ACS712 (5A Ver.) Measure Power Strip

Hey everyone,

So I thought it would be a neat idea to buy a power strip and measure the amount of power that the objects are using that are plugged into it. I'm using an Arduino UNO for this project.

What I have so far...

I cut open the power strip cord and got the hot wire exposed so that I could put the ACS712 in series with the wire. I powered the strip and plugged in a test lamp to make sure that I had correctly made connections to complete the circuit. From here I grabbed my breadboard and a few capacitors that the wiring sheet said I should have.

http://wiring.org.co/learning/basics/currentacs712.html

Once I got the breadboard circuit setup, I connected the ACS712 VCC to the 5v output on the Arduino and the ACS712 GND to the ground on the Arduino. Then, I put the VOUT to the analog input 0 pin to measure. I copied the code from the wiring sheet and started to measure things.

The values I get are not what I expected...I know that the default voltage reference is 5v and without anything being measured I should get a steady 512 reading from the serial monitor. I get 512 (+-2) when nothing is plugged in, but when I connect a lamp that draws .28-.30 amps according to a borrowed kilowatt meter http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU I start to get some weird results. 512 (+-2) 512 (+-2) 512 (+-2) ... 512 (+-2) 522ish 547ish 522ish 512 (+-2) 512 (+-2) ... 512 (+-2) 499ish 474ish 499ish 512 (+-2) 512 (+-2) and is repeats this cycle. I took out the lamp and put my xbox 360 on the circuit to see what more amperage would do to the system. Now I get greater fluctuation, instead of 547ish being a high I go up to the higher 600s and lower 300s with a few more than one intermediate value (the 522ishs and 499ishs). I added more things to the system to draw more current and this followed the same trend. Am I doing something wrong to measure a steady value?

My end goal is to have the ADC reading be converted into watts. I will get this by taking the: % of 1 volt = ADC value / 704 (3.5v is approx a 704 ADC value with a 5v reference) Then take: % of 1 volt * 5 Amps to get the amount of current that is being used and multiply that by 120V to get power in watts.