you can use a 18f45x family pic with AD converter to ensure from 0 to 5 volts
or -5 to 5 volts and build a program to convertr the output for send to the lcd
You hardly need an 18F series PIC for such a simple task, a nice 18 pin 16F88 or 16F819 is plenty, and my tutorials provide pretty well everything required to do it.