There was a Greener Gadgets Contest and the Tweet-a-Watt won. The first place I saw it was on blog.makzine.com.
Eventually a pretty detailed tutorial and parts list appeared at ladyAda.net.
The instructions for soldering together the Serial Receiver are at Assemble your kit.
The instructions for soldering together the Wattcher Transmitters is at Tweet-a-watt, Do the soldering stuff.
Data listening & parsing is at Tweet-a-watt, Build a wireless home-power monitoring system
Storing the data at Google App Engine is at Tweet-a-Watt, Build database.
Making use of the App Engine data is Tweet-a-Watt, show saved data.
Location of Configure the transmitter XBees. It is Step 2 on this page.
Plug the transmitter XBee into the USB connection (put the receiver XBee away) and start up X-CTU. Then configure each one as follows:
- Set the PAN ID to a 4-digit hex number (I'll go with 3137)
- Set the MY address (the identifier for the XBee) to 1 (increment this for each transmitter so you can tell them apart)
- Set the Sleep Mode SM to 4 (Cyclic sleep)
- Set the Sleep Time ST to 3 (3 milliseconds after wakeup to go back to sleep)
- Set the Sleep Period SP to C8 (0xC8 = 200 = 2 seconds between transmits)
- Set ADC 4 D4 to 2 (ADC enable)
- Set ADC 0 D0 to 2 (ADC enable)
- Set Samples to TX IT to 13 (0x13 = 19 samples)
- Set Sample Rate IR to 1 (1ms between samples)
There is a lot more detail on the XBee radio page: Wireless Arduino programming / serial link, including pictures of the various parameter settings. However, these settings are more general in nature and do not do the job for the Wattcher.
The XBee modules come from Digi International.
The manual for the XBee XB24-ACI-001 module we are using is: XB24-ACI-001 Manual (pdf).
There is a discussion thread about accuracy and consistency here on the LadyAda discussion board.
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