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France
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Hello all,

I'm trying to measure current using an arduino. Looking at the forum I've found something looking like what I was trying to do :
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1291988410 points to
http://openenergymonitor.org/emon/node/28
But I just realize that it work only because arduino make a lot of capture to measure AC current.

As my program will do a lot of other things I would like to measure DC directly without sampling a lot of measures.
I wonder if there is something I can do to transform AC voltage to DC voltage with sufficent precision.

Thanks for reading.       
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Red Sea, Saudi Arabia
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Arduino would have to do almost no calculations if you added a separate RMS-voltage to DC converter chip such as this:
http://www.analog.com/en/other-products/rms-to-dc-converters/ad636/products/product.htm

Arduino CAN do the sampling and math to do Root Mean Square calculations, but it would use a lot of computation power.  Or maybe you could just capture a couple of cycles every 10 seconds and do those and assume it doesn't vary that much???

The data sheet is here: http://www.analog.com/static/imported-files/data_sheets/AD636.pdf

This is using this type of add-on clamp-on current transformer which makes it good for Arduino etc. because it's easy to add to existing wiring, and isolates "your" circuitry from the AC Mains stuff...  : http://www.alibaba.com/product-gs/247126409/Split_core_current_transformer_SCT_013.html

I am thinking of making an "Electronic Brick" ( see examples: http://arduino-direct.com/sunshop/index.php?l=product_list&c=17 ) which would have the RMS-to-DC chip on it and have a connector for the current transformer...   But that won't happen Real Soon Now...

Let us know how you make out!
« Last Edit: March 20, 2011, 06:56:14 am by Terry King » Logged

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I think you might find a hall effect sensor meets your needs.  These can measure both AC and DC  current and give a DC voltage output which is proportional to the current.  In effect your arduino would be reading a simple DC analogue input as frequently (or infrequently) as you desire.

http://sensing.honeywell.com/index.cfm?Ntt=csla&x=9&y=11&Ntk=si_all_products&ci_id=154286&la_id=1
gives you a starting point.  Generally these require around 12 volts DC to excite them and give an output signal of around 50mV per amp.

jack
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I think the Honeywell or other Hall Effect sensors still provide a fast current value, not an RMS calculated value. I Think this means you have the same computational requirements to get RMS current as with a current-transformer.  Any opinions??

For any particular application it depends on whether true RMS current values are needed, what kind of accuracy is needed, and to what degree the measured AC waveforms are non-sinusoidal.

If all you need is 'close enough' values on sine waves you can just measure the peak current and estimate the RMS value.

What applications are we seeing??
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France
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Thank you for your fast answers.
I'm going to have a look on the different solutions you sugest me.

One of the objective of my project is to measure :
 - The whole current consumed in my house.
 - The current consumed by the main consumer elements of lesser priority (electric boiler for hot watter, and heaters).
With this informations I'll be able to program some equipment to run the nigth when electricity is cheaper, and if necessary during the daywhile paying attention to overall consumption to be sure that the electric breaker does not break.


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Googling found this transducer http://news.thomasnet.com/fullstory/AC-True-RMS-Current-Transducer-feature-0-25-accuracy-474319 which seem to be what is needed - can't seem to find part numbers though.
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France
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The component seems interesting but the price is a little bit high :"Pricing for a 1027 Series transducer starts at $225"...


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Lancashire, UK
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Code:
The whole current consumed in my house

Cheap easy, dead accurate way :  Sensor on your meter.



This is mine, basically a 'line follower' sensor (Optek OPB705)  http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=455-0947 pointing at the edge of the disk, tracking the black mark.  If you have a new fangled one with a flashing LED, you mount a phototransistor over it and count the flashes

Once you've got that, you soon learn what the heavy users are because they drown out the general other stuff (Lights, TV, Computer etc). In my house its, Electric Shower,Kettle,Oven, Toaster, Tumble dryer........

http://pluggy.is-a-geek.com/index.html
« Last Edit: March 21, 2011, 04:50:30 pm by pluggy » Logged


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Pluggy, I LIKE it  smiley

How 'fussy' was it to align?? Is ambient light a problem?

I wonder if using Infrared emitter and filtered detector would help. (Mine is outdoors, Sunlight to Dark, Vermont Summer-Winter (90F to -20F) ).

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terry@yourduino.com  LEARN! DO! (Arduino Boards, Sensors, Parts @ http://yourduino.com

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Think low tech
Put a black bag over it
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It was a little tricky to first align, but it became a lot easier with experience.  I have an audible beeper on the board which I can turn on that beeps when the black mark comes round, using that helps since I don't have to be looking at two places at once.  Its in a cupboard and it works happily when the door is wide open and fairly light in there.  It may not fare so well in an outside situation with daylight (daylight is pretty broad spectrum so it probably has a lot of light where the phototransistor is most sensitive. )  It provoked the odd question when the meter reader first saw it, but its fairly obvious I haven't been inside the meter and its just an optical device.   Its usual in the UK for meters to be inside or in an external cupboard in newer properties.
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Think low tech ... Put a black bag over it

Hey, I AM Low Tech...

...needs to be easily removed by the Meter reader who slogged through 1 M of snow from his 4WD pickup to my pole out in the yard.  And stay in place in the Howling Winds  smiley-roll
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terry@yourduino.com  LEARN! DO! (Arduino Boards, Sensors, Parts @ http://yourduino.com

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Quote
1 M of snow

In Saudia Arabia ?
« Last Edit: March 22, 2011, 04:07:46 am by pluggy » Logged


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Quote
1 M of snow
...In Saudia Arabia ?

Oh. I'm living here this year as my wife is teaching at King Abdullah University of Science and Technology.  But we're from Vermont USA and will be back there this Summer and at least some part of next Winter.  I actually really miss the snow. 

Not much need here in Saudi for my Snow Depth gauge, or the look-up table of snow temperature to Ski Wax Color...   If I wanted to walk across the Southern, Northern, Western or Eastern (Baharain) borders, a bulletproof vest would need to replace my Ski vest.  smiley-mad  I'll be GLAD to get back to Vermont. 
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Regards, Terry King  ..On the Red Sea at KAUST.edu.sa
terry@yourduino.com  LEARN! DO! (Arduino Boards, Sensors, Parts @ http://yourduino.com

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