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I am working on a project that requires many discrete transistors. Suffice it to say, it is for a transistorized 4-bit CPU project. I came across some oldschool IBM info on Wiki, and would like to do something similar to this:

IBM SMS Cards (scroll through to see application)

I want to follow the traditional approach of having all the logic gates on these cards and have them connect to a wire wrap backplane. I've had a heck of a time finding not only Eagle libraries that support a card edge connector, but it seems impossible to find the exact connector to go with it. Even something as mainstream as PCI has a million variations.

The cards themselves will be 3x4" single sided copper boards that I will etch myself. Ideally, the card edge would connect directly to a DIP wirewrap socket. I'm really not sure the best way to go about this. I would like an affordable way to connect these 3x4 cards to wirewrap, and would prefer to be able to make the PCBs for the cards vs. using proto/vero board.

I've thought about using angled pin headers, but the card edge seems cleaner and saves a lot of soldering.

I know wirewrapping is antiquated and I also know that having multiple logic cards is as well. But, this is a hobby and I would like to use old technology.

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    \$\begingroup\$ Have you considered using shrouded male headers on the backplane, and soldering a female header to the edge of the board? \$\endgroup\$ Commented Dec 31, 2014 at 21:18
  • \$\begingroup\$ @IgnacioVazquez-Abrams I thought about that, but will such headers connect to wire wrap sockets? \$\endgroup\$ Commented Dec 31, 2014 at 21:22
  • \$\begingroup\$ You would get the header itself in wirewrap form so that it could be used directly. \$\endgroup\$ Commented Dec 31, 2014 at 21:22
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    \$\begingroup\$ Search for DIN 41612 connectors. You should be able to find straight wire-wrap sockets for the backplane, and right angled PCB mount plugs for the boards. \$\endgroup\$
    – user16324
    Commented Dec 31, 2014 at 21:29
  • \$\begingroup\$ Yeah, I was thinking about Eurocard connectors but figured they might be overkill for the application. \$\endgroup\$ Commented Dec 31, 2014 at 21:34

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I like to use perfboard and Vector T44 terminals, like these:

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Press the terminals into the perfboard with a hot iron,

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Add wire-wrap sockets and what-not,

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Lay it out, turn it over and wire the whole thing up,

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and Voila! a thing of beauty emerges:

enter image description here enter image description here enter image description here

Sometimes, though, when wire-wrap won't work and I don't want to do a PCB per se, I'll do the layout anyway and use the next best best thing; a piece of copper clad perfboard with the ground plane on the component side and access to the wiring side using T44 terminals pressed into 0.025" diameter holes with the copper on the ground plane spot-faced to keep the terminals from shorting. The wiring's done by cutting the terminals short on the wiring side and making the connections with tinned bus wire.

Here's an old one where the copper's lost its shine, but you get the idea...

enter image description here enter image description here

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The traditional approach is to etch fingers on the PCB, and to mount a female socket on the backplane which has contacts for each finger. These sockets used to be very common, but a combination of market forces have made them rare these days. Wire wrap is a vastly underrated technology. Performed correctly with the right tool, it can produce results that have mechanical stability similar to a PCB, but without the cost of PCB design and etch, especially for designs that would require multiple signal routing layers to achieve that simply become a rat's nest of wires.

Card edge connectors do still exist, and with a little finagling with the parametric search at Digikey I even found a number of them are still stocked even with wire wrap termination. Here's one example: 13 fingers on 0.1" pitch on each side for 26 total circuits.

The mating card can certainly be etched at home, but do be aware that long lifetime and reliable operation usually requires that the fingers be gold-plated or otherwise treated to avoid oxidation. I suspect that gold-plating is not trivially done at home, but tinning is likely practical and will work well enough to get started. Just be sure to wipe the fingers smooth after tinning.

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  • \$\begingroup\$ Digikey stock checked out just now at Qty=3 and Price=$8.02. That sounds like a hard rock to me. \$\endgroup\$ Commented Jan 1, 2015 at 0:13
  • \$\begingroup\$ These things are nearly obsolete technology, so there are fewer makers and users. Haunt some surplus houses, ebay, and the like an you will probably find something cheaper, which will suit a hobby project. But the Digikey listing at least shows you what the real thing looks like and is called which makes finding surplus ones a lot easier. \$\endgroup\$
    – RBerteig
    Commented Jan 7, 2015 at 19:44

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