Braineack

iTrader: (62)

A lot of people keep asking me. So I'll lay it out very easily.

It should take you about 10-20 minutes, you just need 470ohm resistors to
make it happen.



On the top of the board:

The MS-II & MS-III daughter-boards require an alternative method to receive the second trigger. Therefore you must remove the jumpers for D1 and D2. You must also replace R12 with a 470ohm resistor. I used a 1/2watt to match the rating of the supplied resistor.




On the back of the board:

To continue the thought on the alternative method for the tach signal...Remove the jumper from XG2 a& XG1 and from Tachselect & OPOTIN. Now jump Tachselect to XG1.

The Main input is the same, but it's moved to JS10. The Daughter-board has an inline 1K resistor pressed onto the board, so you just need to keep the 470ohm pull-up from 5v. So run your main input from IAC1A to JS10 and then run a 470ohm resistor from 5v to JS10 as well.

Run another jumper from 5v to the top of the c30 pin. This provides a pullup from 5v through the 470ohm resistors you replaced on the front of the board for the 2nd trigger.

Now you must swap your ignition outputs because we all do it backwards on MS-I.




As far as hardware, that's it.

Ben

iTrader: (33)

I just wanted to emphasize that point. Your timing will be 180° out if you miss this step.

Good write-up Scott. Sometime shortly in the future, I want to release a how-to to upgrade the MSPNP. I've built one, just need some time to test it.

Braineack

iTrader: (62)

The is another method for the 2nd trigger, using an opt-isolator identical to the main input, but it seems to run perfectly well this way.

richyvrlimited

iTrader: (1)

Mine didn't fwiw and required the opto. For the extra effort required it's definately worth it.

Braineack

iTrader: (62)

are you using the 96 CAS? I just converted a '97 MS-I and it's fine.

richyvrlimited

iTrader: (1)

Yeah, 96 CAS

Must be my car it's a law unto it's self. I to prefer the Opto circuit for CPU protection though.

cjsafski

iTrader: (2)

Dumb question time. I am going to be upgrading my msI soon which has the tach circuit built as in your writeup.



Is your picture in the the first post the completed circuit or just part of it? What bothers me is what do i do with the other wires like the one that runs from the top right through the 470ohm resistor back to the board. Do i remove them or are they parts of the output and leave them alone?

Braineack

iTrader: (62)

This little write-up assumes you already have done the rest and have been running with MS-I. Really no more or less.

The 470ohm pull-up and 1K inline resistor going to IAC1A get replaced. They are the second trigger input from the CAS, I sorta mention above that you must redo the inputs for the CAS. It's basically the same thing, but the input is on JS10 vs. JS8, and the 1K resistor is already stamped onto the MS-II. So all you need is the 470ohm pull-up from 5vref.

The only other wires in my pictures above are jumpers for my fan control (IAC1B to D15) and the clutch switch (IAC2A to JS7).

I'm using, and I suggest you run, Joe's updated spark output mod using two extra 2n2222 transistors:

boileralum

iTrader: (8)

Can we get this thread added to the SUPER Important MS Threads thread? https://www.miataturbo.net/megasquirt-18/super-important-megasquirt-threads-17498/

Good info as always, Scott.