My first consideration has to be making the peg fit the hole. So, off to the docs!

Now, a big disclaimer here. I will be using imperial measurements here. Inches, mills and hogsheads. This is actually a first for me, but since the mATX spec is using it, our components are all on a 0.1″ pin pitch, and kicad has no problems with it — it looks like it’ll be the path of least resistance. So in all measurements, consider inches/mills/hogsheads canonical, and any annotation in mm simply so I can picture the numbers I’m looking at.

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… aka the braindump post.

We’re always told that “form follows function”, but for this project, the form is the function – If the board doesn’t follow conventions & standards enough to reasonably fit anywhere you’d expect a motherboard to fit, I’ve failed.

Which standard?

So, options!

  • Full ATX. 12″ wide (along the backplate) by 9.6″ deep. (305x244mm)
    • By my math, this would provide 7 slots exposed to backplates (0.8″ spacing), plus 8 more internally.
    • That could be 9 more internally, but I’d rather have a little more space for wider boards like the pi-terminal.
    • So 16 slots total. Gosh.
    • 305mmx90mm “playground” between slots and front edge.
    • About $177 at DirtyPCBs
  • Micro-ATX. 9.6″ wide (along the backplate) by 6.9″ deep.
    • 4 slots exposed, plus 8 more internally.
    • For 12 slots total. Just like the Backplane Pro.
    • 244x90mm “playground” at the leading edge. Still quite a lot more than I know what to do with.
    • About $159 at DirtyPCBs
  • Mini-ITX. 17x17cm.
    • 1 Slot exposed, plus 8 more internally.
    • 9 slots? meh.
    • almost no playground worth talking about. 170 x 15-20mm. Probably enough for a power circuit.
    • $85 at DirtyPCBs. I guess there’s the sell.

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Project Overkill

I have a terrible habit of letting projects simply dry up, once I think I’ve sorted out all the actual challenges, and only the actual implementation remains. So, this time I’ve decided to tell everyone I can, in a hope I’ll embarrass myself into action.

This started out simply as oggling the Backplane Pro for the rc2014. My Backplane-8 is getting a bit cramped, especially as I broke one header out to male pins for ease of breadboarding, so I actually have a Backplane-7 ..

Since it’s not a cheap board, and I wanted to pick up an SIO-2 while I’m at it, I decided to put it off to payday. Then I started to think about moving this thing into an enclosure. I wanted something sturdy enough that I can sit my monitor on top, but malleable enough that I could dremmel a floppy bay into the front. And I wanted it to actually look like a computer, rather than a generic €10 plastic enclosure.

Then I had an idea, and everything started to go terribly wrong. The cheapest enclosures I could find that were sturdy, looked like computers, and were easy to add a floppy bay to .. turned out to be those intended for the job. I couldn’t see a tidy way to make my rc2014 fit a standard PC case, but I figured it couldn’t be too difficult to make one …

The Plan

High-level objectives, in order of priority:

  • Create a backplane with the footprint of a standard motherboard, so it can be used in standard cases
  • Expose slots and IO ports in the correct places
  • Find a productive use for the slack space (ATX & micro-ATX are 244mm back to front, our 40pin slots are 104mm. Lots of slack space)
  • Producing a 100 PCB is not cheap, so I’d like to avoid making choices that would make it too difficult to sell leftovers