You're right, but I just needed a quick solution and, to be honest, the whole stuff is part of a small testing/practice project.
I even have some CTs available but I took advantage of this situation to do some quick researches on this subject. Being an add-on board for an existing circuit, I could further replace it with a more complex one if I'm going to need higher accuracy.
So, could you sugest another simple discrete solution (for educational purpose only)?!