The mini digital volt meter is a neat little project that uses a standard microcontroller for all I/O. The project write-up goes through the build process of the project & shows you how the software algorithm is setup. Hardware schematics & high level software algorithms are explained in detail, take a look.
PyroFactor: 
August 7th, 2008 at 7:36 am
schematic digital volmeter with code.c
thanks before