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 62

6)Appendix

Permissions

Datasheets

References

1

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 by-

products 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 pre-

existing 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.

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 semi-

autonomous 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

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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 1 $225

Patriot 3000mAh Power Bank 1 $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)

○ Hold biweekly meetings to check on progress (week 1-4)

● 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)

○ Hold biweekly meetings to check on progress (week 1-4)

● 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)

○ Hold biweekly meetings to check on progress (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

○ Hold biweekly meetings to check on progress (week 1-4)

● 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)

○ Hold biweekly meetings to check on progress (week 1-4)

● 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)

○ Hold biweekly meetings to check on progress (week 1-4)

● 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)

○ Hold biweekly meetings to check on progress (week 1-4)

○ 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

14

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,

15

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

16

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

17

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 thin-

film 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 non-

crystalline 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.

18

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].

19

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.

20

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

21

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

22

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.

Figure 2.6 (permissions requested)

23

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

24

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

m

$12.99

35495S HS-

5495BH HV

Digital Servo

6.4 kg-cm @

6.0V; 7.5 kg-

cm @ 7.4V

0.17 sec/60° @

6.0V; 0.15

sec/60° @ 7.4V

1.59 oz (44.5 g) advantagehobby.c

om

$27.99

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%

25

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.

Figure 2.7 (permissions requested)

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.

26

Name Length Axle

Diameter

Voltage Holding

Torque

Available Price

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

y 2.5 volts

5200 gram-

centimeters

vetco.net $19.95

JKM Nema 11

Mill Laser

Engraving

51mm 5mm 12V 1200g.cm bonanza.com $25.18

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

27

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 non-

rechargeable 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.

28

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 Nickel-

metal 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.

Figure 2.8 (permissions requested)

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

29

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

30

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,

31

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]

32

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.

33

● 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

34

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.

35

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.

36

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 add-

on

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.

37

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

38

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].

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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.

41

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

42

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

4400mAh Battery Pack

($32) [69]

3.7V

6 Amp

10 Amp

6 oz 2.6in x 1.5in x 0.7in

2600mAh Battery Pack

($40) [70]

7.4V

1-2 Amp

3 Amp (PCB)

3.5 oz 2.8in x 1.5in x 0.8in

2200mAh Battery Pack

($32) [70]

7.4V

1-2Amp

3 Amp (PCB)

3.5 oz 2.8in x 1.5in x 0.8in

2600mAh Battery Pack

($55) [71]

14.8V

2 Amp

4 Amp

6 oz 2.9in x 2.5in x 0.8in

2200mAh Battery Pack

[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.

43

Figure 2.12 DC/DC converter (Permission requested from TI) [72]

44

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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Figure 2.14 (permissions requested)

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.

46

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:

47

■ 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

○ Components dependent of:

■ Feedback System

■ Code

■ Mechanical System

○ 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 dependent of: None

○ 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

○ Components dependent of:

■ Code

■ Circuit Board

■ Light Sensors

○ Components that depend on Feedback System:

■ Panel Adjustment

■ Mechanical 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

○ Components dependent of:

■ Code

■ Connectivity

■ Feedback System

○ Components that depend on Mobile App:

■ Mechanical System

48

● Solar Panel

○ The solar panel will be used to charge and store energy in our main battery

○ Components dependent of:

■ Panel Adjustment

○ 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

○ Components dependent of:

■ Energy Storage

○ Components that depend on Car Battery:

■ Mechanical System

● 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

○ Components dependent of:

■ 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

49

○ Components dependent of: None

○ 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

51

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

53

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.

54

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

55

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

56

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

57

● 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.

58

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

59

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

60

● 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 Linear (7805)

Voltage (V) 3.3 4.8

Current (A) 1.355 0.88

Power (W) 4.47 4.223

Table 4.1

61

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

62

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

63

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

64

Figure 5.3 & 5.4 Solar Panel Charge Controller

Figure 5.5 & 5.6 Microprossesors

65

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

66

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 non-

contact 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

67

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.

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-of-

solar-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

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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

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nimh-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-via-

Bluetooth/?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-your-

business

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

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softwareserial

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-EK-

TM4C1294XL?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

70) http://www.megabatteries.com/cat_featured_items.asp?cat1=24&cat=2&id=206&uid=13

96

71) http://www.megabatteries.com/cat_featured_items.asp?cat1=24&cat=2&id=206&uid=13

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