Apologies for the bone questions...I've asked a few over the last few days. Anyway I'm building my ms2 at the moment. Have completed up to and not including tach inputs as per the msextra manual. Just wanted to clarify a couple of things here:
1. I presume that this replaces the tach input instructions in msextra and I should ignore them?
2. Trying to get my head around the diagram. Is it the same opamp for circuit A and B?
3. I'm not sure I even know what an opamp does...does opamp operate like two transistors in the same 8 pin package.
4. Do the raw signals come in tach select and iac1a and the new signals go out to tsel and js8? Do I need to make any other connections on the board apart from this (not talking about the spark output yet that can wait for another day)

Yes.


It can be.

Op-Amps are extremely inexpensive and simple circuits, and for the purposes of economy, they common come packaged as multiple op-amps in a single chip. The specific device described here (the LM393) is two op-amps packaged in a single housing. So, in the schematic, parts A and B are two separate op-amp circuits that just happen to be sitting side by side on the same chip.


It's a bit more complex than that. At its most basic, an op-amp is a type of non-linear amplifier, with differential (inverting and non-inverting) inputs.

In our case, we are exploiting the extreme non-linearity inherent in most op-amps to create a comparator. Essentially, we apply a reference voltage (created by a simple resistive voltage divider) to the + pin, and apply the signal to be discriminated (the sensor output) to the - pin. When the signal at the - pin (the sensor output) becomes more positive than the reference voltage, the amplifier output turns off. When the sensor output becomes less positive than the reference, the amplifier turns on. There's a bit more to it than that (we are applying a low-pass filter, and also configuring the circuit to exhibit hysteresis, both the the purpose of filtering out noise), but that's essentially the gist of it.

As a matter of trivia, an op-amp generally consists of a few dozen transistors along with some passives.




Yes. And those specific names are throwbacks to the common conventions used in MS1s built on the 3.0 PCB. In particular, MS2/3 builds will use different pins on the output side.


Nope. You just replace all of the bullshit that would normally connect to the pads in question with this circuit and enjoy the benefits of reliable sensor pickup.

Incidentally, this whole circuit is obsolete as hell now that we've discovered the MAX9926. It still works fine in most applications, though my personal preference is for the Maxim chip, as it exhibits noise-rejection characteristics which defy belief.

Thanks for that - can kind of get my head around it now. (ok point number 3 confused the hell out of me but I don't think that matters too much).

Is there any reason for me to need the max9926 circuit. I looked it up on google and it looks bloody hard to solder!

what are you trying to build.


there's honestly no reason to build Abe's circuit or use the max9926.

Use the VR input for the crank, and the ms3x expander board input for the cam (or the invereted opto in for the cam) and be done with it.

Just an MS2 that works!
I'd heard that the msextra circuits cause people problems sometimes. And also found Abe's diagram easier to understand then the instructions on msextra.

I thought the mx5 used hall sensors - so why the VR circuit on the crank?

abe's diagram is easier only because it is proprietary to a miata.

populate the both the VR and opto circuits when builing your MS.

You'll use the VR for the crank input (inverted out) and the Opto for the cam. It couldn't be easier because there's no extra components to populate, you just add the appropriate jumpers and a pull up.

if the circuit cause people problems, then the problem is the people.

Oh so even though its the vr input it doesn't have to be a vr signal - the jumpers and pullups take care of that?

It's not proprietary to a Miata. It's designed to work with any vehicle that uses two open-collector sensors, which I'd dare wager is at least 50% of the cars on the road today.


In electronics, there are rarely absolutes.

The "VR" circuit on the MS is optimized for VR operation*, but capable of functioning with any sensor whose output falls within its range of detectability. In this case, the pullup brings the signal into the range of voltages which the circuit can trigger on.


* = actually, it's not optimized very well at all. Speaking from personal experience, the '9924/9926 have far better false-trigger protection.

Question about the vr circuits braineack mentions in post #106.

Do I only need to install the components mentioned here MS2-Extra Miata Manual

Or do I need to install the components in the ms manual that are part of the vr build process?

Interesting side not...

We are working on the ME221 based PnP for the MX5 NB - We use the Max9926 as our input conditioner - currently we are seeing the crank signal 'dissapear' at around 2000rpm then come back, then go again (at around 500mS interval on the logic analsyer). I am putting this down to the fact we are use 470ohm pull-ups to 5v as opposed to 3k3 (as per OEM) so I suspect the sensor is overheating or something to that effect - going to try 3k3 today and will report back :) Maybe helpful for those who have had this issue (if any!)

Matt

Yup... that was it :)

Hi all,

First off, I'm really sorry to ask these questions, but I'm having trouble getting straight in my head exactly what I need to do to get this to work.

Car: 1998 NB MX5
Megasquirt PCB: V3.0
Processor: MS2

Which circuit(s) should I build to condition the crank and cam inputs? The images on this thread are showing "Bandwidth exceeded" - has anyone got a copy of the diagrams?

Once the circuit(s) are built, do I set the inputs on the PCB up like so?

Megasquirt (V3.0 board) - Tach input

Crank:
"V3.0 board - VR Input for logic input e.g. TFI, EDIS, GMDIS, LS1/24X, modules
a) Solder a link between VRIN and TACHSELECT
b) Solder a wire between VrOUT and TSEL
c) With a small screwdriver, turn the pots, R52 and R56, about 12 turns anticlockwise (sometimes you may feel a "click" when the end position is reached, they can't be damaged by turning too far.)
d) Turn R56 back about 6 turns clockwise. "

Cam:
MS3X card - Cam Input
MS3X card cam
For hall or optical sensor inputs.
a) Install the jumper across JP7
b) Turn both pots (R11 and R32) 7 turns anti-clockwise (sometimes you may feel a "click" when the end position is reached, they can't be damaged by turning too far.)
c) Then turn the top one (R11) 3 turns clockwise.

Is that right?

Sorry again, I'm just having a bit of information overload with this. I'm not new to MS, I have had this particular ECU running on another car before, I'm just not entirely sure what I need to do to make it run on my MX5 :)

what you posted is correct, but youll wanna turn r56 at least 7.5 turns and r11 closer to 3.5.

do you even have an expander board?

What expander board? He says it's an MS2.

Do I need an expander board? That's another thing I've not really heard of.

Sorry for all the dumb questions.

FWIW I plan on running batch fire rather than sequential - isn't the expansion board to provide the extra injector outputs to run sequential?

And does anyone have the circuit diagrams for the input conditioner circuit? All the images in the original post on this thread are still showing bandwidth exceeded.

Cheers :)

You're the one who mentioned r11