Wattcher, twittering Kill A Watt plans posted

kill-a-watt

You probably saw [Phillip Torrone] and [Limor Fried]’s twittering Kill A Watt earlier this week. It was an entry in the Core77/Greener Gadgets Design Competition. We saw a little bit about how it was assembled, but now they’ve posted a full guide to assembling the hardware. Each Kill A Watt gets an XBee radio that transmits back to a receiver that logs the power usage. The difficult part when putting this design together was the XBee required 50mA when transmitting. This is well above the Kill A Watt’s internal power supply. They remedied this by adding a 10,000uF supercap to act as a rechargeable battery. The daily twittering is just a side-effect of the project. The Kill A Watts transmit every 2 seconds, so you’ll get a very accurate report of your power usage. This is a great project for renters who can’t permanently modify their power infrastructure. Each Kill A Watt can support quite a few appliances since they’re rated for 15A, ~1800W.

20 thoughts on “Wattcher, twittering Kill A Watt plans posted

  1. Those xbee radios rock, btw. If you’re only using two, you don’t even have to program anything, they default to acting like a dumb serial link. Send a few commands, tho, and you can talk to any number of them at a time, they are really easy to use!
    -Taylor

  2. this would be awesome to set up on a main line in my house. Maybe I’d realize how much it’s costing if I leave one or two things on while gone.

  3. This is a great project! My meter has an optical readout interface which I would like to use for online logging, but the protocol description (IEC 62056-21) is paid :(

    Do any of you know how I could interface with it, without spending $200 on a pdf?

  4. @ daryl; if you have a ~3000 watt kettle, you must be cooking up more than your regular cup of tea.

    A fridge, or microwave should never exceed 1500 watts, a space heater is 1500 watts, 3000 watts needs special heavier wiring.

    @ icebrain There’s that software toolset that people have used to give robots eyes…basically you program in what to look for with a webcam, and it identifies numbers, etc. There was a hackaday on reading analogue pressure or temp gauges this way. I forget the name.

  5. @frollard: Yeah, I remember that, the meter has a infrared port (diode and led) for digital communication, but I don’t know which bytes I should send and how to decode the data (the protocol).

    I could read the screen, but that would require a full computer, and I was planning to use an Arduino, and transmitting to the computer “on-demand”.

  6. Interesting project. I’d long been curious what was inside the Kill-A-Watt with an idea to do something similar.

    A quick question:
    I can’t tell from the published schematics what the ORG and YEL wires tap into (ORG = Volt sense, YEL = Cur sense, or vice versa?) RED and BLK are clear (5V and Gnd, respectively).

  7. @brett: looking at the instructions page, based off the pictures:

    orange – voltage – AD0 – LM3902 pin 14
    yellow – current – AD4 – LM3902 pin 1

  8. In terms of energy savings, one would have to include the energy cost from the manufacture and distribution of the Kill a watt meters. (i.e. if using several of these to monitor your energy usage, have save a lot in order to make up for the environmental cost of making the meters.)

    One project that takes a simple approach to measuring overall usage is: http://www.bwired.nl/Stroom.asp

    Have toyed with ideas of how to adapt that or the project on monitoring the water heater burner using a cell phone to reading an old electro-mechanical electricity meter.

  9. They use the same “supercap” technique in USB GSM modems… because the GSM transmitter operating at full power would require more current than what is available at the USB port.

    Just for you to know that this hack is actually used in the industry :) although they use a smaller cap and probably some kind of rate throttling in case the capacitor discharges too much.

  10. @myself a more generic solution would be to get a monkey, teach him how to read LCDs and enter the data into a computer

    but that’s not good engineering either

  11. @Winphreak; every home that’s on the grid has a device, that will let you measure how much power devices left on consume while. Simply read the power company’s meter before you leave and again when you come home.

  12. @frollard

    over in the uk, because we have 240V, kettles usually linger around the 9 amp region, our standard cabling is 13A so any plug in the house can support 240*13 = 3120W, space heaters are 1.6-3kw here, so it’s quite possible that he has a 2.8Kw kettle if he’s in the uk (ours is 2.9Kw)

  13. Came back to try this… my Kill-A-Watt has a different board! The IC that he hooked into is absent! (among a few other minor looking changes).

    Saaadneessss.

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