Here a project I did a digital voltmeter upto 220v-dc. You can change this project an use it.
First by changing the voltage divider part you can increase the range over to 415v-ac,
And by using timer and array you can get samples and then by arranging the measured values you can change it into ac,
Be careful about choosing resistor, the scaled resistor's voltage should be less or equal to 5v (use a 5v zener diode to be sure- or over voltage problem) otherwise your pic can burn.