Instruction Book

I have received valuable answers from the forums :

Here is the answer I needed. Figures the only issue I had was the placement of the LED, there is no need for a transistor.

more details here: https://forum.allaboutcircuits.com/threads/trying-to-invert-a-hall-effect-sensor-with-led.200980/

SO, I have obviously tried the circuit and it works as intended !

see file "Hall effect LED - demo 1"

Ball

We managed to put the whole ball together.