so i built a theoritical Comparator. this compares two AC signals.
when two signals are in phase and same amplitude then output is plain DC signal of 4V
and when the two signals are out of phase or of different amplitude or of different freq. then the output of comparator is square wave.
so this comparator only gives DC signal when two AC signals are exactly same.
(Coneect wire which i have cutted to see how it works when there is disturbance)
I am posting my metal detector version 2 block diagram as first is failure (Because we cant stop Mutual inductance of coils)