Ribbon to wire wrap pin adapter PCB

As part of an upcoming project I needed to connect to some wirewrap pins. These are on the back of a nice cardcage with a load of edge connectors.

The original connector that I am replacing was somewhat special, here have a look:

This is what remains of an IDC (insulation displacement connector) that spanned this 0.2″ gap between the pins. IDC connectors are basically connectors that push the insulation out of the way to get to the wire inside, you crimp them on through wire and they make contact. What I mean in this case is something like an IDE connector, it adapts a ribbon to some 0.1″ header pins. The difference here is the spacing between the long rows is not 0.1″, it’s 0.2″ which is very strange to me. Maybe this was common back in the day, but I’ve never seen a connector like this before.

If you look closely you can see these pins are sticking straight out of a card edge connector. An interesting thing about that is they are so long. I called them wirewrap pins above and I think that’s the case. I think the manufacturer designed these square profile pins to be used with wirewrap to connect them. They have very sharp corners so when you wrap the wire around them they ‘weld’ on the corners to make a solid connection (I’m not super familiar with the process). If you look closely you may also notice these connectors are press-fit into the PCB and the sharp corners bite right into the plated holes to make the connection. That means tracing out the connection is pretty hard since the connector is mounted flush on the top with no stand off to look under.

This is a schematic / wiring diagram showing where the connector interfaces with the backplane (bottom left rectangle). This backplane is somewhat interesting in that the connections do not go straight across. There is an ongoing effort to document as many variations of this backplane as we can find (so far at least one real one and one that we only have the schematic for). This connector takes about 18 signals and power from the backplane and sends it to another module. Since I can’t get that connector (and honestly even if I could this is cheaper) I designed a little interposer board to adapt it.

You can assemble it four ways, based on which orientation you place each header and how you plug in the ribbon. 0.1″ pin header fits right on these pins, just like the original IDC connector did. The spacing is such to warrant our own connector though, 0.2″ instead of the more standard narrow DIP IC spanning 0.3″. The board is almost the simplest design you can imagine, 50 pins that adapt to 50 other pins 1:1. This board is sponsored by PCBWay, but you wouldn’t know it by looking at it. It is so small I couldn’t cram anything else on the silkscreen other than what it is and where to find more information on it. When you order boards from PCBWay they usually add a small unobtrusive number somewhere on it for tracability reasons which is good, but this board is so packed they couldn’t fit that anywhere on it. That’s fine because being so simple there’s no way it’s anything other than perfect and you can tell just by looking at it.

I don’t know which orientation is correct yet, but there are parts incoming that will hopefully be keyed on one end and the layout diagram will help on the other. Originally it didn’t matter what the pinout was because the intention was to build something DIY such that the other end can be built to suit. Recently a real button / power box came up so this is in the mail:

Using the diagrams we’ve uncovered we could assemble our own, but this one from ebay is on the way. You may be thinking “breadboard spanning ribbon adapters exist for the raspberry pi, why not use those?” The answer is twofold, first we need 50 pins to pick up all the signals needed on these pins (the pi is either 26 pins or 40 pins depending on the revision), and second:

Breadboard span spacing is 0.3″ because that’s what narrow package DIP chips are, this is something special.

The documentation for the card cage and reverse engineering of this system is on github here, and this adapter board specifically is here. You can buy these at PCBWay if you want (do it unassembled please, until I know the orientation) here, more details are coming on this reassembly project for the cyberamic control system.