Mini-Omnibus backplane for debug and minimal system

[thunter0512]

Thank you George; that looks like a really nice set-up. Nice boost-buck converter with display too!

I've been scrounging through my odds-n-ends and found an open-frame 15Vdc 3A SMPS as well as a 5Vdc 20A SMPS (overkill!) and an appropriate DC/DC boost regulator that I could use for deriving the +15Vdc rail. Still on the fence over whether I'd be short-changing myself on the -15Vdc rail :-<. Decisions, decisions ...

With the Digikey price George quoted for the 3 supplies I wouldn't think to much.
Here in Australia we pay a premium on anything and everything. Additionally everything takes a long time to get shipped here.
I envy our US counterparts for the availability of "stuff", lower prices of the goods and cheap&quick shipping.

 

[pbirkel@gmail.com]

Well, here on the Mid-Atlantic East Coast we envy our SoCal brethren who live amongst so many opportunities to haul away old equipment for what amounts to a song whereas here it's an old-equipment desert :-<. That said, yes we're still closer to the cornucopia than either Europe or Australia. And Mouser/Digi-Key/etc. shipping has increased but noting like the cost of shipping anything traveling from overseas (or even, koff, from Canada). Sorry 'bout that! I expect that OZ has it's compensations; let me tell you about our traffic, shootings, and social breakdown ...

 

[oktology]

You'll probably find the ECS 2418-13-30 connectors are easier to work with and a better match for DEC modules than the Chinese ones.

Where does one physically lay their hands on them, though? Google turns up PDFs and discussion of them only.

 

[gwiley]

Where does one physically lay their hands on them, though? Google turns up PDFs and discussion of them only.

I've never seen one of the ECS connectors but have read discussion in the DEC forum where members have talked about large bulk orders of 100-or-so connectors.

My understanding is that the boards can seat deeper in the ECS connectors so they are more stable, without support. Also I believe the width of the slot in the ECS might be the proper width for DEC Flip Chip modules. Both of these Chinese connector issues have mitigated by the following:
1. Use of 3D printed connector shims to fix the slot width problem.
2. 3D printed card guides that are fastened to the mini backplane PCB by mounting screws. There are different card guides depending on the type of system you'd like to build, which is explained in this post: https://forum.vcfed.org/index.php?t...debug-and-minimal-system.1238621/post-1298466

The 3D printing STL files are in the github repositories:
The card guides, which aren't required but are nice, are here: https://github.com/G-Wiley/Mini_Omnibus_Backplane_3D_Printed_Parts
The connector shim files and document with instructions to modify the connector and install shims is with the design files, here: https://github.com/G-Wiley/Mini_Omnibus_Backplane

 

[pbirkel@gmail.com]

I've never seen one of the ECS connectors but have read discussion in the DEC forum where members have talked about large bulk orders of 100-or-so connectors.

My understanding is that the boards can seat deeper in the ECS connectors so they are more stable, without support. Also I believe the width of the slot in the ECS might be the proper width for DEC Flip Chip modules. Both of these Chinese connector issues have mitigated by the following:
1. Use of 3D printed connector shims to fix the slot width problem.
2. 3D printed card guides that are fastened to the mini backplane PCB by mounting screws. There are different card guides depending on the type of system you'd like to build, which is explained in this post: https://forum.vcfed.org/index.php?t...debug-and-minimal-system.1238621/post-1298466

The 3D printing STL files are in the github repositories:
The card guides, which aren't required but are nice, are here: https://github.com/G-Wiley/Mini_Omnibus_Backplane_3D_Printed_Parts
The connector shim files and document with instructions to modify the connector and install shims is with the design files, here: https://github.com/G-Wiley/Mini_Omnibus_Backplane

Important mechanical issues being adequately (IMO) resolved, that leaves electrical ones, and I've seen no evidence that the Chinese connectors are inadequate in that regard. Often, but AFAICS not uniformly (it's hard to inspect!), the DEC connectors had gold plating at the contact point, resulting in a gold-to-gold mating with the DEC modules. This is important for long-term low resistance and corrosion resistance. However in the absence of a supply of those DEC (or third-party) connectors one "must do", and the Chinese ones seem to me to be "hobby grade" fit-for-purpose. If you can acquire those ECS connectors, use them :->. In the meantime IMO the Chinese connectors are available, affordable, and functional (given the physical adjustments/supports that have been designed).

 

[ftcnet]

I think you'll prefer working with the ECS (DEC) connectors. The single-width ones are available from Todd Goodman for $10. ea. That price is OK for completing extender boards, but gets expensive when trying to populate a full H9194-style Omnibus. It'd be interesting to get a price for the dual-width connectors from ECS for comparison.

 

[pbirkel@gmail.com]

I think you'll prefer working with the ECS (DEC) connectors. The single-width ones are available from Todd Goodman for $10. ea. That price is OK for completing extender boards,

Pretty much absolutely necessary for extender boards, although I suppose that one could make do with the Chinese connectors if one implemented extended module supports (as seen on some types of extender boards for various electronic equipment). In the DEC case I'd just purchase a DEC-standard extender; they do come up on eBay from time-to-time. The build-your-own ones designed by Joerg Hoppe are perfectly acceptable substitutes when used with the ECS connectors.

but gets expensive when trying to populate a full H9194-style Omnibus.

If one *really* wanted to go down that route I'd consider salvaging some uncommitted DEC SU blocks (four slot, two edge) from something odd for the purpose. Unfortunately it would have to be something old-odd since DEC started adding PCBs after a few years, thus committing pins such as power rails and selected signal lines.

 

[pbirkel@gmail.com]

Pretty much absolutely necessary for extender boards, although I suppose that one could make do with the Chinese connectors if one implemented extended module supports (as seen on some types of extender boards for various electronic equipment).

Example extenders (red brackets): https://www.ebay.com/itm/296145822650

 

[gwiley]

Regarding product quality, we really know nothing about the Chinese connectors (gold plating thickness, plating over what metal, rating and consistency of contact spring force, dimensional tolerances, etc.). In my experience, there are usually some compromises of quality favoring low cost for most of the stuff available on AliExpress. For certain items for certain applications this can be acceptable. For someone building a commercial product, materials should be procured from reliable sources where these questions can be addressed and verified by the supplier. However, in my case, the connectors are for my vintage computer hobby projects and the basic functionality of the parts is/has been good enough to perform in devices such as the mini Omnibus backplane, Flip Chip tester, and RK05 emulator.

If you need a card extender, I recommend just buying one from Douglas Electronics in San Leandro, CA. That's where I got mine (in Jan 2022). They sell one preassembled with the edge connectors attached or just the PCB with no connectors. I bought the preassembled Omnibus-compatible board... it's the 6-DE-8 and select the "with connector +$42.00" option.

Douglas Electronics Inc || Board Extender - Breadboards - By Function - Off the Shelf Solutions

www.douglaspcb.com