I am using AC voltage source. i have seen there is fine and coarse tuning available on interface. I am making an inverter now. I am wondering for inside logic for this fine coarse mechanism. help.

 

You can expect that the two adjustments are just two different variable resistors, one with a wide range, and the other with a small range. They could even be placed in series in a circuit that controls the output voltage. Then again, there lots of other ways to do it.