WSN: Tweet-a-Watt

The Tweet-a-Watt is a wireless power meter based on a commercial device called the Kill A Watt which is hacked to include a wireless XBee radio.  It was designed by Limor Fried of Adafruit Industries and she has written up one of the best online tutorials for a kit based project.  It collects data from the Kill A Watt from P3 International and with an added XBee radio sends data to a PC and then on to a twitter feed.  Hence the name, Tweet-a-Watt, a combination of Twitter’s Tweet and the Kill A Watt power meter.

You can build a Tweet-a-Watt by following the tutorial here.

The basic components:

Kill A Watt Power Meter (P4400)

Kill-a-watt

Everyone should own at least one Kill A Watt.  It can tell you the cumulated kilowatt hours (KWh) at the plug load of an appliance, along with the volts, amps, and watts.

With pencil and paper and a little time you can hook this up to the various appliances in your home and look at the meter and simply “do the math”.  With the math, and perhaps a spreadsheet program, you can analyse what your appliances draw in watts and learn what to turn off or use less.  You can get them online for as little as $17 and at your local hardware store for about $25.
XBee Radio
The Kill-a-Watt starts to become a Tweet-a-Watt with the introduction of an XBee radio.  The radio can be hooked up inside the Kill-a-watt and that makes it possible to transmit the readings from the Kill A Watt and send them to a computer for logging and analysis.

The original design of the Tweet-a-Watt project had an XBee radio receiver hooked up to a PC through what is known as an FTDI USB cable; essentially a serial input.  There was a python script that would run on the PC and collect the serial input and  package the data for delivery to a twitter feed.

During my investigations I saw Limor Fried’s short video about using an Asus Wifi Router instead of a PC to collect and send the sensor data to the internet.  If you’re trying to reduce your energy consumption it seems a shame to have to run a PC; even a laptop will draw perhaps 60-90 watts.  The Asus wifi router setup can be configured to run the python script and do the same basic job as the PC but it only draws about 4 watts.  Much better.   See the post about setting up the ASUS WL-520gU.


Next Post: Temperature Sensor
Next Group: Radio XBee

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