Custom Kill-a-Watt Power Meter
Create your own personal power monitor. Using a recent MAKE magazine article, I put this together in a weekend. A customized Kill-a-Watt meter uses XBee radios to send power data to a computer and then to the Web.
Background
The Kill-a-Watt is a small device that plugs in to any standard household outlet and provides power data for any connected device. Each Kill-a-Watt can accept up to a 15-amp load.
The MaxStream XBee radio modems manufactured by Digi allow wireless communication from the Kill-a-Watt meter to a laptop computer. The image below shows an XBee mounted to a break-out board so that it can connect to a laptop via a USB-to-TTL serial connection:
How it works
The transmitting XBee resides inside the Kill-a-Watt case and connects to the op amp inside the Kill-a-Watt. The XBee receives the op amp's signals and then broadcasts the data every two seconds to the receiver XBee connected to the laptop via USB. A Python script reads the data from the XBee and logs it to a csv file. In addition, the Python script can generate a real-time graph of the power data from the connected load. Below is a screenshot of the display showing the two-second update of the power data and the graphing utility while there was a load connected:
Assembly
Most of the assembly was easy to accomplish, however, there is a lot of soldering required. The most challenging soldering was getting the XBee radio soldered to the tiny op amp on the Kill-a-Watt. In all, this project took around 5 hours to complete. I finished it on a Saturday.
The Python script has an option to Tweet the power data. You can see the current power data for my outlet at Twitter @WattBird
Improvements
Currently, I only have one Kill-a-Watt, monitoring one surge protector on an outlet. I am going to purchase additional Kill-a-Watts to monitor my other existing power outlets. Since the XBee radios use the ZigBee protocol, adding additional modules is trivial. I also plan to build a robust website with power meter information and database storage for trending. I already incorporated a Carbon Footprint calculation and cost calculation. I plan to add web-based graphing and reporting utilities once I set up additional Kill-a-Watts.
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-Nick