Montana State University > College of Engineering > ECE Department
Program Information
1. Project Definition 2. Requirements Definition 3. Concept Generation & Eval 4. Critical Design 5. Assembly & Test 6. Product Launch
Internal Docs External Refs Systems Engineering Resources
MSU's 2012 Smart Power Strip |
It has the capability to transmit wireless information about power usage from each outlet, as well
as give the user the capability to shut off each individual outlet. This power strip is geared
towards the environmentally conscience consumer. This person wants a low cost, easy to use
product to monitor and control his or her power usage. It is a “plug and play” type product for
both Mac and PC that can be safely retrofitted into existing homes.
The Smart Power Strip is designed around an “off the shelf” micro-controller and wireless
transmitter. The micro-controller is connected to a current sensor, voltage sensor and electronic
switch on each of the 8 outlets. The information gathered from the sensors is sent wirelessly to a PC or MAC. The user accesses the wirelessly transmitted interface through any common web
browser. From there, the user can set outlets to turn on or off through a calendar, monitor power
usage on each outlet, and see real time cost of operating each outlet. The current market for home power monitoring has a large gap. On the low end the consumer can buy a “Kill-A-Watt” type device. On the high end the consumer can use a contractor to retro fit the home fuse box with a power monitoring system. This power strip will fit in between with a cost between $100.00 and $300.00.
Advisors
Brock LaMeres, Assistant Professor, Electrical Engineering
Hunter Lloyd, Faculty, Computer Science
The goal of this project is to give consumers a low cost, easy to use power monitoring and power controlling device. Specifically, it will help to eliminate “vampire power”, which currently costs the US an estimated $4 billion dollars a year in wasted energy.
$500.00
August 2011- May 2012
Travis Newell: I am a senior in Electrical Engineering with an emphasis on both analog
and digital systems, also a familiarization with micro-fabrication, Cisco networking, and
audio acoustics (particularly with amplifier devices). I will work on the structural design,
placement, and inter-networking of circuit components and find efficient ways to
maximize the stability of the product while minimizing cost.
Colin Young: I am a senior in Electrical Engineering. I have worked on many projects
through the school and I hope to be a leader on the project, as well as, help with the
power electronic switches involved. Also, circuit design will be one of my major
functions.
Sam Sorensen: I am a senior in Computer Science with an interest in systems administration, embedded systems, and networking. I will configure the webserver, build the webpage, and work with Joe on the wireless interfaces and micro-controllers.
Joe Lutgen: I am a senior in Computer Engineering with interest in embedded systems design and digital signals processing. I will be focusing on collecting information on power usage and sending informational packets back and forth from web server to smart power strip.
Client Stated Objectives and Objective Tree (Figure 2)
Figure 2: Objective Tree
Detailed User Requirements
Figure 1: In this section the user requirements are looked at with more depth. Figure 1 above shows a high level flow of the power information and control of the Smart Power Strip.
Feature Matrix
This decision matrix encompasses a wide range of potential features for the smart power strip. The high scoring features will take precedence in their respective categories. The numbers in each entry of the decision matrix were averaged from the entire groups individual ratings.
Higher scores represent positive aspects of individual categories. The different aspects of each feature were based off different scales to compensate for the weighted importance of each category. The weights were made by changing the point ranges for each category. More important categories, for specific features, were given a larger range of point values. The range of all ratings are shown next to each category title.
Case Design
Cost (Low 5 - 1 High) | Safety (Safe 5 - 1 Dangerous) | Size (Small 8 - 1 Big) | Ergonomics (Good 10 - 1 Bad) | Total (28 pts) | |
Rectangle | 3.75 | 4.25 | 6.25 | 3.25 | 17.5 |
Tower | 3 | 3.5 | 4.5 | 7.5 | 18.5 |
Squid | 2.25 | 2.5 | 4.25 | 9.5 | 18.5 |
Rectangular with Rotating Outlets | 2.5 | 3.75 | 5.75 | 4.5 | 16.5 |
Power Pyramid | 2.75 | 3.75 | 3.5 | 5.75 | 15.75 |
Data Transmission
Cost (Low 5 – 1 High) | Implementation Difficulty (Easy 5 - 1 Hard) | Power Efficiency (High 8 - 1 Low) | Ease of Use (Easy 10 - 1 Hard) | Total (28 pts) | |
Wireless | 2.5 | 3.5 | 4 | 9.5 | 19.5 |
USB Cable | 4.75 | 4.25 | 7.5 | 1.5 | 18 |
USB Flash Drive | 4 | 3.75 | 5.5 | 5 | 18.25 |
Bluetooth | 1 | 3 | 2.5 | 5 | 11.5 |
Port Type and Amount of Ports
Cost (Low 5 - 1 High) | Implementation Difficulty (Easy 5 - 1 Hard) | Safety (Safe 8 - 1 Dangerous) | Usefulness (High 10 - 1 Low) | Total (28 pts) | |
120V Outlet: 6 5V USB: 4 | 1 | 2.25 | 4 | 9 | 16.25 |
120V Outlet: 3 5V USB: 2 | 3 | 3 | 7.25 | 5.25 | 18.5 |
120V Outlet: 6 5V USB: 0 | 3 | 3.75 | 5.75 | 5.75 | 18.25 |
Surge Protection
Cost (Low 5 - 1 High) | Implementation Difficulty (Easy 5 - 1 Hard) | Power Efficiency (High 8 - 1 Low) | Safety (High 10 - 1 Low) | Total (28 pts) | |
MOV | 3 | 3.25 | 5.5 | 8 | 19.75 |
Uninterruptable Power Supply | 1 | 1.75 | 3 | 10 | 15.75 |
None | 5 | 5 | 7.25 | 1 | 18.25 |
User Interface
Cost (Low 5 - 1 High) | Implementation Difficulty (Easy 5 - 1 Hard) | Usefulness (High 8 - 1 Low) | Interface Complexity (Easy 10 - 1 Hard) | Total (28 pts) | |
Web-based | 5 | 4 | 8 | 8.25 | 25.25 |
Standalone Application | 4.75 | 2.5 | 5 | 4.25 | 16.5 |
Mobile Application | 5 | 3.75 | 7.5 | 8 | 24.25 |
Brains
Cost (Low 5 - 1 High) | Implementation Difficulty (Easy 5 - 1 Hard) | Usefulness (High 8 - 1 Low) | Interface Complexity (Easy 10 - 1 Hard) | Total (28 pts) | |
Micro-controller | 5 | 4 | 8 | 8.25 | 25.25 |
FPGA | 4.75 | 2.5 | 5 | 4.25 | 16.5 |
Switching devices
Cost (Low 5 - 1 High) | Implementation Difficulty (Easy 10 - 1 Hard) | Usefulness (High 8 - 1 Low) | Power Consumption (High 1 - 5 Low) | Total (28 pts) | |
IGBT | 3 | 7 | 4 | 3 | 17 |
Power Mosfet | 4 | 5 | 5 | 4 | 18 |
Triac | 4 | 4 | 5 | 3 | 16 |
Relay | 2 | 9 | 7 | 2 | 19 |
Measuring Devices
Cost (Low 5 - 1 High) | Usefulness (High 8 - 1 Low) | Implementation Difficulty (Easy 10 - 1 Hard) | Power Consumption (High 1 - 5 Low) | Total (28 pts) | |
Current Sense amplifier | 3 | 4 | 5 | 4 | 16 |
Current Sensors | 4 | 5 | 7 | 3 | 19 |
Thermocouple | 4 | 4 | 4 | 4 | 16 |
Wireless open source monitoring node | 1 | 5 | 7 | 2 | 15 |
Top Candidates Evaluation
After finding several features through brainstorming and evaluating them with the design matrix, the functions were refined to some ideal features:
Case design
Data transmission method
Port Types
Surge protection
User interface
Switching Devices
Brains
Final Design Concept Description
The smart power strip will have the squid case, which is unique looking and has the most adaptability to different electronic plug-ins. The squid will have eight cords, six 120 V outlets and two 5V USB outlets. It will monitor current and voltage using an ATmega 328p. The micro-controller will then send packets to the ATmega 328p through the use of a ZigBee wireless module. The packets sent will contain information about power usage by port number. The web server will send packets back to the powerstrip containing information about scheduled and impromptu outlet shutoff. The user will be able to set on/off timers for individual outlets, monitor power consumption, and monitor cost from their computer or smartphone by way of a web-based program. The web server will be contained in an ENC28J60 Ethernet Controller.There will also be a physical on/off switch on the unit that will cut power from the entire unit. The smart power strip will have metal oxide varisters (MOV) for surge protection. This is a widely used safe and affordable way to protect against surges.
The smart power strip will have wireless TCP/IP networking support, providing the user convenient access to the strip - no cables, removable drives, or adapters will be required. Moreover, networking support allows the graphical user interface to be implemented as a web-based application hosted on the smart power strip. The GUI will be accessed by navigating to a special HTTP address using any common web browser. With this design strategy, a single software system embedded in the Smart Power Strip can support a variety of computer platforms. Switching outlets on and off will be done with a MOSFET and relay with minimal amperage draw in mind.
The smart power strip will use a micro-controller, with its low power applications and timer based events, will be the most attractive solution. The main purpose of this unit is to provide a signal to turn on or off an outlet based on user input or calender events. A micro-controller can handle this function very easily. Wireless networking capabilities is another reason that a micro-controller seems favorable. There are many embedded systems already available that include a programmable micro-controller along with some kind of wireless device for packet communication.
4 DETAIL DESIGN
This section covers the power consumption of the actual circuitry, the parts that will be needed to build the smart power strip, general schematics of the main circuits within the power strip, the graphical user interface as seen by the consumer, and a layout for the software design.
4.1 Computational Analysis
The total power consumed by the power strip while in standby is about 1 watt. This is a form of vampire power, but it is far less than the typical 6 watts that other electronics consume.
4.2 Failure Mode Effect Analysis
The following table shows the components and software which will cause the most problems in failure mode.
4.3 Components List
This is a list of components that will be used in the smart power strip. Appendix B shows the specifications and the data sheet for performance of each component.
Varistor( approx. $0.30)
Metal oxide varistors (MOVs) works as a non-linear resistor. This means that the MOV has a high resistance until a threshold voltage is reached and then the MOV’s resistance starts dropping until it reaches zero. This allows current to bi-pass outlets and protect devices in short term instances.
Thermal Breaker(approx. $0.99)
Thermal breakers are the solution to long term current spikes for protecting equipment after the MOV initially protects the circuit.
Master on/off switch(approx. $0.47)
The master on/off switch will allow for easy shut off to the whole power strip by allowing no current to flow to the receptacles.
Resistors( $0.02 per resistor )
A resistor is an electrical device that decreases energy coming into it by releasing that energy in the form of heat.
Capacitors( $0.05 per capacitor )
A capacitor is an energy storage device that can block DC current and pass AC current at specified frequencies. The energy stored is within the electric field.
Diodes( $0.10 per diode )
The diode allows electrical current flow in one direction but blocks current in the other direction.
Transistor( $0.24 per transistor )
A transistor creates a gate which opens and closes based on different voltage levels at each of the three pins..
Transformer( $3.50 per transformer)
The transformer is a device that allows for the transfer of energy from one inductor in a circuit to another coupled one in another circuit allowing for the transformation of voltage and current levels.
Operational Amplifier ($0.60 per op-amp)
Creates a static point of input and output voltages of desirable nodes.
Microcontroller ($4.99 per controller)
Controls all of the inter-working circuitry by creating a bridge between software and hardware.
Photo-coupler ($0.50)
A device that will prevent voltage spikes from the AC side of the
circuit from damaging components on the DC side of the circuit.
Voltage Regulator ($0.80)
Voltage regulators allow specific nodes to retain a certain voltagelevel. It can be used to regulate multiple DC or AC voltages.
Latching Relay ($7.93 per relay)
Allows for outlets to be shut on and off depending on command of microcontroller and allows them to stay in state and not draw power.
AVR Webserver ($39.98 per webserver) web sites but there are other uses such as data storage or running enterprise applications.
Ethernet Controller ($3.86 per controller)
modulates signals to make them compatible for an Rj-45 connnection
Zigbee Wireless Module ($22.95 per module)XBee and XBee-PRO 802.15.4 OEM RF modules are embedded solutions providing wireless end-point connectivity to devices.
Bridge Rectifier ($.65 per rectifer)
Converts an AC signal to a DC signal
4.4 Schematic Diagrams
The schematics below describe the electrical layout of the smart power strip. The first schematic shows a high level electrical block diagram of the entire power strip, and the proceeding ones show detailed schematics within specific areas of the power strip.
Key: dotted lines are copper connections between components and Microcontroller. Solid lines are power connections
4.4.1 Main Outlets
The main outlet schematic shows the 120V/5V transformer that powers the relay switches in each outlet through “Connect point C”. It also shows the master on/off switch and the thermal breaker which will protect against excessive electrical current. Most of the right half of the diagram shows the six 120V outlets. The boxes labeled “Schematic A” on each outlet can be found in section 4.3.3 and is responsible for the current measurements and the relays that cut off power to the outlets. The USB outlets are connected to “Connect point A” and “Connect point B”, which can be found on the left half of the diagram at the very top and the very bottom.
4.4.2 USB Outlets
This shows a possible circuit for providing a constant 5V of DC power to the two USB ports. It will connect into the main circuit on the left at “Connect point A” and “Connect point B”and both ports will be controlled by the same relay switch. The current measurement will be taken right at the connection to the USB port on the right.
4.4.3 Shut-off Relay / Current Sensor
These circuits will measure the current and activate the relay switch to the six main 120V outlets. The “Schematic A” shows a current source that models the 1:100 current sensor on the main circuit. It is then fed into a current to voltage opamp and a full wave rectifier. At the moment, the circuit can convert a range of 300mA(peak) to 2A(peak) on the main circuit to a 0.5V to 3.3V DC output. This will be scaled up for 10mA(rms) to 15A(rms) next semester. The microcontroller will be able to find power based on this equation: ((Vdc+0.5)*100165*2 *120Vrms = Irms*Vrms = Power
The “Schematic B” shows the latching relay. It is powered by 5 volts coming from the 120VAC to 5 VDC transformer that also powers the 5 VDC USB ports. It is triggered from the microcontroller with a 3.3V DC signal. It is turned off from a ground signal coming from the microcontroller.
Schematic A
Schematic B
4.4.4 Microcontroller
The microcontroller used in this project is the ATmega328p-PU. This was chosen based on the web server module being compatible with this microcontroller. The powerstrip will also use the ATmega328p so as not to complicate the project. Using the same microcontroller in each module allows us to use the same programmer for both modules, reducing the training and cost of development, These microcontrollers have 32K of flash available for programming memory, 1K of EEPROM, and 2K of Internal SRAM. This microcontroller comes with 3 different timers, SPI and I2C interface capabilites, 6 different sleep modes, and 23 available IO lines. The figure below shows how the microcontroller in the powerstrip interfaces to the device.The microcontroller will take input current sensor measurements in the form of a voltage proportional to the main current. The microcontroller will use an equation to find the power usage based on the input Vdc ((Vdc + 0.5) * 1002165) * 120Vrms = Irms*Vrms = Power. This information will be put into a packet and sent to the web server through a ZigBee wireless card. The web server will also update which outlets are on and send the information to the microcontroller in the powerstrip for outlet control.
4.4.5 Full power strip schematic
This schematic shows the full circuit diagram with all connections and switches.
4.4.6 Case Design
The case will be made of clear plexiglass with 1 foot sides. There will be vents and a hinged lid for easy access. The picture below shows the case next to the router-webserver combination and a laptop.
4.5 Wireframes
These wireframe mockups illustrate the features of the web-based graphical user interface. Each wireframe depicts the functional contents and layout of a particular page. These high-level designs will guide the implementation of the JavaServer Pages.
4.5.1 Home Screen
The home screen is the main page for the interface. It consists of three sections, the first is the navigation tabs which include Home, Usage, Schedule, Setup and Help along with print icon on top right. User can navigate to any page any time by clicking on the desired link and this section is common for all pages. Second section shows the last seven day summary of Voltage, Amps, Kilo-Watts, Cost, Money Saved for each six 120V ports and two USB (Universal System Bus) ports. The last section is Monthly summary, this table shows the summary of overall usage of the power strip for the last month, it shows the average data of Voltage, Amps, Kilo-watts and Total cost along with money saved.
4.5.2 Usage History
The Usage page displays the usage of the power strip. User can choose to see the data in range mode and Instantaneous mode. In range mode user can enter any specific date range from last six months from the calender and the data will be displayed automatically. The fields include the Usage graph, Total, Highest point, Lowest point and Average for the Kilo-watts, Voltage, Money and Current respectively.
4.5.3 Instantaneous Usage
The Instantaneous mode can be viewed by clicking on the instantaneous button on top, underneath the navigation tabs. In this mode the instantaneous data of Voltage, Current, Kilo-Watts and Active (Status) will be displayed under their respective ports. The table in the bottom displays the total Voltage, Current and Kilo-Watts of the overall power strip at that instant and all this data can be renewed by pressing the refresh button.
4.4.4 Schedule Setup
The Schedule page will let the user program the ports. This can be done in two ways, user can pick a date and program all 6+2 ports and make it repeat daily, weekly or monthly. The other option is to pick ports individually and program them. User can program ports up to six months in advance.
4.5.5 Data Manager Setup
Setup page is used to setup/modify the power strip’s data and network. The setup page has two sub tabs, Data Manager and Network. In Data Manager page user can reset the information regarding the setup or usage of any or all ports. User can also see and roll back to any previous configuration of the power strip in last 6 months.
4.6 Software Design
4.6.1 Software Design Overview
The software design is organized into three components types:
Web Interface content - The web interface needs to be as lightweight and efficient as possible. Since the web server is AVR-based, any content transmitted to the user needs to be within the computing capabilities of a basic microcontroller. This limits the web interface to mostly static minimalistic content that will fit within just a couple packets. Taking advantage of the default values of various HTML tags will be key.
Device and Protocol Implementations - Working at a low-level, the software running on the microcontrollers needs to contain the code necessary for interacting with the various devices utilized in the system. This code can come from either existing libraries or designer generation.
High-level Subroutines - By abstracting the low-level implementations of the device and protocols utilized, it is possible to minimize the amount of redundant code used for stringing together more advanced operations, such as the handshaking required between an HTTP web server and the connecting client. Using high-level subroutines allows the programmer to focus on the activity as a whole rather than trying to keep track of all the minuscule suboperations required to complete the activity.
4.6.2 High-level Component Diagram
4.6.3 Power Interface Class Diagram
4.6.4 Power Daemon Class Diagram
To Be Determined
To Be Determined