load voltage and current measurement

I am new to this arduino world and there are a lot of questons unanswered but this post is regarding my project. I am trying to make an energy meter, measuring both instantaneous currents and voltages and displaying it on LCD. there is a lot of ambiguity in the circuits and also the limiting values of inputs to pins. my doubts are: 1. can arduino analog input measure negative voltage if I step down the ac to around 5 V?? 2. interfacing a parallel LCD 3. measuring of AC current, please give a circuit..

rahultgeorge: 1. can arduino analog input measure negative voltage if I step down the ac to around 5 V??

No.

Is it for the mains voltage ? For example like this, http://openenergymonitor.org

For LCD, see the library, http://arduino.cc/en/Reference/LiquidCrystal And the tutorial, http://arduino.cc/en/Tutorial/LiquidCrystal

Measuring an AC current can be done with a current clamp. Some information to start with is here, http://arduino.cc/forum/index.php?topic=60490.0

right now I am planning to measure voltage using this circuit… practically testing it tomorrow… any advices or comments please?

It seems okay. One side is lifted to 2.5V and the AC voltage is lowered with a voltage divider.

Two things: (1) The transformer does not accurately show the same wave shape on the secondairy side. It will transfer some higher frequencies better (spikes, noise, and so) than the 50/60Hz. (2) Your Arduino is powered with a power supply. That can be the computer via the USB or a seperate power supply. The power supply has some capacitance and inductance coupling with the mains. So the Arduino is also slightly coupled with the mains. If you connect the transformer to the Arduino you have another path to the mains. Using that to measure something could be inaccurate, so you might reduce the two 470k to 4k7 and the 18k to 4k7. The other resistor could be 22k or 33k perhaps.

The circuit worked fine and I measured the instantaneous voltage but coming to RMS value I had some error in calculation because I was not sure of the sampling rate of the ADC..

Your circuit is already a little inaccurate with the transformer. So the sample rate doesn't need to be very high. I'm thinking about 2kHz (1kHz ... 10kHz).

http://www.youtube.com/watch?v=qLClD2zM0Rs

@magician: wow that video was really inspiring… now I have a gazillion questions :smiley: :smiley:
also the submission date for my project being 18th, I decided to do count the pulses off the energymeter and counted it using the arduino… :slight_smile:

Hope, it's answered question #2. It also would answer #3, if you watch video on youtube, there is a link to the project with drawings. This one: http://coolarduino.wordpress.com/2013/02/08/power-meter/