Yeah, that sounds pretty smart. Adding a DC offset to the idle code doesn't seem *that* hard... As far as a "series of resistors" ... you can just use a big fatty shunt to measure the current output by the alternator, then all you have left is the A/C and the PS pump (since those are mechanical). Presumably those two would just be high/low rather than variable.
What outputs are you referring to? You mean the "outputs that tell the motor that it's on" such as pin 1Q for the A/C?

Just out of curiousity, is this a secret DIYAutotune does not want to disclose to the public? I know it would make a lot of people happy (like me! :) ) and IMO the people that want a complete plug-in EMS solution, aren't gonna see the schematics and suddenly want to do it themselves. Most people look at that stuff like a foreign language and don't want any part of it.

Just thinking out loud.....

Probably more they don't want competition? My little '99+ board will probably at some point compete with them, if they get motivated to make one. I'd assume they are working on one. I just like the little board better, for different reasons, more configurable, etc. It IS how they make their living so it's understandable they'd be a little gaurded. Also I tend to be very aware when I get free info from a source like that not to share it in a way that could hurt them, without express permission to do so.

Yeah - the PS pump and AC have signals to let you know when they are doing something, should be straight forward. But you're always input limited on MS.

To me, MS is just a patch to get things working until I come up with something better. :-)

I'm afraid I can't quite figure out what it is you're referring to. Bear in mind that while the MSPnP is a proprietary creation of DIY, inside the box it's mostly a stock 3.57 MS1 board, with a daughterboard attached to do the Miata-specific interfacing. DIY is not the inventor of the MegaSquirt, they don't own the MegaSquirt design, they didn't write the code, and they don't even manufacture the base MegaSquirt boards. They just happened to be the ones who came up with the rather brilliant idea to take an open-source ECU design and package it in such a way that non-engineers can plug it in and run it without having to build or wire anything.

With regard to what Abe says, I do tend to agree. In fact, I'm a bit surprised about how open the folks from DIY have typically been about the inner goings-on of the MSPnP, insofar as the design of their input and output circuits. It's not rocket science and the stuff is pretty easy to reverse-engineer if you've got one in your hand, but usually all you have to do is ask "How are you guys doing this on the PnP" and they'll tell you, even if it's in a public forum. Trade secrets aside, it really reinforces what a cool bunch of guys they are.

I realize that DIY isn't the creator of Megasquirt or anything else of that nature, I was just wondering what the circuit was they created to make the A/C function correctly (IE bumping up idle when it turns on). Obviously to make it PNP they made a simple daughterboard for the 3.57 PCB, I just wanted to know how the handled the A/C part of it.

If my post came off like I didn't understand what the MSPNP was, I apologize. I also fully respect keeping certain things under wraps as you are trying to make a business out of it, but like you said, they are usually extremely open to helping out the MS community here on things, so I figured maybe they would share what they did to make it work with the PNP. If not, no harm in asking I figure.

The A/C part is just a slightly different approach to doing the same thing as Joe's instructions in the first post. They do NOT do any idle compensation and rely on the closed loop idle control to keep the car from stalling. DIY doesn't do anything to prevent the idle dip when the compressor kicks on (or else I wouldn't have fried that chip in my PNP).

just had a thought on this..
What reason do we have for turning AC off at WOT.
I've built this circuit, but can i not change the settings in megatune to use this circuit to turn off AC when below 1400 rpm instead ?

Hence solving idle problem as AC wont be on at idle.

Surely the AC at WOT off is just to gain back a few horses the compressor will be robbing

But turning the A/C off at 1400 rpm or lower means when you're stuck in traffic you don't get cold air.

dont get stuck in traffic that much over here to be honest, either way it'd make more sense to change the firmware to allow for the WOT off and a ICV pulse at compressor on.

there is a better idle code being work on (PID loop), that may well negate any need for a ICV pulse.

it's only a setting change to disable A/C below 1400rpm, so try it out ;)

in megatune what exactly would i change and to what, soz its a bit confusing for me.. i figured out the above TPS one but the below a value confuses me.

Given that all of these devices only tell the ECU that they are on or off. Why not put the inputs in to a summing amp and then use the different resistor weighting on each input to supply the amount of bump that the idle needs for that particular device or combination of devices.

It's the Hysterisis bit, (assuming the output assigned to A/C has hysterisis, otherwise you'll have to swop them around).

I set mine at 20 and a bloody miracle indeed....no more dip

I thought that was what I was saying? :-)

Man I posted that a while ago. I think when I wrote it I was under the impression that you wanted to have an ADC input for each device.

Looking back it seems pretty obvious.

I cant even get closed loop idling to work on an engine with no additional loads. Maybe I should hold back on the suggestions :loser:

MS-I or MS-II? If it's MS-II there's no shame in that. If it's MS-I.. I hate to be the one to tell you this, but there is shame in that. Sorry.

What happened to the pictures at the start of this thread?

Does anyone have the schematics for getting the a/c to work on an NB miata? It apparently disappeared here. Really appreciate it. Thanks!

its pretty simple.

what's your ECU?


You'd jump 1P to 1S. That will trigger the a/c compressor when the a/c switch is pressed

From 1S, run a diode (banded end towards 1S) to 1I, this will enable the a/c fan.

You don't even need the diode, only if the main fan and cooling fan have been paralleled, this will prevent the a/c fan from activating when the cooling fan comes on.