i have a 0R5 sense resistor in the neutral side of the AC mains. i need to isolate this input and feed it to a PIC microcontroller. how do i do this???? (there is about a maximum of 4A rms curent flowing through it)
A small transformer would do the trick, in parallel with the resistor. It would skew the accuracy of your circuit though so you'd have to do some calibration. Make sure the transformer is safe for mains voltage and has a reasonably high input impedance.
I was going to suggest using an opto-isolator, but I don't know anything about those. Probably a better solution though.