Designing a Ext. Prototyping Breakout (With Raspberry Pi Hat Compatibility)

PCB cost is by the surface, the bigger the more expensive.

As expensive ribbon cables are, they are still cheaper (and either to replace) than extending the PCB to connect both sides.

The only potential issue with the ribbon cable is signal integrity especially with high frequency stuff if not done properly.

As for connecting the ribbon, don’t use an IDC one for internal, just a flex type, but even, I’m pretty sure there is enough space to have a proper pin header ont eh PCB and use IDC cable with already put connector on them (like a good old IDE/SCSI cable)

But for the board to board inside, use a flex instead there are plenty with enough pin, you can always ahve the pinheader on the protoboard to be able to connect a more robust ribbon cable using a proper connector

In fact I’m pretty sure thare are extender cable for that PCIe connecor they use that would fit and allow to no need the small PCB and not have to bother with the connection to the protoboard as all you would need here is the edge connector

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the main board already uses an fpc connector… if i had a reflow station, i’d just put an fpc connector on the ext board if i could… i could still convert that to generic breakout, no need to modify the case, form factor and uniform. but if im sending a a file for print, i might pay the extra for a bigger board.

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I was wondering about trace length too. In some PCB designs, high speed data lines need equal trace lengths. This is a little beyond my knowledge though.

This was the first thing I looked into! I found a couple cables online, but it was difficult to find (specifically the mini pci-e). It then occurred to me that these extensions wouldn’t have any support to keep them plugged in - something that’s solved with a custom PCB and the holes for the standoffs.

I’m pretty keen on using the ribbon cable internally. Ribbon cables can be spliced and soldered to things. Much more versatile for prototyping. For example: Connecting to the proto board is not the only intended use. I’ll post some more images soon for all the use-cases I’m thinking, but imagine wanting to do breadboarding externally or even have the proto board external from the DevTerm while working on it. A ribbon cable (with a few inches extra length) would help with these different use cases.

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I’m still working ouut some details for orientation of pins and such. But this is my current concept for the proto board:

Note: Even with the design emphasis on being pi compatible this board doesn’t need to be used as a pi-hat adapter. It could be used for standard prototyping. Again: versatile!

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when i think about hanging a ribbion out of my devterm… it’s not for raspberry or Arduino type prototyping… im picturing lil john o’conner at the atm in terminator2

Quick update: I got a response from help@clockworkpi.com… we now have the official Ext board outline specs! I’ll be making some revisions to my breakout design soon.

Here’s the DXF they sent me: Ext_Module.dxf - Google Drive

But to save you some time, here are screenshots from that file:

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Something I’m confused about is the PCI-e connector. The specs they sent don’t seem to align with a photo of the actual PCB on instagram. Gonna try to confirm things…

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@yong - could you help us out with the Ext board specifications? Just trying to figure out if this DXF file is outdated, or if the photo on instagram is for a outdated prototype. Thanks!

EDIT: looks like maybe a 2mm discrepancy? (the spacing between the Ext and Main board)

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The DXF file is up-to-date. Thanks.

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Thanks!

Another update on the breakout board: I’ve got the footprint updated with the official Ext specs.
I ran into an issue with the through-hole design on this board, as I scouted for ribbon cable assemblies, I the shortest I could find was 7.8mm tall, but we’ve only got 5mm clearance. So I had to rethink how to connect a ribbon cable with this clearance. Came up with something clever using pads and a 2x20 header! Here’s the new revision:

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i imagine the case will need modification to fit that… not that im complaining or anything… maybe a lil surprised someone actually threw caution to the wind and said to heck wit the case. not many folks seem to feel the way i do about modding the chassis

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Haha, I’m not considering case mods yet! (at least anything that requires breaking or cutting the enclosure).

This should fit just fine without any mods. The Ext board hovers 5mm (on standoffs) above the orange translucent platform.

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I think I’m about done with the breakout. Just need to finalize the proto board, and then I’ll be making a small batch order.

Anyone have color preferences? I was thinking of matching the black of the clockwork PCBs. This purple is looking pretty cool too.

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thats pretty neat, but does that 5mm take a ribbon into consideration? if i can hook up a the usual ribbon to those headers and thread it out the case without chopping… wizardry!
and if thats the case… i may was well make an adapter to connect to an fpc adapter. that way one might make access more form factor, less obtrusive and possibly easier to get to and use while creating some layer of resilience

You should wait to have the thing in you hand before ordering PCB, I know they gave you the right dimensions, but there has been so many time I’ve ordered a PCB without doing proper check against reality and had to throw them because of that…

It is easy to make a small mistake that can make the while PCB useless

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I appreciate your sensibility! On the other hand, last time I ordered a small batch of PCBs it wasn’t more than about $20 w/shipping. The most probable discrepancy would be alignment and fit within the enclosure. Even in this scenario the board could still be connected. It’s a small risk to order them ahead of time, but if they work we could start tinkering right await.

@Godzil could I send you one of these after I order them? If you’re in the states I’d gladly pay the postage.

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Quick update on the Proto board design:

  • made strip board area standard breadboard size
  • exposed traces on back side for easier cutting or jumping
  • shifted everything down a bit to remove need for breakaway standoffs
  • proto area is now detachable
  • added SMD footprint for 4-pin jst connect. Anyone into Quiic?
  • connected all 40-pin traces, so this board can work with a pi, not just in the devterm
  • improved pin breakout and legend

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You are exactly what this community needs! I know it’s been said before, but I am also going to add myself to the “get this guy a cape” list.
You’re making me more excited for the devterm than I already am; and I’m sure I’m not the only one!

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That means a lot, thanks @javelinface! Everyone here seems really cool and enthusiastic. I get the feeling that these forums are really going to blow up when the DevTerm gets shipped.

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Let’s hope not :sweat_smile: :boom:

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