Mysterious Missing Feature Centauri Carbon Under Tool Head Light

Did you know the Elegoo Centauri Carbon has an unused under-toolhead light circuit hiding on the toolhead PCB? In this video, I trace the mysterious “missing feature,” build a bench-test rig from spare parts, and show how to make that circuit actually work. Using a leftover 5 V T10 automotive bulb from my earlier bed-mount lighting mod, I scavenged the LED disc, wired it into the toolhead’s “5 V / LED–” connector, and confirmed that the line runs through a low-side MOSFET driven by PB4 (pin 56) on the STM32F402 MCU. With a simple jumper, the light stays on whenever the printer’s powered — and the results are awesome. You’ll see the test rig in action (yes, the printer thought it was printing while the head ran on the bench), failed soldering attempts, the final bright LED install, and some amazing dark-room Benchy footage that honestly looks like an alien spacecraft hovering over the print bed. I also talk briefly about reorganizing my lab, preparing for upcoming cancer treatment, and why building and experimenting remain therapeutic for me. At the end, I share plans for a new daughterboard that will make hotend swaps easier — and a quick update on my store and available fan-adapter boards. And, of course, a proud shout-out to my son Tegan for bringing home a bunch of A’s on his report card. ⚙️ Parts & Resources (affiliate links support the channel) -T10 12V - (individual LEDs work well on 5V) LED bulbs (same type used in the bed-mount light mod) https://amzn.to/47lLMkR -Fan-adapter boards: https://syntheticelectron3d.com/ -Bench PSU / USB-C 60 W cable: https://amzn.to/49f1osQ / https://amzn.to/49phAro -Continuity probe & digital microscope https://amzn.to/47iC2rq / https://amzn.to/4oyEh0G 💬 Join the Discussion What features would you want in a redesigned toolhead daughterboard? Comment below — I’m collecting ideas for the next SE3D project.