RaspiWatt: discover power consumption using a Kill-A-Watt & Pi

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Say you want to know how much electricity an appliance like an air purifier is consuming?

You can hook it up to the nifty Kill-A-Watt power meter (aka KaW).  The KaW will keep track of and display the killowatt-hours, or kWh, used by the plugged in device.

However, the total will be reset anytime the KaW is unplugged and loses power.  Limor Fried (aka ladyada) recognized this shortcoming and created the clever Tweet-A-Watt project back in 2009. She modded the KaW into a wireless data logger by soldering a XBee wireless module to the KaW's op-amp chip:

The XBee's built-in ADC reads the power sensor signals inside the KaW and transmits it to a receiver XBee module connected to a computer via USB.  This diagram by ladyada gives a good sense of the architecture:

(source: http://www.ladyada.net/make/tweetawatt/)

The Tweet-A-Watt (TaW) is an awesome project, but I felt it's requirement to have a computer receive the data was cumbersome and power hungry.  Thankfully, we now live in an world of powerful, tiny & cheap single board computers (SBCs) like the Raspberry Pi .  I decided to use the Pi in place of a traditional computer.  I also used the Adafruit LCD Pi Plate to display the power usage data. and the Adafruit Pi Box enclosure to protect the Pi (which has a convenient "convertible" mode to accommodate the LCD Pi Plate on top):

The receiver XBee module connects to the Pi via a FTDI USB-to-serial cable :

Ladyada used Google AppEngine for graphing the TaW data, but I decided to take advantage of the newer Cosm graphing service (formerly named Pachube).  Here is a screenshot of my RaspiWatt Cosm feed showing Watts, kWh, and USD$ (based on the cost of a kWh for my power company):

Here is the list of parts I used if you are interested in building your own "RaspiWatt":

You can Add to Cart on Newark element14 all of the above (excluding the Raspberry Pi Model B).

My Pi is currently running a Python program named wattcher_cosm.py which is based on ladyada's original TaW wattcher.py program.  bonnie555 has been a big help in developing it for the RaspiWatt project, and it incorporates code from Adafruit's Cosm tutorial and their LCD Pi Plate tutorial.  In future posts, I'll describe in more detail how I assembled the hardware and provide instructions for installing the software on the Pi.

Cheers,

Drew

http://twitter.com/pdp7

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