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Tweet-a-watt with Kill-a-Watt EZ
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Tweet-a-watt with Kill-a-Watt EZ

by wkoperwhats on Thu Apr 09, 2009 9:44 pm

Anyone try building a tweet-a-watt with a Kill-A-Watt EZ?

It uses the same quad op-amp as the standard unit (P4400?), but even with the 10,000uf capacitor it "resets" every time the XBee tries to broadcast (every second or two). Is it possible that the 5V supply on this smaller unit isn't able to handle the surge? I haven't put a scope on it so I'm just assuming.

Has anybody had success using this one? It's what Costco happened to carry for $25...

Thanks.

-bill k
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Re: Tweet-a-watt with Kill-a-Watt EZ

by adafruit on Fri Apr 10, 2009 1:42 pm

it sounds like the power supply is even weaker. i dont have one so i cant test it :(
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Re: Tweet-a-watt with Kill-a-Watt EZ

by felis on Fri Apr 10, 2009 2:28 pm

Have you tried increasing sleep period of the transmitter? Even though the maximum is 2.56sec, which is not very much longer than 2sec in the default configuration, it may help.

It's hard to say anything without seeing the circuit dynamics, but you can also put a resistor in series with tank capacitor restricting current into it.

Another option would be to move up to Series 2 Xbees; the maximum cyclic sleep time for those is several days. They also consume less in End device configuration.
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Re: Tweet-a-watt with Kill-a-Watt EZ

by wkoperwhats on Fri Apr 10, 2009 3:18 pm

I'll first try setting the interval to 2.56 sec, but I'm not too optimistic. When I find out anything useful I'll report it here. In the mean time I'd recommend staying away from the Kill-A-Watt EZ version if you want to build this project. Ah well, another trip back to the hardware store...
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Re: Tweet-a-watt with Kill-a-Watt EZ

by wkoperwhats on Mon Apr 13, 2009 3:56 pm

Well, setting the XBee interval to 2.56 seconds didn't make any difference. It still "resets" every time transmission occurs. The general consensus is that the power supply in the EZ just can't handle the increased load of the XBee, even *with* the big cap in place.

Re-wired the transmitter into a standard Kill-A-Watt (P4400) and it worked just fine.

Caveat emptor...
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Re: Tweet-a-watt with Kill-a-Watt EZ

by felis on Mon Apr 13, 2009 5:43 pm

There is another option: if your receiver is not too far away, you can lower the transmitter power. It's set to the max. by default.
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Re: Tweet-a-watt with Kill-a-Watt EZ

by adafruit on Mon Apr 13, 2009 6:28 pm

good to know that you tested the EZ against the 'standard' killawatt. note that afaict the datasheet implies that only the Pro can have the power settings changed on non-pro it dont do squat
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Re: Tweet-a-watt with Kill-a-Watt EZ

by wkoperwhats on Fri Apr 17, 2009 3:01 pm

One more note on this subject...

Seeing as I had bought 4 of these "Kill-A-Watt EZ"s from Costco, I decided on the trial and error approach and tried another unit. I wired in the XBee into a different EZ and it worked! No resetting. No oddball behavior. It just worked. In fact it's been logging data on powerstrip providing power to the server and other electronics in my office for the past couple of days.

I'm not sure what the problem with the *first* Kill-A-Watt EZ was, it seems to function fine on its own but doesn't like having the radio attached (yes, it was wired in correctly). I'm going to order a couple more XBees and if I get curious I'll try it again. I'll post some pictures of the physical layout of the components in this smaller unit. The LED had to poke out the side not the top, and the adaptor board was stuck to the main board with a piece of double sided foam sticky tape.

Curiouser and curiouser...
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Re: Tweet-a-watt with Kill-a-Watt EZ

by adafruit on Fri Apr 17, 2009 11:39 pm

ya photos would help other people. thanks!
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Re: Tweet-a-watt with Kill-a-Watt EZ

by wkoperwhats on Wed Jun 03, 2009 4:41 pm

Here are (finally) some pictures from my build of a Tweet-A-Watt using a P3 Kill-A-Watt EZ. Since these units are readily available at Costco for around $25, it seemed like a good starting point. Please excuse the crappy iPhone photos, I didn't feel like dragging out the good camera...

With some effort, I was able to fit all the components inside the unit. You can see that the "transmit" LED had to stick out the side rather than the top
Image

This shows the general placement of the components. The XBee breakout board itself got stuck to the main Kill-A-Watt board with two layers of double sided foam sticky tape.
Image

Here you can see a different angle showing the placement of the super-cap and wiring.
Image

With the sensor board placed back on top, you can see the snug fit of the components. A simple notch in the "seam" was all that was needed to let the LED poke out.
Image

Hope these help.
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Re: Tweet-a-watt with Kill-a-Watt EZ

by adafruit on Wed Jun 03, 2009 8:12 pm

thanks!
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Re: Tweet-a-watt with Kill-a-Watt EZ

by ProfNimrod on Fri Jan 15, 2010 8:44 pm

Would you mind posting the serial number and specs off that huge - what I assume is an X2 rated capacitor - green component. Many thanks, Kurt
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Re: Tweet-a-watt with Kill-a-Watt EZ

by bozo on Sun Jun 20, 2010 7:03 pm

Would it work also with EU compatible plug meters, for example this one (http://www.prodigit.com/index.php?lang= ... o_num=1051)?
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Re: Tweet-a-watt with Kill-a-Watt EZ

by AndrewSoh on Mon Dec 27, 2010 4:54 am

bozo wrote:Would it work also with EU compatible plug meters, for example this one (http://www.prodigit.com/index.php?lang= ... o_num=1051)?

I just received mine, the UK version. After some initial problems looking around for the chip I finally found it behind the LCD panel.
Attachments
IMG_0687 (Medium).JPG
The Op-Amp located behind the LCD of the UK version.
IMG_0687 (Medium).JPG (75.94 KiB) Viewed 5640 times
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