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| 11 || You should end up with something like this before closing the Kill-A-Watt. You can also use an adhesive to prevent the component from moving within the device. In this particular construction we did not. || [[image:Step11.jpg|thumb|]]||
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== Program ==
== Program ==

Revision as of 20:28, 27 July 2010

The Queen's Solar Design Team, in collaboration with the Queens Applied Sustainability Group hopes to modify a typical consumer power meter to provide live internet monitoring and recording of residential power consumption.

The article below is not complete!! Full details can be expected on our before August 31, 2010.

Introduction

With today's rising prices in energy more attention has been towards energy conservation. Manufacturers are now trying to create green versions of their products that utilize less energy. Green options can sometimes be more expensive than their more energy hungry counterpart. Another alternative to reducing consumption is to use a power monitor. This can be pricey, as commercial power monitors can cost upwards of 500 dollars. Fortunately a much cheaper alternative exists but is a little less accurate way of determining energy consumption is to use a plug-in power meter such as a Kill-A-Watt. You can retrofit a Kill-A-Watt with a Zigbee wireless transmitter to create more functionality. For this we will be using Adafruit’s Zigbee adapter receiver ( not covered here please see [2] for more information) and transmitter which uses the popular XBee module by Digi.

Kill-A-Watt

In this demonstration we will be using a Kill-A-Watt. We will be receiving current and voltage data from the Kill-A-Watt’s Op-Amp and is wirelessly transmitted using the Zigbee module. You can use other power meters but you cannot know if will work unless you open it and examine it. Also the kill-a-watt's size is excellent to house the ZigBee unit. The ZigBee RF chip has an embedded micro controller which allows you to do some simple operations without having to program a micro controller. The software provided by Digi X-CTU allows you to change variables such as sleep timer easily. Unfortunately, it also limits you too, without an a third party micro controller you can't insert nonvolatile memory. As a result if there was power outage a portion of your data will be lost.

Figure 1: Schematic of the Kill-A-Watt with Zigbee transmitter [1]

The XBee unit receives it's power from the Kill-A-Watt unfortunately the current received is lower than required to run the Xbee as a result a large capacitor is used to account for the current needed. The C1 and C2 is to provide a constant voltage to the 3.3V regulator and C3 capacitor on the reset pin of the Xbee will help delay the transmitter to allow the other capacitors to charge up again. The voltage divisor is used to decrease the sensors inputs received from the Kill-A-Watt at 5V to 3.3V. The last resistor is used to power the LED. In this demonstration we did not create our own circuit board but instead used one that was meant for the receiver. Creating your own transmitter circuit board will greatly increase the speed and simplicity of putting this together.

Parts List

Material Quantity Approximate Cost ($ USD)
Xbee Chip (XB24-AWI-001 or XB24-ACI-001) 1 $20
Kill-A-Watt 1 $22
1N4001 diode 1 $0.11
10k resistor 2 $0.095
4.7k resistor 2 $0.095
3.3V linear voltage regulator, 250mA current ( MCP1700-3302E/TO ) 1 $0.415
220 uF capacitor 1 $0.189
100000 uF capacitor 1 $1.085
0.1 uF capacitor 1 $0.302
Green/Red LED 1 $0.13
1/8” Heat Shrink 1 $1.62
100 uF 1 $0.255

All resistors listed are 1/4W and 5%

Programming the XBee Unit

Using the host controller we programmed each XBee unit into a transmitting mode using the X-CTU software provided by Digi. You must change these options within the program:

  1. MY address to 1 increment this with every transmitter added.
  2. SM to 4 (Cyclic Sleep) 
  3. ST to 3 (3 milliseconds timer)
  4. SP to C8 (Hexidecimal value for 2 seconds between transmits.)
  5. ADC 4 D4 to 2 (Enable pin AD4)
  6. ADC 0 D0 to 2 (Enable pin AD0)
  7. Samples to TX IT to 13 
  8. Sample Rate IR to 1 

Construction

I decided to use the PCB board created for the XBee host controller by adafruit this saved some time in creating a new PCB board and also using just a breadboard.

Program

Step Instructions Image
1 Solder on LED and its respective resistor to reduce the voltage. The voltage regulator regulates the voltage to 3.3 V which is required by the XBee, the 220uf capacitor helps keep a constant flow of power and also a 0.1uF capacitor to filter out unnecessary high frequencies from the power supply. A jumper is soldered between VREF and VCC to set them equal to each other. The 10k resistors are soldered onto analog input pin AD0 and AD4 and to ground.
Step1.jpg
2 Soldered on two 4.7k Resistors at the end of the input wires for the voltage divider.
Step2.jpg
3 Finish soldering the 4.7k resistors onto the 10k resistors to successfully reduce the voltage of the kill a watt sensors from 5V to 3.3V
Step3.jpg
4 Solder on the 220uF cap to the reset pin and ground.
Step4.jpg
5 Now to solder the 10000uF capacitor. Solder the diode to the positive lead of the capacitor and then connect it to the XBee's power source through the voltage regulator. Then solder then negative lead to it's respective ground
Tep5.jpg
6 Solder on a wire to the positive and negative lead, make sure you use a heat shrink to cover the leads once you are done. This will be used to connect to the Kill-A-Watt's power source.
Step6.jpg
7 This step can be different for everyone depending on what revision of the Kill-A-Watt you received. But it's functionality is still the same. Crack open the Kill-A-Watt and locate the Op-Amp, in this example the Op-Amp was located under the LCD Screen which will make soldering on the leads a bit harder. The Op-Amp is circled in the picture.
Step7B.JPG
8 Make a hole big enough for the LED on top of the Kill-A-Watt's casing.
Step8.jpg
9 This step is optional depending on revision. Make a hole on the PCB board in this case we did the left of the Op-Amp in order to feed through the wires to the other side. Make sure you do not cut through any connections
Step9.jpg
10 This step can be different due to revision. According to the data sheet for the this particular Op-Amp the 2 outputs are located at the far left top and bottom pins. It doesn't matter which lead you solder on as long as you account for it in the program. I would personally suggest connecting voltage lead (AD0) to top pin and current lead (AD4) to bottom pin to avoid having to modify the program. Finally solder the capacitor's positive and negative lead to the Op-Amp's VCC and ground leads respectively.
Step10.jpg
11 You should end up with something like this before closing the Kill-A-Watt. You can also use an adhesive to prevent the component from moving within the device. In this particular construction we did not.
Step11.jpg
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