Help in build a AC 220v sensor

Other Hardware Sensors
1

Need help to build an AC voltage shield. Voltage could go from 0 to 250volts. Any idea is welcome.
Regards

2

http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-an-acac-power-adapter

3

Is this meaning that the voltage has two states being 0v and 250v, or, has any value between 0 and 250 volts?

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