PCB layout - JHarvey

[AbeFM]

Very well said, and it pretty much exactly sums up how I feel.
1) The part is chosen (though keeping an upgrade path to the 144 pin part would be ideal - idiot lights, logging extra stuff, etc)
2) Building a cheaper board *after* we've gotten some bugs worked out - a main board with minimal capabilities AND the CPU is ideal.
3)

I agree a 4 layer board is something serious to look at - for a second spin. I don't think it makes it less "DIY" to have a free layout and free software to go order a board, if you want. Sure, you can spin a 2 layer, but... you don't see me out etching my own op-amps, either. I don't see any practical advantage to a 2 layer board, if the board was an iteratively developed, intelligent design, with fully open design criteria and community input.

Harvey! The thought of a daughter card to run sundry stuff... it hard to decide on. Lots of knock sensors, digital dash projects, etc, that I've seen have an atmel part on board for just this. I'm torn, I like the idea of the CPU being, well, the CPU - doing everything. Then again, it supports the expansion bus idea, too. I guess I like the idea of having a CAN bus or something.

Ok, gtg, will add more later.

[Fred]

Thanks Gearhead, Abe. I'd like to add that those parts were rejected because they don't have enough pins. Single chip with sufficient IO was a criteria. 64 pins does not leave enough to run real world cars with accessories and modern ign/inj setups. Nothing much else matched the chosen chip, and the chosen chip was proven to be more than sufficient to do the job by the MS guys.

The software to do this job and do it well is a big job, even for a hardened software guy like me. If you switch chips, be ready for a big job writing that code.

Fred.

[AbeFM]

To the degree serial communications can be done without crowding the real code too much (is there CAN on the stacking connector??), people could add almost any peripheral they want, and do as much of the processing on their remote chip of choice as needed, which I was trying to get at before. Want something to do traction control? Fine, write the code on your own little chip, and have it send stuff like "limit power 10%" to the freeems HC12, and you can put the thing to modulate the brakes with high current drivers on your little daughter card.

The most important thing for this CPU is pins, followed by analog IO and maybe raw speed and environmental survivability... Fred made a pretty solid choice in this chip - with Xgate and more pins, there's room to grow. I look forward to monitoring oil pressure/temp, water temp, fuel pressure, etc, and even simple things like ambiant air temps (which would help my idle) and idle up pins, speedo logging, and idiot lights galore - in addition to boring stuff like having a really fast car.

Getting back to, you know, the actual board... Is this still a non-via board? I hate to be whiny, but I'd much rather have a few vias than blue wires and jumpers everywhere. And maybe USB. (can you say feature creep?

[AbeFM]

Here's the board, I think this is all you'll need? This is just a zip with the .brd file in it. A little worried since I have custom components in there, but we'll see?

edit: Apparently, I can't figure out how to make a gerber.
edit: Apparently, I laid this out with a 6.2 mil clearance. Uhg! I'd fixed some stuff by hand, but I guess there's LOTS of it.

[AbeFM]

Ok, one last go - a few more proto area holes, and 8.2 mil gaps everywhere instead of 0.006"

I probably should add silkscreen to label the transistors in the alternator circuit, but now I'm thinking this is good. Well, at least, I have no plans of anything I want to change - I could go to 0.010" clearances, but would have to do a lot of moving, and get even MORE vias (this has 9 I think. Or 12, I dunno, I'm really tired.)

[jharvey]

Opened just fine for me. I only got the board, not the sch. With out the sch, it's kind of hard to look at it more closely. I see this as a 2 layer board, about half euro card size. Components on one side.

To make sure I'm barking at the right tree. This is a Jimstim connector card (for you miata) 2 freeEMS, right? You took a best guess at the TA card pinout.

It looks like you included the opamp RPM input circuit, and I think I see a couple power fets driving inductive loads. They appear to be driven by the DB37, not the EMS so I'm scratching my head a bit. My first thought about the fets was one for injection, one for ignition. But that doesn't seem to work.

What's the 1, 2, 3 connector for? Is that just a place to put scope probes and test circuits if needed? Perhaps you intend for an add-on card?

Also you may want to run a ground strip around the outside of the board for RF purposes.

Also also, when your just about done, you may want to flood unused areas. Less etching makes for easier fab, especially for the diy etcher.

[AbeFM]

Ha, no, not at all. I mean, good guess but not right.

It's a board for a miata to a MS-II. I kinda want to put it in "non-free" but then again, this is really about the layout issues. I can send the whole zip but it's large? I just got tired of building harnesses and custom MS-II's for people who couldn't follow simple directions. You can't possibly charge enough to cover the work it takes to hand build these.

Do you know how to get gerbers out of this thing? All I got was "drill files" though they are PCO's and have traces so I'm not sure what it is - one per layer. Anyway, see attached.

[jharvey]

From PCBNEW --> file --> plot, select that layers you need, and check gerber --> plot.

Once you have the gerber file(s), you can view it with gerbview.

Ah so that 1,2,3 thing must be miata, and the db is MS land. That makes much more sence.

[AbeFM]

What 1,2,3 thing? The terminal block? That's for things which are not part of the OEM car- boost solenoid (I don't remember if I left a jumper for the OEM turbo cars to the OEM harness), KnockSenseMS IN and OUT, a lead for an external alternator control box (I put a circuit on there to do it, but I got it from someone else and have never tested it, so I left the option to bypass this if desired)...
-Abe.

[AbeFM]

That's what happened last night - when I do that I get a separate file for each layer - any idea how to join them up into something a boardhouse would want to see?