Any circuit or module to detect fan speed identification to micro controller??

Dear connection

I have a circuit for monitoring fan regulator speed change using ADC (as shown).
here iam using current sensor module for speed change identification..
but the problem is

-current sensor output ranges between small voltage so measurement take so difficult
-even in case input supply voltage (230v ) varies its effect the output of current sensor ..
so it hard to detect the speed changes .

could you please suggest some circuits or module to detect the fan speed changes , it should be identified by the micro controller