Ok I think I have understood the advantages of the two solutions. Indeed the jfet device seems to be quite easier than the wheatstone bridge, but you are right, i'm still in my studies and it will be very recommended for me to be able to use fastly a bridge network.
However thank you very much Docedison for all this information that you gave me and all the time you took to answer me.
->This forum is just perfect. Let go!