Diy 150mm HDMI cable, Identifying Spec constraints, HDMI over IDC cable.

[Stromuslabs]

Hey there, I want to make a pcb with a interboard hdmi signal due to chassis port placement. In the past ive been making a ridiculous in house interboard hdmi cable using aluminum foil tape around the tdms pairs and their ground. Which worked quite well 70% of the time. To avoid the 80 points of solder and misalignment points of failure I thought it would be nice to use A short 150mm idc cable to a male hdmi board mount like some Ribbon cable drone boards.

Ive been looking at specifications and high speed design im not sure if it the cable would need a ground plane or some spec i havnt considered or can calculate. Any advice on looking at specifications to manipulate them over non standard cabling? Ive been thinking of making a proof of concept board to test and learn how to do eye diagram compliance testing but would be nice to be confident of a design before a prototype.

As an aside ive also been looking into laying out the impedance matched tdms on a 2 layer board where most documentation implements a four layer design. Any advice on that? Its a relativly short run from the hdmi to the idc mezzanine and should be able to have a uninterrupted ground plane due to the relative simplicity of it, hdmi is a focus but will also have ethernet and usb on the other side of the board.

Thank you for any advice on this, i strive to offer my own expertise one day. First post gotta have a emoji.

[mariush]

I really have to ask why, when you can buy 15cm or 30cm hdmi cables easily

ex. https://www.ebay.com/itm/15cm-Short-Cable-HDMI1-4-A-Male-to-Mini-HDMI-C-Male-Lead-Power-Adapter-Cord-Wire/273673930599?hash=item3fb83cc767:g:MrUAAOSwPcVVgikP

all kinds of connectors on each here here: https://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=15cm+hdmi+cable&_sacat=0

If you really want cheap cheap, I'd consider using 2 pieces of cat6a ethernet cable.  Each has 4 pairs of wire .. so one could carry the 3 tmds pairs and the clock pair ( and since it's cat6a which has separator between pairs, you should not need the tmds shield wires) and the other can carry all the other crap (5v, i2c ddc, ceac etc)

[Stromuslabs]

Why indeed. When i looked a year ago I couldnt find 100mm hdmi cables specifically right angle ones then moved to 150mm custom job through prototypes. I like the twisted pair idea for future designs. I think ill jump on the quick 3$ right angle here and call it a day. I am still interested in a twist on idc could work for high speed differential signals as they are easy to get manufactured with dirtycables or by hand