https://x.com/pepijndevos/status/1862079466530386130

This thread kicked off the whole madness: I quoted my own gripe about no off-the-shelf CM5 board with a full x16 PCIe slot and 24-pin ATX power, so screw it, time to design one. Starting from the open RPi CM5 IO board, I modded it for mini-ITX sizing (160x90mm to 170x170mm—plenty of extra real estate), swapped M.2 for PCIe, brainstormed that space for Zigbee (ripping the MGM210PA32JIA2 from Home Assistant Yellow with open firmware), storage sans compromising PCIe, or even a full Arduino. Dove deep into KiCad hell: differential pair routing for PCIe (shoutout Digikey tutorial), Claude-generated pin labels for the 164-pin socket, power puzzles like ATX PS_ON# logic with PWR_BUT and MOSFETs, USB-C vs. A port debates, and fan headers (PWM to 12V follower?). Layout fights over PCIe positioning (micro-ATX vs. ISA datum insanity, grid mm/inch mismatches), paper-print sanity checks against my old ATX mobo, and a PCI/PCIe dimension whoopsie. By Dec 9, schematic/layout mostly locked—GitHub repo live at https://github.com/pepijndevos/rpi-cm5io-mini-itx—ready to fab, but sweating the debug without a fast scope.