Joe Perez

iTrader: (8)

The problem is that none of us is 100% certain what he needs, hence my trying to get an MS1 CPU from someone so I can test the NB signals into it on the bench.

For certain, the following will work:
1- Convert the NB's CKP signal into two evenly-spaced pulses per crankshaft revolution, with a falling edge occurring somewhere around 60-80°BTDC and BBDC. Note that this is a falling edge from the perspective of the CPU pin 14, so we'll need DIY to chime in and tell us what circuitry lies between that pin and the outside world (eg: inverting vs. non-inverting.)
2- Convert the NB's CMP signal into two evenly spaced pulses per camshaft revolution, each with a rising edge that does not align with a CKP falling edge.
3- These signals should both be open-collector outputs, with the expectation of an external pullup (inside the MS) to +5.

IOW, to dredge up an old scope cap, you want to transform 1 & 2 into 3 & 4. Note that in this picture, the rising edge of trace 3 (the NA CMP) is the critical one, as it always occurs in the same place.




On the other hand, it may not be necessary to do both, or even either. Matt is of the opinion that when in dual wheel mode, the MS1 is sufficiently forgiving that it will accept the NB's unevenly spaced CKPs, and I am of the opinion that it will accept the NB's single/double CMP pulses, as they are being used only for counter resets (no timing) and the double-pulse occurs entirely within the space between two adjacent CKP pulses.

Given all the trouble that you guys discovered with the NB's CKP going all wonky during cranking however (providing reliable rising edges, but unreliable falling edges) it would be necessary to make it such that the MS1 CPU itself sees an inverted version of that signal, as the MS1's hardware interrupt line is falling-edge triggered only. (the second input is configurable for rising or falling)

Joe Perez

iTrader: (8)

Sure they will. The problem in my case however was apparently a funky CAS. Either that, or funky factory wiring. Or maybe just funkiness related to the length and proximity to the injector wires of the stock CAS wiring. Or maybe something else funky I hadn't figured out yet. Too many damn variables.

Rather than take an incremental approach, I instead decided to bin the whole thing and start fresh. I fabricated a 36-1 wheel mount, and used a VR sensor. All new hardware = no potential of dragging old problems along behind me.

Click the "Wheel 'O Timing" link in my sig the whole whole scoop. My dialogue with the wall lays out the whole reasoning process behind the conversion.

Zaphod

Well, I think this would be really great - though I was already thinking of going the MS2 route... But this way it would save me a lot of time..

Well, we have to talk about the whorehouses though - Prague is only about 2 hours drive away - and yes I think there really are the best looking women in the world in Prague - I don't know why, but it is so!

Unfortunatly I can't give you any help on how the circuit has to be designed...

Joe and you seem to be on a much higher level of knowledge of all that.

Greets

JasonC SBB

Would this work? (see attached) I have the designs to do it.

New CKP will be just like the NA CKP but ~3 retarded. All edges of the new CKP will align with RISING edges of NB CKP. Note that during cranking, FALLING edges of NB CKP can move MUCH earlier, but rising edges are always correct.

New CMP will be triggered from FALLING edges of CKP. The exact location wrt crank degrees will be different than an NA CMP signal, but the edge sequences between CKP and CMP will be the same as the NA signal. i.e. short CMP pulse always "straddles" a CKP rising edge, and the long CMP pulse always straddles the whole CKP pulse 360 crank degrees later. When the NB CKP falling edges go funky, the CMP edges will move much earlier, but the edge sequence will not be violated.

If the MS1 only uses the CMP and CKP edge sequence to determine which cylinder is at TDC compression, and doesn't use the exact location of CMP edges for timing, then it should work.

JasonC SBB

There were only 2 places in the world where my tongue wouldn't stop hanging out onto the floor - Prague, and Rio de Janeiro!

BTW you haven't said yes yet to my request!

Zaphod

I am a married man with 2 little kids - I can't say yes to something like this in an open board...

Greets

Matt Cramer

Those signals ought to work.

Zaphod

So Jason - make it so...


Is that all you need to know to do the circuit?

Greets

JasonC SBB

What's the value of the 5v pullup resistor in the MS1?

Joe Perez

iTrader: (8)

470 ohms is traditional for the NA. I've been reading through some of the historical discussion that took place during the first NB/MS2 experiments, and there's some speculation that the NB sensors may not be able to sink that much current (10ma? c'mon...) and higher values were being experimented with- I saw numbers as high as 4k being thrown around. Seems unnecessarily high to me.

Irritatingly, I can't seem to find a spec at the moment for how much current it takes to make an input pin "high" on the 68HC908GP32.

Matt Cramer

Are you looking for the pull-up resistor for the NB's sensor, or for the pull-up resistor to drive the Hall/Optical circuit? Usually it's one and the same, 470 ohms as Joe mentioned.

JasonC SBB

Well it's moot, I added a TO-92 MOSFET as a pull down.

Joe standard CDxxxx or 74Cxx CMOS IC outputs can only pull up or down < 3mA.

Zaphod your circuit board is ready. I didn't have time to test it on my PC parallel port NB signal emulator because I need to give it to my buddy tomorrow. So keep your fingers crossed.

Give me your address.

If you can't take me to some nice places in Prague, maybe I'll ask you to buy me some Euro style convex driver's side side-view mirrors for my cars. The nanny-government-knows-best in the USA has legislated driver's side sideview mirrors to be flat.

Zaphod

Hi Jason,

thanks a lot - I think we could go to some nice places in Prague - but you would have to come over for that. (So we'll see to that if you are in Germany..)

I send you my adress via PM.

Tell me what kind of mirrors you need - I'll see what I can do (our nanny-government-knows-best doesn't like not TUV approved engine management systems... )

Could please also send me a short explanation what wires have to go where?

Edit: One question just occured to me - do the mods to the board for the CMP/CKP stay?

Thanks

Sven

Zaphod

As I am waiting for Jasons circuit to arrive (should hopefully be here today or tomorrow) - I got a question.

If the circuit outputs the above signal sequence - do I have to change anything to my setup - invert the ingnition lines or something like this (Jason mentioned it in one of the threads - maybe it was for an other circuit though)

The setup procedure for the ignition trigger angle will be the same as usual?

Greets

Zaphod

According my question it I have to remove the changes made to the board for CMP/CKP I got the following reply from Jason:

"Can you show me a before and after schematic of the mod?"

Can someone help me out there? I sent him the pic from Brains "How to" thread - but that doesn't seem to be enough... Maybe someone has a real schematic.


Edit:

I try to give as much information to Jason as possible - so here is an excerpt from the DIYautotune-site.

"Getting the Tach Input Signal:

Run MSnS-E and the "2nd Trigger" Wheel Decoder option (where the missing tooth on the wheel decoder comes from a second sensor, usually cam position). The CAS has a CMP and CKP signal, so you take the outputs of each and run them into the MegaSquirt. Take the CKP signal (4 holes in the Optical sensor wheel, the "outer" ring of the CAS), and run it to the primary tach input on the MS with a 12v pullup resistor - then you take the inner ring of the CAS (1 hole in the sensor wheel) and run it to the secondary tach input on MS (it's pin 11 on the MS-I cpu) with a 5v pullup resistor.

If you follow my documentation for the mods below you'll externally wire the tach inputs like this:

The Primary tach input (CKP) (Reported to be White on Miatas) is connected to pin 24 on the MegaSquirt's DB37

The Secondary tach input (CMP) (Reported to be Yellow on Miatas) is connected to pin 25 on the MegaSquirt's DB37


If you're using a relay board: Pin 24 goes through to position 15, Tach/Ignition for the CKP/Primary Tach Input. Pin 25 goes through to position 7, S1 for the CMP/Secondary Tach Input. You'll need to make sure your relay cable has this wire in place, if so then this will work fine. All of my MS-II ready relay cables have this wire in place. (black loom covered cables are MS-II ready, old MS-I grey cables do not have this wire)


-How to mod a MegaSquirt-I PCB3.0 ECU-

First off when you build up the PCB3.0 board configure the tach circuit for Hall/Opto/Points (step 52). When you get to optional components that say to only install them if you are triggering from the negative side of the coil; you aren't - so don't. Note that normally my pre-assembled MegaSquirt-I ECUs (MS130-C) are assembled and loaded with the standard B&G fuel only firmware, which means they are configured for a fuel only install to trigger from the negative side of the coil. It's easy to reconfigure them, click here for how.



Parts Needed for Input Mod: (1) 1k 1/4w Resistor and (2) 470 ohm 1/4w Resistors (Grab a mk-pullup with your order to get the resistors you need for next to nothing!)

"CMP Signal" -- Lay a 1k 1/4watt resistor across the bottom of the PCB with one end at pin 11 of the processor (U1) and the other end at the IAC1A hole. Bend the resistor leads to raise the resistor just a bit off of the PCB and allow a lead on one end to drop through IAC1A and solder that end in place (while making sure the other end is in place near pin 11 still, and with the resistor still raised a bit off the board so the leads don't short against anything). Then use needle-nose pliers to hold the resistor lead to pin 11 and solder it to the pin. Now to get the 5v pullup use a 470 ohm 1/4w resistor and solder one end of it to the leg of the first resistor to IAC1A and the other leg of it to the 5v+ hole just above the proto area. (This is a long reach so you'll need to use a bit of wire to get across the board.) Once again raise this just enough off of the PCB to prevent it from shorting with any of the leads sticking out on the board. (Heatshrink tubing over the whole wire/resistor assembly works nicely)

The new "cap mod" turns this into a low pass filter that helps avoid misfires caused by a noisy CMP signal. Solder a length of wire to a 0.1 uF capacitor, and connect this capacitor-on-a-wire between JS8 and SG or a ground hole in the proto area.

"CKP Signal" -- We just need a 12v pullup. Install a 470 ohm 1/4w resistor between the right side (non-band) end of D1 and the left leg (banded end) of D9."

Hope this helps at least a bit.

Greets

Matt Cramer

While Sven has a V3.57 board, the mods we did to it are schematically identical to the directions on our website. It starts with the V3.57 schematics here:

http://www.megamanual.com/357/hardware.htm

If you need an illustration, let me know.

JasonC SBB

Swap the (low voltage) connectors to the 2 coil packs (I assume you're using the stock coilpacks).

Also swap injectors 1&4, and 2&3 (I'm assuming your MS runs full sequential - if not, leave them be).

Don't install the 0.1uF capacitors in the above instructions. Take em off if you have.

Joe Perez

iTrader: (8)

Matt, I don't look at the 3.57 schematics all that frequently, so I've never noticed R57 before today. It's the 1k between Vcc and TachIn. Frankly, it confuses me.

Is that thing meant to drive the opto? Assuming D1 and D2 are present, then IF through the U3 LED will be a paltry 1.6ma! Somehow I don't see this being quite enough to get the job done. Even if you bypass D1 and D2, that only gets you to 2.7ma.

So I assume you must be doing the 470 ohm resistor from +12 to somewhere on the "real world" side of D1. But, wouldn't that cause +12 to become present on the Vcc bus by way of backflow through R1?


Jason, here is what the CMP circuit looks like when done "By the book/". JS8 is pin 11 of the CPU. CMP is the open-collector cam output of the CAS- the signal that's one pulse per crank rev.




The CKP input would be basically the exact circuit depicted in page 3 of the schematic Matt linked to, with the caveat that I'm not sure about R57. In the 3.0 world, that resistor would be 470 to +12, rather than 1k to +5. Apart from that, just jumper XG1-XG2, JP1 pins 2-3 and J1 pins 1-2. IOW, we're using the upper-half of the circuit.

Zaphod

Hi Jason,

thanks again. I received the unit yesterday. I will try to install today.

So hopefully the car will start today... (although I don't have a timing light now, because it's free day over here today).

Greets

Zaphod

Got everything installed now... get RPM reading and pulsewidth but no start... swapping over to my build thread with some more questions:

https://www.miataturbo.net/forum/showthread.php?t=26253

If someone could help me out there...

Thanks