Abe & JasonC's NB Cam & Crank input circuits
 

After putting a bunch of time into cleaning up this drawing for a thread over at msextra.com, it occurs to me that it never did get stickied here. Prolem solved:


http://img37.picoodle.com/img/img37/...2m_a6b73d2.gif

Note that it's been suggested that the TL082 opamp may yield better performance than the LM393. The two are pin-compatible, so if possible you should attempt to substitute a TL082 in this circuit instead. The TL082 is available from RadioShack as P/N 276-1715, so this is one more thing in its favor.

As drawn, this is for MS2. You could use it for MS1 as well, by changing JS10 to JS8 on the B-side output.

Noob alert: Is this made on a separate board (like a breadboard)? This may be harder going MS-II than I thought.

If you are careful about your layout, it will easily fit into the proto area of the 3.0, with plenty of space left over for a couple of relay drivers. Abe was good enough to do a nifty 3d layout of the assembled circuit:

http://abefm.smugmug.com/photos/359141699_sJRfL-M.jpg


Of course, you can if you wish to it on a seperate board, as etnad is doing:
http://img26.picoodle.com/img/img26/...6m_ee98ebe.jpg
(note that I do not condone this hideous mess of resistors. Are you listening, etnad? Clean up your goddamn wiring!)


When I abandoned the CAS and went to a wheel, I actually built the new decoder circuit in such a way that it is completely external to the MS, which made it easier to fine-tune. It's in a small external box, which tethers to my MS via a 3 wire cable as seen here: https://www.miataturbo.net/forum/sho...884#post251884

Ah! That is a mess! Lol. I rather build it in the proto area so everything can fit onto just the one board. You only had to build the separate box since you had a custon wheel right?

Yeah. As I explained in the writeup, when I assembled my MS I figured I'd never need the VR circuit, so I left those components out and glued a very large capacitor down to that empty space on the board. So in the end, when I wound up needing the VR circuit after all, I had no choice but to build it on a separate board. (my proto area was already packed with other circuits, including my previous dual pickup circuit)

I decided to put it in an external box since I has just been through a very frustrating experiance with my previous ignition trigger circuits, and I wanted something that was easy to remove, test and modify if need be. As it turns out, it failed horribly the first time, but worked perfectly thereafter, once I flipped one connection around and re-installed it.

But the vast majority of folks build their pickup circuit right on the main board, regardless of what type of circuit it is.

isn't his last name Mara?

did abe do the bottom one?

Uhm... shit. I honestly don't know- I never bothered to steal his wallet and check his drivers license.

Abe, have I been mis-spelling your name all this time?

you think I read?! you know me better than that. I only asked because I've seen some of abe's circuits....this etnad character must have been his padiwan.

Oh, I was responding top Y8s' question about the spelling of his name, You snuck in right before I hit send.

What do you mean by "the bottom one"? The 3d rendering?

Tee hee hee

http://abefm.smugmug.com/gallery/262...38616327_GWT5v

Oh yeah. I remember that day well. We were coming around a big, fast turn, and I was trail-braking. Initially started heading for that wall, then over-corrected, spun 180, and exited the road backwards into those trees which, thankfully, stopped me without doing too much damage to the car.

Shortly thereafter I became a bit more serious about my tires and suspension. Needless to say, the T1Ss went away, as did the AGXs, the big rear bar, etc...

You can cut the parts counts drastically by using a 74C14 (Schmitt trigger input inverter).

And your heavy noise rejection filter will delay the signal by 4° at 7200 RPM. Not good.

Or a CD40106 (which is very similar to a 74C14)

Like so.

You can increase the 470Ω resistor to ~1kΩ and the delay will be <0.5° at 7200 RPM.

This circuit was the result of Abe reverse-engineering the input circuits in his OEM '99 ECU. It is not an attempt at optimization, merely an exact duplicate of the factory circuit.

Delay due to the input filtration can be negated in software, as there is a specific field for entering the hardware latency of the trigger input.

but isn't the delay frequency (rpm) dependent iow, a fixed latency has no(t a lot of) use?

I'm a bit at a loss here. As I understand it, the MS2 has the necessary software for the NB sensors, using this circuit.
Can the NB sensors be used on MS1 as well or does its software not allow this? It prefer MS1 over MS2 if possible (because of better idle and WI control).

Well, I grant you that as f approaches ∞ there will be a phase shift in the voltage across the capacitor, however in practice this seems to be relatively small by way of comparison to the fixed latency of the circuit.

MS1 software doesn't support the NB sensors.

The MS1 software cannot be made to understand the NB's unevenly-spaced crankwheel. One could make it work by trimming the two TDC teeth off of the wheel.

It's also been postulated that, even for an NA, this circuit is likely more reliable than the ones commonly used for 4G63 input. A number of NA owners (myself included) have found that CASs which worked perfectly on the stock ECU exhibited severe problems when used with a MegaSquirt. I'd like to see the next person who runs into that problem try this circuit.

If the capacitors used are Z5U or Y5V, and not temperature stable types such as NPO or X7R, the capacitance can very 2 to 1 over temperature. This means the delay can change by 2° at 7200 RPM. For a high boost, finely tuned engine, that is a bad thing.

Reduce the filter delay and use shielded cable directly from the CAS to the MS.

Frank, the lowpass filter will delay the edges a certain amount of time, not produce a fixed phase shift.

Did nobody read the caption that says C1 and C2 can be omitted if not required? We're not espousing intentionally high-latency circuits here, merely duplicating what the factory did.

It would be a BAD IDEA to have no noise filtering at all by removing C1 and C2.

Joe, no need to be defensive. I'm trying to help.

The factory probably uses NPO caps. Besides, 2° error on the factory map, without FI, wouldn't hurt the engine.

I repeat - anyone who builds that factory circuit is better off reducing those caps by a factor of 4, *and* using NPO or X7R type capacitors.

It would also be prudent to use shielded cable for CKP and CMP. The shield should be connected to the chassis at one end, and one of the inner conductors used for the sensor ground ... connecting from the sensor to the ECU sensor ground.

Anyone who wants a lower parts count circuit, can use the one I posted.

Jason, regarding the circuit in post 14- I see no pullup on the input side of the gate. Seems to me we need one to the left of R1.

Also, we need the control pin to be tied high. That pin isn't illustrated on your symbol. but the CD4016 has one control per gate.

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.

Is the output of the CAS from 99-2005 and 90-93 the same?

Did anyone try Abe's circuit with the 90-93 CAS?

I have built the CMP input using the optoisolator circuit but everytime the RPM reach a certain value (~1750 rpm), they drop to 0 and then recover, the MS2 staying fully powered.
My next try is to connect the CAS CMP input directly to the MS port without the optoisolator and if that doesn't work, try Abe's circuit.

Thanks

They're similar. And frankly, this is a better circuit than the opto-based one for pretty much any Miata.

So it should work if I use this circuit with the 90-93 CAS, right?

Do you know what is the difference between the 2 CAS inputs? Maybe there is a way to account for the difference electronically?

Excuse my ignorance, but what is the purpose of the pulldown in the original circuit. Is that for use in a parallel install with the stock ECU? Just curious as to what the interaction is between two ECU's sharing the signal.

I'm not sure where you see a pulldown in the original circuit. Can you provide me with a reference designator?


Let me clarify a bit how the circuits in question work, and what Jason and I were talking about.

First, understand how the crank and cam sensors operate. They do not output a voltage, instead, they provide what in the EE industry is called an "open collector" output, which Jason is referring to as a pulldown output. The origin of the term "open collector" stems from the fact that historically, this type of configuration was achieved by attaching the output pin of the circuit to the collector terminal of an NPN transistor, with the emitter terminal connected to ground internally.

I know that not everyone is familiar with transistor theory, but in an NPN transistor, voltage is allowed to flow from the collector to the emitter whenever the base terminal is energized. The emitter terminal is the one with the triangle on it, the collector is the one opposite, and the base is the terminal on the left, which acts as a gate between the collector and the emitter. You can think of it as a relay, where the emitter and collector are the contacts, and the base is the coil. PNP transistors are similar, but voltage flows in the opposite direction and the base is active when grounded rather than when powered.

Sidebar: here's a quick and simple tutorial on how transistors work: Transistor Tutorial


Now, to get back on topic. I've drawn a massively simplified version of how Abe's circuit works, in which I have included the sensor itself:
http://img37.picoodle.com/img/img37/...em_d907367.gif
As you can see, there is a pullup resistor inside the MS which causes the CPU to see +5v on its input whenever the sensor is "off". When the sensor turns "on", the transistor conducts all the voltage which is passing through the resistor to ground, causing the CPU to see 0v on its input. This is how the processor knows that something is going on.

Now, here's what it would look like if this were a parallel install with the stock ECU in place:
http://img29.picoodle.com/img/img29/...lm_6854fd9.gif
As you can see, there is already a pullup resistor inside the stock ECU. This is how it works from the factory. Since we can't easily eliminate this resistor, we eliminate the one inside the MS instead. The voltage provided by the pullup inside the ECU backflows into the MS, and provides the same functionality as the one we'd have put there originally.

Note that this is the same reason we must remove R7 from the MS with doing a parallel install with the CLT sensor shared between the two. Again, the ECU already has a pullup on the CLT line, and we don't want to do it twice.


Ok, now here's Jason's originall circuit again:
https://www.miataturbo.net/forum/att...8807-input.gif
As you can see, there is no pullup resistor on the line to the sensor. This assumes that the stock ECU is there providing the pullup voltage.

If we wanted to use Jason's circuit in a standalone application, we'd need to install a pullup, or there would be no voltage on that line, ever. I've modified his drawing to show this:
http://img01.picoodle.com/img/img01/...nm_85a3cb3.gif


One of these eons I'm going to get off my butt and draw a version of Jason's circuit that is complete and ready to use...

Sorry, I should have been more clear. I understand the open collector concept. I was referring to R2 in his original diagram. That appears like a pull down except for the fact that its on the other side of the R1 (filter). Perhaps a better worded question is:

What is the purpose of R2?

Joe I commend your little writeup above.

drytoast, (typing your handle makes me chuckle, was that what your were eating when you were registering?), the purpose of R2 is to have a slight pull down offset effect on the signal, in case there are ground shifts (slight differences in ground between where the above circuit is, and the ground of the sensor). The reason this offset may be needed, is that the Schmitt trigger (CD40106) threshold centerpoint is not 2.5V, but a bit lower. Therefore it is more sensitive to a slightly positive "low" signal from the sensor, than it is to a slighlty negative "high" signal from the sensor. IIRC the minimum votlage for a definite "low" signal on the Schmitt's input is 0.8V, whereas for "high" it's ~3V. Exact values are in the datasheet.

Did that make sense?

The original reason I put R2 in is that with the factory ECU / parallel setup, I observed that the "low" signal was at ~0.4V, a bit too l close to 0.8V for comfort. If you have a standalone setup and the voltage is much closer to 0V, then R2 is not needed.

Ahhh, makes sense.

As for the handle, that is a long story from University.

Too bad, I didn't see this thread earlier as I probably would have started with a schmitt trigger. Didn't even consider an IC that already does the same thing as this circuit. Oh well. I copied the idea from Abe's handiwork and just used the leftover VR opamp circuit on the MS board like in the attached picture.

The shaded area is what's in the proto area. The dashed lines are connections made with wire. The solid lines are traces already on the board. I tried to copy the same layout as the MS V3 schematics so you can see what components I left out, shorted or replaced with different values. You can ignore the opto circuit at the top. Another unused section I commandeered for clutch signal protection. I just wanted to document it so when something breaks later, I can figure out what I was doing. :)

Note: I used slightly different values in the feedback portion as that was what I had at home. Its about same ratios though. My input filter is also based on components left over from the MS kit. The caps are X7R.

I built Jason's Schmitt trigger circuit. Should I add a resistor between the CD40106 output and the MS processor?

Please correct me if I'm wrong, but if there is no current draw by the processor then a 10k resistor wouldn't change the reading. On the other hand, if there is no current draw then I really don't need the resistor.

Jason, do you see any problems using Drytoast's circuit (timingwise or so)? If not, it it would be very easy to use the entire VR area for his circuit, without having to use the proto area even.

frank, I don't see aproblem with the circuit.

arga, you don't need a resistor between the CD40106 and the MS processor unless they're 3 feet apart. I don't understand your 2nd Q - what 10k resistor?

Thanks Jason. I asked one of the EEs I work with about this and he said if the Schmitt trigger wasn't TTL I would need a pull up but I had no idea what the CD40106 was.

No real second question, just trying to understand some things and it came out as rambling. I guess my real question is; does the MSII processor (MC9S12) draw current when it reads a voltage?

thx Jason

Drytoast, I used your design (hope you don't mind) and put Abe's components in it's place. I also reordered the components so they actually fit in the VR area. No need to use the proto area.
Although it looks difficult and there seem to be a lot of wires, it's really not that bad.

Can't find a LM358N locally, would it be ok to use a TL082 instead? Or do I need to change the values of the resistors?

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.

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.

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.

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,
http://img01.picoodle.com/img/img01/...nm_85a3cb3.gif
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?
http://www.boostedmiata.com/MS/harness_MS_pinouts.jpg

Thanks in advance for your help,

Rob

I don't think there's really much reason to run an MSII in a 1.6L

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.

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.

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.
http://abefm.smugmug.com/photos/245423731_rG4NE-L-4.png

And here's what i'm using for my boards:
http://abefm.smugmug.com/photos/358282941_DaFDm-M.jpg
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.

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.

http://westfieldmx5.devocht.com/star...t_circuits.jpg

http://westfieldmx5.devocht.com/star...quirt/back.jpg

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.

I'll give it a try once the car gets back from the UK. Might be a while though :(

"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.

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]

I know it does. I'm saying the chip I'm suggesting implements hysteresis internally, i.e. without needing a bunch of resistors.

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?

Short spikes will get filtered out.

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

Indeed. You'll see "NOT SYNCED" in the display.

I almost forgot, you do NOT do the DIY mods (+12v pullup on CKP, +5V pullup on CMP), right?

Jim

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.

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

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.