I am trying to measure power using the ACS712 hall effect sensor. From what I have read online I would have to use a voltage divider to make voltage measurements and then measure the power. The circuit is something like http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-an-acac-power-adapter. But why is this voltage actually needed? Dont all household appliances run at 230v/110v? Is the voltage measurement really necessary? If so what are some of the good ways to isolate this in a cheap way? Is it optocouplers or tranformers?
Second, is there a need to interface the ACS712 with an energy metering IC? Will this make it simpler or harder for the project? Could you please give me some ideas?