Quote Originally Posted by Normnet View Post
A problem can occur when power to PIC is off, the 5 volts from the divider can power the PIC.
You are correct. But you did not say that the PIC was going to be turned on and off. The voltage monitors that I have made are never shut off and equipped with backup power just incase.

Now that you know two ways to solve your first question and one way for the second. (this is a productive thread ) The most, I think, reliable way to isolate the PIC is an opto isolator. Nothing fancy, LED and a photo diode with a piece of heat shrink between them.