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Kill-A-Watt with Launchpad ?


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1. Low cost wireless transmission.

 

Zig Bees are not the cheapest solution but it is one of the easiest solution. Need more information about what you want to connect to and what you want to send (assuming data pertaining to current). Sending it how far? To what?

 

2. How to measure current.

 

Most likely you dont want to splice the wire you want to measure so you are going to want to measure in a non-invasive way.

 

Something like this http://www.seeedstudio.com/depot/noninv ... ml?cPath=6 would do the trick.

 

Take a look at this Arduino project. http://openenergymonitor.org/emon/node/58

 

Should give you some ideas how to get started.

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Dang. I had this reply half-finished on my laptop since Friday morning (it's been a busy day)

 

I built something like this last year, because I was curious how much power my electric range was drawing each month

 

The results inspired me to buy a single inductive burner for most of my daily cooking, and the energy savings has been substantial. Not only that, but my kitchen doesn't get uncomfortably hot in the summer. It's especially good when making great long-simmered stock, because you can safely wrap the stockpot with a towel, since the burner never gets hotter than the stock pot (212F, 100C). Thus insulated, the simmering stockpot draws less current than my kitchen lights!

 

To measure 230VAC current, I used a current transformer from Foster Transformer The default on they listed ($3) can handle 0-30A, and will measure any one-phase AC from 50Hz to 400Hz, and up to 500VAC rms (250VAC to be on the safe side), so the same measuring circuit could handle, US home 120VAC/230VAC @ 60HZ; old US military/avionics 400Hz; and most European mains with no change. For US 3-phase 208VAC or any case where phase is important you need a toroidal current transformer, instead of this IE unit.

 

One tip: my first order of business is always to *permanently attach* a burden resistor across the secondary. Without it, almost any current can cause a current transformer to blow its secondary coil insulation or any attached measuring device -- even the mere act of measuring the resistance of the primary with a VOM! There are reports all over the net, and videos on Youtube. I used a 50 ohm 1/4W resistor for a transformer output of 100 mVAC(rms)/Amp

 

I used a DAQ (data acquisition device) that I had lying around, because it can handle AC directly, is sensitive in the microvolt to volts range, and can provide averages and totals right out of the box. You should be able to easily do the math with a MSP430, but you'll need some sort of AC front end. Off the top of my head, you might rectify the AC out, use it to charge a small cap for 1 sec, measure the peak voltage and then discharge the cap. I doubt you'll want more than 1 reading/sec.

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