Good day everyone, please I want to build a wireless power meter using an arduino board. I am considering using an arduino Uno or Auduino Due. How do I go about the current measurement? That is, which kind of current sensor will be better for this project? Also what is the difference between the ethernet shield and the wishield apart from that the ethernet shield is wired? Please am quit confused and I will appreciate your responses. Thanks.
I've never done anything wireless, so I'll leave that for someone else to answer.
Assuming this is AC power line current, use a [u]Current Transformer[/u] to measure current.
A current transformer will keep you and your Arduino safely isolated from power line voltages.
Since the Arduino can be damaged by the negative half of the AC waveform, you'll either need to [u]bias[/u] the Arduino's input (2 resistors and a capacitor), or you can use a precision rectifier (an op-amp circuit).
If the voltage from the current transformer is more than 5V peak-to-peak (~1.8VRMS) you'll need a [u]Voltage Divider[/u] (2 resistors... Or, if you already have the bias circuit you can just add one series resistor.)
I would be a good idea to add [u]Protection Diodes[/u] in case the voltage unexpectedly goes above +5V (or goes negative).
In most practical/casual applications you can assume voltage is constant and simply measure current. But, to "scientifically" measure power, or if you are making a Watt-Hour meter for electrical billing purposes, you need to measure voltage and the phase-angle between the voltage & current. (The voltage & current can be out-of-phase with inductive loads such as motors and if you don't take that into account the measured/calculated power will be greater than the actual power consumed.)