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Wireless Upgrade for Typical Consumer Power Meter

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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 also. Another alternative to reducing consumption is to use a power monitor. Commercial power monitors can cost upwards of 500 dollars. Fortunately a much cheaper alternative exists but 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. Using Adafruit’s Zigbee adapter receiver ( not covered here please see [2] for more information) and transmitter we attempted to accomplish this.

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. Design 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