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Here’s what we entered, the Tweet-a-watt, for the Core77 & Greener Gadgets design competition

Using “off-the-shelf hardware”, we have modified a Kill-a-Watt(TM) power meter to “tweet” (publish wirelessly) the daily KWH consumed to the user’s Twitter account (Cumulative Killowatt-hours). We are releasing this project as an “Open source hardware” project – in other words, anyone can make these, modify them and make a commercial product from the ideas and methods.

Here’s how it works, the modified Kill-a-Watt uses a “super-cap” to slowly recharge itself, once there is enough power it turns on the Xbee wireless module which transmits the data to a nearby computer (or internet connected microcontroller, like an Arduino) once the power usage for the day is recorded it uses a predefined Twitter account (it can be your own) to publish your daily KWH consumption for the day, multiple units can be used for an entire household.

We’re publishing the source, schematics and the idea for others to run with – Energy change and consumption can happen many ways, we feel there is a social imperative and joy in publishing one’s own daily KWH – by sharing these numbers on a service like Twitter users can compete for the lowest numbers and also see how they’re doing compared to their friends and followers.

  • Vrogy

    Neat hack, but the implementation is flawed.. seems like it was driven by the “ooh let’s stick an x in y” impulse.

    Better might be a unit which measures electricity at the mains.. but that’s probably not as accessible to DIYers..

  • ano

    What the DIY-ers of the world really need is a cheap, correct way to measure power consumption. Any schematics available?

  • Limor

    @Vrogy, I dont understand your comment: it does measure electricity at the mains, the kill-a-watt analog front end does current/voltage measurement. Can you be more specific about what is flawed?

  • Phillip Torrone

    @Vrogy – i think you answered your own snark :)

    there are a lot of xbee projects, i think this is a great example of a good one, inexpensive, it can use multiple units, measures at the mains, and is DIY accessible.

    @ano – once we’re done you can use ours, it might not get cheaper than this.

  • J. Quim

    I think a problem with this is that it only measures the power consumption at a single outlet, not “at the mains”, which would measure power consumption for the whole house. Also, I’m not sure I understand the advantage of using a super capacitor here instead of a simple power supply IC. Otherwise, great fun!

  • Rob Faludi

    This unit is for tweeting a single appliance or a power strip, yes. But overall consumption is definitely DIY accessible too. If you have access to your circuit box and are comfortable around electricty, you can use a Hall effect clamp to read the current:
    . http://scienceshareware.com/how-to-measure-AC-DC-current-with-a-hall-effect-clamp-.htm

  • David Andersen

    @Vrogy – whole-house power consumption and individual device or powerstrip measurement are both useful. Devices like the kill-a-watt are great for figuring out *which* device is slurping power, tweaking power-saving modes on a PC, etc.; whole-house measurements give a good overall picture. I think what you really meant to say was: “Great project! Maybe next you could do the same to a whole-house monitor!”

  • Limor

    @quim, there is a 5v power supply inside already. however it can only supply 1ma as it is coupled to the 120V power thru a pretty small safety cap. thus, a ‘supercap’ is req’d!
    @rob, current clamp sensors are very safe, but don’t measure voltage. If you have a purely resistive load like a light bulb or iron, this is OK. However, pretty much anything with electronics or motors/inductive will be tougher to calculate and the voltage reading must be taken as well to figure out the correct power consumption.

  • Azzam

    At my work place I would like a device that can monitor the electricity usage and which appliance is consuming what amount. Which device can do this please?


  • makethis
  • Michael Davidson

    This is a clever mashup. You could also Tweet just about any household-related metric: temperature, water usage. When I saw this, my first reaction was “Tweet Frog” (Google “Leak Frog”, it’s adorable… and functional).

  • Anonymous

    Azzam, the device is a Kill A Watt P4400. When placed on sale they cost about $20 from Amazon.com or meritline.com or any number of places. Its biggest flaw is that its memory clears when the power is removed. The newer P4460 has solved that problem but is twice as expensive.

  • WhereIs

    you mentioned,
    >> We’re publishing the source, schematics and the idea for others to run with

    Where can we find this?

  • Phillip Torrone

    here! once we publish it!

  • Wherels

    Ha ha. I can’t wait! Great job I must say. Very nice.

  • Tidal
  • Instructor

    Nice, I teach a dynamic web programming course and was looking for a project for my students. This might be just the front end for an interesting web page. How soon till the plans are available?

  • Phillip Torrone

    30 days or less

  • Christian Kohler

    I’m so glad you guys figured out how to interface with the Kill-a-Watt. It looks like you are reading the power sensor directly. Does that mean you are not reading out the values that the Kill-A-Watt displays? Is the Kill-A-Watt calculating the energy values, or is Arduino doing that?

    The inside of your Kill-A-Watt looks different from my P4460 or P4400.

    Looking forward to the schematics.


  • mike

    Hi there,

    Please check out my website where I am publishing my current power consumption. http://www.currentWatchers.com.

    I am using a TED (The Energy Detective) device to monitor whole home usage. I want to find more discrete devices like the one envisioned here.

    My website encourages folks to post their own energy consumption to the site and discuss ways to reduce and conserve. Please contact me through email at ‘admin at currentWatchers dot com’ if you are interested in collaborating.


  • Energy Solution

    @ Instructor.

    If you are teaching a dynamic web course I can probably do something for you. You can contact me @ support from this site: http://www.brultech.com/HomeEnergy/ecm1240intro.html

  • Crispin

    Hi there,

    I’ve been following this with interest. I have a Wattson energy monitor. I have also written my own application to interface with it and display the results on the website. The idea of the website is not solely for this monitor but an open source site which will accept readings from any monitor people with to use (obviously you have to get the to talk to the site)

    Anyway, I would appreciate it if folks had a look at the site, gave me comments and ideas on how to interface with other monitors.


  • Frank Flynn

    Monitoring whole house is useful so is the individual outlet and so are other factors like temperature (why is the AC using so much power if it’s only 60 degrees?) water flow (how much energy is my hot water heater using?).

    But for $20 this is really cool…

    If you wanted to go whole hog check out http://www.onsetcomp.com/ for their line of sensors and data loggers – they can publish to web (see the sample charts on their site) but expect to spend a few hundred.

    In future I suspect these will become the norm – not to post to Twitter but to collect the data from several devices around your home – how much poser does your TV use even when it’s off? Probably more than you think.

  • Hoba

    The reason why it “only” uses one outlet is because the other has no access to his main power meter, quote:

    “I live in a rented apartment so I don’t have hacking-access to a meter or breaker panel. Since I’m still very interested in measuring my power usage on a long term basis, I will build wireless outlet reporters.”

  • Conway

    I’m looking forward to the plans for building this. The hardware mostly, and communicating with the Zigbee devices. I laready have a good little charting module written that reads data files grabbed from the “Watts-Up” output. https://www.wattsupmeters.com/secure/index.php

    Using your device for real-time data gathering would be even better.

  • Begging

    Looks great. Any chance youcan publish your Do-it-yourself hardware design before February 27th!


  • Limor

    FYI we posted up the instructions for the design at:

    • vc1234


      This is the question I posted at another forum:

      I’ve been thinking of using this nice Xbee+KaW idea to log daily electricity usage. What bothers me however is that the Python code appears to calculate apparent rather than actual power. It will cause a substantial error with non-resistive loads such as electrical motors in dishwashers, air-conditioners, fans etc where the power factor is about 0.6-0.8 depending on the load.

      Do you happen to know what power metering chip Kill-a-Watt uses ? (The Xbee solution takes current/voltage data before the Kill-Watt native chip as I understand). I am wondering whether it is possible to read the chip output which should be much more precise rather than the raw V/I data.


  • SuperDuper

    Very nice instructions, I must say. Thank you for posting this!

  • Joe
  • Dave

    I’ve always felt one really bad feature of the KaW is the lack up internal power supply. Just adding a supercap (and 10,000 uF is only a mini-supercap!) ought to support the display long enough to finesse the damned thing out from behind an appliance and read it, without resorting to a flat-plug extension cord, etc.

    Any idea how much the KaW circuit itself draws at ~5VDC, and how long 10,000 uF would support it? Obviously, the 1N4001 would need to go, and I wouldn’t be powering an XBee.


  • http://pulse.yahoo.com/_EAO3BWQT2OVM2CD3VT6OZUXXGI Tomas

    Is it possible to buy one of these or get schematics how to make it transmit to tweeter?. I have solar array and i want to tweet how much power it produces every day.

  • http://www.facebook.com/people/George-Fraser/666707358 George Fraser

    Ok guys, I have two of these in a drawer and would love to modify and tweet.  Where are the directions?

  • http://twitter.com/naveenrko1 naveen s

    where will i get all the technical know how for this project as i have to do project for my final year

  • http://www.makeabyte.com jeremy

    For those interested in mains monitoring: http://openenergymonitor.org/emon/