Smart Power Strip

Colin Young, Travis Newell, Sam Sorensen, Joe Lutgen

Introduction

Background

Design Specifications

Circuit Layouts

Block Diagrams

Detailed Schedule

Project Costs List

Power Consumption

Future Directions

Parts List for Complete Build

Individual Responsibilities

Conclusions                      

Introduction

As more and more of the world becomes concerned with conserving electric power and the fuels that generate electricity, there is a growing market for products to help the conscientious homeowner keep an eye on and minimize their power usage. Organizations such as Energy Star seek to minimize power consumption at the manufacturer level by providing buyer-recognizable certification on electronic devices. This certification is an easy way for consumers to discern energy-efficient products when shopping, providing an incentive to purchase Energy Star products over their less efficient cousins. This potential for increased revenue provides incentive to corporations to strive for energy-efficiency. Other organizations and products such as Google.org’s PowerMeter, Microsoft Hohm, and P3 International’s Kill-o-Watt aim to facilitate power-awareness by providing a framework for monitoring a home’s power consumption. PowerMeter and Hohm provide an intuitive user interface for recording and analyzing trends in power usage, while the Kill-o-Watt, a device that sits between the wall outlet and a piece of hardware, allows for measuring power consumption at the individual device level. The discontinuation of both PowerMeter and Hohm leaves an unfilled niche for an easy-to-use, centralized monitoring system. When integrated with monitoring hardware similar to the Kill-o-Watt, this monitoring system provides a convenient interface for measuring, controlling, and minimizing a home’s power consumption. The Smart Power Strip is designed to fit this niche and meet the needs of environmentally conscious consumers.This power strip will work like any other six-outlet, surge protected power strip, but will have the capability to wirelessly transmit statistics about power usage on each outlet. Additionally, the web-based user interface will help manage power use by controlling each outlet selectively.

Vampire electronics waste roughly 64 Megawatts of power and cost consumers nearly 4 billion dollars in wasted energy per year according to the US Department of Energy. This type of energy waste is what the Smart Power Strip will help to eliminate by giving consumers a means to monitor their power usage and actively shut down electronics completely when not in use. Also this device will have to be priced somewhere in the median between mid-range power strips, that senses when someone is gone from a room for more than ten minutes and shuts everything down on the power strip, and the high end of power control and monitoring, where  a consumer can hire an electrician to install power monitoring and controlling equipment.

Background

Vampire or standby power is loosely defined as the power used or wasted by electronics while not in active use. Some devices utilize vampire power in a useful manner to provide persistence features such as maintaining clock settings between active sessions, convenience features such as powering the necessary hardware to respond to remote controls, and to eliminate long initialization times by keeping the hardware in a semi-powered state, such as powering the tube heater in CRT displays. Other devices have no advantageous use of vampire power, such as a powered but disconnected mobile device charger or an uninterruptible power supply (UPS) with no active system connected.

The Californian Energy Commission estimated in 2008 that standby modes account for approximately 22% of a home’s power consumption. The US Department of Energy advises that by eliminating vampire power usage, average savings on utility bills lie in the area of $100 yearly, however this depends on local electricity rates. As most electricity is generated using fossil fuels such as oil or coal which produce carbon monoxide and other pollutants, minimizing vampire power will extend the lifetime of existing fuel supplies, reduce air pollution and acid rain, and potentially decrease the rate of global warming, of which increased levels of carbon monoxide has been implicated as a major contributor.

While the elimination of vampire power will not resolve the impending fuel and climate crises, it will grant mankind additional time to research and implement solutions to these potentially world-altering catastrophes.

Design Specifications

1. Electrical

1. Type of outlets

1. 120V outlets

2. Number of outlets

1. Must be enough to cover a reasonable amount of electronic equipment
2. The typical entertainment center will need six outlets. One for TV, DVD player, stereo, and subwoofer.

3. Surge Protection

1. Metal Oxide Varister (MOV) is a cheap easy and safe way to provide surge protection

4. Data Transmission

1. Zigbee Wireless, 2.4 GHz transmission from the power strip to PC or Mac

5. Microcontroller

1. A microcontroller is going to be the brains of the smart power strip.

1. monitors sensors
2. records data
3. controls electronic switches
4. outputs data to user interface
5. Power efficient at running the desired features        

6. Current and Voltage sensors

2. a current transducer for each outlet will be connected to an A/D on the micro-controller
3. voltage will be estimated at 120V given that power must be maintained within a tolerable 5% which doesn’t affect the overall power usage estimation.

7. Electronic Switches

1. Latched Relays - electromechanical switches that turn power on and off through stimulation of a coil and are able to hold last powered stimulation even after power is disconnected.
2. A physical on/off switch will activate or cut off power to the entire system

2. Software

8. Smart power strip program

1. A micro-controller will need programming to interface with the various sensors and switches on the power strip
2. The microcontroller will need programming to transmit data in ways described above to a PC or Mac

9. PC or Mac graphical user interface

1. A graphical user interface (GUI) will have to be programmed into a web based interface.
2. This GUI will be the portal for the user. It will display power usage and cost as well as give the user control of timers associated with turning individual outlets on/off.

3. Physical design

10. Case design

1. Casing with protection in mind, must be able to ground any voltage spikes and be able to reduce static voltage emissions.
2. Able to withstand forces from being stepped on.
3. Indoor use only.
4. Designed around multiple 120V outlets and a physical on/off switch.

Design Requirements

1. Functional requirements - The smart power strip should be able to:

1. Provide at least the minimum number of standard AC outlets to power a home entertainment system. A typical modern home entertainment system has the following components:

1. Television
2. Sound system
3. DVD/BluRay player
4. Home Theater PC
5. Video game console
6. Set-top television box (cable tuner or satellite receiver)

2. Provide the hardware for charging hand-held devices, such as tablets or smartphones used as remote controls for the entertainment center

1. Two USB ports running at or above the USB specification, 1 amp at 5.15 volts

3. Capability to monitor the power usage on a per-outlet basis

1. Current and/or voltage sensors on each outlet

1. Measurable by the analog-to-digital converter component on most microcontrollers.

4. Capability to control individual outlets

2. Relays, power MOSFETs, triacs, thyristors, and physical switches all provide this capability.

1. Relays are easy to control with basic I/O signals from a microcontroller, and are simplistic enough to function reliably.

5. Provide a framework for scheduling when outlets are powered or dead

3. Timer functionality available in most microcontrollers allows for timer-based interrupts which will trigger toggling the state of the outlet switching device.

6. Easy-to-use interface for observing measured power usage, and controlling outlets

1. Web-based interfaces are becoming more and more popular on home electronics

1. By incorporating a webserver into the smart power strip and a module to interface with a home network, an easily accessible interface can be viewed using a standard web browser.

7. User must be able to place the power strip in a desired location, independent of existing network infrastructure

2. Wireless communication through Zigbee modules between the power strip and a network-enabled ground station will allow placement of the power strip in the desired location while maintaining network connectivity.

2. Performance requirements

8. The smart power strip must not draw more vampire power than it eliminates.

1. Low-power components must be used.

9. Real-time usage data

1. The wireless communication must be sufficiently expedient to allow for near real-time monitoring of outlets.

1. This requires minimal and efficient data transmission from power strip to ground station.

2. The web user interface needs to be sufficiently lightweight to allow for rapid updating of displayed information.

3. Interface requirements

10. Power consumption monitoring

1. The monitoring page needs to display real-time usage data along with historical trends for an as-of-yet undecided length of time, possibly in the range of one week to one month.

11. Hardware switches

1. If a user desires to turn an outlet on or off outside the schedule, this should be possible without entering the web user interface. Physical switches for each outlet would be the easiest to implement.

12. Plug’n’play functionality

1. Power strip should “just work” upon initial installation.

1. Default state to outlets on, rather than outlets off until user configures otherwise.

4. Architectural design requirements specified in UML or some other suitable design language:

13. See included diagrams.

5. Development standards

1. Revision control will be used to preserve working sets of code.
2. Similar code functionality between web server and power strip shall be made as portable as possible.
3. Code will be compliant with established HTTP, Zigbee, and other standards, as well as any applicable licensing.
4. Strive for reliability and high availability.

Circuit Layouts

Figure 1:  Overview of entire smart power strip

Figure 2: Detailed Schematic of power strip micro controller

Figure 3:  Detailed schematic of switching circuit

Figure 4:  Detailed schematic of the connection between the Microcontroller and the relays involving the inverter going to the transistors

Figure 5:  Detailed schematic of current sensor.  The current sensor takes the line current and divides it by 1000 and then the Op amp amplifies it by 28 and then the peak is converted to a DC output.  This signal feeds into the micro controller.  The micro controller uses an equation to get RMS power  Prms = 120*Vdc*0.707*1000*28.  The 120 is the line voltage which is simply approximated because the electric utility is required to give 120 Vrms within 5% at the outlet.  

Figure 6: Detailed schematic of the AVR webserver/Ethernet controller

Block Diagrams

Figure 7: The figure above shows the flow of information passing from the user to the power strip.

Figure 8: In this section the user requirements are looked at with more depth.  Figure2 above shows a high level flow of the power information and control of the Smart Power Strip.

Figure 9:  The above figure shows how the current sensors and electronic switching devices correlate with the micro-controllers.

Figure 10: This UML component diagram models the interfaces provided and used by the various modules in the smart power strip.

Figure 11: The above UML diagram describes the interactions of the various components on the web server.

Figure 12: The above UML diagram describes a high level view of the interactions of the various components on the power strip.

Future Directions

This project has potential possibilities in the future.  Calendars could be added to control on and off time of each outlet, optimization suggestions could be made to the user through an algorithm to save power, the current sensors could be upgraded to true RMS detectors to reduce power recording error, multiple Smart Power Strips could be linked together through one web browser. The electronics could be shrunk into a smaller case for a more compact look.

Project Cost List

Figure 13 Total project costs with $500.00 budget

Results

The energy consumption of the Smart Power Strip comes in at about 13.14 kWh per year based on the constant 1.5 W in Figure 13.  The average US home consumes 1100 kWh of vampire energy per year according to the U.S. Energy Information Administration.  The power strip consumes less than 1% of the energy wasted in the average home. If the average person spends 8 hours a day sleeping and 8 hours at work, that is 16 hours when those outlets can be turned off. If every device contributing to the 1100 kWh vampire energy were regulated by the Smart Power Strip and was turned off when the homeowner isn’t using them, this would cut back on 66% of their wasted energy, a cost savings of $63.30 per year at a rate of 8.72 cents per kWh in Montana.  

Figure 13 Power consumption of the Smart Power Strip.

Limitations

Due to the incompleteness of the microcontroller on the power strip, the functionality of the system as a whole is rather limited. In our tests, we have shown that we can control outlets, the current sensor measurements are accurate, the web server can send and receive commands over the wireless module, and those commands can be triggered by a user from the web interface. The calendar scheduling and long-term data logging capabilities were deemed second-tier with respect to the core functionality listed above.

Future Directions

This project investigated and made a product that looked at and attempted to solve the issue of vampire electricity in modern day electronics.  This project could be expanded in the future to accommodate multiple power strips in a home, as well as, incorporate USB power outlets. The webpage could add a calendar, and optimization recommendations for more efficient outlet usage.

Individual Accomplishments

Joe Lutgen was responsible for designing, assembling, and programming the microcontroller in the power strip. This microcontroller reads from Colin’s current sensors and the current state of the outlets, turns outlets on or off by command of the web server, and transmits power consumption data back to the web server for storage or display.

Sam Sorensen worked on the Smart Power Strip’s web server, enabling it to display different web pages and trigger different commands based on incoming HTTP data. The web server is also capable of transmitting and receiving data through the UART connection to the Zigbee wireless module. The sent data consists of commands to the power strip, and the received data is sensor measurements from the power strip, which is then displayed in the appropriate web page.

Travis Newell’s responsibilities include everything pertaining to the physical switching of the outlets on and off. This includes building 6 identical switching circuits for each outlet and will include powering all of the transistors and relays included in each circuit. Each one of these circuits will have to be able to take a voltage stimulation from Joe’s microcontroller in order to turn on each relay, and thus each outlet. Travis will also be working alongside Colin in case design to build a suitable housing for the smart power strip that addresses safety and ease of troubleshooting.

Colin Young built the current sensors that took line current values, and he converted them to a DC voltage that the microcontroller could interpret.  Colin built the power system to supply power to all of the electronics in the Smart Power Strip case.  He also worked on controlling the $500.00 budget, building the case, designing the electronics layout in the case, and mounting the outlets and incoming 120 VAC power line.

Conclusions

The Smart Power Strip could be developed into a mainstream product if further work was done to reduce the size and cost of the unit.  This project served the students working on it by teaching them design skills, implementation skills, and team building. Some of the lessons learned by the team are that communication is key, staying on schedule is a Herculean task, and always overestimate how long each section will take to complete. It is better to come out ahead of schedule than to get behind schedule.

References

"Energy Use of Household Electronics: Taming the Wild Growth." California Energy Commission. California State Government, Sept. 2008. Web. 15 Nov. 2011. <http://www.energy.ca.gov/2008publications/CEC-500-2008-064/CEC-500-2008-064-FS.PDF>.

Raphael, Jr. "Unplug for Dollars: Stop 'Vampire Power' Waste | PCWorld." PCWorld - Reviews and News on Tech Products, Software and Downloads | PCWorld. PCWorld, 09 Nov. 2008. Web. 15 Nov. 2011. <http://www.pcworld.com/article/153245/unplug_for_dollars_stop_vampire_power_waste.html>.

Schueler, John. "Are Energy Vampires Sucking You Dry? | Department of Energy." Energy.gov | Department of Energy. U.S. Department of Energy, 31 Oct. 2011. Web. 15 Nov. 2011. <http://energy.gov/articles/are-energy-vampires-sucking-you-dry>.