CHARGE DU SOLEIL

University of Central Florida Senior Design I

Fall 2014

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

Estimate of Budget……………………………..…………………..………….4

Roles and Responsibilities…………………………..……………....….……5

Milestones……………………………………………….……………....……..6

2)Research and Background

Previous Works………………..……………………………………………...8

Solar Panels…………………………………………………………...……...10

Motors……….…………………………………….…………………………..19

Batteries……………………………………….……………………………....24

Mobile Device Applications………………………………………………….28

Electrical Components……………………………………………..………...30

Microcontroller……………………………………………………………....31

Data Processing………………………………………………….………...36

Clocking Requirements………………………………………….………...37

Memory Requirements…………………………………………….……...39

Wireless Tethering…………………………………………………...…….....40

Wifi (Background, Pros/Cons, Power usage).......................................40

Bluetooth (Background, Pros/Cons, Power usage)...............................41

Power Outputs………….……………………………………………………….42

Battery Comparisons………………………………………………………..42

DC/AC Inverter …….………………………………………………………..43

Charging……………………………………………………………………...45

Estimated Life Cycle………………………………………………………....46

Block Diagrams………………………………………………………………...46

General Block Diagram……………………………………………………..46

Software Class Diagram…..………………………………………………..49

3)Project Design

Physical Robot Mock­Up……………………………………………………….51

Microcontroller…………………………………………………………………..52

Prototype Construction and Coding…………………………………………...54

Data Input System………………………………………………………......53

Power Storage……………………………………………………………….54

PV cells to Battery…………………………………………………...58

Battery to Mobile Device…………………………………………....58

Mobile Device Remote Control Application……………………….….......58

4)Project Prototype Testing

Test Environment…………………………………………………………….60

Panel Adjustment Metrics…………………………………………..61

Software Metrics………………………………………………….....61

Mobile App…………………………………………………………...62

5)PCB Design and Assembly

Prototype PCB……………………………………………………………...63

6)Appendix

Permissions

Datasheets

References

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 it’s relatively infinite supply to power our many devices that use non­renewable forms of energy and also heat to buildings and structures. The problem with non­renewable 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 bio­matter process which takes hundreds of thousands of years. Photovoltaic solar panels have a history of being rather inefficient. Photovoltaic cells currently can convert only 22% of the sun’s energy into electrical energy [1]. This unfortunately means that a lot of surface area is necessary to generate adequate electricity. Apparently the concept of efficiency is relative because solar energy does not produce carbon by­products or the extraction, refinement, and transportation of coal. This has some effect towards evaluating its efficiency. This project is an attempt to further increase the efficiency of solar panel technology. This will be done through a 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 25­35% 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 counterposed by the gain in energy efficiency when compared to stationary panels. An optimization project will be difficult to accomplish because in a realistic scenario, no device or system will be completely optimal. In spite of this, the project aims to at least improve on pre­existing solar tracking systems while also integrating additional features as well. The principal criteria to consider it successful are the devices ability to automatically adjust the angle of the panels to track the sun in the sky, store the collected energy in a battery with the ability to discharge into an external electronic device through USB connection, monitor the capacity of the battery and display the percentage value through a mobile device application. This will be a very challenging task to accomplish due to the complexity of this project, but any new information obtained through the trial and error of the design will be viewed as a success.

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 is renewable, zero­emissions, no­noise 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 career­seeking 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 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:

Solar­powered semiautonomous vehicle with mobile device charging capabilities Sun­seeking vehicle with large, angle solar panel on top USB ports to connect and charge mobile device from solar­charged battery

Motor­controlled 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 20­30

meters) Mobile App with bluetooth capability to control the robot

1.4 Estimate of Budget

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 (Resistors,

Capacitors, etc)

$100 frame/ parts

$25 Arduino starter kit

1 frame

102 piece starter kit

$125

Feedback System Arduino add­on chip 1 $50

Wristband with Free wristband

GPS tracker (optional)

$50 tracker

1 $50

LCD screen(s) on car

(optional)

$25 1 $25

Possible LEDs on Car (optional)

$2 each 4 $8

DC­DC Converters $15 each 3 $45

Expected total cost: $800 1.5 Roles and Responsibilities As a group of three, we decided to break down all of the responsibilities for the completion of this project based off our individual skills as prospective engineers. Below are the list of roles and responsibilities that we each 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 1.6 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 1­2) Contact Duke Energy/Boeing about project (week 2­3) Receive necessary funding either or both companies (week 3­4) Begin researching various areas such as solar energy and autonomous

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

Oct 2014 Continue researching (week 1) Take soldering classes/ gain a mentor for project (week 1­4) Order first part, arduino circuit board, from supplier (week 1­2) Begin programming for basic autonomous portion (week 2­4) Hold biweekly meetings to check on progress (week 1­4)

Nov 2014 Begin ordering other parts like RC car kit / early assembly (week 1­4) Add to programming to incorporate sensors/remote connectivity (week 1­4) Meet and consult with sponsor (week 1­4) Continue with soldering classes/mentoring and expand on knowledge (week

1­4) If possible, begin ordering parts and building first prototype (week 3­4) Hold biweekly meetings to check on progress (week 1­4)

Dec 2014 Begin building first prototype; if necessary, go back and rework design (week

1­3) Rework all early problems (week 1­3) Have most/all parts ordered and planned to be assembled on prototype or

revised model (week 1­2) Complete all necessary research (week 1­3) Complete final Senior Design I paper (week 1­3) Hold biweekly meetings to check on progress (week 1­3)

Jan 2014

Continue building first prototype (week 1­4) Tentative deadline for first prototype complete: Jan 31, 2015 Continue working on programming on car, app, and tracker (week 1­4)

Possibly break up programs between members Hold biweekly meetings to check on progress (week 1­4)

Feb 2014 Test prototype and assess its ability in completing goals (week 1­2) Possible second prototype building process (week 2­4) Show progress to mentor/sponsor and receive feedback (week 3­4) Hold biweekly meetings to check on progress (week 1­4)

Mar 2014 Continue testing and analyzing second prototype (week 1­4) Final codes added (week 2­4) Rework all necessary issues; move on to third prototype (week 2­4) Hold biweekly meetings to check on progress (week 1­4)

Apr 2014 Third and final prototype complete (week 1) Debug all coding (week 2­4) Test all components. Check with a pass/fail chart. Rework/eliminate failed

components (week 2­4) Hold biweekly meetings to check on progress (week 1­4) All aspects of project to be completed by: April 24, 2015 Present project to peers/ board (week 4)

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 step­by­step instructions for many do­it­yourself 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 cut out into an X­shape 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 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 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 photoresistors 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 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 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 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 the it. 1

1 Figure 2.1 Annual solar Radiation in the United States. (reprinted due to public domain)

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 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, 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 blue­colored anti­reflective layer. This anti­reflective 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 non­crystalline 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 large­scale 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 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 car­sized, 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. 2

Monocrystalline Silicon ­ Monocrystalline silicon solar panels are unique because they use a

2

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 first­generation 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 remote­controlled 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 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 thin­film solar panels are so thinly sliced, they can be applied to almost any surface. Steel roof shingles can be replaced with thin­film photovoltaic material so that a home may collect significant solar energy in the daytime. This type of technology has a unique advantage in that it is still receptive to indirect sunlight. This means that even on a cloudy day, our solar tracker should still be able to generate enough power to charge the small electronic device. Another strong advantage is that thin film panels have a high resistance to heat. Heat can actually decrease efficiency of crystalline panels by 10% [15]. Most of these thin­film solar panel applications were non­solar tracking because the energy output was not enough to cover the development and operation costs. Tracking also produces a smoother output plateau around midday, allowing afternoon peaks to be met [15]. Amorphous silicon was the first type of thin film silicon developed. It is derived from the non­crystalline format of silicon as 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. 3

3 Figure 2.3 Light­sensitivity of Uni­Solar Triple Junction Technology

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 turn around [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 electron­volt. 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 no where near that of crystalline silicon solar cells which have a current maximum of 24.7% [18]. 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 it’s 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.

Solar Panel Specifications Price and Availability

Mono­crystalline 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 Thin­Film 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

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 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]. Cutting­edge 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

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 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 S­148 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)

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.

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 SM­S4306R 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 HS­5495BH 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 HS­5495BH HV servo will provide slightly more torque than the SM­S4306R and over twice the torque of the Futaba S148. At the full 7.4 volts, it will provide 7.5 kg­cm 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 SM­S4306R 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 as day.

Name Torque Speed Weight Available Price

Futaba S148 2.7 kg­cm/38 oz­in at 6 V

50 RPM (with no load) @ 6V

43 g/1.5 oz with servo horn and screw

newegg.com $14.95

SpringRC SM­S4306R

6.2 kg­cm (86.25 oz­in)

55 RPM @ 6V

41g (1.45oz) bananarobotics.com

$12.99

35495S HS­5495BH HV Digital Servo

6.4 kg­cm @ 6.0V; 7.5 kg­cm @ 7.4V

0.17 sec/60° @ 6.0V; 0.15 sec/60° @ 7.4V

1.59 oz (44.5 g)

advantagehobby.com

$27.99

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 a 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 it’s 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 non­cumulative, 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 a 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% 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 kg­cm. This is greater than that provided by the Nema 17 (2.8 kg­cm) and the Nema 11 (1.2 kg­cm). 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.

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 approximately 2.5 volts

5200 gram­centimeters

vetco.net $19.95

JKM Nema 11

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

$25.18

Mill Laser Engraving

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 carbon­zinc 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 long­term battery life allows. Up until the turn of the millenium, 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, nickel­cadmium, nickel­metal hydride, lithium­ion, and lead­acid. Rechargeable Alkaline ­ Although it has the shortest shelf­life 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 current­draw devices will simply not benefit from using 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 current­draw 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 current­draw 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 current­draw 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. Nickel­Cadmium ­ Whereas rechargeable alkaline batteries are best suited for moderate power applications, secondary Ni­Cd 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 self­discharge 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 equipments 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 non­linear and thus less predictable. The voltage found on the cell remains at 1.2V until the battery is “discharged”. The output remains 1.2V whether at 30% 40% 50% or 60% of its charge. A traditional non­rechargeable 1.5V battery will provide only 0.75V when it is at 50% charge. This makes this type of battery easy to monitor by using a voltmeter. With NiCd batteries, it is nearly impossible to distinguish if it is fully or partially charged just because the output remains at 1.2V regardless. One of the goals of this project is to monitor the battery life of the battery so that we can see how it is distributing the energy we collected. The main issue with this type of battery is that it will lose about 1% charge per day when not in use [25]. This means that if the battery is idle for a month, it will lose 30% of its original charge. Within three months, the battery is completely depleted and will be permanently damaged. Although the long term life of the battery is not a priority in terms of this project, it would be desired. In addition to this, monitoring the battery status accurately is a major objective and would be very useful to know how effective it is as a whole.

Nickel­Metal Hydride ­ Secondary NiMH batteries are built off of the same basic concepts of the secondary Ni­Cd batteries. They are similar enough to where they will provide the same voltage as Ni­Cd batteries with 30% more capacity [23]. The temperature range is comparable to them as well. Unfortunately, along with the improved capacity comes a higher self­discharge rate of 40%. This means that the battery has an even lower run time per charge. Luckily, Nickel­metal 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 Li­Ion 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 self­discharge rate, 20% is much lower than other types of secondary batteries which makes it highly desirable to charging a cell phone or tablet. Lithium Ion batteries are notorious for being disastrous under extreme temperature situations. If exposed to prolonged heat, these cells may combust resulting in a fire. Like Nickel­metal hydride batteries, they must also be recycled for their high nickel oxide and cobalt content. One corporation who relies on the success of lithium ion technology is Apple. They claim that Lithium­ion 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 lithium­ion batter will allow this device to be used ust 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 an remote­controlled 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 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 self­discharge 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 self­discharge 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 (permissions requested)

2.5 Mobile Device Applications Initially, one of the decision we were faced with was deciding whether to have the robot to be fully autonomous or semi­autonomous. We made the decision to have the robot be a semi­autonomous 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 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, we were tasked between choosing to have the app be Android based or 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, royalty­free, and the best

technology framework offered by the Android community. The architecture of the Android SDK is open­source 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 state­of­the­art 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, 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]

Objective­C (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 exception­handling 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 non­iOS devices or market growth of non­iOS 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 Objective­C lurk the Lovecraftian horrors of 1970s programming. [37]

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. 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 on­screen.

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 can not 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, Read­Only 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 semi­autonomous 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

Figure 2.10 : Basic Design of a Microcontroller [50] (permissions requested) Comparison of Microcontrollers ­ The table below lists the basic features of five microcontroller boards: The arduinos 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.

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, AC­DC 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, AC­DC 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, AC­DC 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

1 MB

4 20

USB 2.0, 2 CAN

User

Tiva C1294 [46]

4.8in x 2.2in

Flash 256kB RAM

pin and 40 pin

add­on parts

32 bit 120 MHz modules QSSI, I2C,

Ethernet

switch,

reset, 4

UART

Recommended Voltage and Current Values [43­47] ­ 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 our purposes would be one that required the least amount of power to work since we will be relying heavily upon solar energy. One of our main goals is to use energy as efficiently as possible, therefore, having an extremely low­powered microcontroller will aide in that goal.

Board Name

Operating Voltage

Input Voltage

Input Voltage limits

DC current per I/O Pin

DC current for 3.3 V Pin

Arduino Uno 5V 7­12V 6­20V 40mA 50mA

Arduino Due 3.3V 7­12V 6­16V 130mA 800mA

Arduino Mega 5V 7­12V 6­20V 40 mA 50 mA

MSP 430G2553 3.6V 2­3V 1.8 ­ 3.6V 20mA 40mA

Tiva C1294 5V 6­12V 4­18V 100mA 600mA

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.

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 is 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.

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 didn’t chose it [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 our 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.

Figure 2.11 : Arduino Uno (Left picture ­ Front side, Right Picture ­ Back side) [52,53]

(permissions requested)

Figure 2.12 : Arduino Uno Schematic Design (Permission requested from Arduino Trademark)

[43]

Figure 2.13 : Arduino Uno Board (simplified) (permissions requested)

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 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 less­than­acceptable 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 said 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.

Figure 2.14: Clock Diagram [61] (permissions requested)

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. 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 our purposes. 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 our 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 our 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 non­volatile 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 our coding expectations. We do not expect to make any complex codes, therefore the 27 kilobytes will work for our needs. 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. Read Template [65] Write Template [66] #include <EEPROM.h> #include <EEPROM.h> int a = 0; void setup() int value; for (int i =0; i,255; i++) void setup() EEPROM.write (i, i); Serial.begin(9600); void loop () void loop() value = EEPROM.read(a); Serial.print(a); Serial.print("\t");

Serial.print(value); Serial.println(); a = a + 1; if (a == 512) a = 0; delay(500); 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]. 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 remote­controlled 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 connected 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 re­charging it, using the solar tracker and it’s 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 real­time 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, pre­existing 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>Wi­Fi you simply choose Dension WiRC. Once you tap the application icon, the interface will appear. Shown on this interface is the real­time 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. 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 pre­existing 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 built­in 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. Its 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 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 our budget.

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

7.4V

1­2 Amp 3 Amp (PCB)

3.5 oz 2.8in x 1.5in x 0.8in

($40) [70]

2200mAh Battery Pack ($32) [70]

7.4V

1­2Amp 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

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]. 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.

Figure 2.15 : DC/DC converter (Permission requested from TI) [72]

Figure 2.16 : 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

Figure 2.17 (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, we can safely assume that our battery will last between two and four hours, give or take different, harsher conditions.

Voltage and Current relation on a 4.2 Volt Battery

Figure 2.18 (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:

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

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

Components dependent of: None Components that depend on Car Model: None

Below is a physical representation of the block diagram showing the dependencies of all the diagrams.

Figure 2.19

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 2.20

3) Project Design 3.1 Physical Robot Mock Up

Figure 3.1

Figure 3.2

The physical mock up 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, solar panel and PCB location). The PCB and microcontroller will be 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 3­5 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 JY­MRC 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 Figure 3.3 below shows how the connection would be made physically.

Figure 3.3 (permission requested)

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. Below is Figure 3.4 showing the physical connection of the photocells with the microcontroller.

Figure 3.4 (permission requested)

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.

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. The 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 shock­resistant. 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 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 most heavy 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 4­Port 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 4­Port Hub can be purchased directly from the manufacturer at Toshiba.com for only $11.99. This device features plug­and­play 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.

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

Below is a diagram detailing how the process of integrating the regulator, USB hub, PowerBank and solar panel together.

Figure 3.5

Figure shows more detailing of the integration between the solar panel, voltage regulator and powerbank.

Figure 3.6

3.3.2.1 PV Cells to Battery The Figure 3.7 below shows how a stand alone 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 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 stand­alone 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 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 3.7 (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 self­sustaining, 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 JY­MRC class 2 Bluetooth Module (slave). The JY­MRC 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 at a time, Master­Master and Slave­Slave 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 JY­MRC module and the 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 mock up of the application layout detailing the description above.

Figure 3.8

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 be come lit.

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, light­weight covering to be designed and built Possible further research into wheels and car maneuverability improvements Analyze extent of affected parts and search for solution

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

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 is 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

5) Printed Circuit Board Design and Assembly 5.1 PCB Prototype Parts 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 Off­Grid systems [79]

Shown in the figures below are more descriptive forms of the Arduino Uno board.

Figure 5.2 (Permission requested)

Figure 5.3 (Permission requested)

Figure 5.4 (Permission requested)

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/solar­energy/advantages­and­disadvantages­of­solar­energy/

2) http://www.greenenergychoice.com/green­guide/fossil­fuels.html 3) http://www.solarika.org/blog/­/blogs/10­best­things­about­solar­energy 4) http://www.instructables.com/id/Arduino­Solar­Tracking­Robot/?ALLSTEPS 5) http://www.instructables.com/id/Solar­phone­charging­system­featuring­sun­tracking/ 6) https://www.youtube.com/watch?v=ATnnMFO60y8 7) https://www.youtube.com/watch?v=lrP0XZaKwOo 8) http://planetfacts.org/what­is­solar­radiation/ 9) http://www.windows2universe.org/earth/climate/sun_radiation_at_earth.html 10) http://www.pveducation.org/pvcdrom/properties­of­sunlight/motion­of­sun 11) http://www.livescience.com/41995­how­do­solar­panels­work.html 12) http://www.evoenergy.co.uk/solar­panels/our­technology/pv­cell­comparison/ 13) http://www.solar­facts­and­advice.com/monocrystalline.html 14) http://www.solar­facts­and­advice.com/polycrystalline.html 15) http://www.solar­facts­and­advice.com/thin­film.html 16) http://www.solar­facts­and­advice.com/amorphous­silicon.html 17) http://www.solar­facts­and­advice.com/cadmium­telluride.html 18) http://www.solar­facts­and­advice.com/CIGS­solar­cell.html 19) http://www.beneq.com/transparent­conductive­oxide­tco.html

20) http://www.solar­facts­and­advice.com/solar­panel­temperature.html 21) http://www.solarpower2day.net/solar­cells/efficiency/ 22) http://depts.washington.edu/matseed/batteries/MSE/classification.html 23) http://mechanicalmania.blogspot.com/2011/07/types­of­battery.html 24) http://lenpenzo.com/blog/id710­why­rechargeable­batteries­are­rarely­cost­effective.ht

ml 25) http://www.hardwaresecrets.com/article/The­Truth­About­NiCd­Batteries/292/1 26) http://www.batterystuff.com/kb/articles/battery­articles/proper­care­and­feeding­of­a­ni

mh­battery.html 27) https://www.apple.com/batteries/why­lithium­ion/ 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/wirc­wifi­rc­receiver 33) https://www.youtube.com/watch?v=myHoHxX0qXM&list=UU1uvDiinAjp_hxPeue033Jw 34) https://www.youtube.com/watch?v=xsJ7176fLNw 35) http://pocketnow.com/2014/03/21/tethering­methods 36) http://www.instructables.com/id/Connect­Arduino­Uno­to­Android­via­Bluetooth/?ALLS

TEPS 37) http://techcrunch.com/2013/11/16/the­state­of­the­art/ 38) http://www.rishabhsoft.com/blog/5­advantages­of­android­app­development­for­your­b

usiness 39) http://www.teazel.com/articles/which­platform­is­better­ios­vs­android/ 40) http://www.kinvey.com/blog/2360/what­are­the­pros­and­cons­to­building­an­app­for­io

s 41) http://arduinobasics.blogspot.com/2011/06/arduino­uno­photocell­sensing­light.html 42) http://42bots.com/tutorials/arduino­uno­and­the­jy­mcu­bluetooth­module­with­software

serial 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/SW­EK­TM4C1294XL?keyMatch=Tiva%20C%20Series&ti

search=Search­EN#descriptionArea 47)http://www.ti.com/product/MSP430G2553 48)http://electronics.howstuffworks.com/microcontroller1.htm 49)http://www.circuitstoday.com/basics­of­microcontrollers 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

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750 70) http://www.megabatteries.com/cat_featured_items.asp?cat1=24&cat=2&id=206&uid=1

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396 72) http://www.ti.com/lsds/ti/analog/webench/overview.page?DCMP=PPC_Google_TI&k_c

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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/estimating­battery­charge­time­from­solar/ 76) http://www.researchgate.net/post/How_can_I_calculate_the_life_cycles_of_a_battery 77) http://www.rchelicopterfun.com/rc­lipo­batteries.html 78) http://www.powerstream.com/LLLF.htm 79) http://www.aladdinsolar.com/standalonediagram.html 80) http://physics.ucsd.edu/do­the­math/2012/07/my­modest­solar­setup/ 81) https://faculty­web.msoe.edu/prust/arduino/