Devlog: Building a Custom Airbus-FCU Macropad

Total Build Time: 18 Hours, 45 Minutes

Project Overview: This project was a multi-day journey to design, route, and program a custom Airbus-FCU macropad from scratch. Powered by a Raspberry Pi Pico, the board features 4 EC11 rotary encoders (with push-button functionality) and 6 Cherry MX switches. While heavily inspired by the A320 FCU for use in Microsoft Flight Simulator 2020 (via the Fly-By-Wire A32NX API), it’s also mapped to serve as a daily-driver productivity pad featuring media controls, zoom, and copy/paste functionality.

Hardware & PCB Design (KiCad): I originally planned to use an Epal Arduino Mega 2560 Pro Mini clone, but after falling down a rabbit hole trying to create a custom, dimensionally accurate footprint, I pivoted to the RP Pico.

• The Routing Grind: I spent hours meticulously mapping the tracks to ensure zero intersections while matching the physical layout of the real FCU (minus the displays due to size constraints).

• The “Oops” Moment: Right as I was moving to the firmware stage, I realized I completely forgot to wire the “B” pin for one of the encoders (EC8_B) to the microcontroller. I had to jump back into KiCad, route the missing pin, and re-lay the tracks to accommodate the fix.

Enclosure & CAD (Fusion 360): Autodesk Fusion 360 (an absolutely goated CAD program) was used to design the enclosure. I aimed for a minimalist aesthetic with clean, rounded edges.

• Fitment: A significant chunk of time went into troubleshooting physical tolerances—ensuring the top plate cutouts, the PCB, and the input hardware all sandwiched together perfectly. I also designed a custom window cutout in the case to keep the RP Pico visible.

• Engravings: I wanted neat text engravings to label each input. My initial font choice had overlapping geometry that broke the extrude tool, so I compensated by swapping to a simpler, cleaner font that rendered perfectly.

Software & Firmware: I researched both MobiFlight and QMK MSYS to handle the brains of the board. MobiFlight’s recently updated UI introduced a bit of a learning curve since they moved away from a traditional text editor to a mouse-driven GUI. Ultimately, I used VS Code alongside QMK to write the firmware.

• The Code: I wrote out the keyboard.json and carefully matched the keymap.c file to handle my dual-purpose setup (Mute/Vol, Brightness, Zoom, Horizontal Nav, Next/Prev Track, and Copy/Paste).

• Compiler Woes: On the final day, I hit the dreaded QMK compiler errors when trying to generate the final .uf2 file. The culprit turned out to be an outdated keycode naming scheme I was using for the horizontal scrolling. Once I tracked down the correct syntax, the firmware compiled smoothly.

Final Thoughts: Between re-routing traces, fixing geometry errors in CAD, and debugging C code, this build was a massive test of patience and problem-solving. The final result is a highly functional, dual-purpose sim and productivity tool packed into a sleek custom case!