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Power Pi – The Green Revolution
Kevin Okiah, EE, Christopher Finn, CSE, Paulo Leal, EE, and Tim Mirabito, EE
Abstract — The goal of the Power Pi is to monitor energy
consumption from electrical devices within a home, store that
data, and report it to the user in an understandable but
detailed manner. To accomplish this goal, electrical usage
will need to be gathered from a device using a watt meter. This
information will then be transmitted to a central processing
server that users can access online. This online interface will
provide the user with their energy consumption data over
different time periods as well as a logical analysis of the
processed data. Once completed, the project will provide the
user with the pertinent data required to engage social and
behavioral change.
I. INTRODUCTION
he Power Pi seeks to capture the attention of
Tresidential home owners, similar to how energy audits
interest businesses, by bridging the gap between the
technological barriers surrounding energy consumption to
an environmentally conscious and monetarily driven
general public. Energy conservation has a significant
social and economic impact in our society. Energy
conservation initiatives to date thought have been
restricted due to the limited quantitative data on energy
consumption, limited social awareness on the need to
conserve energy and limited residential control over the
same. In the US for example, energy consumption and
cost have steadily been increasing over time which calls
for the urgency to increase social awareness on the need
to conserve energy [1]. Figure 1 below shows a
significant gap between the amounts of energy produced
in BTU to the energy consumed in the US.
Total energy production and consumption in the
US, 1980-2035 (quadrillion BTU)
Fig. 1. T aken from U.S. Energy Information Administration; Annual
Energy Outlook 2012 Early Release Overview shows a gap between
energy production and consumption which is met by importing energy
by the U.S. government [1].
.
From 1980 to 2010, the US experienced a steady rise in
the energy consumption, in BTU, that has remained
higher than then energy produced over the same duration
of time. As a response to this, the US government has
been forced to import energy to meet the gap between
production and consumption. The US for instance depend
Canada to supply electricity to New England, New York,
the Upper Midwest, the Pacific Northwest and California
to meet its unmet energy need [7]. Projections also
viewed this as a trend likely to continue into the future
[1]. This clearly incites an initiative to rethink our ways
of conserving energy which begins with social
awareness.
II. REQUIREM ENTS
A. Requirements List
The following are a set of general performance
parameters needed to design the Power Pi:
1. System must be safe to use and operate. The final
designed system must provide full safety to the
user in the circuitry side as well as the user
interface.
2. Energy monitoring for all types of household
devices connected to an outlet through the
Power Pi.
3. System must
assimilate
new
electrical
outlets/areas.
4. Establish wireless communication within each
room, with the estimated range of 50-100ft per
room.
5. Account for potential wireless dead spots
6. System must provide switching control (On/Off) to
the user
7. Information must be delivered to the user in visual
form through a user interface.
8. Information must be meaningful.
9. Allow for the development of future applications.
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The requirements listed above each dictate an
important aspect of the products intended functionality.
The first requirement that the product must be safe to
use and operate is a parameter consistent for all
electrical designs but will require special attention in this
design as the product will be directly interacting with a
120V source. The second requirement that the system
must monitor all house devices speaks to the fact that
although the vast majority of household devices are
designed to operate at 120V, there are a select few
appliances that utilize a larger 240V design such as a
refrigerator and a stove. The system would need to
account for this variation to be universal to all
households. Requirement three is the parameter that the
system must be scalable to include additional outlets both
within a room and within a household. This ensures that a
greater proportion of a household’s energy consumption
can be accounted for. Requirement four defines the
more complicated form of our information transmission.
Since outlets within a room are certainly spaced out, the
method to collect the data monitored from each outlet
would be solved by implementing a wireless
communication network between the Power Pi units.
Requirement five takes the basic premise of requirement
four and establishes the contingency that there may be
areas within a household not suitable for wireless
communication. In this case, another means to
communicate information remotely needs to be
established. Requirement six sets up a design parameter
for the implementation of a remote switching capability
for the system to control a device connected to the
monitoring network. Requirement seven states that in
addition to acquiring the energy and electrical information
using the watt meter and storing it within the system
memory, the information must be presented to the user of
the system. Requirement nine increases the demand of
requirement eight in that the information collected and
presented to the user needs to be both a reflection of the
technical sensing results as well as a streamlined analysis
for a user without a technical background. Finishing the
list of primary requirements is to utilize equipment and a
logical style that allows the system to be open to iterative
improvement by both the designers and inspired users.
III. DESIGN
A. Overview
We aim to bridge the gap between energy consumption
and production by increasing consumer awareness and
control over their energy consumption. Our belief is the
more information you have about your energy
consumption the better equipped you are to actually
modify and execute personal energy conservation
initiatives.
We will use the Kill-a-Watt P4400, a Raspberry Pi, a
XBee, and a HomePlug to build a system that measures
energy consumption of individual electronics appliances,
store the data and present the data to the user in a way
that is visually easy to understand. With respect to the
wireless communication modules, a similar product on the
market to the XBee is the JeeNode [28]. The JeeNode is
a small breakout board with an attacked 8-bit
microprocessor and an attached RFM12B radio. In terms
of cost and functionality both products are essentially
equal. There are also a few other energy monitoring
systems commercially available that seek a similar goal
to our project. One of the more prominent systems is the
eMonitor from Powerhouse Dynamics [26]. This system
is installed inside the circuit breaker panel in a home and
monitors the electricity usage on a given home circuit.
This information will then be communicated with the
home’s wireless network. One disadvantage of this
system however, is that is doesn’t provide the user much
ability to control the devices plugged into the circuit.
Another energy monitoring system currently implemented
is a smart meter. This is an electronic device that
connects the home to the power grid to communicate
with the utility company. This device however has also
generated significant controversy regarding privacy
exposure. There is also quite a bit of debate over the
paradigm of electricity usage as a byproduct of this
product’s use. Ultimately, the scope of the problem is
different between the smart meter and the PowerPi.
Research into the field of energy conservation has also
provided some of the motivation behind our project. In a
meeting with Professor David Irwin, assistant professor
at the University of Massachusetts, some of the
problems currently facing the research field were
introduced to us, and we were shown a publication of his
to reference, “Smart*: An Open Data Set and Tools for
Enabling Research in Sustainable Homes” [29]. This
meeting also revealed the data limitations of currently
implemented wireless sensors from which the idea to use
the HomePlug format arose.
From this information, we therefore believe if users
have a system to both monitor their energy consumption
coupled with the ability to inject outlet level control over
their devices, they will be more motivated to manage
their energy usage. Figure 2 below shows the block
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diagram of the Power Pi.
Fig2. Power Pi block diagram showing how individual blocks are
interconnected.
In the following section each of the major modules of
the system are described in great deal.
B. Block 1: Watt Meter
The first and perhaps most critical component of the
project is the Watt Meter. This is the device necessary
for the measurement and transmission of the host
electrical information. The imperative electrical
information monitored within each watt meter model will
be the current and the voltage. From these two
characteristics the power will be calculated.
In an AC system such as this, the measurement of
“power” is actually the apparent power; the magnitude of
the complex power vector. The apparent power is
calculated as the vector sum of the real power and the
reactive power. The real power is the term used to
describe the energy of purely resistive load whereas the
reactive power is the term used to describe the energy of
a purely reactive load; the effect caused by a capacitor
or an inductor whose voltage and current phase will be
90 degrees apart. Mathematically, this calculation is the
product of the root mean square of the voltage and
current. Therefore, by continuously sampling both the
instantaneous voltage and current, the apparent power
can be determined. In addition, the reconstruction and
analysis of these waves can reveal other electrical
characteristics such as, total power consumption and
power factor; the efficiency measurement shown by the
ratio between the real and apparent power.
To accomplish the goal of monitoring household power
consumption, three different types of metering devices
will be used. The first is a modified Kill-a-Watt meter
used to monitor 120VAC household outlets. The second
is a proprietary design also used to monitor 120VAC
household outlets. The third is a proprietary design used
to monitor 240VAC household circuits.
The modified Kill-a-Watt meters will serve as the
primary means for setting up satellite sensor nodes in our
network. Since the Kill-a-Watt meter can be easily
modified, and is an inexpensive product to obtain, it
served as a starting point to gain insight on the processes
and integrated circuits involved in power measurement.
In the Kill-a-Watt, the current is sensed by the
differential voltage across a current shunt resistor on the
bottom PCB. This voltage is then placed across the input
pins 2 and 3 of the A op amp within the LM2902 quad op
amp chip. The output of op amp at pin 1 will produce the
current hardwired into the A/D4 pin of the XBee’s built
in microcontroller. The voltage meanwhile is acquired by
taking the output at pin 14 from op amp D of the
LM2902 and hardwiring it to A/D0 pin. This voltage is
derived from its inputs at pins 12 and 13 which are fed by
the neutral line and a reference voltage from the wall.
The next evolution of this module was a proprietary
design which will use an improved architecture and
streamlined design for our specific application. This
device will serve as the Watt Meter design used in our
model A. Due to the higher overall cost of a proprietary
design, this prototype will be best utilized as a hub sensor
in a quantity of one per room. At the root of this new
design is replacing the LM2902 quad op amp with the
INA128 instrumentation amplifier. This specific
instrumentation amplifier model will provide an overall
improvement in performance over the traditional 741 op
amp within the LM2902 chip. Some of the advantages to
utilizing this chip include a high common mode rejection
ratio of 120dB, a supply range from 2.25V to 18V, a
single resistor adjustable gain from 1 to 10000, and a
nonlinearity of 0.001 %FSR. The high CMRR is desirable
for our application to sense the small voltage fluctuations
from which the current measurement is derived. The
wide range of voltage supply will allow greater flexibility
in the design of the power supply. The adjustable gain
will decrease the feedback network complexity required
to normally set the gain for a 741 op amp. Finally, having
a small 0.001 %FSR nonlinearity will reduce the output
distortion and provide a more accurate signal to the A/D
inputs of the XBee. All of these improvements should
push the accuracy of the new design to beyond the 0.2%
error margin listed for the Kill-a-Watt P4400.
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The other important design improvement is the creation
of an internal power supply. One of the central
constraints of the transmission rate for the XBee is the
ability to provide it 50mA of current. Since the Kill-aWatt P4400 is designed to be a low power system, the on
board power supply doesn’t have a 50mA output
anywhere. Testing the device with a standard lab
ammeter and oscilloscope confirmed these assumptions.
My first intention was to design a transformerless
power supply capable of providing 5V to the rest of the
circuit and 50mA to the Xbee for transmissions.
However, after showcasing this initial design to Prof.
Salthouse, he recommended that I should simply proceed
to purchasing a power supply, as my own design was
inefficient. The power supply chosen for this task is the
vsk-s5 by CUI, as this will provide the voltage and
current necessary, but at an efficiency of 69%.
Fig. 3. Initial PCB layout for the transformer less power supply
design schematic with a 15V and 50mA output.
A second improvement to the power supply would be
the use of a polymeric positive temperature coefficient
device in conjunction with a breakaway fuse. A PPTC is
a circuit protection device which increases in resistance
as a response to the internal heating of an excessive
current flow. This increase in resistance will only allow a
small non-damaging leakage current through the device
in overcurrent conditions. Though this device does not
have the current interrupt ability of a fuse provided by
the creation of an open-circuit, the advantage for home
electronic deployment is that PPTC’s are self-resetting
once the fault conditions are cleared. It should be noted
that many commercially available PPCT’s are compliant
with the UL-60950 standard. [14]
Each of these improvements was implemented into a
PCB design, constructed through Eagle CAD. The board
manufacture was then completed through the company
Advanced Circuits.
Finally, to construct the 240VAC monitor, the design
for the 120VAC monitor was used for a base design.
However, since 240VAC household circuits generally
have appliance specific wiring, the prototype for our
240VAC design uses the NEMA-10 outlet specification.
This specification is based on a 20A circuit with two
120V active contacts, a neutral contact, and a ground
contact. Each of these contacts is passed into the
240VAC PCB design through header pins and passed
back to the device through another set of header pins. In
between, the voltage on each of the active contacts is
extracted through the use of voltage dividers and passed
into a unity gain instrumentation amplifier. The current,
will be extracted using a similar method to the 120VAC
design, with the only difference being that the current
sense resistor will be placed on the active line instead of
the neutral line. This is due to the fact that a complete
circuit is constructed in a 240VAC design by offsetting
the phase between the two active lines instead of the
active line and the neutral line. Replacing the INA128
instrumentation amplifiers found in the 120VAC design
will be two INA2126 instrumentation amplifiers which
have similar electrical characteristics but will encompass
two instrumentation amplifiers per IC. Likewise, the two
active lines will be connected to two 30A single pole
single throw relays triggered in unison by the Xbee
module, and the relay circuit.
In order to implement this solution, the primary
techniques used in its actualization have come from selfgathered research. Some previous course work in
understanding AC calculations came from ECE 212
Circuit Analysis II and the bridge rectification circuit
analyzed in ECE 323 Electronics I. Learning how to use
PCB layout software came from various online tutorials
including PCB Design Tutorial. [15] Part selection was
primarily conducted through reading numerous technical
documents, many of which were produced by Texas
Instruments. [16]
Fig. 4. Voltage vs. Current in AC. T he above figure is demonstrating
the measurement of the voltage and current in an AC setup relative to
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the phase. It is important to note that the voltage and the current will
only be in phase for a purely resistive load [27].
Fig. 5. Circuit schematic for the 120VAC Watt Meter complete with
relay circuit, power supply, and circuit protection devices.
decision was made based on the fact that XBee
modules are designed for high-throughput
applications requiring low latency and predictable
communication timing. These devices also present a
series of different aspects [17] such as:
• Indoor Range: 100ft, which is more than
enough for average room
• RF Data Rate: 250Kbps, Sufficient for this
project
• Frequency: 2.4 GHz, which will create
channel hopping to avoid Wi-Fi interference
• AES encryption, thus providing secure
wireless data transmissions
• Analog to Digital converter, which will
digitalize the analog inputs from watt meter
• Fairly small, which will allow the final design
to be fit in a smaller enclosure
XBee radios operate under the ISM (Industrial
Scientific and Medical) frequency band which is
2.4GHz. The API structure utilized to process the
data can be seen in figure 2.
Fig. 6. Circuit schematic for the 240VAC Watt Meter complete with
relay circuit, power supply, and circuit protection devices.
Fig.7. Basic API Fame Structure. T he above figure is showing how
the XBee API protocol is setup[5].
C. Block 2: Networking Circuit & Switching Circuit
Block 2 is a combination of the networking circuit along
with the switching circuit. The main idea behind this
block is to transmit and receive information wirelessly,
and to control outlet switching by turning it on or off. The
two different circuits included in this block can be
explained the following way:
- Networking Circuit: A pair of XBee Series-1 devices is
utilized to transmit and receive information wirelessly
to models A and B. XBee modules are embedded
solutions providing wireless end-point connectivity to
devices. These modules use the IEEE 802.15.4
networking protocol for fast point-to-multipoint or
peer-to-peer networking [17].
Network in a home can also be created by using a
wireless router, a DSL modem, or a cable modem
with built-in wireless networking support. However,
XBee radios were the number one choice for setting
up the wireless network aspects in this project. The
One of the applications included in our project is the
multi-room communication. The goal is to monitor
multiple outlets wirelessly in different rooms and
report their data to the master model. The multi-room
networking structure is shown in the diagram below
in figure 8. When setting up the wireless network
amongst the radios there are two characteristics that
have to be taken into account: PAN ID and NI.
PAN ID or Personal Area Network ID is the unique
number to assign to XBee so XBee can talk to the
right XBee in the same Network Area. By default all
XBee's use PAN ID #3332. The ID is 4 bytes of
hexadecimal and can range from 0000 to FFFF.
Xbee’s will only send & receive data to other
modems on the same PAN. The NI or Node
Identifier is a unique characteristic held by every
XBee. It allows the user to keep track of the data
flow. In our case, the microcontroller is able to
manage each XBee through its specific NI.
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The diagram below replicates the networks setup in
two different rooms:
- Room 1: The XBee’s of NI 1 and 2 are the model
B’s placed on outlets 1 and 2; The Xbee of NI 100 is
the master module placed on a different outlet of room
1.
- Room 2: The XBee’s of NI 3 and 4 are the model
B’s placed on outlets 3 and 4; The Xbee of NI 101 is
the master module placed on a different outlet of room
2.
Fig. 8. Multi-room communication flow in a house. T he diagram shown
above is a replica of how the room-to-room network is setup. Each
individual XBee’s of NI 1 through 4 replicate model B, whereas XBee’s
of NI 100 and 101replicate model A.
- Switching Circuit: this block, shown in figure 9, utilizes
an XBee device that will control an SPDT relay for
up to 220VAC. The relay will be used to transition
the desired outlet thus turning it on or off. This relay
was essentially chosen for the following reasons:
• Single pole switching: 20A, which is enough to
handle high current in a household such as a
fridge, air conditioning and others.
• Driving Voltage: ~5VDC, which perfectly fulfills
the requirements in the designed circuit.
The coil within the relay requires up to 80mA. This is
more than a GPIO (General Purpose Input Output) pin
can handle which is 20mA by default. Therefore an
NPN transistor is used as a controllable connection to
ground. The NPN transistor can handle up to a 200mA
which is more than the coil and the LED combined which
would be approximately 100mA.
When the trigger pin (RELAY) goes high, the NPN
transistor connects to ground sending current through the
coil thus activating the relay, and through the LED which
will turn the activation LED on.
Resistor R1 has the function to pull the trigger pin to
ground so if anything goes haywire the relay will remain
in the safe, off position.
The 1N4148 diode is placed between power and
ground in a reverse fashion. When the coil of the relay is
de-activated, it acts like an inductor, trying to suppress
current change. This can cause some havoc on the 5V
power rail. When this happens, the diode will forward
bias causing the current stored in the coil to flow back to
the 5V rail protecting the power supply and the near-by
parts.
Fig. 9. Switching Circuit Schematic. Direct actuation is a basic
example of remote control. T he actuator circuit shown above will
control the relay switching based on an input given by the user. T hat
input signal will subsequently be transmitted to the XBee, thus triggering
the switching mechanism [4].
The primary techniques used in order to understand
and work with the different technologies in this design
were obtained from different tutorials in how to use
XBee radios, found in a few specific websites and books
[5]
. The knowledge acquired in the courses Circuit
Analysis I & II (ECE 211 & 212) and Electronics I
(ECE 323) certainly contributed to the circuit design
aspect of the switching circuit. Data was also collected
from the devices datasheet found in the company’s
website [18].
In order to build the network mesh used to transmit
and receive data we learned about XBee protocols and
the different functionalities associated with it. We also
have learned and understood how relays work and how
to handle high current devices in order to implement the
switching circuit.
A simple way to test the functionality of the
networking circuit is by the passing in an input signal to
the coordinator XBee (master) and transmitting it to the
router XBee (slave). Upon completion of the process, the
transmitted signal was checked against the received
signal.
The XBee software X-CTU allows the visual
representation of the transmitted data packets, which will
help in the debugging process. An oscilloscope was also
used to check the integrity of the signal.
The switching circuit will be triggered by an output
signal coming out of the XBee and the relay stability will
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be checked by connecting different devices (high or low
current) to the controlled outlet. The results from the test
methods mentioned above can be clearly analyzed from
the action response given by triggering the process.
D. Block 3: Microcontroller
The microcontroller is the “brains” of the system. The
microcontroller is responsible for sampling the outlet data,
storing this data in a database and creating and parsing
command and data packets. The microcontroller also
runs a web server service and serves up the user
interface web page which queries data from the
database.
Fig. 10. T he Raspberry Pi. T he above figure is showing the model used
in our system. [21]
The microcontroller we are utilizing is the Raspberry Pi
[19], a credit card sized ARM GNU/Linux computer.
The Raspberry Pi was chosen primarily because it can
run ARM Linux distributions, giving us the ability to
utilize the vast array of Linux packages available. The
Linux distribution we are using is the Rasbian “wheezy”,
an optimized version of the Debian Linux distribution.
The Raspberry Pi also has an Ethernet port which we
are using for internet connection as well as to
communicate with other Raspberry Pi’s via a network of
HomePlugs [20]; devices that plug into the outlet and
covert transmission over Ethernet wire to transmissions
over the household power line. The Raspberry Pi also
has two USB ports, one of which we are using for
interfacing with an XBee module.
For the web server and database functionality we are
using Apache [22], MySQL [23], and PHP [24] Linux
packages (commonly referred to as LAMP). We chose
to utilize a LAMP server because it is free, open source,
modular (allowing for a light weight, high performance
webserver) and has a strong development community
behind it. To ensure our web server and database are
secure, firewall rules and user permissions have been set
accordingly as well as having security updates install
automatically. Also the user interface connection utilizes
the Secure Sockets Layer (SSL) protocol providing an
encrypted connection as well as requiring users to login
to the user interface before being able to access its
functionality. Finally, to secure the communications of the
entire Power Pi system, the Ethernet transmissions from
Raspberry Pi to Raspberry Pi and the wireless XBee
transmissions are encrypted using AES encryption.
Python scripts are used to sample and parse the input
data from the XBee and then store it in the MySQL
database. Python [25], a dynamic programming language
was chosen to fulfill these functionalities due to its
simplicity, libraries and because programming in Python
is a useful skill we wanted to learn.
The communication flow is depicted in Fig. 7 below.
The Raspberry Pi connects to the internet through a WiFi dongle. As mentioned previously, communication to
and from the server is encrypted using SSL. An XBee
module attached via USB is used to receive local data
packets as well as transmit relay control packets. The
Raspberry Pi Ethernet port is connected to a HomePlug
and is used to receive external data packets (via TCP)
and transmit relay control packets (via UDP broadcasts).
The primary techniques used to implement the
microcontroller functionality involved utilizing online
tutorials for the specific software packages. The
development communities for all the open source
software packages have provided a tremendous amount
of information for much of the functionality that we
sought to implement. In order to build this block, I needed
to learn about the structure and management of a
MySQL database, how to properly setup a web server
and how to receive data through the USB and serial
connection on the Raspberry Pi.
Networking techniques and Ethernet packet creation
learned from ECE 374: Computer Networks & Internet
are being utilized in the packaging of command & data
packets as well as for handling user connections to the
web server. Network security techniques learned in ECE
544: Trustworthy Computing are being implemented in
order to secure the web server connection transmissions
as well as the transmissions of command and data
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packets.
E. Block 4: User Interface
The purpose of this block is to present energy
consumption data to the consumer in a way that is clear
and visually easy to understand. The user interface
provides feedback to the user based on their energy
consumption in relation to an average American family
which is aimed enhancing the user’s energy conservation
initiative. The gives the user control over how they
would like to view their energy data; be it hourly, daily,
weekly, monthly or within a given time frame. Based on
user input, this block will access the database, collect,
manipulate and present the data to the user as annotated
plots for a given time frame. Besides, this block allows
users to calculate and compare the contribution of
individual outlets they are monitoring to their total energy
cost and remotely turn on off an outlet when they are not
using it.
When picking a user interface design, we aimed for an
interface that is cross functional across all operating
systems. We settled for a browser based system since it
could support all Operating Systems be it windows, Mac
OS, android just to name a few. This user interface can
be accessed from a phone, laptop, and any other
electronic device with a browser that is connected to the
internet. Our user interface software is based on
following web programming languages; HTML5,
JavaScript, PHP, and CSS. The four programming
languages each play a special role. HTML5 provides us
with a framework in which we can host and structure the
contents of our user interface on the browser [9]. CSS is
a style language that defines layout of the HTML5 user
interface we just created. CSS covers features such as
fonts, colors, margins, lines, height, width, background
images, advanced positions and many other things [8].
JavaScript adds functionality to our user interface such
validating forms, taking in user inputs, and communicating
with the server to plot the given data. PHP on the other
hand acts a link between the user interface and the
database. It provides an avenue in which we can query
the data from the MYSQL database then pass the data
to the JavaScript function for visualization.
Fig.11. Below show the communication flow between the clent side
and the web server and the programming languages involved
We use plotting scripts from flotcharts and
awesomechartjs to present visual data to the user.
Awesomechartjs JavaScript allows us to plot data in the
form of pie charts and bar graphs which will be ideal for
displaying a summary and comparison of energy usage
between different outlets as a percentage of total energy
used for a given period as shown in Fig. 7 below.
Fig.12. Screenshot of the User Interface showing a bar graph plot
using Awesomechartjs JavaScript displaying comparison of energy
usage. Plots are from mock data.
Flotcharts JavaScript on the other hand allows us to
plot data as line graphs which will be ideal for displaying
real-time energy data and data for an entire period the
PowerPi has been used to monitor energy. Fig. 8 below
shows an example of a flot line graph
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VI. ACKNOWLEDGM ENT
Personal thanks go to Professor Leonard, Professor
Bardin and Professor Gao for their helpful input during
our design reviews, Fran Carol for assisting with our
project budgeting and part acquisitions, and Professors
Salthouse & Hollot for their steadfast dedication to our
success.
APPENDIX
Fig. 13 T aken from flotcharts.org shows a sample flot line graph
showing real-time plot of data. T his will come in handy where we display
real-time energy utilization at any instance [11].
Based on good programing paradigm learned from
Data Structures, Computer Systems lab and Software
Intensive Engineering classes, we have designed a user
interface that is robust in the sense that is doesn’t easily
crush. The interface redirects users using a built in error
recovery function which monitors wrong user inputs. It is
simple with lots of feedback, guidance and online help to
support multiple skill levels of users from sophisticated to
naive and is clear, simple, and easy to learn.
To design an effective user interface, we first had to
understand the basics of human computer interaction.
Referencing Alan Cooper’s work, ‘About Face: The
Essential of User Interface’, we learned mechanism of
designing a good user interface that is simple, user
controlled, aesthetic, clear and consistent [12]. We also
had to learn new web based programming languages;
HTML5, JavaScript, PHP, and CSS to develop browser
based software.
IV. P ROJECT MANAGEM ENT
A. Team Member Roles
Appendix D and G
V. CONCLUSION
In closing, Power Pi offers a comprehensive system for
monitoring energy consumption of individual outlets in a
household and presentation of data in a way that is clear
and easy to understand enabling users to make sound
energy conservation decisions and save on their energy
bill.
A. Application of Mathematics, Science and
Engineering
ECE 323 and 324 (Electronics I and II): Knowledge
from these two courses came in handy in our hardware
design. Tim used previous circuit design and simulation
knowledge that he had acquired classes to design,
optimize and check the functionality of our designed
hardware.
ECE 374(Networks): A significant portion of our
design involved communication between individual
subsystems. We utilized knowledge about wireless
networks and wired networks that we had learned from
our networks coursework to establish a mesh network
communication for our system.
ECE 353 and 354 (Computer Systems Lab I and
II): Based on the knowledge we had learned from this
two classes we programed the two embedded systems;
Raspberry pi and the XBee which formed the bulk of our
system.
ECE 242 (Data Structures) and ECE 121 (Intro to
Programming in Java): Having gained fast had
programing paradigms from this classes, we quickly
learned several new programming languages i.e.
HTML5, PHP, CSS, JavaScript, JQuery, MySQL and
python, which we used to design a functional, visually
attractive and easy to use user interface.
B. Design and Performance of Experiments, Data
Analysis and Interpretation
After the construction of both the initial and final
versions of the Watt Meter, its functionality will be tested
by first plugging into it a simple resistive load.
Subsequently testing a highly capacitive or inductive load
will occur. For the resistive load, the measurement of
both the instantaneous voltage and current amplitude
should be in phase and can then yield a basis for a
reasonable calculation of the apparent power. In this
case the apparent power should closely resemble the real
10
power. Likewise, monitoring the phase difference
between the current and voltage for the highly reactive
loads will show the influence of reactive power on the
apparent power calculation and help calibrate the
accuracy of our electrical characteristics
C. Design of System, Component or Process to Meet
Desired Needs within Realistic Constraints
See Section III above
D. Multi-disciplinary Team Functions
Although each member of the Power Pi team comes
from a similar academic background, special interests in
the various sub disciplines have allowed each member to
bring a unique perspective and problem solving ability to
the team. For example, through the summer research
program at the University of Massachusetts Kevin has
developed an interest in VLSI. Christopher meanwhile
has used internship positions at MIT’s Lincoln Labs to
learn more about computer networking and systems
integration. Paulo, in this case, has applied his experience
with radar and sensing systems to the wireless
communications of the project. Tim meanwhile, has used
his research experience in polymer science and device
physics to aid the group in designing analog circuits.
Due to these different backgrounds, the roles of the
project were dictated according to each person’s
preference of field after the project had been broken
down into both its hardware and software components as
well as the specific concentrations within each.
After deciding on the four major blocks that would
need to be addressed, the group split the project into two
general groups of software blocks and hardware blocks.
Chris and Kevin had decided to work on the central
processing server and the user interface respectively.
Meanwhile, Paulo and Tim had taken on the role of
designing, modifying and building the wireless
communications and the watt meter respectively.
Chris chose the Raspberry Pi as the central processing
unit because of its low cost and functionality. Its
ARM1176JZF-S 700 MHz processor makes Raspberry
pi an attraction as a powerful small computer. Kevin
looked at different available programming languages that
could form a good user interface. He settled on a web
based user interface as it offers the advantage of being
cross functional over different operating system. Tim
researched different techniques of measuring power and
settled on a Kill-a-Watt P4400 which he is modifying to
meet our targeted requirement. On the other hand, Paulo
came up with a means by which our individual Power Pi
modules could communicate. In doing so, he settled on
using the XBee as they offer the advantage of a secured
wireless mesh network.
Given the nature of our system there needed to be
consistent communication between each group member
to make sure of hardware compatibilities and that the
data format being synchronized between the modules
was understood and able to be processed appropriately.
Summary of team member’s roles
– Circuit Design
– Networking
– Microcontroller Programming
–User Interface design
E. Identification, Formulation and Solution of
Engineering Problems
It is fairly common that things usually don’t work the
first time in a project, and that the complexity of an idea
is not realized until it is used in a real-life application. The
Power Pi presented many challenges when the system
was implemented in hardware, from providing the correct
voltage to the right components in the PCB layout to
analyzing and translating the data properly.
The identification process was done in hardware and
software with the help of devices such as a multimeter,
oscilloscope, power supply and function-generator. The
formulation and solution were tackled by using
techniques learned in classed, research done on the
material and the help of Professors in our department.
F. Understanding of professional and ethical
Responsibility
Just like any other system that use live electric power,
the power pi system faces professional and ethical
responsibilities that we had to adhere to as a team. The
system possess a potential danger associated with it
operation. As such, safety of team members and
observers and other electrical systems that may share
the same connection as our system has to be ensured at
all times.
Professionally are responsible for the honesty of the
idea. As engineers we are not to give off the impression
that we came up with our design scheme based on our
11
knowledge only but acknowledge any sources we may
have used to aid in our design of system.
G. Team Communication
With these specific concentrations recognized it would
be easy to isolate each project demand to its expert,
however since the team is consistently seeking the
benefit of alternative viewpoints to optimize solutions, the
members consistently communicate. Doing so effectively
involved the use of an application called GroupMe. This
is an application used as both a group text message
program but setup to operate like a continuous chat room
for mobile phones. The setup of this application was
straight forward as each member could simply download
the application onto their smart phones and accept the
group invitation for all the design team members.
Alternatively, email was also used to forward
important messages and files between the course
instructors, the team faculty advisor, and the team
members.
The scheduling aspect of our communication was
mainly handled by verbal communication due to the close
friendship of the team members for appropriate meeting
times and locations. It should be noted however, that
Google Calendar was used to a lesser degree for
scheduling between the team leader and the team
advisor.
Every Monday at 2pm the team met with their advisor,
Professor Leonard to discuss issues, current progress,
and future goals. This helped direct focus and stay on
track, as well getting advice from Professor Leonard.
Finally, for the project files consolidation and sharing
the Dropbox application was a critical cog in that
mechanism. Given the nature of the application to
automatically update any file worked upon that is opened
from the Dropbox folder, it promoted the real time
sharing of information through the installed application on
all of our individual computers as well as the SDP lab
computer.
H. Understanding of the impact of engineering
solutions in a global, economic, environmental and
societal context
It is primordial to understand the main problems that
are highlighted in our society from an engineering
standpoint. The mindset behind this fact is to tackle any
possible barriers by providing the best solution through
the design of a product. Our project will impact society
from one big perspective, energy waste.
In order to cause an impact in the environment it is
necessary to start in a small scale. The Power Pi
envisions a solution for energy waste in a household. The
target is families all over the U.S and the rest of the
world.
The aimed results are the reduction of energy waste
around the globe, which will positively affect the families
in an economically speaking.
I. Application of material acquired outside of
Coursework
The following are some of the materials used that are
outside our coursework:
1) Web Programming: We have come up with a
user interface that is web based. This involved
learning how to use programming languages like
HTML5, CSS, PHP, JavaScript, MySQL and JQuery
none of which are taught in our engineering
coursework.
2) Embedded Systems: Raspberry pi is the brain of
our system. We settled on it as a design choice
because of it numerous functionalities which we
learned through our own online research.
3) Eagle CAD: Was used to design the PCB layout
for our designed circuit.
J. Knowledge of Contemporary Issues
As we stated above, our goal is to come up with a
system that will bridge the gap between lack of
information on energy consumption and conservation
initiative. We want to provide people with more
information on their energy use to empower them to
make sound energy conservation decision thus save
money. We want to provide user with more control over
the energy use by use of relay circuits to turn off outlets
when they are not using features which typically don’t
exist in a normal household.
K. Use of modern engineering techniques and tools
1. PSPICE, an analog circuit and digital logic
simulation software tool for our circuit
simulations
2. PCB Design using Eagle CAD for the design of
the circuit board used to contain our circuitry.
3. HTML5, CSS, JavaScript, JQuery, PHP,
MySQL, and Python; Modern programming
languages for software creation and system
management
4. Embedded systems i.e. Raspberry pi and XBee
5. X-CTU, a software mainly used to program the
used XBee’s to the desired characteristics.
12
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