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Are all of those ethernet cables? I can't say I know much about wiring, but that seems like a bit overkill.

Looks like they are. Actually a good idea IMO assuming they are just using them as robust 8 bit interconnects and not actually Ethernet.

Considering two of the bits will have large coupling between the two, that sounds like a bad idea...

A 4 bit differential output would be pretty darn good.

Actually, that might be the case: some boards have 4 presumably output ethernet ports.

edit: https://bighexmachine.github.io/hexModuleSpec/ looks like I'm right?

They are, and the interconnects are 4 bit. These were used by first year undergraduates for years before the Big Hex Machine was built, so sturdy Ethernet cables were cheaper and more reliable than many other options.

Yup, we used 4 wires for data and 4 for power - there's a 12V supply which is spread around and downregulated to 5V on each board. We picked ethernet because it's extremely cheap, hard-wearing, widely available and has enough wires to play with.

Really, it beats having to fab your own connectors. Making your own isn't a big deal for most projects, but with that number of boards, this is a smart choice.

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