Well we had two choices, either cut the extra parts off, or something else. Given that I have yet to find a Kill-A-Watt locally, and I had this external/internal thermometer I'd been wanting to computerize for 10 years, I knew what I had to do:
I had to use the Thermometer to measure the temperature of my hot tub, and then tweet it!
I had recently given Minion #1 an assignment to describe a hot tub controller with no boundaries. He mentioned, well we could make it wireless, but no, that's silly...
I love it when a 10-year plan comes to fruition.
See it on Twitter
Step 1: Build the Xbee Recievers
The trick to the Tweet-A-Watt is the configuration . In effect you set one of the devices up to repeat the values from the Kill-A-Watt with:
This sets the address (1), sets the sleep mode, timer, and period, and then sets Pins 4 and 2 to Analog input mode (2), which will send 0x13 (19 decimal) packets, 1 ms between samples.
The trick here is the Analog Input. You can read small voltages (0-5V) directly by the XBee.
In the Tweet-A-Watt you would set pins 4 and 0 to sending the Amps and Volts measured by the Kill-A-Watt. In reality it does not send that, it sends the small voltage measured by the chips in the Kill-A-Watt to the receiver XBee which is attached to a computer. The software at the computer constantly reads the packets received and it recalculates the actual voltage and amperage, and then it calculates the Wattage.