to correct the diagram shown in the MS2Extra manual which is completely wrong.
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Old 01-13-2009, 01:35 PM   #59
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Quote:
Originally Posted by Joe Perez View Post
The circuits being discussed here are alternatives to the one which you refer to. In addition to not doing the pullup mods you listed, the CKP portion entirely replaces the whole Tach Input circuit described on page 3 of the schematic, including the optoisolator U3. Its input comes direct from the sensor, and its output goes straight to the CPU.
Wow, I missed this part alltogether.
I went ahead and built a circuit around the LM339 which I already had around from another project. Like the attached schematic. I hope it is ok...

Jim
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Abe &amp; JasonC's NB Cam &amp; Crank input circuits-lm339_circuit.png  
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Old 01-13-2009, 01:57 PM   #60
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Quote:
Originally Posted by Joe Perez View Post
I agree that this is all getting a bit confusing. Does anybody have a suggestion for how we can come up with a definitive schematic? I'd really like to be able to correct the diagram shown in the MS2Extra manual which is completely wrong.
Pretty much it comes down to thinking through the Schmitt Trigger thing. I wonder why Mazda didn't use it - could be something as simple as they already had the opamps on board in a 4 pack. But I doubt it, all those resistors and caps really mean a lot of space/parts. I think they kept it because it's tunable.

Maybe I will just go ahead and print up that little board I showed earlier, with only the inputs. Then folks can populate it as they will, but it's a lot easier.
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