Senior Design II Documentation

Transcription

CHARGE DU
SOLEIL
University of Central Florida
Senior Design II
Spring 2015
Group 12
Daniel Zapata
Aaron Mitchell
Alan Champagne
TABLE OF CONTENTS
Charge Du Soleil Executive Summary
1
1)Description
Motivation
2
Goals and Objectives
3
Specifications and Requirements
3
Roles and Responsibilities
4
Standards
4
Realistic Design Constraints
6
Estimate of Budget
8
Milestones
10
2)Research and Background
Previous Works
12
Solar Panels
13
Motors
21
Batteries
26
Mobile Device Applications
29
Electrical Components
32
Microcontroller
33
Data Processing
37
Clocking Requirements
38
Memory Requirements
39
Wireless Tethering
39
Wifi (Background, Pros/Cons, Power usage)
40
Bluetooth (Background, Pros/Cons, Power usage)
41
Power Outputs
41
Battery Comparisons
41
DC/AC Inverter
42
Charging
44
Estimated Life Cycle
45
Block Diagrams
46
General Block Diagram
46
Software Class Diagram
49
3)Project Design
Physical Robot Mock-Up
50
Microcontroller
51
Prototype Construction and Coding
51
Data Input System
51
Power Storage
52
PV cells to Battery
54
Battery to Mobile Device
55
Mobile Device Remote Control Application
55
4)Project Prototype Testing
Test Environment
58
Panel Adjustment Metrics
58
Software Metrics
59
Mobile App
59
Testing Results
60
5)PCB Design and Assembly
Prototype PCB
6)Appendix
Permissions
Datasheets
References
62
Executive Summary
Using the energy provided by the sun is a very viable method of alternative energy. Throughout
time, man has only dreamed of harnessing its relatively infinite supply to power our many devices
that use non-renewable forms of energy and also heat to buildings and structures. The problem
with non-renewable energy is exactly that; once depleted we have no known means to fabricate it
quickly. Oil is a perfect example of that because it is based on a bio-matter process which takes
hundreds of thousands of years. Photovoltaic solar panels have a history of being rather inefficient.
Photovoltaic cells currently can convert only 22% of the sun’s energy into electrical energy [1].
This unfortunately means that a lot of surface area is necessary to generate adequate electricity.
Apparently the concept of efficiency is relative because solar energy does not produce carbon byproducts or the extraction, refinement, and transportation of coal. This has some effect towards
evaluating its efficiency. This project is an attempt to further increase the efficiency of solar panel
technology. This will be done through an automatic solar tracking device that stores captured
energy in a battery that can be used to charge an external electronic device.
Optimizing this project for maximum efficiency will be a challenge this project will attempt to
address. A solar tracker will be used to track the movement of the sun throughout the day and also
throughout the year as the seasons change. The more photovoltaic cells in direct sunlight, the more
power can be collected. In certain cases, using a solar tracker can improve efficiency 25-35% using
less surface area and less panels. However, in certain applications, if the location of the tracker
does not allow it to operate ideally, efficiency may be compromised. The weight and cost of the
solar tracker technology would have to be counter posed by the gain in energy efficiency when
compared to stationary panels.
An optimization project will be difficult to accomplish because in a realistic scenario, no device
or system will be completely optimal. In spite of this, the project aims to at least improve on preexisting solar tracking systems while also integrating additional features as well. The principal
criteria to consider it successful are the devices ability to automatically adjust the angle of the
panels to track the sun in the sky, store the collected energy in a battery with the ability to discharge
into an external electronic device through USB connection, monitor the capacity of the battery and
display the percentage value through a mobile device application. This will be a very challenging
task to accomplish due to the complexity of this project, but any new information obtained through
the trial and error of the design will be viewed as a success.
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1) Description
1.1 Motivation
The process of burning fossil fuels contributes ¾ of all carbon, methane, and other greenhouse gas
emissions [2]. The combustion of this material is the primary means of electricity production and
it adds harmful pollutants to our air and water supply. The atmosphere is absorbing more and more
solar radiation due to an increase in these emissions. The atmosphere acts as a blanket of insulation,
absorbing heat and eventually leading to global warming. Renewable energy is generated from
natural processes that cannot be depleted. Examples of these include sunlight, geothermal heat,
wind, tides, water and also biomass.
Solar energy is so abundant that is makes us wonder why we have not done more to utilize it as an
alternative fuel source. 173,000 terawatts of solar energy strikes the earth continuously [2].
Advantages of this energy from the sun is that is renewable, zero-emissions, no-noise pollution
and low maintenance [3]. The potential for solar energy has manifested itself into a growing
economy driver. There will be many jobs created involving designing and installing photovoltaic
solar panels worldwide. As career-seeking college graduates, this group is interested in joining the
industry of solar energy as it will be very profitable. Although there are many reasons to consider
using solar energy for our global needs, it is worth to note that the technology is early development
stages. Solar energy is an intermittent energy source and the amount available depends on many
factors. Storing the energy collected in an efficient manner at times for when the sun is not shining
is a major challenge. Luckily, our electricity demands peak around noon which lines up with time
the sun reaches maximum energy output. This project attempts to overcome these obstacles facing
solar power [3].
In today’s society, people are looking for devices/electronics that does more which in the end,
makes them do less physically. This change in society stems from the rapid advancement in
technology. This advancement has technology has electronics become smaller and shifting from a
stationary focus to a mobile focus. Examples of these include tablets with the processing power to
replace laptop computers and mobile phones that can replace some tablets. Mobile devices are
expected to accomplish more tasks or run multiple applications and this requires a great deal of
energy. As your battery drains, users seek the nearest wall outlet which may already be occupied
or not in proximity. If the main objective of a mobile device is to be useful anywhere, then why
shouldn’t it also be chargeable anywhere? The following question also led to another question:
what would be the most effective and efficient way that could charge electronic devices?
These questions then led to the idea of Charge DU SOLEIL. Charge DU SOLEIL is a semiautonomous robot that has a solar panel mounted to the top of it. The solar energy gathered would
be stored in a battery in which the battery powers the robot itself as well as charge other electronic
devices. We label this robot is semi-autonomous because it will be able to seek the strongest source
of light to charge itself but can still be controlled wirelessly via an app.
1.2 Goals and Objectives
The goal of CHARGE DU SOLEIL is to create a solar powered battery charging system integrated
on an autonomous light seeking wheeled robot. The robot will automatically head towards the
direction of the strongest light source. A storage system will be added to store energy for when
there is no light available. Because the solar panels are mounted on wheels, the energy can be
physically transported to where it is needed and there is no need for expensive transmission lines.
Solar panel technology will be used in order to charge various electronic devices in direct sunlight
or artificial light. One main objective is to use the surface area of the robot to house the solar cell
panels to remain sleek and aesthetic as possible. The solar panels will of course be lightweight and
portable. Once the solar panels are attached to the device, they will be covered in a durable and
transparent material which will protect the fragile solar panel cells but also allow light to penetrate.
In order to replace the phone charger, the battery specifications must be met. A PC USB charger
delivers 2.5 Watts of power (5 volts at 500 mA). An iPhone charger delivers 5 Watts (5 volts at
1000 mA). A Retina iPad mini charger delivers 10 watts (5.1 volts at 2100 mA). These will all
charge an iPhone safely but ultimately, it’s really the amperage that determines how fast a charger
will supply power to a device. Due to the small size of the solar cells, a realistic goal would be a
delivery of 2 Watts of power. This may take a while longer to charge, but the advantages of
portable charging far outweigh the charging speed. The robot also serves as a fun toy which is
smart, interactive, and easy to use.
Main goals:
● Solar-powered semiautonomous vehicle with mobile device charging capabilities
○ Sun-seeking vehicle with large, angle solar panel on top
○ USB ports to connect and charge mobile device from solar-charged battery
● Motor-controlled solar panel that will seek optimal angle of sunlight
○ Light sensors will instruct motor which angle is most optimal for sunlight
○ GPS wristband will alert user of car/device status
○ Possible LEDs on car itself to show when charging/ fully charged
● Minimize reliance of electrical power via wall outlets
○ Create an efficient, convenient, portable solar charger that will prove more useful
than waiting by power outlets to charge devices
● Create a fun, innovative way to charge electronic devices using an alternative energy
source
1.3 Specifications and Requirements
● Power Generation System that is capable of using solar energy to deliver a minimum of 2
Watts of Power
● Light seeking robotic car; searches for areas of high light intensity to charge
● Length: < 24 Inches
● Width: < 10 inches
● Height: <12 Inches
● Weight: <10 pounds without load; <15 pounds with load
● 36% efficient Amonix solar modules hold the overall solar PV module efficiency record
● mini Solar panel with Max work voltage: 2V, Max work current: 150mA, and Dimension:
60x60mm
● Bluetooth/Wifi connectivity Class 1: range up to 100 meters (in most cases 20-30 meters)
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● Mobile App with bluetooth capability to control the robot
1.4 Roles and Responsibilities
As a group of three, it was decided to break down all of the responsibilities for the completion of
this project based off the individual skills each member possessed as prospective engineers. Below
are the list of roles and responsibilities that the each group members have for the project.
Aaron Mitchell
● All of the code required for the project which include
○ The code for the light sensors to correctly work and detect the strength of light
needed to efficiently charge the solar panels
○ The code that makes the solar panels shift to its optimum angles for charge based
off the feedback form the light sensors
○ The code for the mobile app we plan to use to control the robot with basic functions
such as forward, backwards, turn left and turn right
○ The code that connects our mobile app with the control system of the robot
● The standards and guidelines used for our prototype testing
● The mock ups for the final design of the robot
Alan Champagne
● The physical model design for the robot
● The storing of the energy obtained from the solar panel to the car battery
● The charging port on the robot that will be used to charge devices via an USB port
● The mechanical system that will move the actual robot
● The research for the solar panels we plan to use and how to optimize the use of these
panels(MPPT)
● The research for which model of connectivity we plan to use
Daniel Zapata
● The overview of our budget and spending for our supplies and parts
● The details of the specifications and requirements for the robot
● The integration of all our physical parts
● The research on all of the electrical components we will be using which include
○ Microcontroller
○ Memory and Clock requirements
○ Power
● The prototype of the Printed Circuited Board being used for the robot
1.5 Standards
A Standard is a document established by consensus and approved by a recognized body that
provides for common and repeated use, rules, guidelines, or characteristics for activities or their
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results, aimed at the achievement of the optimum degree of order in a given context.” (82) Below
are the components used in our project and their respective standards.

Batteries - A 9 volt battery and five AA sized batteries were used in the prototype design
to power the Arduino Uno, and the DC motors, respectively. Both batteries have a standard
dimension size, with the 9V measuring 48.5 x 17.5 x 26.5 mm (83), and the AA measuring
50.5 mm length and 14.5 mm diameter (84). The 9V are designated by ANSI and consist
of ZInc-Manganese Dioxide chemical system. The negative side of the battery is positioned
on the top left of the battery and has a hexagonal shape for its junction, while the positive
side of the battery has a circular shape for its junction on the top right side. Both
components are positioned in the middle of the top surface of the battery with 12.95 mm
distance in between the respective diameters.

Universal Serial Bus (USB) - The USB connection itself is a standard created to define the
cables, connectors, communication, and power between computers and electronic devices
(85). The specific USB connectors used in Charge Du Soleil were the standard USB-A 2.0,
USB-B 2.0, and micro USB 2.0. Data signaling rate has a maximum 480 Mbit/s, but due
to bus access constraints, the effective signal rate signaling rate is limited to 280 Mbit/s.
Max voltage is measured at 5 DC volts and max current is between 0.5amps to 0.9 amps.
The given dimensions for each USB connector are: USB-A (12 x 4.5 mm) USB-B (8.45 x
7.78 mm), micro USB (8.45 mm x 1.45 mm). The pin mapping is as follows:


Pin 1
VCC (+5V, red wire)
Pin 2
Data− (white wire)
Pin 3
Data+ (green wire)
Pin 4
Ground (black wire)
Table 1.1
Solar Panels - The standards set for our panels as well as every other solar panel
manufactured is controlled by a handful of committees, the largest of which is the
International Electrotechnical Commission. They are responsible for regulating and
approving the various size and power outputs of all types of panels, including our own
monocrystalline photovoltaic panel. Specifically, since our panels were originally designed
to work as solar car chargers for electronic devices, our panels must have a small power
output of 5 volts that can be easily regulated and charged into the devices. Also, the weight
of the panels (9 ounces), must be light enough to be held by only the four suction cups
connected to the panels (88).
DC motors - The 6 volt DC motors, like all motors of various sizes and costs, must comply
with a strict set of efficiency and environmental rules set by the National Electrical
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Manufacturers Association (NEMA). One of these standards is that a motor cannot exceed
over 320 degrees Fahrenheit or have an efficiency rating below 62% (90). In addition, the
carbon monoxide expelled from the motor must not exceed 0.5% of total expelled
waste(89). This is to prevent inefficient motors from being made that can damage the
environment with excess heat and carbon monoxide loss.

Printed Circuit Board - The design of the PCB came with several standards, all which can
vary slightly based on the manufacturer. For our purposes, we will be using the standards
set by Osh Park. The minimum trace width and spacing is 6 mil, 15 mil clearance between
traces to the board edge, 13 mil drill size, and 7 mil annular ring (86). In addition to the
said manufacturing sizes, some electrical components need to be strategically placed in
order to avoid electrical issues. For instance, all passive components must be close to the
associated Integrated circuit chip, and all power traces that carry large amounts of current
should have a minimum thickness of 25mm for a current max of 1.5 amps (87).

Arduino - Since Arduino is an open source company, the board can be manufactured with
simple components, including an AtMega328 microcontroller, voltage regulator, 16 MHz
clock crystal, USB-to-serial interface (AtMega16U2), and SPI programming interface (91).
However, when regarding the actual Arduino Uno development board, some
considerations must be understood. This includes a header pin size of 1 x 1mm, a DC jack
input of 7 -12 volts, DC current input of 40 milliamps, and a max current input of the USB
input connector of 900 milliamps (92).
1.6 Realistic Design Constraints
With the standards set in place for Charge Du Soleil, it was necessary to begin with a car chassis.
The weight will have to be relatively light because we are relying on solar energy to propel the
rover. A more complex chassis could have been used, but must be accompanied by a proportionally
larger solar panel array, motors, and power banks. These modifications will certainly increase the
cost of this project. The DFRobot 4WD kit was chosen because of its compatibility with the
Arduino development board, which was already to be used. The size dimensions are
(200x170x105) mm which is approximately 8 by 7 by 4 inches. The size dimensions were not to
be constrained by design but weight instead. This kit has the lightweight design desired of 660g.
This weight is approximately 1.5 lbs and will allow the total weight of Charge Du Soleil to stay
below 6 lbs (2721.55g).
Included in the kit is four (4) DC motors. Each motor weighs 45g at a total weight of 180g. These
motors operate on between 3-12V and the rotational speed is directly proportional to the voltage
applied. Based on the added components on the car, a voltage on the high side of that range is
desirable. Each of the four wheels are independently powered by a DC motor. This allows for
turning without the use of a rack-and-pinion steering assembly. An assembly such as that would
allow for more precise cornering on a racetrack, but the goal here is to decrease weight and increase
simplicity.
When choosing photovoltaic solar panels, weight was a large factor. The solar panels chosen were
only 323g each. Three (3) solar panels were to be used at a total weight of 969g. These solar panels
are 5W 12V each. Most batteries charge well below 12 volts, so it will be necessary to decrease
the voltage using a buck DC/DC regulator. Connecting the solar panels could be done in either
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series or parallel configurations. In the series configuration, the voltage triples and the current
remains constant. However in the parallel configuration, the voltage remains constant and the
current triples. This effectively decreases the voltage drop, allowing the regulator to not overheat
and increase the charging time of the battery.
The input of the voltage of the solar panel must be regulated lower to 5V to charge the power
banks. A linear switching regulator will be simple to implement but are highly inefficient over a
large voltage drop and become very hot. A switching regulator will help to increase the power
obtained from the panels and efficiency is a considerable design constraint. During testing, using
a linear regulator with the input on only one panel and the output on the power bank to be charged,
the voltage dropped from 5V to 4.8V, supplied 0.88A of current and the power was only 4.223W.
Using the switching regulator, the voltage dropped lower to 3.3, but supplied more current at
1.355A with a power output of 4.47W. This value more closely approaches the solar panel rating.
Although the panels are rated to 5W, it is realistically impossible to reach this power output as it
was measured in absolute optimal conditions.
A major feature of Charge Du Soleil is charging a mobile device. Power banks are equipped with
an internal Li-Ion Polymer battery and a USB output to connect any device. It was preferred to use
this because it’s high power to weight ratio. The battery of an Apple iPhone 5 has a capacity of
1440mAh. A 9000Mah power bank would be able to charge it 6.25 times before depleting,
however the motors are also to be powered by this source. It is only necessary to charge the phone
just once before depleting giving design preference to the motors. The weight of the larger power
bank is 181.437g and the smaller is 45.3592g. These were chosen for their small size and high
capacity of 9000mAh and 2200mAh. A design constraint that became apparent during testing is
the lack of pass-through charging on the power banks originally purchased. When the solar energy
on the panel array was sufficient to charge the power bank, the power bank would not power the
motors, board, and mobile device. In order to simultaneously charge the power bank and power
the components, pass through charging was necessary to consider in the design.
The photo resistors that were used for the light-seeking subsystem of Charge Du Soleil had to give
accurate readings in luminescence. At first, they were placed directly into the same board as the
LEDs accompanying the ultrasonic sensor. The light from the LED flashed and immediately threw
the photo resistor measurements out of place. Constrained by this, it was necessary to raise the
photo resistors on stalks as to isolate them from the rest of the rover and obtain better
measurements. At this level, only the light directly above the photo resistors will be sensed. When
there is a 70 lux difference between the two (2) photo resistors, the rover is told to turn in the
direction of the lower resistance or higher light. This difference was originally set too high and did
not allow for accurate turning. Limited by the sensitivity of these basic photo resistors, the
difference had to be set higher in order to allow the rover to travel straight primarily. In addition
to this, the rover will stop when there is over 900 lux on either photo resistor instead of turning in
that direction. This had to be altered from an OR statement to an AND statement so that only when
there is sufficient light on both photo resistors could it come to a complete stop and charge.
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1.6 Estimate of Budget
1.6.1 Initial Estimate
Item
Cost
Quantity
Total Cost
Chassis with wheels & DC Motor,
Panel motor batteries
$80 Chassis
$30 DC motor
$45 Panel motor
$20 batteries
1 each
$175
1 Large
Solar Panel,
5 smaller panels (optional)
$50 large
$5 small
1 large(> 12”)
10 small(<4”)
$75
Electronic Device
for App
(optional)
$200
(Ipod Touch 5th Gen)
1
$200
Arduino circuit board
$30
1
$30
Cell phone app
Free Apple Program
1
Free
Car sensors
(Light intensity, Bluetooth/Wifi)
$2 per light sensor
$9 bluetooth piece
4 sensors
1 bluetooth
$17
Board attachments/ misc. pieces
$100 frame
$25 Arduino starter kit
1 frame
102 piece kit
$125
Feedback System
Arduino add-on chip
1
$50
Wristband with GPS tracker
(optional)
Free wristband
$50 tracker
1
$50
LCD screen(s) on car
(optional)
$25
1
$25
LEDs on Car (optional)
$2 each
4
$8
DC-DC Converters
$15 each
3
$45
Table 1.2 (Initial Budget Estimate)
Expected total cost: $800
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1.6.2 Final Bill of Materials
Item(s)
Quantity
Cost
Chassis
1
$59.95
Arduino Uno Starter Kit
1
$62.99
Bluetooth Module
1
$14.99
Solar Panel (5V 12 W)
3
$67.97
Vinsic Power Bank
1
$49.90
Motor Shield
3
$97.46
Photoresistors
20
$5.30
Patriot 9000mAh Power Bank
1
$30.69
Motion sensor
2
$9.98
Potentiometer
2
$19.76
Sunny Buddy Charge Controller
1
$28.96
Kmashi 10000 mAh Power Bank
1
$13.98
Aukey 3000 mAh Power Bank
1
S9.99
Constant Current Switching Regulator
2
$28.24
Switching Regulator
2
$15.80
Printed Circuit Board
Patriot 3000mAh Power Bank
1
1
$225
$9.99
Table 1.3 (Final Bill of Materials)
Amount Spent:
$751.95
Amount Remaining: $49.05
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1.7 Milestones
Below are our dates in which we look to achieve all of our objective milestones. The dates start
from September 2014 since that is when we first began our planning and shows our overall
progress to date.
● Sept 2014
○ Agree on two set meeting times during the week (week 1)
○ Revised and specified all necessary requirements for project (week 1-2)
○ Contact Duke Energy/Boeing about project (week 2-3)
○ Receive necessary funding either or both companies (week 3-4)
○ Begin researching various areas such as solar energy and autonomous designs
(week 4)
○ Hold biweekly meetings to check on progress (week 1-4)
● Oct 2014
○ Continue researching (week 1)
○ Take soldering classes/ gain a mentor for project (week 1-4)
○ Order first part, Arduino development board, from supplier (week 1-2)
○ Begin programming for basic autonomous portion (week 2-4)
● Nov 2014
○ Begin ordering other parts like RC car kit / early assembly (week 1-4)
○ Add to programming to incorporate sensors/remote connectivity (week 1-4)
○ Meet and consult with sponsor (week 1-4)
○ Continue with soldering classes/mentoring and expand on knowledge (week 1-4)
○ If possible, begin ordering parts and building first prototype (week 3-4)
● Dec 2014
○ Begin building first prototype; if necessary, go back and rework design (week 1-3)
○ Rework all early problems (week 1-3)
○ Have most/all parts ordered and planned to be assembled on prototype or revised
model (week 1-2)
○ Complete all necessary research (week 1-3)
○ Complete final Senior Design I paper (week 1-3)
● Jan 2015
○ Continue building first prototype (week 1-4)
○ Tentative deadline for first prototype complete: Jan 31, 2015
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○ Continue working on programming on car, app, and tracker (week 1-4)
■ Possibly break up programs between members
● Feb 2015
○ Test prototype and assess its ability in completing goals (week 1-2)
○ Possible second prototype building process (week 2-4)
○ Show progress to mentor/sponsor and receive feedback (week 3-4)
● Mar 2015
○ Continue testing and analyzing second prototype (week 1-4)
○ Final codes added (week 2-4)
○ Rework all necessary issues; move on to third prototype (week 2-4)
● Apr 2015
○ Third and final prototype complete (week 1)
○ Debug all coding (week 2-4)
○ Test all components. Check with a pass/fail chart. Rework/eliminate failed
components (week 2-4)
○ All aspects of project to be completed by: April 24, 2015
○ Present project to peers/ board (week 4)
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2) Research and Background
2.1 Previous Works
In the research phase of this project, it is a vital step to consider all the previous advances made.
The idea of a solar tracker is not brand new. As a matter of fact, we should take the time to reflect
on these devices.
Arduino Solar Tracker [4] - Instructables.com is a website that offers step-by-step instructions
for many do-it-yourself projects. The user “Bot1398” posted a how to on how to build an Arduino
based solar tracker. This design has some very valuable key features such as being able to track
the sun’s movements. This will be very important to the design of our project. For this solar tracker,
2 servo motors are mounted on top of one another. One servo motor is for horizontal movement,
and the other for vertical movement. There are 4 LDRs (Light Dependent Resistors) which will be
later discussed in detail. The most important item of all however is the Arduino Uno. The total
part cost was estimated to less than $30 excluding the Arduino and the tools used. Although no
solar panels were used at all in this project, it is mentioned in the intro that if you place solar panels
on this robot, productivity can be increased by 90 to 95%. The breadboard diagrams and all
Arduino codes are provided. The main component of the sensor assembly is a cardboard cutout
into an X-shape to separate each LDR and the light shining on each one. If we were able to simply
replace the cardboard pieces with PV panels, this just might be a viable option to create our solar
tracker.
Solar phone charging system featuring sun tracking [5] - On Instructables.com, user
“h2osteam” shares his design for a solar phone charging system featuring sun tracking. This one,
unlike the other has integrated solar panels into it. Also, it includes a battery pack instead of being
completely dependent on the solar power. A pair of LDRs act as sensors for the light sensitivity.
The project is split up into two different circuits on separate breadboards. The LDRs are best built
on a completely separate PCB than the main control board. It is stated that the optimal location of
the phototransistors is behind the solar panel and facing the east. Normally the circuit is open, but
when the sun is shining, the MOSFET is turned on and current flows from the batteries to the
tracking circuit. However, when the sun is not shining, or the apparatus is indoors, the MOSFET
is off and the current can flow from the batteries to the electronic device that is being charged. It
is required to use a boost converter to regulate the voltage in order to charge your device. A switch
mode regulator was said to be very difficult to design, so it is best to purchase one instead. This
user used a ptn04050 module from TI, and built a small supporting circuit around it. In addition,
he recommends minty boost from Adafruit, The end result is a circuit that sustains until VOUT is
less than 3.4V, and uses no power on idle.
Sun Tracking Solar Panel w/ Arduino - Powers ITSELF!!! [6] - Youtube user Luke Dub posted
his prototype of a solar tracking solar panel with an Arduino. This particular setup uses a servo
motor. Hot glue, compact disks, styrofoam, and solar panels from pathway lights were used to
compose it. These solar panels were flat and disk shaped and in ambient light, the voltage output
is 5.75V. Three photo resistors were used to measure the light shining on each of them, and move
in order to make the middle sensor the one receiving the most light. When indoors, Luke Dub
noticed that the tracker faced the window because it is the greatest source of light indoors. When
the module was relocated outdoors, it was actually able to charge itself! The panels were plugged
in directly into the Arduino to power it. This particular design lacks a battery to store the energy
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that was collected, and we need this in order to charge your electronic device. I like the design of
this project because instead of tilting, it relies on rotational motion.
How to build a Solar Powered USB Charger [7] - Youtube user Lukas Steffan shared how he
created a 5V solar powered USB charger. For our project, we will need a way to get the collected
energy from the PV panels to an external electronic device through USB in a reliable and effective
method. According to Lukas, 5V is sufficient to power any phone, iPod, or small tablets. He
purchased a kit and instructions from BrownDog Gadgets. A 5V USB charging circuit found in
any USB charger and it converts electricity into a USB format so that we can charge a device. A
4V solar panel was used to capture the sun’s energy to use as usable electricity. 2 AA rechargeable
batteries were used in this design so that we can store energy in them when not in use. This is used
in a situation where you know your phone will die, so you charge the batteries now to power the
phone later on. A AA battery holder with positive and negative terminals hold the batteries securely
in place and allows the connections to be simple. A 1N914 diode was used to make sure the energy
doesn’t get backed up into the solar panels. Wires, solder, and a soldering iron are tools needed to
assemble all the parts together. The first step is connecting the 1N914 diode to the solar panel and
one of the wires is connected to the diode as well. The solar panel was placed outdoors in direct
sunlight, with the iPhone USB charger connected to the USB port. The iPhone used in the video
was able to charge completely off solar energy. At the end of the video, we learn how much energy
can be saved by switching to solar powered USB charger. This can be very useful to designing
how to better optimize the solar tracker. First we take the volts in the wall which is 120V for the
United States, and multiply it by the amount of amps in the charger which is about 0.2. Because
power is equal to current times the voltage, we have 24W which is 0.024kW. This is multiplied by
the amount of hours spent charging (in the case of overnight charging it is 8 hours). 0.192 kW
hours/day is multiplied by the number of days and this is about 70kW hours/year. This is not much
energy, but when multiplied by the number of cell phones in use today which is about 6 billion,
420 billion kW hours/ year are saved! This is a significant amount of energy considering the typical
US home uses about 11,000kW hours/year. This design accomplishes the goal of charging a
smartphone through solar power and USB connection.
2.2 Solar Panels
The main objective of this project is to charge an electronic device using solar energy. In order to
collect solar energy, we must use photovoltaic solar panels. Solar panels collect sunlight and
converts it into electricity. The following section is an assessment of which solar panel will be best
to use in this optimization project.
Solar Radiation - Radiation is a form of energy transmitted through waves. It is safe to say that
all energy consumed on earth originates from the Sun [8]. This is because fossil fuels are derived
from plants and animals that once depended directly on the sun for food. Energy from the sun
travels through the depths of space through this process of radiation. Solar radiation is the is the
electromagnetic radiation released by the sun. This electromagnetic radiation is generated by
nuclear fusion at the Sun’s core. Extreme pressures, temperatures, and very complicated atomic
factors work together to release a large amount of energy. When a hydrogen atom is converted into
helium, neutrinos and photons are discharged. Energy in the core travels through the convection
zone into the photosphere where it is radiated through space. It takes photons 100,000 years to
travel from the core to the photosphere and only eight minutes to reach the Earth. The Inverse
Square Law can be used to measure solar intensity which is just how much light is striking objects.
Scientists put the energy output at 63,000,000 W/m2 (watts per square meter)[8]. Obviously, a
13
great amount of the energy will be dissipated along the path to the earth and in its outer atmosphere.
Radiation in the outer atmosphere amounts to approximately 1,367 W/m2. Of these, only about
forty percent will reach the surface of the Earth [8].
The very small percentage of a percentage of energy that actually collides with earth, is actually
enough to provide light and heat for the entire planet [9]. 1,368 watts of electromagnetic radiation
falls onto one square meter of Earth’s surface. If the distance between the Sun and Earth were
shorter, this measurement would be greater. According to the inverse square law mentioned earlier,
a planet twice as close to the sun as the Earth is will receive 4 times as much energy, and a planet
twice as far will receive ¼ as much energy.
Figure 2.1 displays how solar radiation is distributed to different areas in the United States. It is
clear based on the visual that some southwestern regions are very deep orange will benefit most
from using this solar tracking project. However, parts of central Florida are light orange are
acceptable locations to develop it.
Figure 2.1 PV Solar Radiation Map
Effects Due to Motion of the Sun - From a stationary perspective on the Earth’s surface, the sun
appears to revolve around us. The position of the sun in the sky varies on three main independent
factors such as that specific location on Earth, time of day, and time of year [10]. This perceived
motion has a large effect on how we can use solar panels. In the previous section, it was explained
that the solar energy produced by the sun travels in rays. The angle at which these rays collide with
the photovoltaic surface, means all the difference in maximum (or minimum) energy collection.
When the sun’s rays are perpendicular to the absorbing surface of the solar panel, the surface power
density is equal to the incident power density. When the sun’s rays are parallel to the absorbing
surface, this light intensity drops to near zero. If the rays are located at any angle between these
extremes, we can calculate the light intensity trigonometrically as a function of theta. For these
intermediate angles, the relative power density is cos(θ) where θ is the angle between the sun's
rays and the module normal [10]. Using a stationary solar panel placed out in direct exposure,
14
various light intensities will be experienced throughout the day. However, using these principles
it is ideal to keep the absorbing surface perpendicular to the rays of the sun as long as possible. In
fact, it is a major objective of this project to perform more efficiently than a conventional solar
panel assembly.
Photovoltaic Cells - Necessary for harnessing usable energy from the sun, solar panels are
comprised of photovoltaic cells. These cells employ many semiconductor related concepts in order
to convert this natural light and heat into flowing electricity. Solar panels are able to operate when
photons (light particles) collide with atoms releasing electrons. The constant release of electrons
creates the current [11]. As magnetic fields are established due to opposite poles of negative and
positive, electric fields can occur due to charge separation. It is simple to imagine a photovoltaic
cell as a “silicon sandwich” composed of two layers. Scientists are actually able to “dope” or inject
the silicon with other materials in order to make one side strongly negative and the other strongly
positive. Phosphorus is used to increase the amount electrons (with a negative charge) on the top
layer. Boron is used to decrease the amount of electrons on the bottom layer. Due to the highly
contrasting charges, an electric field is created at the junction between the layers. When a photon
of light strikes the cell, electrons will be broken free from the silicon junction due to the electric
field created there. Metal conductive plates on the sides of the cell collect the electrons and transfer
them to wires. At that point, the electrons can flow like any other source of electricity [11].
Solar PV Cell Comparison - All photovoltaic cells are not created equally. There are many
different types that use varying technology and all have their independent advantages and
disadvantages. For designing this specific project, it is crucial to use what will be most effective
for our budget. The most significant material used in these panels is crystalline silicon [12]. There
are four main types of PV technology commercially available today. These types are
Monocrystalline Silicon PV, Polycrystalline Silicon PV, Amorphous Silicon PV, and Hybrid PV.
Right now, monocrystalline and polycrystalline silicon are the most common and are used in 93%
of large and small scale solar power applications. Amorphous silicon is only used in 4.2%.
Monocrystalline silicon is created from growing a cylindrical ingot. This crystal is sliced into many
smaller circular segments with thickness ranging from 0.2 to 0.3mm. These segments are then cut
into a hexagon in order to squeeze more into a smaller surface area. Out of the types of silicon PV
cells, monocrystalline is the most efficient with efficiencies of 13% to 17% [12]. However, because
of the time and resources necessary to fabricate them, these PV cells are slightly more expensive
than the other types. Polycrystalline silicon uses the same exact materials, but it is melted down
into a square silicon block. Then these square blocks are cut into small slices and treated with a
blue-colored anti-reflective layer. This anti-reflective layer is a way to optimize the energy
collected because we want as much light to be absorbed rather than reflected. When mass
produced, polycrystalline silicon cells have efficiencies of 11% to 15% [12]. Amorphous silicon
is non-crystalline silicon. A good example of their use would be in pocket calculators where you
can cover the panel to inhibit its ability to generate energy and the display on the screen fades
away. These are unusually thin from between 0.5 um to 2.0 um (where 1um equals 0.001mm).
When compared to both monocrystalline and polycrystalline, these types of panels require less
resourced to manufacture thus making them much cheaper. Sadly, this type of technology only
possesses 6% to 8% efficiency and it is not suitable for large-scale applications (such as residential
developments) because of this low efficiency. Hybrid photovoltaic cell technology uses two or
more different types of existing technology. An example of this is a cell made from Sanyo and is
15
a simple monocrystalline cell coated in a thin layer of amorphous silicon. These hybrid cells are
suited for high temperature environments and have an efficiency around 18%! As you may have
guessed, these cells are cost more to purchase due to the research and development used to
maximize performance and efficiency.
Monocrystalline silicon PV is more efficient than polycrystalline silicon PV, so is recommended
for applications where surface area is limited. In the case of the project, the whole module will
have to be able to be roughly RC car-sized, so there probably will not be much surface area
available. Amorphous silicon PV requires more surface area, but it performs better under high
temperature environments and is more receptive to light during times of shading. Figure 2.2 shows
a comparison chart between different PV cell materials, PV Module Efficiency, Energy Density
kWp/m^2, and Cost. It is apparent that there is an inverse correlation between the efficiency of a
certain type of material with the cost. Monocrystalline Silicon - Monocrystalline silicon solar
panels are unique because they use a single crystal of clean and pure silicon.
Figure 2.2 Comparison chart between various PV types (permissions requested)
Sunpower currently manufactures the highest efficiency monocrystalline solar panels [13]. These
solar panels boast an efficiency percentage of 22.5%. Researchers claim that it is only theoretically
possible to reach a maximum number around 29% under absolute ideal circumstances. According
to Tom Werner, the CEO of Sunpower, the realistic limit of solar panel efficiency is around 24%
because of various thermal factors. One benefit of using monocrystalline silicon is the longevity.
This technology is first-generation and has withstood the test of time [13]. There are modules in
existence today from the 1970s still collecting solar power. Various websites state that these solar
panels can last 50 years. If this solar collector being designed here can last even half of that, it is a
very strong product. Even in the worst case scenario, replacement panels can be offered. It is
estimated that solar panels can experience a natural decay of efficiency of around 0.5% annually.
This means that if we purchase the most efficient monocrystalline solar panel mentioned earlier,
it would not be long before replacement is financially wise. Monocrystalline silicon is also a very
viable option for those with limited such as urban settings or in this case, a small remote-controlled
car. It is important to note that monocrystalline silicon does not contain cadmium telluride (CdTe).
This is a carcinogenic heavy metal that accumulates in living tissue. I would do my best to avoid
using something so toxic to myself and the environment. Once the outside temperature reached
around 115F(50C), monocrystalline cells suffer from disappointing output reduction of 12% to
15%. This loss of efficiency is lower than what is typically experienced by owners of PV panels
made from polycrystalline cells [13].
Polycrystalline Silicon - Polycrystalline Silicon cells solar panels are the most common and least
expensive [14]. The reason it is so cheap is due to the manufacturing process. Instead of just one
16
crystal, molten silicon is poured into a cast. The act of molding and using multiple silicon cells
requires less resources when opposed to monocrystalline silicon. This drastically reduces the cost,
but also reduces the efficiency. Actually, the efficiency is believed to be less than 80% of a
comparable monocrystalline solar panel [14]. Achieved by aggressively reducing resistive loss in
the cells, Mitsubishi set two world records for photoelectric conversion efficiency in
polycrystalline silicon photovoltaic (PV) cells [14]. These numbers only peaked around 19%
however. This is not too far from the numbers achieved from the most efficient monocrystalline
silicon cells. Using cheaper but slightly less efficient panels may be a better way to keep
development cost down on this project. If we use more expensive, but more efficient panels we
will definitely achieve better results but it has its price.
Thin Film Silicon - Thin film silicon is much, much thinner than monocrystalline or
polycrystalline silicon. Thickness of the active materials is 0.9nm compared to the 200 to 300nm
in the crystalline silicon cells [15]. Creating the semiconductor junctions can be done in various
ways but in most cases, a conducting oxide layer forms the front contact and metal forms the rear
contact. One of the major advantages to using this type of solar cell is the cost. The original goal
when developing this technology was to get a watt of power for under $1.00. Since then, we have
achieved this and the goal was lowered to $0.70 per watt. These super cheap photovoltaic panels
however, are only half as efficient as a monocrystalline solar panels. There are three specific types
of thin film silicon cells commercially available; amorphous silicon, cadmium telluride (CdTe),
and Copper Indium Gallium Selenide (CIGS). Since thin-film solar panels are so thinly sliced,
they can be applied to almost any surface. Steel roof shingles can be replaced with thin-film
photovoltaic material so that a home may collect significant solar energy in the daytime. This type
of technology has a unique advantage in that it is still receptive to indirect sunlight. This means
that even on a cloudy day, our solar tracker should still be able to generate enough power to charge
the small electronic device. Another strong advantage is that thin film panels have a high resistance
to heat. Heat can actually decrease efficiency of crystalline panels by 10% [15]. Most of these thinfilm solar panel applications were non-solar tracking because the energy output was not enough to
cover the development and operation costs. Tracking also produces a smoother output plateau
around midday, allowing afternoon peaks to be met [15].
Amorphous silicon was the first type of thin film silicon developed. It is derived from the noncrystalline format of silicon as a result, possess only 1/300 of the active material available in the
crystalline form. This technology is currently used in low cost, low power situations such as pocket
calculators and other small electronic devices [15]. These cells have an aversion to overheating
and because of this, Sanyo has coated a monocrystalline silicon cell in a thin layer of amorphous
silicon. Amorphous silicon can be produced in various shapes and sizes and it is for this reason it
is used in small modules [16]. This is beneficial to this project because we might need to minimize
solar panel size and maximize output. As shown in Figure 2.3, the absolute BIGGEST advantage
to using amorphous silicon for a solar tracker is its reaction to light. These panels are receptive to
the same exact wavelengths (400 to 700 nm) of light as the human eye. This allows the solar panels
to double as light sensors.
17
Figure 2.3 (UNI-Solar Triple Junction Comparison) (permissions requested)
Cadmium telluride (CdTe) is the first photovoltaic technology to surpass crystalline silicon as far
as watts of power per dollar. This price advantage is quickly offset by environmental concerns.
Cadmium is one of the top 6 deadliest and toxic materials known [17]. The highly reactive surface
of this material alone will cause oxygen damage to human and animal cells. This makes it
cancerous if ingested, inhaled, or handled without proper precaution. The disposal and safety of
this material is a serious issue when it comes to recycling them after their useful life. Researchers
have discovered that during actual operation, no pollutants are released. This means that their
environmental benefits of displacing fossil fuels is retained.
CIGS technology has achieved high efficiency levels of 20%. It is highly efficient as solar panel
technology and does not contain the toxic material, Cadmium [18]. Although it sounds very
promising to use this on a solar tracking application such as this one, mass production of these
solar panels has been difficult. Major roadblocks have hindered production of them such as delays,
personal problems, and renovation of processes. In addition to this, the high efficiency statistics
gained in the laboratory have not been replicated. It is estimated that the sale of these solar panels
will grow from $321 million in revenue in 2009 to around $1 billion by 2013, despite the fact that
many of today's CIGS companies won't be there to see the turnaround [18]. Heterojunction
structures are used in these cells where the junction is formed by semiconductors with different
bandgaps. The “G” in GIGS represents the addition of small traces of gallium to the absorbing
layer to increase the bandgap up from its default setting of 1 electron-volt. This addition increases
both the voltage and efficiency of the device. For several years, laboratories have reported a record
of 20% of efficiency for CIGS solar panels. Solopower reported that it has achieved 11% efficiency
on their panels and this is competitive compared to other CIGS manufacturing companies. Using
this technology has its unique advantages, and one of them is that the active layer can be used in a
polycrystalline form rather than growing large crystals. Growing large crystals unfortunately
requires more energy. The most significant advantage is that CIGS solar panels show the same
resistance to heat as CdTe panels, but contain a much smaller amount of Cadmium [18].
Occasionally, zinc is used to replace the cadmium sulfide altogether. Of all thin film technologies
available today, CIGS is the most efficient. However, it is important to note that the efficiency is
nowhere near that of crystalline silicon solar cells which have a current maximum of 24.7% [18].
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Since it has already been established that a main objective is to maximize efficiency, so the heat
resistive properties of CIGS technology should be explored against its lower efficiency rating when
compared to crystalline silicon panels. It is perfectly possible that the manufacturing issues and
production costs will be solved in a few more years and we just do not have access to that mature
CIGS technology yet. In Figure 2.4 it is shown what parts compose a CIGS solar cell. At the top
level is a TCO or transparent conductive oxide coating. This layer acts as a thin film and is very
crucial because 99% of light will be absorbed within the first micrometer of the material [18]. The
TCO uses electrode materials to allow over 80% of incident light [19]. Under that layer, there
exists a layer of CdS or Cadmium sulfide. This material is the most common for the window layer
of CIGS devices [18]. Underneath that, is what is known as the active layer.
Figure 2.4 (permissions requested)
Solar Panel Summary - Table 2.1 is a table highlighting the key specifications of certain
available photovoltaic cell solar panels. The format allows for a simple comparison between
features and cost.
19
Solar Panel
Specifications
Price and Availability
Mono-crystalline
Solar Panel
5W rated power at 12V operating voltage
Max Power Voltage(Vmp): 17.6v
Max Power Current(Imp): 0.278A
Open Circuit Voltage(Voc): 21.6v
Short Circuit Current(ISC): 0.306A
Size: 265x220x18mm
$33.99 from
truehomecomfort.com
Polycrystalline
Solar Panel
12V DC for standard output
Maximum Power ( Pmax ) : 5 Watt
Voltage at Pmax ( Vpm ) : 17.0 Volt
Current at Pmax ( Imp ) : 0.29 Amp
Open Circuit Voltage ( Voc ) : 21.6 Volt
Short Circuit ( Isc ) : 0.34 Amp
Dimensions: 222mm x 270mm x 18mm
Weight : 1.65 lbs / 0.75 kg
$29.00 from eBay.com
Go Power 5 Watt
Thin-Film Solar
Battery Charger
Rated power: 5W
Peak current: 260mA
Peak voltage: 15VDC
Open circuit voltage: 19.6VDC
Dimensions (mm): 355 x 336 x 12
Weight: 1 kg / 2.2 lbs
$35.96 from
theenergyconscious.com
Five (5) Solopower
Flexible
Lightweight CIGS
Solar Cell
1.25 - 1.5W (each)
6.25 - 7.5W (total)
Size(mm): 368.5 x 44.5 x 0.253
Individual Cell Weight: 0.32 oz
$19.99 on ebay.com
Table 2.1 Solar Panel Comparisons
Temperature - One frustrating fact about solar technology in general is that as the panels absorb
more light, they also absorb more heat [20]. This added heat causes the performance of electricity
production to suffer. The output can be reduced by 10% to 15%! Obviously, there is no way to
separate the heat and light of solar energy, because it is one in the same. However, with all the
various solar cell technologies available, some are more heat resistant than others. Solar panels are
given an official rating “temperature coefficient Pmax”[20]. Hypothetically if temperature
coefficient Pmax of a specific solar panel considered for use was -0.48%, this means that for every
degree over 25C, the maximum power is reduced by 0.48%. 25C is equivalent to 77F. Living in
Central Florida, the daily peak temperature for most of the year is well into the upper 80’s. This
means that at the time of day when our energy demands are highest, and we have the most energy
available to fulfill them, the solar panels suffer from the greatest efficiency loss. When
temperatures in Florida drop below this critical temperature in late fall and winter, the amount of
electricity produced will be above the maximum rated level. In northern climates further away
from the equator, where there are as many days under that temperature as above it, the problems
20
of heat loss are problematic. However, in locations closer to the equator such as Florida, the heat
loss issues can be counteracted. The “temperature coefficient Pmax” is a measure of how much
the maximum power output is affected directly. As solar panel temperature increases, its output
current increases exponentially while the voltage output is reduced linearly [20]. Power is equal to
voltage times current so as the solar panel gets hotter, the less power it generates. Crystalline solar
panels typically possess a temperature coefficient around -0.5%. Sunpower offers a
monocrystalline solar panel is the best in its class with its temperature coefficient of -0.38%. This
is the most efficient commercially available solar panel and should be considered in a high
temperature such as Central Florida. Amorphous silicon has been able to achieve a lower
temperature coefficient of -0.34%. When considering loss due to heat factors, Cadmium Telluride
panels are the best with the absolute lowest temperature coefficient of -0.25%. It is worth
mentioning that those panels are not as efficient at converting sunlight into electricity [20].
Cutting-edge photovoltaic cells technology such as CIGS are still being tested in research
laboratories for their temperature coefficients. Once their datasheets are recorded and published,
it will be known how they are affected by thermal radiation. Hopefully the numbers will be less
than -0.1%. Figure 2.5 illustrates how the efficiency of a solar panel decreases with increasing
temperature. This is caused by the conductivity of the semiconductor being increased as well [21].
This in turn, balances the charges within the movement and weakens the electric field due to strong
opposing negative and positive sides. This inhibits charge separation which lowers the voltage
present. Rising temperature increases mobility of electrons thus increasing the current. However,
the rise in current is negligible when considering the drop in voltage. Observing Figure 2.5 very
carefully, it can see seen that the current increases slightly as the voltage decreases drastically.
This ultimately results in a decrease in maximum power output.
Figure 2.5 I-V curve at various temperatures
2.3 Motors
In order for the solar panels to track the sun throughout the day, and collect the most amount of
energy possible, they must be incident to the sunrays at all times. This would be accomplished
through some form of rotation. Motors will be controlled using the microcontroller to determine
when and exactly how much to move so that it constantly adjusts itself and remains aligned with
the sun. There a few types of different motors but they should all be able to accomplish the same
basic task.
Servo Motors - A servo is a small, basic device with an output shaft. This shaft can rotate to
certain angular positions by sending a coded signal [29]. Once that code remains, the shaft stays
21
at its position. Once the coded signal changes, the angular position of the shaft changes as well.
These are most practical in low power applications such as radio controlled cars and airplanes,
puppets, and robots. Servos have tiny lightweight motor, built in circuitry, and are relatively
powerful. An example of a standard servo motor is the Futaba S-148 with 42 oz/inches of torque.
The power is drawn proportional to the mechanical load, which basically means that if the servo
is not required to do much mechanical rotations then the energy consumed will be low. The main
components of a servo are the control circuitry, motor, gears, and case. There are also 3 wires; one
for power (+5V), ground line, and for control or signal line. The main component of the servo
motor is the potentiometer or variable resistor. This is what allows the control circuitry to monitor
the current angle of the output shaft [29]. If the output shaft is already positioned at the desired
angle, the motor will shut off. If the angle is not desirable, the motor will rotate the output shaft
until it is. The output shaft is usually only about to travel approximately 180 to 210 degrees, but
this varies by manufacturer. All servos should position the the servo output shaft or arm at the
midpoint of its range of motion [30]. When the servo has a minimum input of 1.0 ms and a
maximum of 2.0 ms, the servo should balance directly in the center at 1.5 ms. The amount of power
supplied to the motor is proportional to the angular distance it must travel. If the shaft has to rotate
from 0 to 180 degrees, the motor will run at full speed. However, if the shaft only has to travel a
few degrees, it will run at a much slower pace while consuming less energy. This is known as
proportional control. The angle that a servo rotates is determined by a method called Pulse Control
Modulation (PCM).
Figure 2.6 displays how pulse control modulation affects the angular rotation of the output shaft.
A pulse is applied to the control wire and the duration of this electrical pulse determines the
rotation angle of the output shaft. A 1.5 ms pulse will make the motor turn to the 90 degree (neutral)
position. If the pulse is shorter than 1.5 ms, the motor will turn the shaft closer to 0 degrees. If the
pulse is longer than 1.5 ms, the motor will turn the shaft closer to 180 degrees.
22
Continuous Rotation - A continuous rotation servo is one that has no limit on its range of motion
[30]. The input signal does not determine at which position the output shaft should rotate to.
Instead, the servo is able to relate the input to the direction and speed of the output. An input Pulse
Width Modulation of 1.5 ms represents the middle, 90 degree, or neutral point and the output shaft
or arm does not move. If the signal sent is 1.0 ms, the arm will rotate full speed in the clockwise
direction. If the signal sent is 2.0 ms, the arm will rotate full speed in the counterclockwise
direction. If the signal sent is between 1.0 ms and 2.0 ms, it will rotate at the proportional speed
and direction as shown below in Table 2.2.
Table 2.2
The Futaba S148 converts standard pulses into continuous rotational speed. What’s great about
this servo is that is can be controlled directly by a microcontroller without any additional
electronics. To control it using an arduino, it is recommended to connect the white control wire to
pin 9 or 10 and use a servo library included with the Arduino board. If given It includes an
adjustable potentiometer that can be used to adjust the rotational speed and direction. According
to the specifications found online, if the control line is given a 1.5 ms pulse, the servo arm will
stay stationary at 0 degrees. If a 2 ms pulse is given, then the arm moves at full speed forward to
90 degrees. Finally, if a 1 ms pulse is given, the arm will move full speed backwards to -90 degrees.
The Spring RC SM-S4306R features two ball bearings on the output shaft for reduced friction.
This modification will allows it to outperform the Futaba in terms of performance numbers. At full
supply of 6V, this servo motor will provide over twice the torque, slightly faster rotations per
minute, less weight, and at a lower price! The specifications look very promising for this
continuous servo motor in terms of performance vs cost.
The 35495S HS-5495BH HV Digital Servo has karbonite gears and is commonly used for sport
airplanes up to 25% scale weighing under 25 pounds. This seems like the perfect power to weight
ratio that will be necessary for this project. The servo is special in that it has a maximum voltage
capability of 7.6V rather than 6V. At the equivalent 6 volts voltage, the HS-5495BH HV servo
will provide slightly more torque than the SM-S4306R and over twice the torque of the Futaba
23
S148. At the full 7.4 volts, it will provide 7.5 kg-cm of torque. Looking at the speed data at 6 volts,
the servo output shaft will rotate 60 degrees in 0.17 seconds. This means that it will complete a
full rotation or 360 degrees in 1.02 seconds and the servo arm will complete 61.2 rotations in one
minute. Ultimately, the speed of this servo is 61.2 RPM at 6 volts. This is substantially faster than
the other two servos considered here. The price however is over twice the price of them.
Referencing Table 2.3 shown below, the SpringRC SM-S4306R appears to be the best option as
has as continuous servo motor controllers. Although it is desirable to have the solar tracker react
as quickly as possible to the sun’s movements, they are very slow and predictable. Speed is not
the main concern but rather accuracy is. Realistically, any of these servos will suffice but when
considering budget, weight, and cost, the choice is clear.
Name
Torque
Speed
Weight
Available
Price
Futaba S148
2.7 kg-cm/38
oz-in at 6 V
50 RPM (with
no load) @ 6V
43 g/1.5 oz with
servo horn and
screw
newegg.com
$14.95
SpringRC
SM-S4306R
6.2 kg-cm
(86.25 oz-in)
55 RPM @ 6V
41g (1.45oz)
bananarobotics.co $12.99
m
35495S HS5495BH HV
Digital Servo
6.4 kg-cm @
6.0V; 7.5 kgcm @ 7.4V
0.17 sec/60° @
6.0V; 0.15
sec/60° @ 7.4V
1.59 oz (44.5 g)
advantagehobby.c $27.99
om
Table 2.3
Stepper Motors - A stepper motor is a brushless, synchronous electric motor that converts digital
pulses into mechanical shaft rotation [31]. A full revolution is divided into multiple separate but
equal parts, and an individual pulse must be sent for each. The pulses cause the motor to rotate at
a specific rotational angle, and this makes feedback unnecessary. As the control receives more and
more digital pulses, the incremental rotation becomes continuous with the speed of rotation
directly proportional to the frequency of pulses. Stepper motors can be found in industrial and
commercial applications due to low cost, high reliability, and high torque to speed ratio [31]. What
makes them reliable is simply a matter of absent contact brushes inside. Without contact brushes,
the lifetime of the motor depends solely on the bearing. A notable advantage of selecting a stepper
motor for a solar tracker is its accuracy. Frequent pulses will cause the motor to rotate continuously
with an accuracy of 3% to 5% of one individual step. These rotations are also non-cumulative, so
a rotation will not be affected by the pulses before it. There are three different types of step motors.
These motors are: variable reluctance, permanent magnet and hybrid. The hybrid motor combines
the best characteristics of variable reluctance and permanent magnet motors, so this type will be
focused on and considered as a possible part in the solar tracker. Hybrid motors are capable of
high static and dynamic torque and high step rates. These attributes are particularly useful in
computer disk drives, printers, and compact disk players [31]. Step modes on the stepper motor
are selectable configurations that affects the number of steps per revolution. In the FULL STEP
mode, the revolution is split into 200 steps or 1.8 degrees per step. One digital pulse from the driver
is equal to one step. The HALF STEP mode further divides one 360 degree rotation into 400 steps.
This means that the rotor will rotate at half the distance or 0.9 degrees per step. It provides 30%
24
less torque, but has a much smoother motion rather than being “choppy”. MICRO STEP is the
breakthrough motor technology that will divide the full step into 256 subdivisions. This means
51,200 steps per revolution or 0.007 degrees per step [31]. This microstep configuration is used in
applications that require accurate positioning and a smoother range of motion over various speeds.
Microstep configuration also provides 30% less torque than the half step. In Figure 2.7, it is shown
that there are two very distinct ways to connect a stepper motor. The series connection will increase
the inductance thus resulting in greater torque at lower speeds. The parallel connection will lower
the inductance thus resulting in greater torque at faster speeds. This ultimately means that the
connection of the motor is dependent on the intended application and it is recommended to try
both series and parallel connections.
Table 2.4 compares 3 different stepper motors from various suppliers. The JKM Nema 17 has a
motor length of 34mm which makes it much shorter than the JKM Nema 11’s length of 51mm. It
is desirable to have a shorter motor length so that the motor will be able to fit in a small location
on the RC car platform being designed. The axle diameter of these two motors is identical however.
The Nema 23 however has an axle diameter of 6.35mm and is able to operate at only approximately
2.5 volts. The holding torque that this motor provides is 5.2 kg-cm. This is greater than that
provided by the Nema 17 (2.8 kg-cm) and the Nema 11 (1.2 kg-cm). The price of the Nema 23 is
only about $3 more than the cheapest option which is the Nema 17 and $5 less than the most
expensive option which is the Nema 11. I would choose the Nema 23 due to its larger axle diameter
provides, lower operating voltage, higher holding torque, and reasonable pricing.
25
Name
Length
Axle
Diameter
Voltage
Holding
Torque
Available
JKM Nema 17
Two Phase
Hybrid
34mm
5mm
12V
2.8kg.cm
37oz.in
banggood.com $16.55
NEMA 23
Bipolar Hybrid
_______
_
6.35mm
approximatel 5200 gram- vetco.net
y 2.5 volts
centimeters
$19.95
JKM Nema 11
Mill Laser
Engraving
51mm
5mm
12V
$25.18
1200g.cm
bonanza.com
Price
Table 2.4
2.4 Batteries
Batteries come in different shapes and sizes using different technologies. These technological
approaches each have their unique advantages and disadvantages. Since we want to use a battery
to be charged by the solar panels and discharged by an external electronic device, we need to
further explore what options are available. Batteries are separated into two main categories which
are known as primary and secondary [22]. Primary battery cells are ones which cannot be easily
recharged and reused. The chemical reactions are not reversible, and they cannot be returned to its
default chemical composition [23]. Battery manufacturers will recommend to avoid any attempt
to recharge disposable batteries. They are designed to be used one time. Familiar examples of
primary batteries are carbon-zinc dry cells and alkaline cell batteries [22]. Once these batteries are
depleted completely, they will be discarded. These are the most common type of battery mainly
because of how easy and cheap they are to produce. A secondary battery cell is one that can be
electrically recharged to its original state. This means that it can be charged, deleted, and recharged
up again as long as the long-term battery life allows. Up until the turn of the millennium, this
market was dominated by industrial and automotive applications [22]. When the sun makes contact
with the solar panels, the batteries will need to be able to store the energy. Once battery is charged
to capacity, it will be discharged by the connected external device we are charging. For this
application, a secondary type of battery is preferred. The types of battery technology to be analyzed
are rechargeable alkaline, nickel-cadmium, nickel-metal hydride, lithium-ion, and lead-acid.
Rechargeable Alkaline - Although it has the shortest shelf-life of any secondary battery
technology, secondary alkaline batteries are the lowest cost rechargeable cells [23]. These batteries
combine the benefits of primary alkaline cells (such as its moderate power capability) and the
obvious added benefit of charging for later use. Perhaps the most notable benefit is that they do
not contain toxic chemicals and will not be harmful to humans or the environment. An article by
Len Penzo [24] tells of a personal story where he witnesses a man in the grocery store with a
shopping cart full of battery chargers and AA rechargeable batteries. According to Penzo, this
particular man spent over $100. The man was bragging about how much money he would save by
recharging those batteries instead of purchasing replacements when necessary. Sadly, the man was
not aware of the fact that if his home uses standard electronic devices, he spent unnecessary money
on those batteries and chargers. Low current-draw devices will simply not benefit from using
26
rechargeable batteries, so there so no need to spend extra funds on them and the chargers associated
with them. The batteries used in a low current-draw device are replaced so infrequently that it does
not justify the investment of replacing traditional ones with rechargeable batteries. Traditional
alkaline batteries are best suited for those low current-draw devices in the home such as wall
clocks, radios, smoke detectors, programmable thermostats, and television remote controls
because they lose power at a slower rate than the rechargeable kind [24]. These batteries can
remain charged for years of no use. It is now apparent that these kind of low current-draw
appliances in the house all fit into this category. Len Penzo [24] was able to find that the Nintendo
Wii is an example within his own household that would benefit from using rechargeable batteries
instead of traditional alkaline. The only real benefit of purchasing these rechargeable batteries is
the low cost and no need for special recycling. This type of battery requires an additional special
charger. Penzo makes sure to remind the reader not to confuse traditional alkaline batteries with
the rechargeable ones because the traditional ones cannot be safely recharged.
Nickel-Cadmium - Whereas rechargeable alkaline batteries are best suited for moderate power
applications, secondary Ni-Cd batteries can be used for high power. It also has a wide operating
temperature range [23]. This is crucial to consider anything involving heat, because this entire
module will be placed outdoors on a sunny Central Florida day. These batteries also have a long
cycle life but suffer from a low run time per charge. With a self-discharge rate of 30% a month,
these batteries must be replaced approximately once every three months. In addition to this, it
contains 15% Cadmium and must be properly handled and recycled. This technology is widely
used in electronic equipment such as laptop computers and wireless phones [25]. It suffers from
the infamous “memory effect”. The memory effect causes the battery to lose charge faster as it
ages as opposed to when it was brand new. Memory effect occurs when your battery thinks it is
fully charged but it really is not. When your battery reaches 70%, it will stop charging. This makes
that charge cycle 70% shorter than it was originally at 100%. The Memory effect occurs due to the
formation of Cadmium crystals within the battery. The best way to avoid the crystals from forming,
is to keep the battery away from high temperatures. It is advised to only recharge the battery when
fully discharged rather than partially. This brings up another issue in that NiCd batteries cannot be
fully discharged or they will be damaged [25]. When referring the “fully discharged” this usually
means below 1 volt per cell. The correct way to discharge these batteries and prevent memory
effect is to use them normally until the device gives a notification that batteries are low. Monitoring
the status of the NiCd batteries is also very difficult because the discharge is non-linear and thus
less predictable. The voltage found on the cell remains at 1.2V until the battery is “discharged”.
The output remains 1.2V whether at 30% 40% 50% or 60% of its charge. A traditional nonrechargeable 1.5V battery will provide only 0.75V when it is at 50% charge. This makes this type
of battery easy to monitor by using a voltmeter. With NiCd batteries, it is nearly impossible to
distinguish if it is fully or partially charged just because the output remains at 1.2V regardless. One
of the goals of this project is to monitor the battery life of the battery so that we can see how it is
distributing the energy we collected. The main issue with this type of battery is that it will lose
about 1% charge per day when not in use [25]. This means that if the battery is idle for a month, it
will lose 30% of its original charge. Within three months, the battery is completely depleted and
will be permanently damaged. Although the long term life of the battery is not a priority in terms
of this project, it would be desired. In addition to this, monitoring the battery status accurately is a
major objective and would be very useful to know how effective it is as a whole.
27
Nickel-Metal Hydride - Secondary NiMH batteries are built off of the same basic concepts of the
secondary Ni-Cd batteries. They are similar enough to where they will provide the same voltage
as Ni-Cd batteries with 30% more capacity [23]. The temperature range is comparable to them as
well. Unfortunately, along with the improved capacity comes a higher self-discharge rate of 40%.
This means that the battery has an even lower run time per charge. Luckily, Nickel-metal hydride
batteries contain no Cadmium, but with high levels of nickel oxides and cobalt, they must be
properly recycled in appropriate facilities. These batteries generally have a better performance than
NiCds. Unlike NiCd batteries, the new generation of NiMH batteries do not experience the
memory effect [26]. This means that the battery can be recharged at any time during its life cycle
without consequence. These batteries are best suited in applications with a high energy
consumption. Constantly charging and discharging the battery is an example of high energy
consumption and this project performs this very task.
Lithium Ion - Secondary Li-Ion is the latest breakthrough in rechargeable battery technology [23].
They allow for 30% lighter weight and also 30% more capacity when compared to NiMH batteries.
There is a high current capability and a long cycle life. The self-discharge rate, 20% is much lower
than other types of secondary batteries which makes it highly desirable to charging a cell phone or
tablet. Lithium Ion batteries are notorious for being disastrous under extreme temperature
situations. If exposed to prolonged heat, these cells may combust resulting in a fire. Like Nickelmetal hydride batteries, they must also be recycled for their high nickel oxide and cobalt content.
One corporation who relies on the success of lithium ion technology is Apple. They claim that
Lithium-ion batteries charge faster, last longer, and have more power density when compared to
traditional battery technology [27]. This is true because you can charge this battery whenever you
want and there is no need to wait until 100% discharge. One charge cycle is completed once you
have drained 100% of the energy from the battery, but not necessarily in the same charge. If you
were to use 75% of the battery on Thursday, and fully recharge it that night and use 25% on Friday,
those two days would add up to just one charge cycle. This technology looks great for this solar
tracker being designed. This lithium-ion battery will allow this device to be used just as reliably
as you can use the outlet in the wall. Figure 2.8 displays the concept of charge cycles further in
that they are more convenient to use and boast a longer lifespan when compared to NiCd batteries
for instance.
Lead Acid - Secondary lead acid batteries are the most popular type of rechargeable battery
available worldwide. The final consumer product and also manufacturing process are proven safe,
economical, and reliable [23]. Although this sounds reassuring as a possible component to include
in this project, this type of battery is composed mainly of lead. Lead is very heavy. Due to its
weight, Lead acid batteries are not suitable for small or portable applications. It is intended for this
system to ride on a remote-controlled car chassis so a heavy battery simply will not work for this
scenario. Adding insult to injury, lead is a known toxic carcinogenic compound [23]. However,
93% of the lead recycled eventually goes on to become new lead acid batteries. Lead acid batteries
are so popular because they are the main storage device in automotive use [28]. Common 12V car
28
batteries have six cells, each with a rating of 2V. As the battery discharges, the electrodes turn into
lead sulfate and acid turns into water. When the battery is recharged, this chemical reaction is
reversed. These batteries are cheap and easy to obtain, however they are the oldest technology
available with the worst energy to weight ratio.
Figure 2.9 is a table comparing the various types of rechargeable batteries researched and
discussed. The squares represent a quality that each type of battery possesses and the colors
represent the magnitude of the desirability of that quality. Green is basically good, yellow is okay,
and red is bad. This is similar to streetlight colors which are universal. The specifications of the
batteries can be directly compared to the necessary requirements to build the most efficient solar
tracker. In order for this to be a reliable product, the battery cannot be susceptible to memory loss.
This makes Nickel Metal Hydride or Lithium Ion batteries viable options. A self-discharge rate is
also a quality that will be essential for this project to be a success. Lithium Ion is the only kind of
battery suggested with a low self-discharge rate. In the case of capacity, Lithium Ion is again the
best choice. At this point it will be acknowledged that we must make compromises. Sometimes
when it comes to efficiency, these compromises become sacrifices. According to this table,
Lithium Ion batteries are the best battery available for this application but it does contain toxic
materials and has a higher price point. The battery will have to be handled very carefully as to
avoid any exposure to the toxic materials present. The budget will also allow for a Lithium Ion
battery to be purchased.
Figure 2.9 Battery Comparisons (permissions requested)
2.5 Mobile Device Applications
Initially, one of the decisions that occurred was deciding whether to have the robot to be fully
autonomous or semi-autonomous. The decision was made to have the robot be a semi-autonomous
robot which meant we would have to decide on a way to control the robot from another source.
We chose to develop a mobile application that would be able to control the robot using a classic
29
directional pad to have the robot accelerate forward, decelerate, and move in either a left or right
direction. When it comes to mobile app development, the was the option between choosing to have
the app be Android based and IOS based.
In comparison to IOS based app development, many advantages for Android based development
presented itself. These advantages include:
● Application Configuration [37]
○ Android has a single manifest file and Eclipse builds your app in its entirety
(usually) every time you save any file. [37]
● Market Sharing [37]
○ Publishing an Android app is easy as a dream. Just sign your app via a handy
Eclipse wizard, and poof, you have an APK file that can run on any device. Email
it, put it up on a web site, or upload it to Google Play and make it available
worldwide (probably) within the hour. Could hardly be simpler. [37]
● Open Source Licensing [38]
○ Get the open source advantage from licensing, royalty-free, and the best technology
framework offered by the Android community. The architecture of the Android
SDK is open-source which means you can actually interact with the community for
the upcoming expansions of android mobile application development. This is what
makes the Android mobile application development platform very attractive for
handset manufacturers & wireless operators, which results in a faster development
of Android based phones, and better opportunities for developers to earn more. [38]
● Simple Integration [38]
○ Are you looking for complex technical customization and integration of a web
application or just a smartphone application you already have? Yes. Then an
android app can be the right solution for you. The entire platform is ready for
customization. You can integrate and tweak the mobile app according to your
business need. Android is the best mobile platform between the application and
processes architecture. Most of the platforms allow background processes helping
you to integrate the apps. [38]
Along with advantages, Android based app development has it fair share of disadvantages which
include:
● Development Environment [37]
○ The current state-of-the-art IDE is Eclipse, customized with Android plugins, and
it is embarrassingly bad. Slow, clunky, counterintuitive when not outright baffling,
poorly laid out, needlessly complex, it’s just a mess. [37]
● User Experience [37]
○ While Android theoretically has a comparable visual tool, the less said about it the
better. In practice you wind up writing XML files which provide layout guidelines,
30
as opposed to rules, so that apps are rendered (hopefully) well on the entire vast
panoply of devices and screen sizes out there. [37]
● Platform Fragmentation [37]
○ This often occurs when applications are updated and the newly updated application
are slightly incompatible with older operating systems
● APIs [37]
○ What iOS has which Android doesn’t is an extra set of frameworks and features
and a generally cleaner, better designed system. Another metric, albeit a flawed
one: lines of code. These apps are very nearly functionally identical, but the iOS
one has 1596 lines of custom code, including header files, compared to 2109 lines
of Java code and XML for Android. That’s a full 32% more. [37]
Research was also done regarding finding both the advantages and disadvantages of IOS based
app developed. The results advantages are listed below:
● Higher Quality Applications [39]
○ With IOS based applications, bets versions of applications are not allowed to be
published, only the final version. Since only the final version of applications are
published, higher quality applications are consistent compared to Android based
applications.
● Platform Fragmentation [37]
○ Since IOS operating system typically remain the same across all IOS powered
devices, the issue of fragmentation does not occur.
● Base Coding Language [37]
○ Objective-C (IOS language) in comparison to Java (Android language) is known to
be better and cleaner than Java. It has blocks: Java does not. It has categories; Java
does not. It does not require you to wrap much of your code with vast swathes of
boilerplate try/catch exception-handling whitespace: Java does. [37]
○
IOS based app development has its disadvantages as well which include:
● Closed Platform Development [40]
○ iOS apps only run on Apple products so you can’t take advantage of features (like
NFC) available only on non-iOS devices or market growth of non-iOS devices. [40]
● Publication/Approvals [40]
○ The App Store’s app approval process is notoriously more time consuming than
Google Play’s process. [40]
● Configuration [37]
○ Beneath the sleek, seamless exterior of Xcode and Objective-C lurk the
Lovecraftian horrors of 1970s programming. [37]
31
2.6 Electrical Components
Microcontroller
● Functions: Receive environmental variables and command motor to move to areas of
higher concentrations of light. The “brain” of the robotic car. Must be able to control all
aspects of the car (motion, sensing), as well as command the solar panel to move via the
panel motor.
● Required traits: Supporting input and output pins for all information- gathering devices
(light sensors, bluetooth, motor functioning, etc.), relatively small size to fit on the rover
chassis, memory to hold roughly 1000 lines of code minimum, cheap price to remain under
budget.
AC/DC Adapter
● Functions: Convert the voltage from the battery to the operating voltage of the
microcontroller.
● Required traits: Basic circuit design for minimal cost, small pieces, compatible with both
the battery and the microcontroller.
Battery
● Functions: Supply microcontroller with sufficient charge to perform operations.
Rechargeable via solar energy. Small enough size to fit on rover chassis. Long battery life
(~2 hours) for a small battery. Cheap cost to prevent going over budget.
● Required traits: Lithium polymer, quick charge, slow discharge, minimum 2 hour lifespan.
Bluetooth
● Functions: Can connect to the phone application and relay information to and from the
rover device.
● Required traits: Compatible with Arduino Uno microcontroller. Cheap price to remain
under budget.
Light Sensors
● Functions: Able to interpret light intensity of the environment and relay information to the
microcontroller.
● Required traits: Compatible with Arduino Uno microcontroller. Cheap price to remain
under budget.
Motors (Wheels and solar panel)
● Functions: Can move the rover vehicle wheels as well as rotate the solar panel. Powered
by electricity from the battery or microcontroller. Low power consumption. Relatively
lightweight and durable
● Required traits: Enough torque to move rover and rover load. Enough rotational torque to
move solar panel a full 360 degrees around.
Solar Panel
● Functions: Charges in sunlight to fuel battery and rover. Energy efficient. Relatively large
storage capacity. Can store solar energy for some time after reaching full charge.
32
● Required traits: Relatively large charge capacity, light enough to move angularly, will fit
on rover.
Phone App
● Functions: Connects via bluetooth to the microcontroller. Commands are shown on app,
and with a button press, the rover will move as instructed. Possible feedback instructions
displayed on-screen.
● Required traits: Compatible with at least iPhone phones. Downloadable. All operational
commands function correctly.
2.6.1 Microcontroller
What is a microcontroller? In order to understand what is necessary for a microcontroller in the
project, one must first understand what a microcontroller is. By definition, microcontrollers are
extremely low powered computers that operate one special purpose in; they cannot run multiple
programs like general purpose home computers and laptops [49]. The main components of a
microcontroller are the Central Processing Unit (CPU), Input and Output ports, Read-Only
memory (ROM), Random Access memory (RAM), and an oscillator that acts as a system clock
(See Figure 1)[48,50]. Several microcontrollers can be connected via USB ports to a computer and
can be programmed with code from its corresponding software component [48]. Microcontrollers
come in various sizes, capabilities, and prices. For our purposes, a desired microcontroller would
be one with enough memory to store the code for all the instructions the semi-autonomous car will
do, relatively small size to fit onto the chassis, and a cheap purchasing price.
Advantages and Disadvantages of Microcontrollers [51]
Advantage
Disadvantage
●
●
●
●
Does not use digital parts
Reduced cost and size
Easy to maintain and troubleshoot
Pins are programmable for performing
different function
● Low clock rate for operations
● Interfacing between RAM, ROM and
ports is simple
● Newer microcontrollers can be quite
complex
● Only a number of operations can be
done at the same time
● Cannot control high power devices
directly
Table 2.5
33
Figure 2.10 Basic Design of a Microcontroller [50] (permissions requested)
Recommended Voltage and Current Values [43-47] - It is crucial to know the necessary voltage
and current values of the microcontroller to avoid overpowering the circuit with too much voltage
and potentially causing irreparable damages. In addition, an ideal microcontroller for the purposes
of the project would be one that required the least amount of power to work since it will be relying
heavily upon solar energy. One of the main goals is to use energy as efficiently as possible,
therefore, having an extremely low-powered microcontroller will aide in that goal.
Board Name
Operating
Voltage
Input
Voltage
Input Voltage
limits
DC current
per I/O Pin
DC current
(3.3 V Pin)
Arduino Uno
5V
7-12V
6-20V
40mA
50mA
Arduino Due
3.3V
7-12V
6-16V
130mA
800mA
Arduino Mega
5V
7-12V
6-20V
40 mA
50 mA
MSP 430G2553
3.6V
2-3V
1.8 - 3.6V
20mA
40mA
Tiva C1294
5V
6-12V
4-18V
100mA
600mA
Table 2.6 Voltage/Current Comparison
Arduino Uno ($25) [43] - the Uno R3 uses a new ATmega16U2 driving chip, which allows for
faster transfer rates as well as more memory. It is a highly versatile microcontroller, as it is able to
function on any computer operating system. This is definitely a plus for the group since versatility
is essential for our goals. The 14 pins for inputs and outputs are more than enough for our expected
light sensors, bluetooth, and motor operators. It is a very efficient piece, being tied with the
Arduino Mega for the lowest overall power requirements. All in all, it may be one of the slower
microcontrollers on the list, but speed is not as critical to have as a cheap, power efficient
microcontroller, which the Uno is.
34
Arduino Due ($45) [44] - This 32 bit ARM core processor microcontroller is an improvement on
the Arduino Uno. With 56 more pins, larger flash memory, and a much faster clock speed than its
predecessor, the Due can do many operations and store much more than the Uno. The only serious
drawback is that it consumes the most power of the five microcontrollers examined. Its extra length
versus the Uno is also a cause for concern, since it would make it somewhat more difficult to fit
the board along with the other pieces onto the solar vehicle.
Arduino Mega ($45) [45] - The Mega is the most efficient microcontroller on the list, especially
considering its larger size. It is very similar to the Uno, except it has more input and output ports
as well as various connections. It has much greater memory capacity than the Uno, allowing it for
more operating and coding to be stored. The Mega is easily the best overall microcontroller on the
list, considering power consumption, usability, and memory.
MSP 430G2553 (Free) [47] - The oldest of the microcontrollers observed, the MSP430G2553 has
the smallest memory as well as the least amount of flexibility. However, his makes it probably the
simplest board due to the feasible coding as well as the limited ports. It is also very power efficient.
The MSP430 was used in Embedded Systems, therefore, a prior knowledge of the device is useful.
On the downside, extra pieces are needed to add light sensors and a bluetooth, since there are no
pins directly connected the device.
Tiva C1294 ($80) [46] - The largest of the five microcontrollers, the Tiva C is also one of the most
power costly. Also, although it has the capability of having the most input and output pins of the
five, many pieces are required to be added on to the microcontroller. Regardless, it is easily the
fastest board with the largest memory. It could easily handle the demands of the project with plenty
of room to spare.
Comparison of Microcontrollers - The table below lists the basic features of five microcontroller
boards: The Arduino’s Uno, Due, and Mega, the MSP 430G2553, and the TIVA C 1294. The
categories listed are the essential categories for the project. Any category not listed was not listed
due to some reason. For instance, weight isn’t listed since all microcontrollers are very light and
thus the board weights can be made negligible. Also, temperature range of operation wasn’t listed
since all boards can operate in a wide range of hot and cold temperatures. No extreme
environmental threat is expected, therefore temperature range is not necessary.
35
Board
Name
Size
Memory
I/O
Ports
Bit
size
Clock
Speed
Connection
type
Other
ports
Arduino Uno
[43]
3.1 in x
2.5in
32kB Flash
2kB SRAM
1kB
EEPROM
14 pins
16 bits
16MHz
USB 2.0,
AC-DC adapter,
Battery
6 analog
inputs,
reset,
2 UART
Arduino Due
[44]
4.1in x 2in
512 kB
Flash
96 kB SRAM
70 pins
32 bit
84
MHz
USB 2.0,
2 DAC,
2 TWI,
AC-DC adapter,
Battery
12 analog
inputs,
reset,
erase,
4 UART
Arduino
Mega
[45]
4in x 2.1in
32kB Flash
2kB SRAM
1kB EEPROM
54 pins
32 bit
16
MHz
USB 2.0,
AC-DC adapter,
Battery
16 analog
inputs,
4 UART
MSP
430G2553
[47]
2in x 2.6in
16kB
Flash
512B RAM
20 pins
16 bit
16
MHz
USB 2.0
LEDs, push
pins,
2 UART
Tiva C1294
[46]
4.8in x
2.2in
1 MB
Flash
256kB
RAM
4 20 pin
and 40
pin addon
parts
32 bit
120
MHz
USB 2.0,
2 CAN modules
QSSI,
I2C,
Ethernet
User
switch,
reset,
4 UART
Table 2.7 Microcontroller Comparison
Reasons for choosing Arduino Uno Microcontroller - Arduino boards in general are very
popular for coding projects, especially in the field of robotics [52]. This is because of an easy to
understand and open source development software. For this reason, Arduino boards were heavily
researched in our group. In addition, our Computer Engineer, Aaron, has worked on Arduino
boards in the past, so it makes sense for us to pursue such a microcontroller. The MSP430
microcontroller is power efficient, but the extra pieces required as well as limited flexibility are
the reason why we it was not chosen [47]. The Tiva C was not chosen as well because has much
greater capabilities than we require and consumes way too much power to be efficient [46]. Of the
three Arduino controller researched, the Arduino Uno serves the purposes the greatest. It is the
cheapest of the three, has an optional starter kit which comes with the compatible software and
instruction, and a group member is already familiar programming code in Arduino. The most
beneficial aspect of the Uno is that is has the capabilities for our input and output devices while
also being power efficient. Although it is not the fastest microcontroller, speed is not a priority
since most of the time the robot will be charging still in sunlight. The Due was not chosen due to
its power consumption, and the Mega was not chosen due to its price and unnecessary extra ports.
36
Figure 2.11 Arduino Uno Schematic Design (Permission requested from Arduino Trademark)
[43]
2.6.2 Data Processing
Definition - Data processing is simply collecting pieces of data in order to create some sensible
information out of it [54]. It is a subset of information processing, therefore, observed or detected
data is changed to fit the needs of the operator [55]. Data processing can have several smaller
processing functions, which can include validation, summarization, analysis, sorting, aggregation,
classifying and reporting. Validation is done to confirm a said data piece is useful and precise.
Summarization reveals only the main aspects of data, blocking out unnecessary factors and noise.
Analysis reads and interprets the data recovered. Sorting organizes the data in a sequence legible
to the operator. Aggregation simply puts data parts together. Classifying places data in some
categories. Finally, reporting creates a list of the data usually for documentation.
Data Processing in Robotics - In robotics, gathering information is done by electronic data
processing, usually by a computer device such as a microprocessor or microcontroller [56]. By
following its instructions in coding, electronic processing can perform several of the subprocesses
mentioned above all at once and within picoseconds. As a result, electronic devices can receive
plentiful amounts of data, interpret and document the data, and send out response signals or
commands [57].
Data Processing for Charge Du Soleil - The Arduino Uno will be the electronic data processing
center for our project. Using Arduino code programmed onto the chip (which will be discussed in
a greater capacity in the programming section), several variable will be observed, organized, and
interpreted. Also, responses will be made for each foreseeable data input. For instance, if the light
sensors are at a low intensity, then the rover will command the wheel motor to start in order to
travel to areas of greater light intensity. Some data to be analyzed for will be light intensity, solar
37
panel angle and charging speed, battery fuel amount, bluetooth connectivity and phone application
communications, and possibly rover speed.
Does Arduino Uno Meet Data Processing Requirements? - The main processing requirements
of our project will be a microcontroller that can hold enough code to factor in the environmental
conditions and compute data gathered. Speed of processing as well as efficiency of instructions
need not be considered since as faster and more efficient data processor wouldn’t improve the
rover’s performance in charging in sunlight. With that known, the 32 kilobytes of flash memory
will be more than enough coding space for all necessary lines of code to be written.
Possible Errors in Data Processing- There are two types of errors: a systematic error and a
random error [58]. A systematic error occurs when there is some damage or imperfections within
the system itself, causing data readings to be either too high or too low. For example, if a light
sensor is cracked or overheating, it will read the intensity of light as higher than what it actually
is. This will cause the rover to believe it is at a desirable light source, stay in place, and charge at
a less-than-acceptable speed. A random error happens when a data reading has an equal chance to
measure either high or low. An example of this would be when a voltage input through a pin on
the microcontroller is in between the threshold value for ‘1’ meaning ‘on’ and ‘0’ meaning ‘off’.
This could cause some pins to be on while others will be off although both have the same voltage
going through them. As a result, the sensors connected to those specific pins will read the data
incompletely. In order to avoid systematic errors, the system must stay calibrating as well as
regularly check in time intervals. Thus, light sensors should scan at a given intensity range, within
small integrals, and only send the signal to travel when below the minimum intensity value. To fix
random errors, more data must be taken into account. In the case of the voltage, more voltage
should be added to approach the ‘1’ or ‘on’ state.
2.6.3 Clocking Requirements
Definition - The clock rate is the speed of which instructions can be executed via a
microcontroller’s processor [59]. Each instruction requires a certain amount of clock cycles to
execute, therefore, the higher the frequency of a microcontroller, the more clock cycles can be
done in a given amount of time, and the more instructions can be executed at once. For instance,
as seen in Figure 2 below, one clock cycle is considered one positive half and one negative half.
The frequency is the measure of how many clock cycles pass through one point in time each
second.
Arduino Uno Clock Rate - The oscillator on the Arduino Uno microcontroller goes at a speed of
16 Megahertz. This means that if an instruction takes 20 clock cycles to execute, the Uno will
process the instruction in 1.25 microseconds. This was found with the equation:
CPU time = (Number of Instructions * Cycles per Instructions) / Frequency [60]
CPU time = [(1 instruction * 20 cycles per instruction)/ (16*1,000,000 Hz)] = .00000125 secs.
For a larger and more realistic example, let us imagine the final code to have 2,000 instructions at
15 cycles per instruction. The resulting CPU time to process every single possible instruction at
once would be:
CPU time = [(2,000 instruction * 15 cycles per instruction)/ (16*1,000,000Hz)] = .001875 secs.
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Thus, even if every instruction was executed at the same time (which is basically impossible), the
Arduino Uno will compute the data in under 2 milliseconds. This goes to show that although the
Arduino Uno wasn’t the fastest microcontroller researched, its speed is more than enough for the
purposes of the project. The board will mostly likely execute somewhere in between 1 and 2000
instructions at any given time during testing. Speed was already mentioned in the previous section
to not be a big focus in the design. Regardless, computing instructions in the milliseconds range is
still very fast. The clock rate of the Uno will more than suffice the goals of the project.
2.6.4 Memory Requirements
Types of Memory - Most microcontrollers contain three types of memory: Program memory,
Data memory, and Data EEPROM memory [62]. Program memory (SRAM) will contain the
coding and instructions. Data memory (ROM) will contain variable data values such as
information from any data gathering devices such as light sensors. Special Function Registers
(SFR) such as control, configuration, and status registers for the Input and Output ports can be
found here. Electrically Erasable Programmable Read Only Memory (EEPROM or flash) will hold
non-volatile data; this data is rewritable. These values are stored even when the power is turned
off.
Does the Memory on the Arduino Uno Meet Project Requirements? - On the Uno
microcontroller, there is 32 kilobytes of flash memory (5 kilobytes are reserved for the bootloader),
2 kilobytes of SRAM, and 1 kilobyte of EEPROM [63]. Since there are 27 kilobytes remaining in
program memory, there is a bountiful amount of room for the coding expectations. The project is
not expected to contain any complex codes, therefore the 27 kilobytes will work for the needs of
the project.
Arduino Memory Restrictions - The small SRAM can be used up quickly if too many strings are
written in the Arduino code. This could result in program running issues and potential failure. To
address this issue, strings will be written as short as possible when writing code.
Using the EEPROM Library - The library is broken into two functions: read and write. This is a
useful feature that works like a hard drive. It can store important values even after the device is
turned off. Below are code templates first for read and then for write [64]. To read a value, the
syntax “EEPROM.read (address) must be used [65]. The address must be an integer starting from
0, and the the return is what was stored in the given location. To write a value, the syntax
“EEPROM.write (address, value)” must be used [66]. The address must be an integer value starting
from 0, and the value must be between 0 and 255. This function will be useful in writing some
constant, unchanging values in the future coding.
2.7 Wireless Tethering
In this project, the intent is not only to collect solar energy and store it, but to also allow the user
to control the device remotely. The car will be directed using an application developed to either
run of iOS and/or Android. The application will feature a classic directional pad complete with a
way to turn the front wheels right or left and increase or decrease acceleration. The connection of
two independent devices is known in electronics and communications as “tethering”. Modern
tethering is done using one of three methods. These three methods are USB cable, WiFi, and
bluetooth [35].
39
Tethering consumes energy when it sends signals from an antennae in the process of
communication. When using the USB cable method, the device receives the power via USB cable
[35]. This means that if a cell phone is wirelessly tethered to a laptop, it will expend the energy
stored within the battery as it communicates. If the cell phone is tethered using a USB cable, then
the battery will release energy as a much slower rate. Since this is a physical, hardwired connection
we can expect it to be both more fast and secure. The obvious drawbacks of this approach is that
not all devices can be tethered and modifications may need to be made to devices with possible
custom software installation [35]. Since the goal of this solar tracker project is to have the device
able to control remotely, we this method is not a viable option mainly due to the length
requirements of the USB cable.
2.7.1 WiFi
The WiFi method of tethering is one of the most universally compatible with the most devices. If
both devices are already enabled with WiFi connectivity support, the connection should occur
quickly. A great advantage of using this is that multiple devices can be connected simultaneously.
In this remote-controlled car application, it is not necessary to connect more than one device to the
Arduino controller because there only needs to be one remote. It is still a wise decision to
remember this feature as we can use it in later development if an additional device needs to connect
wirelessly. Depending on the security configurations, the level of protection of the transmitted data
ranges from “not secure at all” to “fairly secure” [35]. It is not necessary to consider securing the
connection between the two devices in this project. Since you’re not required to plug in to a USB
port, your battery is going to drain while you’re thusly tethered [35]. When the smartphone is
tethered to the Arduino board in order to control the direction of its motion, it will die fairly
quickly. Luckily we have a method of re-charging it, using the solar tracker and its connected
battery.
During the search for a way to control a model car wirelessly through an iPhone app, the Dension
WiFi RC was discovered. This device is a plug and play wireless RC receiver [32]. This receiver
is not just limited to cars, boats, robots, and tanks, but can be used on any remote controlled device.
The application is available for free and is compatible with both iOS and Android operating
systems. The controls to operate the vehicle are virtual joysticks, but you can also tilt the screen.
Another interesting feature is the ability to connect the provided camera and receive a real-time
video stream from the vehicle. The power consumption of this wifi receiver is 100mA @ 6V when
idle but doubles to 200mA @ 6V with WiFi and camera turned on and activated. According to an
official Dension video [33], included in the box is a user manual, power cable, USB dongle,
mounting hardware, WiRC unit and USB camera. In this video, a man is seen installing the unit
onto a remote controlled speedboat. The first step of this installation was the removal of the old,
pre-existing receiver. The servo and ESC are then connected to the WiRC unit. The USB wifi
dongle and camera are connected. The next step is to connect the power cable to both the WiRC
and the battery. Once the on switch on the model is activated in the on position, the receiver should
be ready. On the iPhone, in the wifi networks menu under Settings>Wi-Fi you simply choose
Dension WiRC. Once you tap the application icon, the interface will appear. Shown on this
interface is the real-time stream from the camera’s perspective and also joystick controls. The
joystick controls were able to control the direction the rudders will turn on the speedboat. It is
mentioned that the WiRC components are not waterproof and must be placed in a sealed tray.
40
2.7.2 Bluetooth
Bluetooth is another method of tethering devices and comes with many of the features of WiFi.
You can connect multiple devices to your smartphone easily, but power consumption is present
and must be considered [35]. The advantage that Bluetooth has over WiFi is that due to its specific
development to mobile devices, it energy consumption is significantly lowered. The disadvantage
of Bluetooth is its exclusivity. Configuring a bluetooth connection is more involved as opposed to
WiFi or a simple plug and play USB connection [35]. It is only advisable to use bluetooth if power
consumption is a concern. In this solar tracking project, power consumption is a major component,
so bluetooth might just be the way to go.
Searching for an alternative method to control an RC car remotely using a smartphone, a YouTube
video [34] titled DIY Smartphone Controlled RC Car. In this video, an android enabled phone is
used along with an Arduino microcontroller. A bluetooth module is also used to link the phone to
the Arduino. An Arduino motor controller is also necessary. The four pins on the bluetooth module
are labeled VCC (5V) for power, GND for ground, Rx for receiver, and Tx for transmitter. When
connecting the bluetooth module to the Arduino board, the power pin should be connected to the
5V pin and the Ground pin to the ground. The Tx should be connected to the Rx, and the Rx to the
Tx. This is done so that the two boards can communicate with one another and establish bluetooth
connectivity. The RC car when disassembled, had two DC motors in it where each one controlled
the rotation of one rear wheel. The pre-existing logic board was removed and replaced with the
Arduino motor controller. One DC motor was connected to the Out A and Out B terminals and the
other motor to the Out C and Out D terminals on the motor controller. In A through In D were
connected to the Arduino digital pins 2 through 5 respectively. You can connect VCC to the 5V
output of the Arduino and ground the ground pin. The VCC can also be connected directly to an
external power source if the RC car’s built-in battery pack is insufficient. This process completes
the hardware configuration.
2.8 Power
Definition - Power, more specifically electrical power, is how fast energy is consumed in an
electrical circuit. It is defined by the equation:
Power (Watts) = Energy Consumed (Joules)/ Time (seconds); P = E/t [67]
For DC circuits, Power can be described as voltage (in volts) times current (in amperes) and its
variations using Ohm’s law: P = V*I or P= I*I*R or P = V*V/R (Resistance is in ohms)
For AC circuits, power can be measured in three parts: real, reactive, and apparent. Real power (P)
is the power that is used to do the work on a load. It is described by this equation 1. Reactive power
(Q) is the used up power not used for work, seen in equation 2. Apparent power (S) is the power
that the circuit supplies, seen in equation 3. The impedance phase angle, phi, is the phase difference
between the current and the voltage.
1) P = Vrms*Irms*cos(Φ) [67]
2) Q = Vrms*Irms*sin(Φ) [67]
3) S = Vrms*Irms
[67]
2.8.1 Battery Comparisons
From the research done in the earlier section on batteries, lithium batteries were proven to be the
most suitable [69]. They are rechargeable with quite long life spans in one use. In addition, lithium
41
batteries can be charged at any time, without any memory loss. This is probably the most useful
trait in our case, since the battery will likely be charging constantly. The entire battery packs below
are precautions from overcharging as well as good integrity from temperature damage [69]. There
were 4 main categories of lithium batteries, divided by voltage output: 3.7V, 7.4V, 11.1V, and
14.8V. All but the 11.1V were examined. This was because have two high voltage batteries above
10 volts when only 5 volts would be needed to power the microcontroller. Also, the 11 volts
batteries were one of the most expensive to find, thus they would not stay within the budget.
As our design requires a 5 volt input to power the microcontroller, the 3.7 volt batteries would not
be sufficient alone; they would need to be two pack connected in parallel to reach the necessary 5
volts. However, this would create a one pound load on the car chassis, possibly weighing down
the entire rover vehicle. Conversely, the nearly 15 volt battery would supply more than enough
power. However, due to the high price and possible damaging through trial and error in prototyping
stages, the extra cost for useless extra voltage hardly seems necessary. That leaves the last two 7.4
volt batteries. It would be wise to purchase two of each battery. The lessor amperage per hour
batteries can be used for preliminary trials, and the larger ones for the final design. The larger
batteries would be the most suitable for our purposes because it will supply longer charge life per
battery lifespan. For instance, if the microcontroller require 500 milliamps per hour to stay
activated, it would survive longer on the larger amperage 7.4 volt battery (2200/500 = 4.4 hours,
and 2600/500 = 5.2 hours). As a result, nearly an entire extra hour of battery life is gained [69].
Name
Voltage Max Charge/ Discharge
Weight
Dimensions
6600mAh Battery Pack
($40) [69]
3.7V
3 Amp
6 Amp
9 oz
2.7in x 2.1in x 0.7in
($32) [69]
3.7V
6 Amp
10 Amp
6 oz
2.6in x 1.5in x 0.7in
($40) [70]
7.4V
1-2 Amp
3 Amp (PCB)
3.5 oz
2.8in x 1.5in x 0.8in
($32) [70]
7.4V
1-2Amp
3 Amp (PCB)
3.5 oz
2.8in x 1.5in x 0.8in
($55) [71]
14.8V
2 Amp
4 Amp
6 oz
2.9in x 2.5in x 0.8in
[70]($50) [71]
14.8V
2Amp
4 Amp
6 oz
2.8in x 1.5in x 0.8in
Table 2.8 Comparison of Power Banks
2.8.2 DC/DC Converter
Since a 7.4 volt battery will be used and the microcontroller will require 5 volts, a DC/DC
converter that has a voltage output at 67.57% of the voltage input is required. An AC/DC converter
is not required since the battery internally converts AC voltage and outputs DC voltage. This will
supply the microcontroller with the correct voltage and avoid frying the circuit. As seen below,
this schematic would be 94% efficient and extremely cheap.
42
Figure 2.12 DC/DC converter (Permission requested from TI) [72]
43
Figure 2.13 Efficiency Table, Duty Cycle, and Cost [73]
2.8.3 Charging
Charging the Battery with Sunlight - The solar panel absorbing sunlight energy will connect via
a solar lithium ion polymer charger, which in turn will connect to the 7.4 volt battery (see picture
below). A median piece is necessary because it will act similar to an AC/DC converter. This must
be done due to the varying amounts of energy which the solar panel will receive based on the
sunlight intensity. Voltages on the panel can vary up to 24 volts, much greater than the 7.4 volts
of the battery. Although lithium batteries can’t be overcharged by excess voltage, efficiency must
be accounted for. One of our main goals of this project is to build an efficiently charging device;
the median piece will minimize any lost energy from overcharging [74]. Although not a true Max
power point tracker, this device acts similar to one without the need of an extra, pricier piece called
a buck converter. This is a cheaper way to gather as much current from the solar panel as possible,
and it works in almost any condition of sunlight. In order to have this piece work correctly, these
factors must be addressed:
● Charger must charge 7.4 volt battery
● Must connect to solar panel via 2 pin JST cable
● Must have some feedback system attached to microcontroller and phone app
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Charging Time - Since gathering charge is all dependent on the solar panel, charge time will vary
based on the conditions in which light intensity is hitting the panel. It is obvious to assume that
low light intensity areas will take longer to charge than high light intensity. Regardless, the rover
is designed to seek the most possible sunlight, therefore, it should logically charge in the fastest
charging nearest area. Using basic circuit laws to make an educated guess, one would believe that
the 2600 mAh, 7.4 V battery would be fully charged at: (7.4 *2.6) = 19.24 Watt hours.
However, even in perfect conditions, this is never the case; the real amount is usually greater by a
factor of 2.5 [75]. The real result would be, given that the solar panel is 6 watts: [(19.24/6)*2.5] =
8.02 Watt hours. This difference is due to some factors, including some energy is lost by heat,
voltage will drop down to the load value connected to it, and the wattage value is open circuit
voltage multiplied by peak current, therefore, current value will vary somewhat.
2.8.4 Estimated Life Cycle
Several Factors Involved - Just like in charging, estimating life cycles will vary even in ideal
conditions. This is because there are several factors involved in any battery’s life cycle [76]. Some
of these factors, such as if the battery is overcharged or not, can be neglected since lithium batteries
do not overcharge. Other factors, such as charge levels, chemistry, environmental factors, battery
damage, electrolyte breakdown, and uncontrolled operating conditions, have to be considered.
Unfortunately, there is no one concrete equation that puts into effect all of said factors. As a result,
the best way to estimate a battery life cycle is to look back at the historic life cycles of the battery.
Average Life Cycle of a 7.4 volt, 2600 mAh Battery - Although no precise answer can ever be
solved for, viewing the average lifespans of the same battery with similar discharge conditions can
give a general idea. For example, the same battery used on an RC plane will last an average of
three hours when fully charged [77]. Therefore, it can be safely assumed that the battery will last
between two and four hours, give or take different, harsher conditions.
45
Figure 2.15 Voltage and Current relation on a 4.2 Volt Battery (permissions requested)
2.9 Block Diagrams
2.9.1 General Block Diagram
The block diagram shown above is a representation on how we plan to integrate all of our parts for
the robot. Certain components are dependent on one another in regards to its implementation.
Below are descriptions on each component and the components that they are dependent of and the
components when depend on it.
● Code
○ the code will be used to program the mobile app, the solar panel adjustment, the
light sensors, the feedback system, the connectivity and the circuit board
○ Components dependent of: None
○ Components that depend on Code:
■ Connectivity
■ Panel Adjustment
■ Light Sensors
■ Feedback System
■ Circuit Board
■ Mobile App
● Circuit Board
○ The circuit board takes the inputs from code and feedbacks system and then outputs
to the next function
○ Components dependent of:
■ Code
■ Feedback System
○ Components that depend on Circuit Board:
46
■ Mechanical System
● Panel Adjustment
○ The panel adjustment component finds out the optimum angle the solar panel needs
to be shifted to charge the panel most efficient
■ Feedback System
■ Code
○ Components that depend on Panel Adjustment:
■ Solar Panel
● Light Sensors
○ These sensors will detect the strength of the light and will give feedback to the
feedback system on whether the robot should move towards the light to charge
○ Components that depend on Light Sensors:
■ Feedback System
● Feedback System
○ The system which controls all of the feedback received from components to allow
the robot to moves and make actions
■ Code
■ Circuit Board
■ Light Sensors
○ Components that depend on Feedback System:
● Mobile App
○ The mobile app will be controlling the movement of the car and the panel
adjustment. These movements will be basic forward, backward, left and right
movements as well as controlling the angle movement of the panel
■ Code
■ Connectivity
■ Feedback System
○ Components that depend on Mobile App:
47
● Solar Panel
○ The solar panel will be used to charge and store energy in our main battery
○ Components that depend on Solar Panel:
■ Energy Storage
● USB Charger
○ The is what will be used to power any USB connected devices
○ Components dependent on:
■ Energy Storage
○ Components that depend on USB Charger: None
● Car Battery
○ The battery that is used to move the actual robot
■ Energy Storage
○ Components that depend on Car Battery:
● Energy Storage
○ This is where all of the energy from the solar panel is stored. This energy is used to
power the car battery as well as charge other devices via the USB charger
○ Components dependent on:
■ Solar Panel
○ Components that depend on Energy Storage:
■ Car Battery
■ USB Charger
● Mechanical System
○ The mechanical system is what actually moves the robot. This includes the motor
and wheels in motion
■ Feedback System
■ Car Battery
○ Components that depend on Mechanical System: None
● Car Model
○ The physical base of the robot. The car model is where all of our physical
components will be placed
48
○ Components that depend on Car Model: None
Figure 2.16 System Block Diagram
2.9.2 Software Class Diagram
Since about half of the components of the robot depend of the software and code, a separate class
diagram was created to go further in detail about those functions and components. The class
diagram is listed below:
Figure 2.17 Software Class Diagram
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3) Project Design
3.1 Physical Robot Mock Up
Figure 3.1 Front and Side View Mock Up
Figure 3.2 Top View Mock Up
The physical mockup was made based off the physical specification listed previously in the
document. Those specification were:
● Length: < 24 Inches
● Width: < 10 inches
● Height: < 12 inches
In the mock up, it is color coordinated showing the location of the main components (light sensors,
motor, battery location, and solar panel and PCB location). The PCB and microcontroller will be
50
enclosed to prevent any air/water damage to the components, the battery will be located directly
under the enclosed PCB but still in a location when it can be easily connected with the solar panel.
There will be mechanical arms attached to the solar panel that will be used for
increasing/decreasing the angle of the panel.
3.2 Microcontroller
When looking to design this project, a design was made to use the Arduino Uno microcontroller
to handle all of the main functions of the robot. The Arduino Uno microcontroller was chosen due
to its compatibility with the photocell light sensors that will be used to detect the strength of light,
compatibility with the RC control for the mobile app, and compatibility with the battery that will
be storing the energy obtained from the solar panels.
The Arduino Uno can be powered by numerous different power sources as long as the input voltage
is between 3-5 V. The voltage that will be coming from the solar panel will be around 12 V so a
voltage regulator will be used to regulate the input voltage. The microcontroller and battery
compatibility will be discussed in more detail shortly.
In regards to the compatibility with the bluetooth device, the Arduino microcontroller meshes well
with the JY-MRC bluetooth module. In order for the module to work perfectly without any
damages, a voltage regulator need to be used. The regular used with regulating the energy from
the battery to the microcontroller can be used to regulate the bluetooth module and the
microcontroller. The input voltage going into the bluetooth module needs to be around 3.3 V. A
combination of resistors will also be needed to help regulate the voltage to 3.3 V. When connecting
the bluetooth module to the microcontroller, the 5V output of the microcontroller will link to the
VCC of the module, ground will link to ground, TX on the microcontroller links to port 2 on the
module and RX on the microcontroller links to port 4 on the module.
The light sensing photocells are connected to the microcontroller similarly to how the bluetooth
module is connected. In this particular case, the 5V output from the microcontroller links directly
to one end of the photocell while the other end of the photocell is linked directly to port 0 of the
microcontroller. A voltage regulator would again be needed in order to decrease the possibility of
damaging the photocells of the robot.
3.3 Prototype Construction
3.3.1 Data Input System
One of the main components of the robot is the use of a fully functioning feedback system that
which handles all of the data inputs and uses those inputs to figure out the next set of functions
that can happen based off those inputs.
This feedback system will include 6 functions that will be used. These functions and descriptions
of the functions are listed below.
● Directional Movement (Sensors)
○ This function will be used for the directional movement of the robot based off the
feedback received from the sensor state. An active state reading from the Get
Sensor State function will then determine the direction that the robot will move in
as well as avoid all objects in the vicinity.
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● Directional Movement (Mobile App)
○ This function will be used or the directional movement of the robot based off the
feedback received from the mobile app regarding the direction. A second function
would be needed since in direct sunlight, all of the sensors will be active causing a
conflict with the directional movements. There would no need for object avoidance
like with the Directional Movement (Sensors) function since the user would be in
full control of the robot.
● Get Connection State
○ This function will be used to determine the state of the bluetooth connection. The
return value of the function will be either “Connected”, “Connecting” or
“Disconnected” and this return value with correspond with a reading shown on the
mobile app letting the user know of the connection status.
● Is Connected
○ This function will be used once the user has connected the mobile app to the robot.
Inside of this function will contain all of the subroutines necessary when the mobile
app is in use and disables the use of the autonomous capabilities as long as the app
is connected
.
● Get Sensor State
○ This function will be used to return the state of the sensors. An active state being
returned means that light has been detected and the robot will then begin to
autonomously move towards that light source. An “Inactive” state being returned
means that no source of light has been detected the robot will remain stationary
until a light source is detected.
● Get Battery State
○ This function will be used to return the state of the battery. LEDs (green, yellow
and red) will be on the robot that will shows the status of the battery charge. The
green LED being lit represents the charge of the battery being greater than 75%, the
yellow LED being lit represents the charge of the battery being in between 30 and
75% and the red LED being lit represents the charge of the battery being less than
30%.
3.3.2 Power Storage
An extremely reliable and portable USB Solar charger can be built for relatively cheap. This design
takes into consideration that such a device must be extremely lightweight in order to be mounted
on a remote controlled car chassis. One main feature of this design includes a USB PowerBank
which acts as a battery reservoir and makes night time charging possible. It will only take 40 to
120 minutes to full charge the PowerBank and includes a 4 bar battery indicator. A 10 volt 3 watt
solar panel is under consideration and will preferably be one that is waterproof and shock-resistant.
It is recommended to use a solar panel of at least 6 to 10 volts at 3W to 10W in order to minimize
charging time. A 2800mAh PowerBank with a 2A output will be used because of its compatibility
with the iPhone 5 charging specifications. Other parts include a 4 port USB hub, a 7805 regulator
52
chip, micro USB cable (a stripped end), wires, and super glue (Gorilla or Mighty Bond). The 4
port USB hub simply acts as a divider on the PowerBank output to charge multiple devices
simultaneously. All necessary components will be mounted on the posterior surface of the solar
panel as seen in Figure 1.
The solar panel in this case produces 10 volts (3W) but the PowerBank only needs 5V. This causes
an issue because the PowerBank internals will be damaged due to excess voltage. The problem
can be solved by using a 7805 regulator. The regulator will need to be placed within the terminal
box on the backside of the solar panel. The stripped end of the micro USB cable will be soldered
to the pins 2 and 3 of the regulator (Figure 2). Two wires will be soldered to pins 1 and 2. These
two wires will need to be soldered to the appropriate positive and negative terminals. A small
droplet of superglue will be used to secure the 7805 into the terminal box. The heat sink mount
can be trimmed if necessary. The heat sink mount is simply the metal piece protruding from the
top and serves no purpose in this application. The powerbank and 4 port USB hub will then be
mounted on the backside of the solar panel. The stripped micro USB cable end that was connected
to the solar panel terminals is now the charging cable. This cable will be connected directly to the
PowerBank charge input. The USB hub will be connected to the Powerbank output and up to four
devices can be charged through it.
The major components, which are the solar panel, USB PowerBank, 4 Port USB Hub, and 7805
regulator chip will be selected in order to obtain the highest performance for the lowest price. A
12 Volt 10 watt polycrystalline solar panel is available on Amazon.com by Solar Odyssey. The
specifications meet the requirements of at least 6 to 10 volts and 3 to 10 watts. The dimensions of
this panel are 13.8 in x 11.4 in x 0.67 and the weight is 2.6 lbs. This makes it relatively small and
lightweight for the heaviest component. At the time of writing this, the price is $34.95 and there
are 14 units in stock. A 12000mAh USB PowerBank is offered by Focalprice.com and meets the
requirement of an output of 5V and 2A. There is a secondary USB output with a lower current of
1A but will probably not be necessary here. This particular module comes equipped with a
convenient LED indicator which features four lights, at 25% intervals. Once all four LEDS are lit,
the PowerBank is fully charged. The Powerbank is compatible with nearly all kinds of mobile
phones and tablet PCs. With size dimensions of 19 x 11 x 2.7 cm and a weighing only 251.45
grams, this is a very small and lightweight option. It is available for $21.49 and is in stock with
free shipping. The Targus 4-Port USB 3.0 SuperSpeed Hub is available on Bhphotovideo.com for
$40.98. This admittedly pricey component is capable of file transfers of 615MB/sec. As previously
stated, the only function of the USB hub is to allow multiple devices to be charged simultaneously.
It would be wiser to possibly purchase a cheaper USB hub. A Toshiba USB 2.0 4-Port Hub can be
purchased directly from the manufacturer at Toshiba.com for only $11.99. This device features
plug-and-play compatibility and does not require any additional drivers or software installation.
The cheapest but most crucial component of the project, the Texas Instruments 7805 regulator chip
can be purchased from Mouser.com for only $0.60. This one fits the specifications quite nicely.
The minimum input voltage is 7 volts which will be provided by the 12 volt solar panel selected.
The output voltage is a fixed 5 volts, which will be compatible with the PowerBank requirements.
The output current is 1.5A which should be sufficient to charge an iPhone 5. Since this component
is so miniature, size and weight are negligible characteristics.
53
Part
Price
Size
Weight
Website
Solar Panel
$34.95
13.8 in x 11.4 in
x 0.67
2.6 lbs
Amazon.com
PowerBank
$21.49
19 x 11 x 2.7 cm
251.45 g
Focalprice.com
USB hub
$11.99
3.2" x 1.4" x
1.3"
2.5 oz
Toshiba.com
7805 Regulator
$0.60
N/A
N/A
Mouser.com
Table 3.1
Below is a diagram detailing how the process of integrating the regulator, USB hub, PowerBank
and solar panel together.
Figure 3.3
3.3.2.1 PV Cells to Battery
The Figure 3.7 below shows how a standalone photovoltaic system function [79]. The cells, once
invigorated by the sunlight, are set through a DC disconnect device. Then, the charge controller
acts as a converter and lets the appropriate amount of current through. The released current
branches into three directions. In the first direction, the current will flow into a low voltage
disconnect. Then this will be sent to a DC distribution center, and finally to other DC loads.
Through the second branch, the current is sent through a stand-alone inverter, where some current
is sent back. This inverter is powered by a backup generator. Then the current from the inverter is
sent to an AC distribution center and finally to AC loads. In the final branch, the current is sent
through one last DC disconnect device and stored in battery banks. This is an overview as to how
54
Solar panels charge real life circuits. In our case, similar procedures are done. However, since our
circuit is much less sophisticated as the one seen on the figure on the next page, very few pieces
are needed to run it. No DC connects are needed, and only one DC to DC converter is used. The
current does follow a similar path to the battery. It is important to note that the solar panels and
PV cells do not direct power the microcontroller or rover. Instead, they will be responsible for
charging the battery that in turn powers the rest of the machine. It would not make any sense to
have a solar panel directly power the car since no part of the car can retain charge; the car would
turn off as soon as light no longer struck the panels.
Figure 3.4 (Permission requested)
3.3.2.2 Battery to Mobile Device
The solar energy will be accessible to cellular phones via the USB outlet on the microcontroller
port. The phone will be able to charge will self-sustaining, renewable energy from the sun. This
will accomplish one of our goals to minimize the dependence of wall power outlets.
3.3.3 Mobile Device RC Application
The decision was made to use Bluetooth as the means of connectivity when connecting the mobile
app for RC control to the robot. Bluetooth offered more advantages than WiFi RC. When deciding
the type of Bluetooth unit to use, there were numerous components to choose from the component
that will be used is a JY-MRC class 2 Bluetooth Module (slave). The JY-MRC module would ask
as of that of a serial port. One of the main advantages of this particular Bluetooth module is that it
did not need any software related configuration from Arduino. The slave type module would be
needed over the master type module. There are two types of devices: Master and Slave; a Master
can communicate with more than one Slave while a Slave can communicate with a single Master
55
at a time, Master-Master and Slave-Slave communication is not allowed. Since the Bluetooth
module in all smartphones is of Master type, the one we need for Arduino must be a Slave [36].
When connecting the phone to the robot, the Arduino board must be turned on as well as the
Bluetooth on the phone. Once both is active, you would be able to search for the Bluetooth signal
given off by the JY-MRC module and connect the module to the phone. Once connected, it would
then be possible to use the mobile app to control the robot.
The research presented previously in the document concluded that Android based app development
had 4 advantages and 4 disadvantages while IOS based app development had 3 advantages and 3
disadvantages. Since both development platform boasted a 1:1 advantage to disadvantage ratio,
the decision is made to have an app made on both platforms. Having an app on both platforms
allow for ample testing to be conducted and allows for multiple users to sample the robot among
the final demonstration and showcase. Even though there will be two different applications, the
layout for both will remain the same. The layout will include a directional pad, a red circle that
denotes not that the app is not connected to the robot (this circle will be lit), a yellow circle that
denotes that the phone is connecting to the robot (this circle will be lit), a green circle that denotes
that the phone is connected to the robot (this circle will be lit), a button that disconnects the phone
from the robot (this button will be labeled “Disconnect”), and a button that connects the phone to
the robot (this button will be labeled “Connect”).
On the following page is a Photoshop mockup of the application layout detailing the description
above.
Figure 3.5 App Mockup
56
● Only one of the colored status circles will be lit at a time
● The red status circle (disconnected) will become unlit once you tap the connect button
(which makes the yellow status circle for connecting to be lit)
● Once the phone and the robot is connecting, the yellow status circle will become unlit and
the green status circle (connected) will become lit.
57
4) Project Prototype Testing
4.1 Test Environment
Since the project uses solar panels, the testing environment would need to be in an area where
there is sunlight. There will be three different environments to best test the effectiveness of the
robot. There three different environments are listed below:
●
●
●
●
●
●
●
●
●
Outside; forecast of a sunny day with no clouds
Outside; forecast of a partly cloudy day
Outside; forecast of a cloudy day
Outside; during dawn hours
Outside; during peak sunlight
Outside; during dusk hours
Inside; facing the sun
Inside; shined on by artificial light
Inside; no particular light source (will it search for one?)
By using these three testing environments, conclusions can be drawn to determine the charge rate
of the panel and also determine the optimum angle the panel would need to be in order to achieve
this optimum charge efficiency. Questions to be asked here are:
●
●
●
●
●
●
●
The effect of clouds/shade to light intensity?
The charging time difference of the battery?
The discharge vs.charge rate; will the battery run out?
Does the rover search for a new location?
Does precipitation go into the sensitive electrical components?
Can the rover maneuver around treacherous environments?
Are any other parts besides the solar panel affected?
Once said questions are addressed, design process must be done to improve the rover. Solutions
must be made for possible new problems could be:
●
●
●
●
●
●
A sensory trigger for clouds/shade; search for a better lit area
A feedback monitor on charge speed, possibly on the app
A warning that battery is low
Light sensors must be quite sensitive to stimuli
Protective, light-weight covering to be designed and built
Possible further research into wheels and car maneuverability improvements
● Analyze extent of affected parts and search for solution
58
4.1.1 Panel Adjustment Metrics
For the solar panels, testing would be done in three varying light intensity testing environments in
which the panels would be set an angle to determine the optimal angle needed for the best charging
efficiency. Listed below are the angles in which the testing would be done on:
●
●
●
●
●
●
●
●
0 degrees
7.5 degrees
15 degrees
25 degrees
30 degrees
37.5 degrees
45 degrees
50 degrees
…
...
● 337.5 degrees
● 345 degrees
● 352.5 degrees
All angles would be perpendicular to the ground, thus the angle would be movement in the
horizontal axis. In addition, possible rotation in the vertical axis from the panels set tilt to 90
degrees should be research. If the sun happens to be right above the rover, then a full 90 degree tilt
would be the most optimal position for the solar panel. The horizontal axis angular position would
not be important during this instant. Factors to note in each positioning would be:
●
●
●
●
●
●
Light intensity
Charging speed
Variation in intensity from previous and next position (possible mapping on app)
Reset counter for every full rotation to avoid going over 360 degrees
Small locating; will it seek light traveling minimum horizontal distance?
Microcontroller function at certain locations
Finding the optimal angles and recording them during specific times of the day is the key to having
the most efficient solar charging rover.
4.1.2 Software Metrics
Listed below are the features that will be tested in regards to the software portion of the project.
The Mobile Application feature has its own section in which features from that portion of the
software that will be tested as well.
● Feedback System
○ Is information recorded and sent back to the microcontroller for processing?
○ Information shown as an led light or app notification
○ Calibrated to the right measurements
59
● Bluetooth Component
○ Connecting to Application?
○ Relaying and displaying correct information?
● Autonomous Movement
○ How well can it move by itself?
● Mobile Application
○ Good connectivity?
○ Responsive controls?
○ Feedback information?
● Coding Efficiency
○ Does code take up as little space as possible?
○ Can it be shortened/simplified for faster instruction speed?
Damage or poorly function software can ruining the performance of the entire rover.
4.1.3 Mobile Application Metrics
As stated previously, the purpose of the mobile app will be to control the movement of the robot
as well as controlling the movement of the panel in an angular motion. Stated below are the
guidelines used for the mobile app testing:
●
●
●
●
●
●
●
●
●
fully functional application that can be download to mobile device
capacitive touch for directional movement
connecting to the app to the robot
forward movement
backwards movement
left movement
right movement
positive increase in angle
negative increase in angle
4.2 Testing Results
4.2.1 Output Voltage Comparison
Switching Regulator
Voltage (V)
Current (A)
Power (W)
3.3
1.355
4.47
Linear (7805)
4.8
0.88
4.223
Table 4.1
60
4.2.2 Charge/ Discharge Time
2200 mAh Power Bank
9000 mAh Power Bank
Charge Time
3 – 5 hrs
7 – 9 hrs
Discharge Time
1.5 – 3 hrs
5 – 7 hrs
Table 4.2
4.2.3 Photo Resistor Readings
With the photo resistors, the readings fall within a range of [0, 1023] lux with 0 lux meaning that
the photo resistor are in pure darkness and 1023 lux meaning that the photo resistors are in pure
sunlight. Below in Figure 4.1 is a table showing the curve of the photo resistor readings as they
are exposed to more light.
Figure 4.1
Within the means of the project design, the table below shows the conditions the photo resistors
were in and the actions that were taken by the rover if that specific condition was met.
Condition
Action
Left > Right and Difference > 100 lux
Move Slightly Left
Right < Left and Difference > 100 lux
Move Slightly Right
Difference < 100 lux
Continue Forward
Table 4.3
61
5) Printed Circuit Board Design and Assembly
5.1 PCB
5.1.1 Prototype
Due to time constraints, the multisim circuit board design could not be made before the
predetermined time. However, the overall idea of the entire circuit board can be discussed in some
detail. First, the center of the design is the microcontroller. It is directly connected to the DC/DC
converter, motor control wires for the wheels and panel rotator, and light sensors and the bluetooth
chip. The DC/DC converter is connected to the battery and the battery is connected to a small
lithium polymer DC converter which is connected to the solar panel. The energy comes from the
panel to the battery and then to the microcontroller. Certain resistors and capacitors will need to
be strategically placed to maximize output voltage. This circuit analysis will be done at a later time
before final PCB design. It is important that all voltage drops from each stage correspond to the
correct input, in order to avoid circuit damage from overcharged or exploding parts.
Figure 5.1 Basic Board Design of an Off-Grid systems [79]
5.1.2 Final Design
Using CadSoft Eagle Professional Edition 6.5, Charge du Soleil constructed a two layer printed
circuit. This board shown above in Figure 9, incorporates the Arduino Uno ATMega328 to run the
coding environment and the ATMega16U2 to send and receive information via USB port. These
sections can be found on the bottom right of Figure 7. In addition, on the far right edge of the
board, just alongside the ATMega328 lies the locations for mounting the photo resistors and the
motion sensor. This locations were strategically placed due to the fact that the motion sensor
needed be in the front of the chassis in order to properly detect for obstacles directly in front of the
rover. Also, both the photo resistors and motion sensor were situated near the center of their
locations in order to give the most precise readings for light from both sides from the resistors, and
to see directly ahead of itself for the motion sensor’s case. Rigid extension cables are to be placed
in the photo resistor junctions to be extended a few inches in the air. This will avoid interference
62
in light sensoring when the LEDs on the board turn on. Some additional parts to mention along
this same area are the Bluetooth junction and the USB-B port.
Near the top right of Figure 5.2 is the motor shield. The PWM microcontroller of the shield is
powered via the VCC port of the ATMega328, while the H bridges that control the motors are
powered by the regulated output of the larger power bank. From the far left of Figure 5.2 all the
way down are two charge controllers: one for the larger bank, and the second for the smaller bank.
Both controllers connect to the panels via USB stripped wires soldered onto the through hole cables
on one end, and output via stripped cables to USB to each power bank/ and can have their output
voltages adjusted by moving the respected potentiometers. The bottom left of Figure 5.2 showcases
two possible input connections for the motors via the larger bank: DC jack and through cable
soldering. Although no other connection on the board utilizes a DC jack, this connection was made
is a safety precaution and alternative method to charge the entire printed circuit board in case the
USB connection did not function correctly for any unknown reason.
The schematic diagrams were modified from webench and atmel template models of their
respective components. Any excess and unneccessary components of the original models were
scraped, and only the most essential parts were kept on the final schematic. The board is 4.4” by
3.5” long, making it quite longer than the original board and motor shield. However, it contains
both the main Arduino components and motor shield, 2 charge controllers with MPPT capabilities,
a switching regulator the boosts the input of the power bank, and a USB-B port as well as a DC
jack. Therefore, for its size, the printed circuit board is a quite complex and powerful electronic
device.
Figure 5.2 Final Completed PCB Design
63
Figure 5.3 & 5.4 Solar Panel Charge Controller
Figure 5.5 & 5.6 Microprossesors
64
Figure 5.7 Motor Shield
Figure 5.8 Final Rover Design
5.2 Changes from Initial Planning
Over time, changes were made from the initial planning in which additional features were added
to the project and certain features were taken away from the project. Initially, the project was
designed to be controlled via an android/iOS application but was later developed to be fully
65
autonomous (light seeking). Along with being fully autonomous, an object avoidance system was
also implemented to allow the rover to avoid objected while seeking the strongest source of light
to charge the power banks which powered the rover itself. Listed below are how the new
components would be used within the overall system of the project.
Object Avoidance - In order for the robot to navigate safely, object avoidance must be
implemented. In order for Charge Du Soleil to sense objects in its path, the HC-SR04 was selected.
The HC-SR04 is an ultrasonic sensor that uses sonar to determine the distance to an object similar
to the system bats or dolphins are naturally equipped with. This package offers excellent noncontact range detection and stable readings. One major benefit of using this sensor is that its
operation is not affected by sunlight. Charge Du Soleil intends to operate mainly in direct sunlight.
Light Seeking – Charge Du Soleil is able to seek the best possible light source to improve energy
collection. Light sensing is done using photo resistors. Two photo resistors are used in Charge Du
Soleil to sense the light exposure. If the reading on the sensors is below a certain value, there is
not enough light and the robot will continue to search for a better area to charge. Once the reading
on the sensors is above this value, there is sufficient light and the robot will send a signal to the
motors to stop running. At this location, Charge Du Soleil is satisfied and will stay. If the difference
in resistance values of both sensors is above a certain value, Charge Du Soleil will then turn in the
direction of the higher reading value. If the difference in reading values of both sensors is less than
this value, Charge Du Soleil will continue to travel straight until the sensors receive equal light.
5.3 Design Issues
Throughout the completion of this project, numerous design issues occurred in which reflect
differences between the initial project bill of materials compared to the final bill of materials.
Listed below are the issues that were faced with the design of this project and the actions that
were taken to overcome these issues.

Component Support
o The biggest initial issue that was faced was finding a suitable rover chassis that
can support both the weight of the solar panels and the weight of the power banks.
Initial thoughts were to possibly build it but after doing more research, a steel
rover chassis with strong motors was ideal and helped solve this issue.

Component Mounting
o In order to remain within the dimension specifications of the project, the issue of
finding a way to mount all of the components arose. By using an additional metal
platform along with metal extension, the panels and power banks were effectively
mounted without causing interference with the circuit boards and wiring.

Pass-through Charging
o Within the design of the project the power banks would be receiving charge but
also would need to give off charge simultaneously. This issue first arose when
building the prototype and it was noticed that the power banks initially purchased
would not give off charge when the bank is charging itself. More research was
66
conducted to solve this issue and as reflected in the final bill of materials, three
power banks were acquired before purchasing two power banks that offered the
pass through charging capabilities.

Maximum Power Point Tracking Design
o The project design calls for using solar panels to charge the power banks. In order
to charge the power banks, the input voltage from the solar panels needed to be
regulated down to 5 volts output. One issue that may arise is that when regulating
voltage down to a specific amount, power may be lost. The use of Maximum
Power Point Tracking allows for the voltage to continuously be regulated down to
the specific amount while outputting the maximum power based on the output
metric. This issue was overcame by designed a charge controller with MPPT
capabilities that effective/efficiently regulated the voltage from the panels to the
maximum power point to most efficiently charge the power banks.

Printed Circuit Board Design
o The biggest issue faced with the design of the project was building and
completing the printed circuit board. This process took the longest to complete
due to the complexity of the design as well as no prior knowledge of using Eagle
to build the schematic. After completing the design the first time, it needed to be
redone in order to fix traces and passive components to fit the necessary
specifications needed for final fabrication.
67
6) Appendix
6.1 Permissions
Majority of the permissions requested are currently pending approval
All Arduino names, logo, and boards shown are property of the ArduinoTM Company. I do not
own or distribute any products or logos.
6.2 References
Listed below in list format are the links of the sources used when writing this document. Due to
the nature of some sources not having sufficient information for citation purposes, it was best to
leave the links in list format.
1) http://exploringgreentechnology.com/solar-energy/advantages-and-disadvantages-ofsolar-energy/
2) http://www.greenenergychoice.com/green-guide/fossil-fuels.html
3) http://www.solarika.org/blog/-/blogs/10-best-things-about-solar-energy
4) http://www.instructables.com/id/Arduino-Solar-Tracking-Robot/?ALLSTEPS
5) http://www.instructables.com/id/Solar-phone-charging-system-featuring-sun-tracking/
6) https://www.youtube.com/watch?v=ATnnMFO60y8
7) https://www.youtube.com/watch?v=lrP0XZaKwOo
8) http://planetfacts.org/what-is-solar-radiation/
9) http://www.windows2universe.org/earth/climate/sun_radiation_at_earth.html
10) http://www.pveducation.org/pvcdrom/properties-of-sunlight/motion-of-sun
11) http://www.livescience.com/41995-how-do-solar-panels-work.html
12) http://www.evoenergy.co.uk/solar-panels/our-technology/pv-cell-comparison/
13) http://www.solar-facts-and-advice.com/monocrystalline.html
14) http://www.solar-facts-and-advice.com/polycrystalline.html
15) http://www.solar-facts-and-advice.com/thin-film.html
16) http://www.solar-facts-and-advice.com/amorphous-silicon.html
17) http://www.solar-facts-and-advice.com/cadmium-telluride.html
18) http://www.solar-facts-and-advice.com/CIGS-solar-cell.html
19) http://www.beneq.com/transparent-conductive-oxide-tco.html
20) http://www.solar-facts-and-advice.com/solar-panel-temperature.html
21) http://www.solarpower2day.net/solar-cells/efficiency/
22) http://depts.washington.edu/matseed/batteries/MSE/classification.html
23) http://mechanicalmania.blogspot.com/2011/07/types-of-battery.html
24) http://lenpenzo.com/blog/id710-why-rechargeable-batteries-are-rarely-cost-effective.html
25) http://www.hardwaresecrets.com/article/The-Truth-About-NiCd-Batteries/292/1
26) http://www.batterystuff.com/kb/articles/battery-articles/proper-care-and-feeding-of-animh-battery.html
27) https://www.apple.com/batteries/why-lithium-ion/
28) http://www.cdxetextbook.com/electrical/princ/batteries/leadacidbatteries.html
29) http://www.seattlerobotics.org/guide/servos.html
30) http://www.education.rec.ri.cmu.edu/content/electronics/boe/robot_motion/1.html
31) http://www.omega.com/prodinfo/stepper_motors.html
32) http://www.dension.com/product/wirc-wifi-rc-receiver
33) https://www.youtube.com/watch?v=myHoHxX0qXM&list=UU1uvDiinAjp_hxPeue033J
w
34) https://www.youtube.com/watch?v=xsJ7176fLNw
35) http://pocketnow.com/2014/03/21/tethering-methods
36) http://www.instructables.com/id/Connect-Arduino-Uno-to-Android-viaBluetooth/?ALLSTEPS
37) http://techcrunch.com/2013/11/16/the-state-of-the-art/
38) http://www.rishabhsoft.com/blog/5-advantages-of-android-app-development-for-yourbusiness
39) http://www.teazel.com/articles/which-platform-is-better-ios-vs-android/
40) http://www.kinvey.com/blog/2360/what-are-the-pros-and-cons-to-building-an-app-for-ios
41) http://arduinobasics.blogspot.com/2011/06/arduino-uno-photocell-sensing-light.html
42) http://42bots.com/tutorials/arduino-uno-and-the-jy-mcu-bluetooth-module-withsoftwareserial
43) http://arduino.cc/en/Main/arduinoBoardUno
44) http://arduino.cc/en/Main/arduinoBoardDue
45) http://arduino.cc/en/Main/arduinoBoardMega
46) http://www.ti.com/tool/SW-EKTM4C1294XL?keyMatch=Tiva%20C%20Series&tisearch=Search-EN#descriptionArea
47) http://www.ti.com/product/MSP430G2553
48) http://electronics.howstuffworks.com/microcontroller1.htm
49) http://www.circuitstoday.com/basics-of-microcontrollers
50) http://www.engineersgarage.com/microcontroller
51) https://www.youtube.com/watch?v=jKT4H0bstH8
52) https://www.sparkfun.com/products/11021
53) https://www.sparkfun.com/products/11589
54) http://en.wikipedia.org/wiki/Electronic_data_processing
55) http://www.webopedia.com/TERM/D/data_processing.html
56) http://www.cs.utsa.edu/~paulrad/opencloud/research-patrick.html
57) http://rock-robotics.org/stable/documentation/data_processing/
58) https://www.youtube.com/watch?v=50iFTcCsG_Y&list=PLE9E765B2D2701FF2
59) http://www.webopedia.com/TERM/C/clock_speed.html
60) http://www0.cs.ucl.ac.uk/teaching/B261/Slides/lecture2/tsld015.htm
61) http://www.electronics-tutorials.ws/waveforms/waveforms.html
62) http://ww1.microchip.com/downloads/en/DeviceDoc/ramrom.pdf
63) http://arduino.cc/en/Tutorial/Memory
64) http://www.arduino.cc/en/Reference/EEPROM
65) http://arduino.cc/en/Reference/EEPROMRead
66) http://arduino.cc/en/Reference/EEPROMWrite
67) http://www.rapidtables.com/electric/electric_power.htm
68) http://www.societyofrobots.com/battery_calculator.shtml
69) http://www.megabatteries.com/cat_featured_items.asp?cat1=24&cat=2&id=497&uid=17
50
96
96
72) http://www.ti.com/lsds/ti/analog/webench/overview.page?DCMP=PPC_Google_TI&k_cl
ickid=1ef70b61-a746-c489-f381-00004df8eb54
73) http://webench.ti.com/webench5/power/webench5.cgi?lang_chosen=en_US&VinMin=7.
4&VinMax=8.4&O1V=5&O1I=0.5&op_TA=30
74) http://www.adafruit.com/product/390
75) http://www.voltaicsystems.com/blog/estimating-battery-charge-time-from-solar/
76) http://www.researchgate.net/post/How_can_I_calculate_the_life_cycles_of_a_battery
77) http://www.rchelicopterfun.com/rc-lipo-batteries.html
78) http://www.powerstream.com/LLLF.htm
79) http://www.aladdinsolar.com/standalonediagram.html
80) http://physics.ucsd.edu/do-the-math/2012/07/my-modest-solar-setup/
81) https://faculty-web.msoe.edu/prust/arduino/
82) http://www.ieee.org/education_careers/education/standards/index.html
83) data.energizer.com/PDFs/522.pdf
84) http://en.wikipedia.org/wiki/AA_battery
85) http://en.wikipedia.org/wiki/USB
86) https://oshpark.com/guidelines
87) http://en.wikipedia.org/wiki/Printed_circuit_board
88) http://en.wikipedia.org/wiki/International_Electrotechnical_Commission
89) http://www.ohioelectricmotors.com/a-guide-to-motor-compliance-standards-835
90) https://www.nema.org/Standards/ComplimentaryDocuments/Contents%20and%20For
91) http://www.arduino.cc/en/main/policy
92) http://www.arduino.cc/en/Main/ArduinoBoardUno

Senior Design II Documentation

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