Step 11: Assemble and create the transmitter - 5
Now its time to open the Kill-a-Watt! There are only 3 screws that hold it together, and they are found on the back.
Use a 3/8 drill bit to make a hole near the right corner of the case back. This is what the LED will stick out of. (Ignore the white tape and #4, this is a recycled kill-a-watt :)
Now find the LM2902N chip. This is a quad op-amp that senses the power line usage. We're going to piggy-back right on top of it, and borrow the ground, 5V power and 2 sensor outputs!
With your soldering iron, melt a bit of solder on pin 1, 4, 11 and 14 of the chip. Make sure you have the chip oriented correctly, the notch indicates where pins 1 and 14 are
Solder the white wire (5V to the XBee) to pin 4. Solder the black wire (ground) to pin 11 directly across.
Now solder the yellow wire to pin 1 and the orange wire to pin 14.
Use two small pieces of sticky foam and stick them onto the back of the case.
Then place the XBee adapter and capacitor on the tape so that the LED sticks out of the hole drilled earlier
Tuck the excess ribbon cable out of the way so that they are not near the 120V connections which could make them go poof.
Close it up and plug it in.
You'll notice its a bit finicky for a few seconds as the big capacitor charges up. The display may not come up for 15-30 seconds, and it may fade in and out at first. The numbers may also be wrong for a bit as it powers up. Within about 30 seconds, you should see the display stabilize and the indicator LED blinking every 2 seconds!
Go back to your computer, plug the receiver XBee into the USB adapter and make sure it has the latest firmware uploaded and set it to the same PAN ID as the transmitters. You will see the RSSI LED (red LED) light up. That means you have a good link!
Open up the Terminal in X-CTU (or another terminal program) and connect at 9600 baud 8N1 parity and you'll see a lot of nonsense. Whats important is that a new chunk of nonsense gets printed out once every 2 seconds, indicating a packet of data has been received.
The hardware is done. Good work!