Add feature (filament runout sensor on pin 29)
As seen in
from teaching tech, he uses pin 27 for the bl-touch and pin 29 for the filament runout sensor.
its at 8 minutes when he talks about how to use the pins on a ender 3.
Would be great if you added that!
Honestly, if you're looking at going through that much hassle, it would be easier and more reliable to upgrade the mainboard to a v4.2.7 replacement.
These have simple, plugin ports for the BLTouch and the smart filament runout sensors and are supported out of the box.