AC Volatge divident

How to measure 240V Ac current (5A 50Hz Mains) ? Will the below circuit help me ? |500x494

No, that is very dangerous and won't work. See this.

Right, it's unsafe (for you and the Arduino) to connect directly to the AC power line, even with a voltage divider. It needs to be electrically isolated.

Isolation can be achieved with a transformer, with an optical isolator, or a relay. To actually measure the voltage you need a (step-down) transformer because the output-voltage is proportional to the input voltage.

The link jremington gave you is for a current transformer. To measure voltage, you need a regular transformer.

Also, the Arduino can be damaged by the negative half of an AC waveform even if it's low voltage. Note that transformers put-out AC so you need a rectifier (or other circuit) prevent the negative voltage from getting into the Arduino.

And, without a ground reference (a ground connection to whatever you are measuring) you can't measure/detect the voltage. You'll notice that multimeters have two leads and you can't measure voltage, current, or resistance with only one connection.

sonnyyu: The method of sensor AC:

Voltage Sensing Unit:

  • Resistor divider
  • AC Voltage stepdown transformer

Current Sensing Unit:

  • Current transformer
  • Hall effect-based current sensor
  • Rogowski coil sensor
  • Shunt resistor

Rogowski coil sensor is my favor.

http://forum.arduino.cc/index.php?topic=312824.msg2170749#msg2170749