Thanks for all the answers !
Can't remember precisely where i took this one.
The idea of an old and basic rotary encoder is the good one !
I manage to plug it and obtain some "0;1;0;1....." for two complete revolution of the wheel !
Not precise at all !
And while i'm turning the wheel slowly, and i stop it where i can feel it's between two step, the numbers are becoming crazy with the never ending 0;1;0;1;0;1 !
So every digging in old devices not brings up gold 
Thanks again for help !