-Optimized Cart (SPOC)

Senior Design Project Documentation

Due: April 28, 2014

Group #28 Members:

Jacob Bitterman

Cameron Boozarjomehri

William Ellett

SPOC Table of contents 1. Executive Summary1

2. Project Description 2 2.1. Motivation and Goals…………………………………………………………….2 2.2. Goals……………………………………………………………………………...3 2.3. Objectives………………………………………………………………………...4 2.4. Project Requirements and Specifications……………………………………..6. 2.5. Limitations………………………………………………………………………..7

3. Research related to Project Definition 10 3.1. Existing Similar Projects and Products………………………………………1. 0 3.1.1. SEV (Solar Electric Vehicles)...... 1..0.. .. 3.1.2. Tindo Solar ………………………………………………………...12 3.1.3. NUMA 7…………………………………………………………………13 3.1.4. UCF ZENN……………………………………………………………...14 3.1.5. EVOENERGY SOFLEX 600………………………………………….15 3.1.6. Star EV…………………………………………………………………. 16 3.2. Relevant Technologies…………………………………………………………17 3.2.1. Tesla Motors Rapid Battery Charging………………………………..1. 7 3.2.2. Grape Solar……………………………………………………………..19 3.2.3. Electric Energy and Power Consumption by Light­Duty Plug­In Electric Vehicles………………………………………………………..20 3.2.4. Battery Requirements for Plug­In Hybrid Electric Vehicles – Analysis and Rationale…………………………………………………………...19 3.2.5. Designing a High­Efficiency Solar Power …………21 3.2.6. Choosing a Microcontroller……………………………………………2. 2 3.2.7. Bluetooth Vehicle integration Components………………………….2. 3 3.2.8. Additional Bluetooth component considerations…………………….2.5 3.2.9. I2C and the Atmega328P­PU…………………………………………26

3.3. Strategic Components…………………………………………………………27 3.3.1. Cart……………………………………………………………………... 28 3.3.2. Atmega328P­PU……………………………………………………….31 3.3.3. User Interface…………………………………………………………...33 3.3.4. T105­H Signature Line Flooded Deep Cycle 6V Battery…………..3. 4 3.3.5. Solar Array……………………………………………………………...36 3.4. Possible Architectures and Related Diagrams………………………………39 3.4.1. Solar Array Architecture……………………………………………….3. 9 3.4.2. Motor, Battery, Micro Controller Integration…………………………4..0

3.4.3. User Interface Layout…………………………………………………..4.5

4. Project Hardware and Software Design Details 47 4.1. Initial Design Architecture and Related Diagrams…………………………..4.7 4.1.1. Photovoltaic Optimization……………………………………………...47 4.1.2. Drive Circuit……………………………………………………………..47 4.1.3. User Interface…………………………………………………………...48 4.2. Solar Array………………………………………………………………………48 4.3. Cart……………………………………………………………………………... 50 4.4. Power Control Subsystem…………………………………………………….51 4.5. User Interface Subsystem……………………………………………………..52 4.5.1. Hardware Components………………………………………………..52 4.5.2. Stretch Goals…………………………………………………………...54

5. Design Summary of Hardware and Software 56 5.1. Charge System……………………………………………………..56 5.1.1. Buck Converter…………………………………………………………57 5.1.2. Maximum Power Point Tracking (MPPT)...... 5..8.. . 5.1.3. Panel Mounting and Adjustment………………………………………6.0 5.2. Battery Motor Integration………………………………………………………6. 3 5.3. Sensor Integration………………………………………………………………65 5.3.1. Photodetectors………………………………………………………….66 5.3.2. Thermistors……………………………………………………………...67 5.4. User Interface…………………………………………………………………...67 5.5. Microcontroller…………………………………………………………………..70 5.6. Vehicle Modeling……………………………………………………………….72 5.6.1. Normal Mode……………………………………………………………72 5.6.2. Performance Mode……………………………………………………..72 5.6.3. Eco Mode……………………………………………………………….73 5.6.4. Safety Measures………………………………………………………..73

6. Part Acquisition and Bill of Materials 75

7. Project Prototype Testing 77 7.1. Hardware Test Environment…………………………………………………..7. 7 7.1.1. Location…………………………………………………………………77 7.1.2. Ground Environment……………………………………………………77 7.1.3. Weather Conditions…………………………………………………….78 7.2. Hardware Specific Testing…………………………………………………….79

7.2.1. Testing…………………………………………………….80 7.2.2. Electric cart Testing…………………………………………………….81 7.2.3. Battery Testing………………………………………………………….81 7.2.4. Microcontroller Testing…………………………………………………81 7.2.5. Component performance Table……………………………………….82 7.2.6. Prototype testing………………………………………………………..82 7.3. Software Test Environment……………………………………………………8.3 7.4. Software Specific Testing……………………………………………………...84

8. Administrative Content 87 8.1. Milestone Discussion…………………………………………………………..87 8.1.1. Phase 1………………………………………………………………….87 8.1.2. Phase 2………………………………………………………………….88 8.1.3. Phase 3………………………………………………………………….88 8.1.4. Phase 4………………………………………………………………….88 8.1.5. Phase 5………………………………………………………………….89 8.1.6. Phase Calendar………………………………………………………...89 8.2. Budget and Finance Discussion………………………………………………90 8.2.1. Outside Funding………………………………………………………..90 8.2.2. Personal thanks to Duke………………………………………………9. 0

Appendices Appendix A­ Bibliography 92 Appendix B­ Initial PCB Schematic 96 Appendix C­ Initial PCB Board Layout 97

1. Executive Summary

This project sprang out of a desire to create an electrically powered, cheap, efficient, and clean method of transportation for use over short to moderate distances. Many products currently exist that achieve the goal of electric transportation, but comparatively few of these use to dynamically charge while driving. As a result the project proposed had solar panels mounted both on top, and to the rear of the cart such that the panels could work in conjunction with the batteries to both charge and drive the vehicle. In addition, the vehicle did not need to be plugged in reducing the strain electric technologies place on metropolitan power grids.

The primary objective of this project was the creation of a solar-assisted electric cart capable of recharging its own batteries via the sun’s rays. This objective included several secondary objectives that were dependent partially on efficient use of funds. The clearest method of evaluating the completion of the primary objective was by the vehicles ability to charge while driving, and to compare its performance to its none solar counterparts. Elements such as range were affected by a number of other attributes, such as , electrical system design, multi-mode operation, as well as the quality of the parts in used for the projects construction.

Designing and building a vehicle like this had a powerful impact on the way American consumers traveled between locations in urban and suburban settings; particularly in large cities or other close-packed communities. The large majority of commuters use fossil fuel driven vehicles of disproportionate sizes to traverse short distances, where the vehicles would then sit in wait while in disuse. The project intended to counter this imbalance by providing a smaller, more maneuverable vehicle that would spend the time it was not in use collecting energy. The solar cells would allow for charging without the cost of additional infrastructure, appealing to both consumers and communities alike.

However this dynamic design for charging such a vehicle proved to be a complicated proposal. It became necessary to set specific milestones to ensure continuous progress throughout the course of the project. Each stage on the project timeline is discussed in greater detail in Section 8. These stages were individually significant while keeping the scope of the project in focus. Primary goals were that this project achieve: environmental sustainability, market feasibility for a maximum number of viable consumers, power optimization for increased range, and financial minimization to stay within our desired budget.

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2. Project Description

This section goes about explaining what the primary focus of many of our project elements were. It also further tied in what motivated us to approach the project in this manner. Primary concerns for this section included how to distinguish our project from its non-solar counter parts. We also emphasize that this project, while still a proof of concept, is laying the groundwork for what could be a revolution in human transport in urban areas.

2.1 Motivation

Our team has desired to confront a series of problems common to cities across the globe. For centuries, cities have struggled with pollution from fossil fuel driven technologies. Since the invention of the internal combustion engine, global urban air environments have grown thick, dirty, and unhealthy. Gasoline-based engines still exist as our primary source of transportation. The development of electric cars has come a long way, and ideally will be the key to not only more efficient, but all around better human transportation. However current electric vehicles indirectly depend on fossil fuels to charge. The potential to take these vehicles off of the city grid, and integrate them with solar technology would both reduce the load on city grids, and improve vehicle performance by carrying their fuel source with them.

Transportation in America has become terribly inefficient, specifically within densely populated regions. Americans live with privilege and prosperity, but this has created unnecessary issues in our transportation systems. We transport 100 people within a city in a little less than 100 cars, trucks, or vans. The design of our streets and the dense population of the city does not allow for this ratio of people to cars. There are two obvious solutions: maximize the number of people per vehicle or minimize the “footprint” of the personal transportation. The advantage of this second solution relates to the individual autonomy of private transport that Americans strongly cling to. Our team decided to approach the issue of inefficient inner city transport from this “small vehicle” approach.

Lastly, the rising cost of fuel has placed financial pressure on individuals to turn- away from the “traditional” gasoline-fed car. This financial pressure is a game- changing motivation for our country and our world to seek new solutions. Our team sought to address these issues and provide a feasible alternative for the cities of the world. Our whole approach to the following design was to create a personal transport that will drastically reduce pollution, alleviate common inner- city gridlock, and pull us away from our dependence on foreign non-renewable resources. We desired to leave this world better than we found it for future generations to enjoy.

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2.2 Goals

To the above stated issues and problems, our design reached out to provide solutions that are feasible and affordable to many. We sought to harness the energy of alternative and renewable resources while responsibly optimizing the use of that power for specific applications. An environmentally conscious and user compatible Solar Power Optimized Cart (SPOC) seemed obvious due to the solutions it provided to this inefficient and transportation centric world.

Even with its current limitations, solar energy is a very strong answer to several problems facing America at the moment. Solar energy is accessible to all and functional in so many applications. Solar-powered components are incomparably cleaner than their gasoline-powered counterparts, reducing the dangerous effects of exhaust, carbon monoxide, and hydrocarbon-based pollution. Solar power is cheap and obviously renewable, whereas gasoline has become cripplingly expensive and hard to acquire with domestic regulation and foreign conflict in the Middle East. Although solar tech has struggles to provide adequate power for larger transportation vehicles, there are many smaller scale applications, which naturally fits with a cart-sized platform.

Using a cart-sized platform provided transportation at a fraction of the footprint of modern sedans. Cutting the size of the vehicle will maximize traffic flow and power usage from the cart’s batteries and solar cell arrays. Retaining the autonomy of a personal transport while maximizing the efficient use of space on the roadways. With inner-city transport, most of the distances covered are less than 5 miles. A solar-powered cart could provide the necessary transportation with minimized traffic. Our design sought to provide a simple and maintenance- minimized vehicle for the busy commuter. Whereas current electric vehicles need frequent recharging, our designed SPOC could be sustained with solar energy for most short distance inner-city commuting. Most electric cars are too expensive for the average consumer; our condensed and simplistic model SPOC proved inexpensive to purchase and maintain for most potential users.

Our designs sought to meet several goals: sustainability, market feasibility, power optimization, and finance minimization. The SPOC of the future will drive quietly and require minimal cost or maintenance. It will be pollution free and run on clean solar energy. Efficient sizing will allow for a better flow of traffic in our cities across the globe. Simple designs allow for reasonable pricing and a larger customer base. An environmentally conscious and user compatible Solar Power Optimized Cart (SPOC) offers positive answers to questions that need answering in our commuter-focused transportation world. While our project was a mere prototype it was also a substantial proof of concept for a shift in the paradigm of urban transportation.

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2.3 Objectives

We had a wide range of objectives, so that we can most effectively meet the needs of the user. Our primary goal was obviously solar power, specifically our project could not be charged by any means that other than solar energy. We specifically sought solar powered design that optimizes energy efficiency, vehicle range, velocity, capacity, size, charge time, intuitive user interfacing, dependability, & safety while at a reasonably low cost.

Beyond the solar energy itself, our design focused on the power interface to efficiently optimize the energy of the photovoltaic cells and the stored power in the cart batteries. We designed the battery bank to be charged whenever there was solar power available, and to dynamically choose the best method with which to charge the on board batteries and/or power the motor. By focusing on purchasing the best photovoltaic cells within our financial budget, we were able to acquire components with significant output while doubling as the vehicles structural reinforcement.

The range optimization of the SPOC was the easiest measure by which to judge our projects performance when compared to its non-solar counterparts. We looked for ways to substantially increase the range of the electric cart while going through our design process. We sought to maximize the time that the cart could be in use in various discharge modes based on the different ways we could configure the dissipation of power form our panels. Using the solar cells and power optimization, the electric cart was able to travel much further than previously designed. However the vehicles performance suffer somewhat in terms of its ability to quickly accelerate and decelerate as a result of the amount of power that could be distributed by each panel throughout the system.

While the range of the cart was our main focus, we did consider the potential for users that wanted to get the most power for their performance. In an effort to appeal to the speed enthusiast our project allowed for a variant where we poured as much power into the motor as possible while keeping components within their physical tolerances. Our design maintained safe standards of maximum velocity and acceleration considering those physical limitations. We hoped to maintain the industry speed standard for electric carts between 15-25 miles per hour in terms of top speed, however some of the vehicles drive modes did not reach this goal considering the emphasis on range.

The less a vehicle weighs, the better its performance in terms of power and acceleration. To this end we looked to minimize vehicle weight while incorporating our additions to the vehicle. Our team even went so far as to improve the carrying capacity of the vehicle while modifying it with these hardware additions. The ability to properly transport large loads, pending the user’s needs, was part of our appeal to the common person who would ideally use our product to transport both people and goods. As a result we attempted to

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stay as close to if not increase the vehicle load limit while we made our modifications.

Additionally we were concerned with the overall dimensions of the vehicle. That being said we were able to keep the vehicles physical dimensions to no greater than that of a standard golf cart. By limiting our size and weight we also improve the effectiveness of our vehicles components in being able to move and maneuver the vehicle. The minimalist design naturally decreased the overall weight which was reflected in the increase in range.

Quicker charging times allowed the cart to continue functioning even when battery levels began to drain. The best way to go about this was to ensure that the vehicle never needed to stop to charge but instead charged while in motion. By designing drive modes that used the solar cells to power the motor in conjunction with a battery, or charge the batteries themselves, our design made it such that the user would almost never be left without a useable motor. The only limitation to our parallel/dynamic charge system was the weather itself, since Solar cells work best in the presence of the sun. However our design yielded additional improvements in that even in low light, the potential to “trickle charge” our Lead Acid batteries would actually improve their longevity.

User compatibility was our final primary concern for this project. All of our design features were designed to be customizable by the user. The cart user was able to control the distribution of power in a simple format, while relaying useful information about the vehicle back to the user. The user interface itself was both simple and intuitive; the user would have access to a simple 16x2 character screen that would display the current battery charge, data on the solar panels, vehicle component status, and the vehicles current drive mode. The cart user would then be able to adjust the mode to optimize range or speed based on various factors.

Our design had included the use of a global positioning subunit to use with the power optimization and user interface subsystems of the SPOC. The GPS functionality of the cart would allow the user to optimize cart and panel positioning such that the user could get the best angle for charging the cart when stationary.

Finally the cart had to be able to operate safely at all times. The speed of the SPOC was limited to not exceed the given limits of its specified model. The power interface systems would be designed to prevent dangerous power use of the batteries. And as always, the electrical components had to include safeguards to prevent damaging electrical fires. After the creation of a prototype, the cart would be subject to moderate testing to ensure its safety. With a uniquely designed electrical system, our first concern would be with electrical shorts and temperature control.

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Working on a tight college budget with limited outside sponsorship from Duke Energy our project was able to meet several of these objectives, particularly in temrs of the drive mode. Our team would attempt to implement our design while minimizing the cost to us and to our possible consumers since we intended for a commercial market. We bought the best possible parts and materials for our design, while staying within our budget. While this did limit the technological level of the design, it also means that our design would be far more feasible to produce in a cost effective manner. In a real world scenario, a cheaper product to produce and design is usually a better product to market to customers

2.4 Project Requirements and Specifications

Our intended design for the Solar Power Optimized Cart was required to meet a number of specifications. These specifications defined the purpose and detailed goals of the designed cart. Range specifications were the core of the design, since the purpose of any transport is the range it can travel for its occupant. Specific speed goals were also a must, as most commuters demand a reasonable speed of travel to arrive at their destination with punctuality. Although the cart design was smaller than intended, a multi-person carrying capacity could still be implemented using the current design. Charge time was a focus to increase the feasible use of the cart throughout the course of any day for the various needs of the user. Cost goals were to optimize the efficient use of our own funds as well as providing a quality product to a larger consumer base with a lower retail value.

In table 1 below there are several points made for the desired, quantifiable goals of this project. First and foremost is range, the range described in table one is typical of most modern golf carts and similar . The end goal being to exceed this distance when possible. The most likely means was by the dynamic drive settings. Additionally the target charge time was a real desirable feature. Common vehicles such as these carts can charge in just a little over this time using a conventional wall outlet. To beat this using solar technology required very high level design in ensuring that the solar tech was capable of charging at a rate that would be considered realistic for such a vehicle. Finally the project had to meet its budgetary requirements to ensure that funding was kept within reasonable bounds. In this way the project was expected to be expensive but to an extent.

Vehicle dimension goals must maintain the spatial convenience and stability of the average cart platform. Optimal vehicle length minimized the space taken on the roads and in tight inner city parking places. Vehicle width was the primary factor in the stability of the cart design, while the vehicle height was also factored into the stability and aesthetics of the design. Vehicle weight was extremely important as we attempted to maximize the range and speed of the SPOC. Excess weight would put extra strain on the carts structural components while

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effecting the electronics and battery reserves, lowering our maximum possible range and speed of the final design.

Table 1: Desirable characteristics

Characteristic Required Minimum

Range 25 miles

Speed 10 miles per hour

Capacity 2 people

Charge Time 6 hours (in full sunlight)

Cost $2500.00

Vehicle Length 72’’

Vehicle Width 48’’

Vehicle Height 66’’

Vehicle Weight 800 lbs

2.5 Limitations

The design for the Solar Power Optimized Cart (SPOC) had many goal design specifications that factored into our intended design for our final project implementation. Limiting our ability to easily reach those goals were a number of limitations to our design. The defining specification of the final design of the SPOC was its range which was limited by our energy efficiency. The solar cells were only able to return so much power to the batteries, while the energy draw from the electric motors powering the vehicle was also minimizing the range of the electric cart over time.

The main factor minimizing the speed of our vehicle was the desire to maximize the range. Increased speed would equal increased drain on the batteries, so the speed of the cart was optimized to maximize the traveling speed and range. The capacity, size, and weight of the project were limited by the power supply and output of the batteries and , respectively. We needed a practical design to fulfill the needs of an average inner city commuter while maximizing the efficient use of the energy stored in the batteries and drawn by the solar cell array. Cost was the most obvious limiter that would prevent the acquisition of some “high-end” parts, but resulted in a financially feasible product for a large number of consumers.

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In table 2 below primary limitations and requirements of the project were reviewed to determine how they effected the project and could be overcome. These primary points of concern included but were not limited to: range, speed, capacity, cost, and the vehicle size and weight profiles. While these characteristics were explained in more specific detail in later sections, the primary take away is that the design was to be as sophisticated as possible considering its many limitations. Though limited in its cost it had to exceed the speed limitations a normal cart of its type might experience. In the case of speed, that actual quantifier was acceleration, the vehicles ability to accelerate was solely a factor of energy dissipation where as speed was physically limited by the design of the motor itself.

Table 2: table of goals versus limitations

Goal Characteristic Limitations

Range Our range was limited by the energy output of the photovoltaic cells and the energy intake of the electric motors. Weather was also a specific limiter of our desired efficiency.

Speed To maximize our range, the cart’s speed was limited by factors determined by the user when selecting form the different drive modes. Faster speeds limited battery life. Safety also limited the maximum allowed speed.

Capacity The solar array was only able to keep up with a limited draw on the battery reserves. Our maximum carrying capacity was determined by the power supplied by the batteries and solar cells.

Cost With limited sponsorship and personal assets, we sought to design our project with responsible financial expectations and limitations. This meant that future implementations would have greater room for improvement as technology improved.

Size & Weight We were limited by the standard size and weight dimensions of electric carts. Our additional design modifications added little additional weight while still providing the required mobility.

Finally the design of the vehicle had to meet the standards set by urban transportation vehicles with a two person capacity rated for these consistently short distance. Some additional characteristics that are not shown here will be explained where appropriate but the table provides the best representation of our projects primary components. Over all the vehicles integration does become a factor of time since the project is over a 16 week course, but accounting for

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errors the majority of the components associated with it which could take a significant time to acquire. This was also a brief glimpse in to what was another wise extremely complex project with many unexpected components used to implement its high level design. The most surprising part was the unexpected amount of electrical engineering that is reflected in the dynamic charging that makes this project entirely possible.

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3. Research related to Project Definition

Our current project is best considered an electric, solar powered, human transport. The focus being that it is a vehicle that receives all its via photovoltaic cells, and has been optimized for maximum electrical performance. The reason for this designation was to establish that the end product was not a common such as a Fisker, Tesla, or Chevy Volt. Instead this was an innovation in transportations technology that required absolutely nothing from a city grid to be able to move.

Though the intended goal was to produce a four-wheeled vehicle, our design required certain new approaches that do not fit the design of conventional electric vehicles. For instance, in a commercial grade electric people carrier recharging is handled via a standard 120 to 240 volt outlet, and produces a regulated and constant flow of electricity. For our design we had to consider photovoltaic cells that would act in a similar manner at peak efficiency but still provide high output in low efficiency situations, while maintaining a steady flow of energy. In addition our design could not follow the same convention for battery charging due to these fluctuations so we had to explore different designs for energy transfer under fluctuating input. Finally we had to set a baseline for beating that existed within current technologies. For this we chose UCF’s own purely , which we then explored in depth.

3.1 Existing Similar Projects and Products

This section focuses on projects and products that are currently on the market. The majority of these are vehicles that follow our model of a strictly solar powered electric vehicle meant to be driven in suburban/urban areas. We also looked at existing technologies pertaining to our components such as Photovoltaic cells, battery technologies, and battery control technologies. Most importantly the goal of this section was to analyze existing system to see if we could improve upon them, or better integrate them into our own design. An important note to make is that some of these products are experimental and others are commercialized so the cost factor for either may not be accurate.

3.1.1 SEV (Solar Electric Vehicles) Our product had several existing versions such as those made by SEV (solar electric vehicles) which was not a ground-up electric vehicle. Models advertised in SEV’s product line involves the conversion of fossil fuel dependent vehicles into solar powered vehicles by the addition of a mono-crystalline photovoltaic cell roof, batteries, and electric motors. Advertised are the Toyota Highlander, Toyota Rav4 EV, Ford Escape Hybrid, Dodge Sprinter Hybrid, and the most notable Toyota Prius as seen below. These products also includes solid state device electronics for monitoring battery charging and dissipation over the course of the vehicles operational lifetime. The intent was to boost fuel economy by 34-60%

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pending user driving habits by improving fuel efficiency of the vehicle and giving it a more intelligent control over how the vehicle distributes its energy.

In figure 3.1 the photovoltaic cells are clearly present atop the vehicle. Toyota Prius’s themselves being hybrids, required little additional modification to become electric vehicles in their entirety. While this feature is interesting it is important to note that contoured panels such as those shown below rarely, if ever effectively collect sunlight. Over all this design is not much better than its hybrid counterparts.

Figure 3.1: Solar Electric Vehicle’s modified Toyota Prius with PV cell roof [1]

This was relevant to our product in that we also intend to have intelligent vehicle energy dissipation that could improve vehicle driving via selection of different drive modes. In addition our design would involve the fabrication of a vehicle that was electric from the ground-up. This was in contrast to SEV’s line of “electric” vehicles that are essentially hybrid vehicles intended to boost performance in regard to the vehicles original fossil fuel design.

The current price for a SEV converted recycled Toyota Prius is $25,000. This was one of their cheaper products and it was our goal to produce a machine that was as efficient as the Prius but at a significantly cheaper cost. However it should be noted that our product had a lower top speed. However, in regard to its intended purpose and the cost benefits, this difference in speed was mostly negligible. Additionally our projects smaller profile was more conducive to the target urban environments, and allowed for improved cargo capacity after modification putting it on par with SEV in terms of use.

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3.1.2 Tindo Solar Bus Other Solar vehicles currently being designed for daily use include the Tindo, a solar bus being used for public transit in Adelaide, Australia (a cit on the cutting edge of solar technology due to its location). Since it is a bus it is designed to carry up to 25 passengers a range of 200 kilometers before requiring a full recharge. That being said the bus itself does not have integrated solar cells for recharging. Instead they rely on a $AU550,000 Solar at the central . However it’s design allows for efficient energy recharge regaining 1km of range per minute charged meaning a full recharge takes no longer than 3.5 hours. It was considered a huge step in Solar technology in 2008 when it was first debuted with each bus costing $460,000.

Considering that the project did not produce a solar powered bus it did have the potential to be expanded from a simple people carrier to a much more elaborate mass transit vehicle. The real relevance of the Tindo was that it is a powerful people transport using cutting edge charging and solar collection technology. The principle of having a central power system that collects energy at all times and is capable of quickly transferring it for short charge times makes it extremely relevant to our design.

The key difference was that our vehicle stored the energy collection system on board; additionally our system never shut off, it could always charge because it just switched between a power supply that was being charged, and one that was constantly dissipating. In this way we could have an easy to regulate system that was constantly charging during drive time, while a parallel system powered the vehicle; then the 2 systems could switch roles which would boost range, or merge to boost performance.

Finally as you can see in figure 3.2, because the Tindo is a bus it is better suited to carrying a large quantity of batteries. But this also meant the cost of fabrication would also be significantly higher due to size and number of parts. Also have large physical dimensions and this can affect maneuvering, especially in urban areas. This further emphasized our desire to make an efficient, maneuverable vehicle. A real question is why is an object with such an astonishingly large profile not have its own paneling. Surely an object of that size could hold at least five panels with a negligible change in its physical dimensions.

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Figure3.2: Tindo Bus on the streets of Adelaide, Australia [2]

3.1.3 NUNA 7 Solar Racecar In 2013 the NUNA 7, a designed and built by students on team Nuon from Delft University of Technology, won the World Solar Challenge. The world solar challenge, established in 1987, is a solar energy research competition where teams submit vehicles powered solely by solar energy. These vehicles travel 3000 km across Australia from Darwin to Adelaide. In 2013 Team Nuon won with a time of 33 hours, 3 minutes, and an average speed of 90.71 km/hr. This was team Nuon’s 5th time winning the competition. The vehicle is a testament to the potential performance and speed that can be expected of such electric vehicles. However this vehicle is a prototype and therefore it’s cost could not be properly factored.

The real appeal of the NUNA 7 is that it demonstrates three important factors when designing a solar vehicle. The first is weight, in all vehicles efficiency can instantly be improved by a reduction in the overall vehicle weight. Second, the racer demonstrates how panel placement is key to proper and efficient solar collection. Since the vehicles photovoltaic cells were mounted across the entirety of it’s frame and at various angles, it was constantly receiving direct sunlight. The only limitation is that at no point were all cells receiving maximum energy, a problem we intend to address.

Furthermore, as you can see in figure 3.3 the NUMA has little to no extra spaces for batteries causing the design to solely rely on solar energy. Though designed performance is always crucial for an electric vehicle to be able to carry an additional electrical energy source to ensure that the a shift in sunlight does not drastically affect performance. Our vehicle, having 2 sets of 3 large Trojan deep cycle batteries, circumvents this issue ensuring that SPOC still would perform consistently even in the absence of abundant solar energy.

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Figure 3.3: NUMA 7 Solar Race Vehicle [3]

Finally the vehicles design allowed it to charge while driving which is the optimal performance condition for photovoltaic cells. This is due to photovoltaic cells losing their efficiency above a certain temperature due to the temperatures effect on the rate of reaction in the semiconductor materials that produces the electricity. Since the vehicle is charging while driving, the air moving past the cells with naturally radiate heat away allowing for efficient energy conversion. Our project incorporated this same minimalist approach to allow for optimal charging while reducing wind resistance which added to the performance of the cart. [4]

3.1.4 UCF’s ZENN ZENN stands for Zero Emission No Noise. The company’s primary product is a 2 person people carrier capable of reaching 25 mph. The company’s goal is a cheap and affordable short range, electric people carrier. Based on a letter put out by the company in 2009 their model costs the customer a net total of $9,995 after rebate, but the base cost was recorded as $15,995. With a range of up to 35 miles and an estimated recharge time of 4 hours using a conventional 120 volt outlet this product seemed like an excellent starting point for the foundation of our approach to our project.

In 2009 UCF purchased and retrofitted a ZENN with 3 Photocells attached to the roof (as seen in figure 3.4) that provide a combined 72 volt charge to the vehicle under optimal conditions. In winter the vehicle averaged 15 miles per day and needed no auxiliary power support. This range reduction was primarily due to a lack of abundance of solar energy as one is more likely to expect. ZENN was also a simplistic realization of solar technology in that they converted the 3 bulky panels into a solar array that work on practically the same level as a wall outlet, in order to power the vehicle. And even then ZENN could only charge when not in use.

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Figure 3.4: UCF’s solar adapted ZENN Electric Vehicle [5]

Our goal was to start with what ZENN was capable of and build on its design, exceeding all these parameters with our design for the SPOC. First off our intended product would travel a comparable distance, if not further, on a single charge due to a variety of performance modes controlling power dissipation throughout the vehicle. Furthermore our design had significantly deeper component integration since we could not simply mount a simple photovoltaic cell on the roof of the vehicle. This being that it would have hindered performance due to the way the shape and additional mass would effect the vehicles profile when mounted directly atop the carriage. Our product also cost significantly less though the components were mostly second hand and limited by our budget. However the fact that these were not excellent components that were still yielding acceptable results showed our projects room for growth. Above all our design intended to focus on boosting efficiency of currently existing technology in a manner that could even improve the ZENN and by extension other electric vehicles. This was done by high level software integration that provided a degree of oversight to how SPOC governed both its charging and performance for optimal performance. [6]

3.1.5 EVOENERGY’s (SOLFEX Primos 600) EVOENERGY is a UK based solar technology company that installs and maintains photovoltaic cells on personal residences. Their releveance is due to the technology they apply in maintaining cells. First off they use brackets intended to withstand gale force winds at all angles. This is of significance to our project as the panel were attached to a moving vehicle and as a result had to be stable regardless of the direction in which wind effected the vehicle. However the real interest of EVOENERGY work comes from the SOLFLEX Primos 600 Digital Solar Thermal Controller.

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As mention before, a crucial aspect of our project was that the panels needed to maintain a certain temperature in order to remain efficient. This is because as the semiconductor material that allows for conversion of sunlight to electricity will lose its efficiency as it heats up. EVOENERGY solution to this was the Primos 250 and 600 models which automatically regulate all facets of the PV cell via external monitoring. The system regulates system temperature and measures energy output through the use of six temperature sensor inputs. It performs Data- logging and recording of its function with microSD card technology to keep a record of the system performance history. It also used pumps connected to cylinders of coolant and antifreeze to pump through/around the PV cells in order to maintain the optimal temperature for the cells. And the system could be integrated to store data in a PC.

Our goal was to implement a system very similar to this in our energy array so as to maintain optimal charge rates for our vehicle. In addition we wanted to store metadata from the system so we can improve energy use and performance over the vehicle lifetime which we sadly could not implement due to time and budgetary constraints. The major takeaway of the SOLFLEX was tracking temperature of major components. In our case tracking the thermal energy of the battery was crucial to avoiding battery overheating which is the leading cause of fires in commercial electric vehicles currently on the market. Since dynamic charging and dissipation can put a significant strain on the batteries themselves, our primary concern was sensor integration that would keep us informed as to when components were becoming dangerously hot. This would allow us to take action to preserve vehicle components prior to the components failure. [7]

3.1.6 Star EV The smile is a street legal urban transit vehicle made by StarEv (a division of JH Global Services, INC). With a top speed of 25mph and a range of roughly 50 miles, this 2 person people carrier is intended for short local trips, but it only source of power is by outlet. This vehicle uses a 48V DC motor that produces 5.5 horse power. That is also why its power source is six 8V Trojan batteries, the type you would typically find in electric powered motor vehicles such as the cart that became the vehicular frame of our project.

This is why the Smile was of interest to our project. Since we were incapable of using Lithium Ion cells for our project we had to use standard Trojan lead acid batteries much like the Star EV. The designers at Star EV created this vehicle with the performance standards of a Mercedes smart car which is reflected in its profile as seen in figure 3.5. However the entire vehicle was the product of six integrated lead acid batteries running on nothing more than electric charge. The cart also has multiple on board electronics such as radio, lights, and signals which all put a drain on the battery. Additionally all 6 batteries work in series to provide one contiguous power source. Our project looked past this to understand that our battery components could be separated so that we have more options in power dissipation.

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Figure 3.5: Star Electric Vehicle’s Smile model recreational electric vehicle

This being said one of the greatest hurdles Star EV has overcome is the issue of thermal protection that keeps the batteries from overheating. As mentioned, a common problem with electric vehicles and devices that have large electrical draw is that they have heat issues. In the course of their use the flow of energy into and out of the batteries causes them to become extremely hot if not properly monitored. Electrical components lose a significant amount of their efficiency the hotter they get. Worse, the batteries can often get so hot that they catch fire and combust, damaging the vehicle and endangering its passengers. To avoid this Star EV has perfectly tuned their vehicle so that the draw is as closely matched to the supply, minimizing any thermal overhead that might affect the performance. This is including the draw from the previously mentioned internal components such as lights and radio. [8]

3.2 Relevant Technologies

This section focuses on research done in the main components of the cart such as the Photovoltaic cells, Cell mounting, Batteries, and Vehicle Drive Optimization. For our product we needed highly efficient photovoltaic cells that allow for consistent electrical output at different times of day and in differing weather conditions. We also needed high performance batteries capable of holding a large charge, and then being able to dissipate and recharge quickly, frequently, and consistently with minimal loss in rate of charge and maximum charge capacity. We also needed particular photovoltaic cell brackets that allowed for the cells to be positioned at different angles as well as withstand high wind speeds from any angle while the vehicle was in motion.

3.2.1 Tesla Motors Rapid Battery charging Tesla Motors is pushing rapid charge technology by introducing new quick charging technology and subsystems. The new implementation does very little to make any change to the vehicles internal battery. Instead the focus was on

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distributing power substations that would enable vehicles to charge in 30 minutes or less. As of right now Tesla has achieved a 20 minute recharge time but their goal is 5 minutes. This is done by super capacitors which store solar energy which they collect over time, and then rapidly dissipate them into the vehicle battery. Figure 3.6 shows one of these stations and it should be noted that the added infrastructure is more expensive and due to the number of necessary stations would have a high real-estate cost with little benefit since it is only for Tesla Vehicles.

Figure 3.6: Tesla high voltage solar powered electric charging station

The relevance is that this technology focuses on the substations collecting energy via solar/wind turbine. This means the systems will be self sustaining and capable of storing large quantities of electrical energy. A second point of interest is their research with superconductor technology which is what makes this system possible. In their research Tesla found a way to optimize their system by focusing on the communication between the battery charging station and the vehicles internal battery monitor. By improving communication they were able to optimize battery charge time while reducing the risk of overheating which is often the main concern for all electric vehicles. An approach we similarly implemented for preserving the longevity of out project. [9]

3.2.2 Grape Solar Grape Solar is a company selling some of the most advanced Photovoltaic technology on the market. They have become our go to company for seeing some of the most industry leading commercial products for both photovoltaic paneling and controlling. The product we felt best met our requirements for this project was their 250-Watt Polycrystalline Grid Tied Photovoltaic Solar Panel which can withstand high load stress of up to 50lbs/sqft which is key for a vehicle that will be experiencing wind forces from multiple angles. Additionally they can continue to maintain efficient energy conversion at higher temperatures than other similar panels which is important when living in one of the hottest states.

In figure 3.7 the panel shown is 64.6” x 39.0” which are near the exact dimensions of the roof of our cart. Furthermore the cost of this panel was low

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enough that we could afford to buy 2 allowing us to design our different charge and power modes with greater flexibility. Using Maximum power point tracking it was possible to get a voltage of around 30.7 V at 8.15A in near direct sunlight, and we noticed almost no voltage drop as we moved the panel to different locations. All this was at around a 15.4% rate of efficiency as described, but not confirmed by the data sheet. All this within an operational temperature of -40 ºC to +85 ºC [10]

Figure 3.7: Grape Solar’s Model: GS-S-250-Fab5 High Efficiency Mono-Crystal Photovoltaic Module (left), and reference size schematic (right)

But that is not the only technology they sell, the company also sells flexible solar paneling (PhotoFlex-100W) that can bend to curved surfaces and still maintaining efficient energy conversion on par with the GS-S-250-Fab5. With this product we could maximize the surface are of the cart used for energy absorption while also limiting concerns that the panel is not optimally angled for direct sunlight. [11] Finally the company sells a host of equipment targeted at improving energy storage and electrical flow such as the Rhyno-500 power case with built in 40 Ah lithium-ion battery with 500 watt pure sine inverter to maximize energy flow both into and out of the system. [12] While most of these additional products are extremely appealing, only the 250 Watt panel was used for our project. However these other technologies would have provided a significant benefit to any later variations of our project.

3.2.3 Electric Energy and Power Consumption by Light-Duty Plug-In Electric Vehicles This is research done by the Iowa State University Electrical & Computer Engineering Department. In this work they did mathematical models to determine typical energy dispersal patterns of cars in different urban environments. These models focused on typical user commutes to locations such as work, school, grocery store, etc. The research was particularly significant because the models produced allowed for accurate tracking of power dissipation in electric vehicles in

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conditions that are usually stop and go due to low speed limits, frequent turns, and short trip times.

The models are particularly useful to our project since our vehicle was intended for lower speeds, typically less than that of highways. The research also showed models intended to optimize power consumption over both a 24 hour and 7 day period in a manner that was self adjusting. The combination of these elements means we can design the on board computer to improve vehicle efficiency as the vehicle is used more frequently. Furthermore the stop and go nature of urban commutes meant that anytime the cart was not operating the motor it would be collecting energy. Considering the frequency with which this would likely occur, as well as the fact that urban vehicles spend most of their time in a stationary position it would not be surprising to get significant charge time meaning that our project would be able to maintain excellent charge regardless of rapid changes in weather conditions.

Additional points of consideration for our vehicles onboard monitoring were to collect data about vehicle use, charge rates, and dissipation. This way we could monitor how much more use the batteries would have had before requiring replacement. As well as get a realistic idea of typical charge times for the current components. [13]

3.2.4 Battery Requirements for Plug-In Hybrid Electric Vehicles – Analysis and Rationale Research done by Professor Ahmad Pesaran, Ph.D has given insight into the battery demands of electric vehicles. His work gave current and future projections of battery demands of these vehicles based on the systems they incorporate, projections of the future of battery material’s technology, and the different purposes of the vehicles themselves. He determined there were two categories of batteries for all-electric range cars (vehicle relying solely on battery for operation), one for a 10-mile(Low E/P) range and one for a 40-mile range (high E/P) were selected. The batteries then had to be chosen of the criteria of: charge-depleting HEV mode (available energy and power) charge-sustaining HEV mode (available energy and cold cranking) system-level (cost, volume/weight, calendar and cycle life) battery limits (voltage, current and temperature)

To expand these goals mean how well can the batteries dissipate charge, how well can they hold charge when not in use, how much does the battery cost in comparison to it’s purpose and longevity, and finally what were the physical limits of the material of the battery in terms of maximum charge it could dissipate or receive while maintaining safe and operable temperature. The research

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determined that in these low range vehicles the difficult to meet many of the requirements being demanded by this proposal for long range cost/life/energy density batteries.

This research also touched on different battery depletion modes. For our project we intended to use an efficient, performance, and eco-boost as our primary vehicle drive modes. All of which will be operating on a constant charge depleting mode as expected in electric vehicles. These components would dynamically change to account for a drop in charge rate or battery depletion. [14]

3.2.5 Designing a High-Efficiency Solar Power Battery Charger The results of dynamic algorithm tracking for Maximum Power Points by altering the load and observing changes in panel output are the key to receiving optimal energy output for any solar technology since power itself is directly proportional to the load. Although a constant volume approach is a simpler method for finding optimal angle of intake it is subject to unnecessary readjustment due to passing clouds and partial occlusion. Dynamic tracking methods such as alter and observe, algorithm can continue to seek changing values for Maximum Power by mildly altering and then detecting either improvement or degradation. For most installations, this algorithm is a significant improvement over basic constant voltage approaches.

However due to model cost and component limitations we performed this same feat by finding optimal amperage for a given voltage range that was what is expected by the cart. We would then have to manually adjust this value via a potentiometer in order to maintain the range due to sporadic fluctuations that one might expect with Florida weather. This being said a tracking system was design and intended for implementation for our vehicle for purposes of data collection. It provides a reliable means to find optimal sun positioning for a local area. It also ensures that intake is optimal regardless of environmental conditions. However due to the excessive amount of interaction this system only proved practical if our system implemented a manner of constant panel adjustment.

Preferably some sort of automated tracking system integrated into the PV cell mounts. This was only possible on one panel which hindered the effectiveness significantly. However one we had a rudimentary panel adjustment system we could set a frame work for later models to have an integrated optimal solar positioning controlled by the micro controller. The microcontroller would not need to do recalculating if it has a preset number of coordinates that are best for solar tracking. In this way upon parking the vehicle the computer would be able to indicate the best angle for that time and need minimal interaction from the user outside of the initial adjustment. [15]

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3.2.6 Choosing a Microcontroller Most known for the Arduino Uno the Arduino family of Microcontrollers are popular with hobbyists and programming novices alike because of the simple User interface and their AVR C and C++ native Programming script. The Arduino is open source hardware built around either an 8-bit or 32-bit Atmel AVR Microcontroller. The Arduino compiler allows easy communication between the host computer and the onboard boot loader that can run any number of simple functions on the Arduino’s I/O ports. Furthermore there are many I/O shields intended for visual displays and buttons that make I/O simple and easy which is crucial in a time sensitive project such as ours.

Even the Arduino itself served as an excellent programmer as seen in figure 3.8. That 28 pin connector where the atmega328P-PU sits meant code could be sent over USB to the Arduino, then once the atmega328 was programmed, it could be removed from the Arduino and move it to our custom micro controllers dispersed throughout the vehicle. This was particularly useful due to this shift in modular design which allowed for easy replacement of damage parts. All of this being a testament to Arduinos drive to make simple forgiving micro controlling platforms integrating the high level atmel design.

Figure 3.8: Arduino UNO Microcontroller top down view

Considering its minimalist profile and design the Arduino and by extension our chosen microcontroller, the atmega328P-PU, had minimal power draw. Arduino development board have a power draw of 2.5-12 volts due to their highly sensitive voltage regulators, meaning that they cause a nearly negligible strain on the power supply and can be powered by many different sources including the cart components. In effect, they could run entirely off the solar paneling meaning that they would not affect any sort of power loss in the battery supply. However due to the varying levels of power coming from our project, ensuring a spike in electrical flow would not destroy our components was a primary concern.

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Though we intended to use an MSP430 microcontroller we found the Arduino documentation and functionality to be exceptionally useful to our design because of how it is similar to the MSP430. Both use an atmel processor, both are C compatible, and both can reliably run large blocks of code in a linear manner. However the design of the Arduino Uno provided something that was crucial in our multicomponent project and that was that the Arduino could work in a Master/Slave manner. This way different microcontrollers could be assigned to difference functions such as monitoring the buck converter, displaying and monitoring data from cart sensors, and handling the dynamic drive modes.

Following the simple master and slave design as seen in figure 3.9. This versatility is crucial to how we intended to implement different driving modes since we required a system that could track battery life, energy absorption/dissipation, and still bring minimal draw to our system. Finally the extensive documentation for different Arduino energy projects has been extremely useful in helping our team determine how we wished to design the different energy distribution modes. All these modes are being made from scratch and required an absolute control over every watt that the vehicle used in order to attain the most energy efficient system possible. [16]

Figure 9: Arduino Microcontroller master/slave configuration using the atmega328P-PU schematic as reference

3.2.7 Bluetooth Vehicle integration Components Further things considered about the Arduino and how it compliments the MSP430 are the shields and multiple variants. The Arduino has a variety of different integrated and dedicated peripheral components designed for User

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interface in addition to a display shield. The one we were most interested in was arduino’s Bluetooth shields and a base Bluetooth arduino model. This is important to our project in that users could interact with our vehicle using Bluetooth on their handheld devices such as phones and laptops. This way users could choose their preferred method of interfacing and be able to receive diagnostic and efficiency statistics on their vehicle. Not to mention the ability to select drive modes based on a user interface designed for these platforms.

It should be noted that we intended to add local hardware I/O so the user would not have to rely solely on Bluetooth but have an option to use physical controls or their own device. That is why the Arduino Bluetooth variant seen in figure 3.10 was part of additional considerations for the basis of what would be the final microcontroller design. Using nearly the same implementation as the Arduino Uno with the addition of a few simple user friendly libraries the Arduino Bluetooth variant would be able to perform normal microprocessor functions while sending a redundant bit stream of all vehicle data to a paired device. This would have allowed for better user interfacing and the ability for the user to wirelessly manipulate the vehicle. Had it not been for time constraints there is a significant chance this board might have had a chance to find its way on to SPOC. This overlooking the tedium of programming such a microcontroller and its corresponding phone applet.

Figure 10: Arduino Bluetooth Microcontroller Board

Here, documentation is still the key to our interest in the arduino Bluetooth technology. Since we were using technology that none of our group members have experienced before it was important that we have a baseline means by which to understand what we are capable of with the Bluetooth technology for microcontrollers. The fact that the MSP430’s Bluetooth technology operates so similarly to the Arduino lends itself to that fact. However the Bluetooth aspect was less of a determined feature and more of a desirable. Yet it was this

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advanced user integration that we felt would let our project stand apart from prior solar vehicle technology, and represent a new generation of modern energy conservation projects. Furthermore it would be a familiar and wide spread feature that many future users would have had prior experience with. [17]

3.2.8 Additional Bluetooth component considerations The cc2560 is one of TI’s highest rated Bluetooth receiver devices. It has data rates of 2.1 Mbps, ultra low transmission power control, and integrated Bluetooth antenna. It is also an ultra low power device meaning that it can run at the same voltage as its alternative intended counterpart, the MSP430BT5190. It would be ideal for this project especially considering its hardware performance and integration. However the primary limitation for this model in terms of our needs is that it uses too much of the MSP430’s hardware, to run.

As shown in figure 3.11, the cc2560 holds its antenna, internal clock, and firmware protocols which means that it is optimized at the hardware level for its intended purpose of sending and receiving as a Bluetooth device. However as a piece of hardware it is surprisingly heavy in terms of processing despite having all low-level protocols stored with the firmware. This is due to how much of its counterparts MCU it uses in terms of need to storing the Bluetooth stack, applications, and operating system. For our project the MSP430 must communicate with the receiver while tracking the behavior of internal components. It cannot have such a significant amount of its processing power weighed down by a local peripheral. Especially when considering how little the Bluetooth receiver will actually have to react with the MSP430.

Figure 3.11: Texas Instruments CC2560 Bluetooth Adapter module (left) and Device integration block diagram with the MSP430BT5190 Microcontroller (right)

Other Bluetooth transmitters such as the RN-42, our finalized intended Bluetooth receiver should the project time frame allow it, stores all necessary data and

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performs that majority of functions locally on itself. The tradeoff is that since it has so many components it has a higher power draw. That being said in a system as large as ours this draw is nearly negligible. It should be noted though that it maybe better to consider the cc2560 and the MSP430BT5190 as a whole communicating with the onboard MSP430 so that the computational draw is at a complete minimum in addition to the lowered power costs. [18] However when addressing these microcontrollers in the method of the master and slave the overall Bluetooth implementation for the Arduino becomes negligible due to the high instruction throughput combined with modular microprocessor control.

3.2.9 I2C and the Atmega328P-PU Our final major consideration as to why we primarily want to use the Atmega328P-PU in a manner associated with the Arduino Uno as our final Microprocessor is because of its ability to use I2C (pronounced “I squared C”). Using a configuration described in figure 9 and again in figure 3.12, we can combine 2 or more Atmega328P-PU microprocessors so that they will function similarly to a multicore microprocessor. In figure 3.12 the processors are connected on analog 4 and 5, using the 5V output, Universal Ground, and 2 1.5kohm resistors to produce a stable signal.

This design is minimalistic in that all controllers on the line can be connected in parallel. When it is time to call one of the microprocessors the master simply calls the selected slave using a hex address, makes the necessary exchanges and then re opens the communication line. There are a multitude of Arduino libraries and tutorials on I2C which further proved ease of learning and value for implementation in our project.

Overall the I2C technology was an excellent solution to the troubling issue of a damage PCB. It gave the SPOC all the functionality of a PCB while still maintaining a simple profile. Modularity meant systems didn’t need each other to function which is key on a motor vehicle. And the ease with which this could be achieved was beautiful. The documentation was so accommodating that included video tutorials.

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Figure 3.12: Arduino Master/Slave circuit using I2C for communication [18]

3.3 Strategic Components

Strategic components refers to the design integral components. This section is primarily focusing on what components were being considered as actually viable options given the nature and needs of the project. The focal point of the project were a stable cart. Ideally a cart capable of supporting the passengers, and added weight from the batteries and solar panels as specified in previous sections. This also had to have a small physical profile. And above all due to cost restraints, needed a motor of adequate size to be used by our system since the carts were designed specifically for these particular motors.

Other primary components were the batteries themselves. Necessarily ones that can hold a powerful charge, dissipate efficiently, and be recharged a great many times. Photovoltaic solar panels were also a key concern in that since we needed technologies that would allow for charging at varying levels that could be adjusted on the fly to meet our design requirements, while still having significant output. Additionally, since this is Florida, we needed paneling that would be able to operate effectively at hot temperatures. The limitation is that the majority of this technology loses its efficiency the hotter it gets so this particular feature would be crucial to how the project went forward.

And the final key components for consideration was the microcontroller. For this our focus was something easy to program. It needed to have low power draw and ideally be capable of standby modes considering that solar technology is

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only efficient during the day. Finally it would need to handle many different I/O’s. In this case the inputs would include voltage, thermal sensing, and finally, photodetectors. Outputs would include LCD displays and possible Bluetooth antennas. For this we would go through multiple different microcontrollers but the final model might have to be an integration of multiple controllers instead of one singular one.

3.3.1 Cart We needed a proper platform for our unique electrical platform to function properly which meant choosing an existing cart design that was stable, compact, and electrically sound. All this while having the best industry electric motor that was able to have reasonable output at our given energy levels. There were several options to choose from for our electric cart platform. Due to the variety of options that could potential meet these requirements, we shifted our attention to cost and secondary requirements of the vehicle so that we could get the most ‘bang for our buck’. Ideally, in addition tto being cheap and having a decent motor our chosen vehicle would also have the batteries desired included. With these considerations, our decision was made from some of the following models.

“Star EV Smile” Design To reiterate Star EV makes high end electric vehicles for a myriad of purposes and users. Their “Smile” design uses a highly efficient electrical motor system to power the vehicle from a bank of 6 8V Trojan batteries. This design rides the rail between electric car and cart with its fully enclosed body and street legal specifications. Though it has a stylish exterior and an efficient electrical platform for our design to be built from, the financial cost of this design prevented its use in our chosen design. [19] As can be seen below in figure 3.13, the enclosed body, and awkward profile mean that the vehicle is heavier than we would have preferred. Also the profile would make mounting of the panels difficult if not impossible given our limited access to certain power tools and additional hardware. Most importantly its battery compartment is difficult to reach and the profile again limits our ability to mount extra components such as microcontroller and relay housings.

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Figure 3.13: Star EV “Smile” Model Cart

Other considerations that would have made it a very nice choice include the fact that the vehicle is street legal. With a modern design and all necessary aesthetics of a street legal vehicle this body would not have had to make a significant transition in order to become integrated into metropolitan transit. However cost and design still made this choice unrealistic given our specifications.

GEM Cart Design Global Electric Motorcars (a subsidiary of Polaris) has designed a new style of cart in past years that has gained a wide base of support. The GEM cart offers added features but at a price. These carts drive at an average of 20 mph on a 72 volt battery system. Their electrical design offers greater power efficiency and battery usage. This design is obviously more aerodynamic, stylish, and safe with its featured seatbelt. Our main concern with this GEM design is the financial cost: most of these carts price at twice the cost of the classic “Club Car” design. [20]

In figure 3.14 the vehicle shows a blend between the tight design of a Star EV smile and a common club cart. While the design is fiercely efficient you will note that it is equally difficult to access the GEM’s batter compartment. And much like the smile the GEM’s profile makes it a poor choice for mounting solar panels in a stable fashion.

Figure 3.14: Polaris GEM Cart design

Custom Cart Design Acquiring and/or constructing a custom electric cart offers several unique advantages. We can pick more of the aesthetic components while optimizing the electrical design of the electric cart. Since our SPOC design will include the drastic amending of the electrical format of the cart, this route is very appealing.

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Choosing a custom cart will allow us to tune and optimize our desired frame, motor, battery layout, capacity, and aesthetics. However cost and time being a factor it does not seem viable to purchase a custom cart which brings us to our final and most likely option. [21]

“Club Car” Cart Design Our most financially viable option is the classic “Club Car” or “EZGO” cart design popular on golf courses worldwide. Their construction is simple and inexpensive; the cart’s are made of light materials such as plastic and fiberglass. The frame is made of aluminum to reduce weight. These vehicles usually have a varying amount of power of 9-12 horsepower, running off of an array of lead-acid batteries underneath the seats. The main draw of this design is the affordability for our team’s budget. Classic electric carts are plentiful, widespread, and inexpensive. Additionally a simple craigslist search provided us with a wide array of carts in the local area that both included batteries and stayed within our price range [22]

In figure 3.15 we can see an E-Z-GO club cart. As can be seen in the picture the vehicle has many components that can be easily removed to minimize weight and/or be replaced by paneling. Most notably the roof of the vehicle. In addition there is space under the seats where these carts store 6 to 8 lead acid batteries which could be easily integrated with our drive circuit do to their flexible operational rate. As well as their ability to charge and discharge in a practical amount of time. Finally the fact that the batteries are so easily accessible makes them ideal for both component integration as well as housing.

One interesting consideration for such a vehicle is that many of them are at their lifetimes and their batteries are the only parts dyeing. Were a user to take one and modify it in the manner described there would be great potential to quickly and cheaply erect a fleet of SPOCs to aide in the majority of metropolitan areas.

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Figure 3.15: “Club Car” brand classic golf cart platform

3.3.2 Atmega328P-PU For our project we had chosen to go with the Atmega328P-PU 32k microcontroller similar to the one found on the Arduino Uno R3. The Atmega328P-PU is one of Atmega’s most popular chips. With 14 Digital I/O and 6 Analog ports 328 was an easy to use consideration for our project. When used in conjunction with Arduino IDE the Atmega 328 could be easily programmed to meet any number of tasks using high level coding , then have this code uploaded to the chip where it could then be physically transferred to our microcontroller housing.

In figure 3.16 we show the Atmega328P-PU used in our project. This 28 pin microprocessor, sold by spark, fun fits directly onto and Arduino Uno 28 pin femal receiver for easy microprocessor code upload, similar to the receiver seen in figure 8. The processor can then be ejected and placed on our custom fabricated microcontroller boards. This microprocessor is also much less sensitive than other similar logic components making its integration that much easier. Finally, as you can see across the top all pin information is clearly labeled such that there will be no confusion when assigning I/O ports while coding.

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Figure 3.16: Atmega328P-PU with Optiboot for Arduino Uno

This particular microprocessor has extensive documentation for integration with a vast variety of different shields with which we can modify our user interface design. Since our project has a heavy emphasis on power conservation, one of the most crucial aspects to the 328 is that it can operate in a 1.8-5V range, and be expanded by addition of a 16MHz Crystal clock for improved computation and inter-processor communication.

Another excellent feature for this processor is Memory management. The large onboard flash memory meant each microprocessor could handle large portions of code for different purposes. Better than that the 328P-PU which is targeted by Arduino IDE, is excellent at handling messy code which proved useful in cases where we were working with technologies we had never experienced before. This further extended to its ability to easily recover from sudden power loss even when registers were mid write.[23]

We can not stress enough, the value of the extensive documentation associated the with the Atmega328, Arduino IDE, and its many importable Libraries such as OneWire and I2C. Sparkfun itself provides a comprehensive software portfolio that gives many useful examples on how to integrate User Interfaces, different shields, and how to test and optimize code execution. Their open source products cover hardware integration for Capacitive touch screens, Bluetooth stack, and a multitude of other components which would prove central to meeting the desired goals of our project. None more than the included LCD Drivers which made our vehicle interfacing easy to execute so that we could simply output new data on the fly allotting more time for working on how to make our different drive modes and improve vehicle performance statistics via our buck converter. [24]

3.3.3 User Interface In order to allow for some degree of user control, we need to include both input and output options for the user. These options will include the display, audio alert,

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and hardware buttons shown below. Additional software was designed to link these components.

Blue Character OLED 16x2 For the project we chose the OLED 16x2 blue LED screen found on the adafruit website. This display allowed for dynamic response to changing conditions, both user-decided and environmental. As the primary component of the user interface through which the user receives data about the current status of the cart, it was important that we choose a screen that was readable under many conditions. With this in mind, the clear choice for readability under many lighting conditions was an OLED display. The output for this display was driven by a dedicated microcontroller the microcontroller via a series of pins on the back of the localized UI perforated board that connected to the microprocessor via Ribbon cable. Additionally as can be seen in figure 3.17, the display has very high contrast even though it uses the same power draw as the microprocessor it relies on for data output. This along with the high refresh rate made it optimal for choosing how to best display primary cart information to the user, considering that both the cart and display would spend a significant amount of time in direct sunlight.

Figure 3.17: Adafruit 16x2 Character OLED (Blue) [25]

Tactile Switch Buttons In order to allow for user input, mode selection, and feedback; a series of buttons were mounted throughout the vehicle that would manipulate primary cart functions via user interaction. Due to the fact that the buttons had to be easy to mount and access we chose to go with the 4 prong Mini Push Button Switch, intended for use on bread/perf boards. This switch was widely abundant, being

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sold in RadioShack’s’ many online stores, and included in many project development packages. Furthermore users are very familiar with this method of input so it seemed intuitive to include these in our design.

As seen in figure 3.18 the button is relatively small which made it easy to position and place on to boards with other necessary components. Having had moderate with these switches and their configurations our team was able to quickly design entire interfaces around interactions with one or more buttons. And as mentioned before the small profile meant they could be placed in all manner of locations making implementation of certain cart components such as panel adjustment significantly easier than previously thought.

Figure 3.18: Mini Push Button Switch [26]

Electric Buzzer Though only used for a small function of manually adjusting panels, the Piezo Element 1500-3000Hz Buzzer served as an excellent and simple implementation in our design. Since it could be operated at 5 volts it was easy to integrate into our microprocessor design since direct I/O could trigger it. Additionally it was very small and cheap with a cost of under $2.50 it made for a quick but necessary addition to our design. [27]

3.3.4 T105-H Signature Line Flooded Deep Cycle 6V Battery For this project the model battery chosen was the Trojan Model T105-RE. This is a Flooded/wet lead-acid battery with an operational range of -4 to 133 degrees Fahrenheit (-20 to +45 degrees Celsius). This was our preferred choice in battery. Though Lithium-Ion would have been a nice alternative we preferred the Lead Acid for multiple reasons. Though not having as high of longevity compared to

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Lithium-Ions, Lead Acids are more flexible due to their ability to easily charge and discharge at practical rates for our design.

Furthermore this choice of Battery was optimal because it was included in the cost of the vehicle upon purchase. Even if the batteries used were inefficient they could be easily swapped for new ones at a significantly cheaper cost when compared to Lithium-Ions. Also it has a decent range of operational temperature which is excellent for electric vehicles since the battery use tends to cause the battery itself to become very hot. That being said the battery also has a reasonably shorter lifespan than a lithium polymer, and the battery will lose more of its maximum storable energy per recharge.

Over all though its flexibility was the key to our project. [28] In figure 3.19 you can see the batteries included with the cart in their previous configuration. You will note that they are in series, and leave plenty of extra space in the battery compartment for additional components. Our final product had these batteries in parallel such that they could easily dissipate and charge when incorporating energy distribution from our panels.

Figure 3.19: Six Trojan T105-H volt batteries in their standard configuration in our E-Z-Go TXT Freedom Electric Golf Cart

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Ideally for our project we had to be able to implement several batteries in parallel. Base on other designs we had determined that in order to best regulate the heat produced by the battery we used the same total voltage as might be pulled from the system so that their is no concern for a lack of power. Another interesting concept is to somehow have depleted batteries cycle into a charge state so that we could have batteries charging while the vehicle was in motion without fear of too much load being put on the cart.

This would help boost performance and energy output. However the most limiting factor in all these ideas was still weight. Lead Acid batteries can be very heavy so they become rather impractical very quickly considering how much their own weight can affect drive performance. That being said the vehicle was already designed to accommodate at least 6 of these batteries making this concern negligible. [29]

3.3.5 Solar Array For our solar panel implementation we had several options in how to model our solar array in terms of panel arrangements for the SPOC’s final charge design. Options ranged significantly in size, price, and power output performance. Because of the size of the cart we are limited to a solar panel size less than 8 feet long by 4 feet wide. For the specifications required in Section 2, our design needed a solar array design producing at least 300 Watts to the batteries in any number of configurations.

Trina Solar TSM-240PA05 We could have a standard flat panel solar array that would be inexpensive and relatively easy to mount, though it would likely be rather unwieldy. The panels are usually large and not designed for optimal use of surface area; these are the solar panels most often used for home energy efficiency on residential and commercial roofing. Also, these panels mostly performing at lower power specs than desired. [30] While this design is inexpensive, it is also inefficient in its use of the space on the panel. In the table below we described the primary components of the Trina, according to our research in addition to lesser efficiency the panels are also somewhat unreliable. Additionally they are impractical to ship within our time frame.

In Table 3 below there is a basic mock up of the appeals of the trina. While this model is cheap it lacks a degree of efficiency. The wattage could be improved. The size is too bulky, and the overall design is average at best when compared to its counterparts.

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Table 3: Basic Specs for the TSM-240PA05

Electrical Characteristics Performance

Rated Power (Pmax): 240 Watts

Watts (PTC): 211.5

Max System Voltage: 600 V

Cell Efficiency: 14.7 %

Price: $273.60

Size: 64.96” x 39.05” x 1.57”

Power Film Solar Flexible Panel We also have the option of flexible solar arrays like the one shown below (figure 3.20). This design offers a sleek and light option for our solar needs, though the price and energy output then becomes a major factor. Flexibility maximizes the surface area and sunlight incident angles on the panel. Due to their design, most of these panels are rather expensive, compared to the others, while producing far less than the desired 300 Watts of power output. [31] However as seen below they are designed to contour to the shape of the vehicle making installation and manipulation much simpler.

Figure 3.20: Power Film Flexible Solar Panel

In the table below you can see more product data for why the Power flex was not viable. In addition to the fact that it has one of the lowest efficiency values on the market the panel was also unreasonably expensive. Most importantly this project demands power requirements on par with what would normally be seen by a conventional cart charger.

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On Table 4 is a cost breakdown of the prior flex panel with major documentation values. As shown the product is even worse than the fixed technology. This seems somewhat counterintuitive since they should be able to meet any angle. All this in conjunction with such low wattage, and similarly low efficiency.

Table 4: Basic Specs for the Power Film RV-15-3900

Electrical Characteristics Performance

Rated Power (Pmax): 60 Watts

Watts (PTC): 54.5 Watts

Max System Voltage: 200 V

Cell Efficiency: 10.6 %

Price: $875.00

Grape Solar 250W MonoGS-S-250-Fab5 technology has allowed the design of high efficiency solar panels for use in compact electric vehicle designs. These array designs are less popular because of their higher cost, but is completely ideal for our carts final design. The higher quality silicon used in these panels has led to the maximized wattage for the surface area of the panel. Grape Solar is the largest manufacturer of these high performance arrays; their company specs are listed above in section 3.2.2. [32]

The table 5 shows the cost breakdown for this product. One of the major benefits is that within this price bracket of our project we were able to purchase 2 of these panels. One was mounted on top while the other was adjustable to power the cart in parallel while driving as well as to find the optimal energy absorption angle while parked. Furthermore this model had some of the highest efficiency ratings on the market and the combined power ability meets all of our energy requirements for this project. For further details on this panel refer to the above section.

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Table 5: Basic Specs for the Grape Solar MonoGS-S-250-Fab5

Electrical Characteristics Performance

Rated Power (Pmax): 250 Watts

Watts (PTC): 222.1 Watts

Max System Voltage: 1000 V

Cell Efficiency: 15.4 %

Price: $370.00

In this section we show that the overall primary cost of the project was in the cart and panels. These are the cornerstones of our project and the key to its function so they would obviously be the main point of contention. The best part of this project is that it will only become more efficient as technology improves.

3.4 Possible Architectures and Related Diagrams

This section is intended to show our preliminary design considerations for all facets of our vehicle. These focus primarily on solar array integration and battery hookup designs intended to maximize our energy intake. There are points regarding microcontroller integration and Battery to Motor hookup. Peripheral components are also addressed here such as sensor integration, User interface, and potential for different components that were up for consideration at a later time.

3.4.1 Solar Array Architecture In order for SPOC to be tuned for maximum range and energy efficiency using the power from the solar array subsystem the vehicle required Maximum Power Point Tracking. This subsystem includes an array of photovoltaic cells; most of the dimensions our team has considered had 96 of these cells built in a 12 x 8 configuration. These photovoltaic cells were mounted on a supporting structure; a pv module typically includes a panel, an array of solar cells, a power inverter, interconnection wiring, and a bank of batteries.

As represented in the block diagram in figure 3.21. For our cart the roof and rear would be covered by the set of Photovoltaic panels. As you can see these connected to a buck converter which was able to dynamically change the load seen by the panels to determine the optimal Voltage/Amperage coming from the panels to power the Cart components. This would also account for changes in sunlight and temperature that affected the panels output. From here power was dissipated to the rest of the cart via a series of relays and cables controlled by the microcontroller. These lines determined which batteries would charge, at

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what rate, as well as how they would dissipate. [33] Though the chart does not display the full power circuit the green lines do show the distribution of power, while the blue lines show microprocessor control over the components.

Figure 3.21: Overall Block Diagram of Primary Component Integration

Since we desired a high performance solar array to give us the adequate power output needed for our design, the SPOC vehicle utilized the monocrystalline silicon solar panels similar to those described above. These units came prefabricated in a design similar to the one mentioned and displayed in 3.2.2 above. One specific architectural adjustment we made was including a pivoting hinge mechanism for the rear panel to allow it to be repositioned for optimal charging. The overall project would have to be able to handle up to 30 Amps from the panels, and 60 Amps to the motor which proved to be a great challenge considering the team’s low level understanding of high power components. However no matter what, safety was our top priority.

3.4.2 Motor, Battery, Microcontroller Integration In this section we display our designs and schematics for different parts of our design and how we intend to implement and integrate these parts. The primary components for our vehicle are the connection of the Photovoltaic cells to the battery, the battery connection to the motors, and the manner in which energy was distributed following this design. This was the ground work for what became our drive modes. [34]

Microcontroller integration across these parts, and Microcontroller connection to the User Interface were a significant aspect representing the high level aspects of this portion of our design. All these were fabricated using simple high power

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relays as specified in the following sections. These designs give an accurate representation of what the final electronic component interactions of the vehicle resulted in.

Temperature Sensors

For this project we incorporated 4 temperature sensors into the vehicle housing. Each sensor sat between two batteries and was able to take real-time values of the batteries respective temperatures. Should any of these sensors return a temperature near the upper threshold of the batteries safe operational range then the microcontroller would cut power intended for that bank of batteries preventing any danger to the vehicle, or the user. The energy for that battery would be diverted to the alternative battery bank and the user would receive a visual warning on the LED display. For optimal temperature tracking we chose 3 pronged Thermistors capable of 8 bit precision that was able to record temperatures accurately within the full range of safe operating temperatures for the batteries used.

Photodetectors

Two photodetectors were placed on the rear panel to work in conjunction with one of the previously mentioned toggle switches and the buzzer. The components make up the rear panel adjustment design. The rear panel, connected to three door hinges, pivots from an angle of 60 degrees to perpendicular to the ground, to 25 degrees parallel to the ground for a total of roughly 85 degrees of freedom. Once lifted the panel has a pin at its far end that slots into a rod with segmented holes along its length. Each hole is labeled for its corresponding angle, and as the user holds down the pin button with their thumb, they can adjust the rod so that the panel is at whatever angle best suits their current position.

However it is difficult to guess where the sun is when you are standing beneath it, so our design called for two photo resistors sitting in the middle of the adjustable panel with a small divider between them. The two photo resistors would sit as close as possible on opposite sides of the divider so that when both received the same amount of sunlight, it could be assumed that the user found the optimal angle. To relay this information to the user the handle used for adjusting the panel had a button and buzzer built into it. By holding the button the microcontroller would know you were searching for the optimal sunlight and begin tracking values from the photo resistors. Once both photo resistors read the same value, the microcontroller would signal the buzzer informing the user they found the optimal angle. At this point the user could release the button so that the buzzing would stop, and quickly slot in the rod so that the panel would maintain this angle. An unexpected benefit was that this made for excellent shade, which added to our projects marketability.

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Atmega328P-PU Circuit Board Fabrication At this point we would like to notes that our project intended to utilize an Atmega2560, the larger, faster, and more powerful big brother to the atmega328 model. The original design called for one 2560 sitting on one Printed Circuit Board which all other low power components would connect to. Once configured these components would drive controllers for the higher powered components so that any spike in power, or feedback would not affect these low power components. If you refer to Appendix B you can see our full PCB Schematic and all primary components. Below in the figure 3.22 we show the primary relay driving step up components used to drive the high power circuit relays. These were some of our primary modifications to the original circuit board intended for our final design.

Figure 3.22: PCB Power Driving Circuit for Atmega2560

Unfortunately our design suffered a major setback when a large portion of the PCB was damaged due to an electrical spike resulting in damage to the 2560 making it no longer usable. Our solution was a design modeled after the Arduino Uno R3 that not only cost less but also proved to be better in a modular sense and can work independently as well as in tandem. In figure 3.23 below you can see the rudimentary design for out Atmega328P-PU microprocessors. The key to this design is the crystal which improves the microprocessors design for more efficient instruction execution. In addition all components could be found at local electronics stores, and in abundance allowing us to easily make back up modules in case of an incident. It should be noted that the reference schematic in figure 25 is compatible with the 328. The only difference between these two processors is that the 328 has a larger cache.

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Figure 3.23: Atmega168/328 Reference Schematic [35]

The overall schematic was able to be made for less than $10 dollars a board, and could be replicated on a perforated hobby board so that we could make them ourselves. For the final model we used a female 28pin socket so that we could remove and replace the processor when need be, the processor itself behaved exactly as described prior. To program our Atmega328s we required some work with a breadboard since we did not have the complimentary Arduino as shown before in figure 3.23. Overall this ended up proving much easier than our previous PCB design, and it still accommodated the necessary I/O which was a driving reason between our initial move toward the 2560.

MPPT with Variable Buck Converter In order to generate optimal wattage off of the PV panels, it is important to ensure that the effective load on the panel is appropriate for the operational conditions of the PV panel. This requires a bit of intelligence, as well as a variable DC-to-DC converter. The converter will downgrade the voltage coming off of the panel to a level appropriate for the battery bank currently being charged, thus ensuring that the panel can operate at its point of maximum power.

The choice of DC-to-DC converter design is very clear-cut and straightforward in this situation. It has to be variable, as well as high efficiency to minimize the losses from the solar panels, thus maximizing the power being delivered to the motor or batteries. With these considerations in mind, the best option available is a switching buck converter. If the components are chosen properly, buck converters can reach efficiency points of up to 95%, which is ideal for our

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application. The basic design of a buck converter is very simple, as shown in the schematic below.

The below schematics in figure 3.24 shows in simplified form the basic underlying schematic for a switching buck converter. As shown, the buck converter functions because of the current-sustaining capabilities of an inductor. As the switch is opened and closed, the current through the inductor and the voltage drop across the inductor follow a triangular waveform. The capacitor across the load helps to smooth out this variance to provide a linear voltage output that is dependent on the percentage of time the switch is closed (the duty cycle of the driving clock signal). The final design that we implemented is very similar to this diagram, with the addition of a capacitor across the source to reduce input voltage ripple as the switch is turned on and off.

Figure 3.24: Buck converter schematic: on-state (left), off-state (right) [36]

Relay Design For this project we needed to be able to switch high voltage lines that might have up to 30 Amps on any line at any given time pending the output of the panels. For this our project incorporated eight, Single Pole Double Throw (SPDT), Relays rated up to 40 Amps. In figure 3.25 we describe the manner in which our project utilizes these relays to distribute power. A pair of SPDT Relays were modified to act as simple switches to turn on and off the power flowing from the panels in case of an emergency shutoff. From the converters a pair of SPDTs select which battery bank receives power. The pair of SPDTs past those choose polarity so that the batteries can either be set to charge or dissipate based on the SPDTs state. Finally an SPDT chooses which battery is dissipating to the motors.

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Figure 3.25: High level connection diagram for power flow of energy from Panel to Motor

This is very similar to our final implementation but we made some modifications due to difficulties in limiting the voltage across these components since the motor cannot handle more than 48 volts. This was done by keeping the system in parallel so that voltage never went higher than 48 volts even in optimal weather conditions. However there was no Single Pole Single Throw relay putting the batteries in parallel. Instead we connected that relay directly to the motor so that it could dissipate in parallel. We also added two more SPSTs from the negative side of the batteries to ground to better handle energy flow during charging so that both could charge in tandem when parked.

3.4.3 User Interface Layout The interface for the SPOC was based on how to best relay the most relevant information to the user from the data given. These interfaces each focus on highlighting a specific set of relevant information, and feature user feedback based on current usage statistics. Furthermore it was intended that the user be able to cycle through the key features by holding a button, and choose among different drive modes with another. In figure 3.26 we demonstrate the rudimentary I/O as previously described. This screen sat on the dash directly adjacent to the driver. By holding key ‘B0’ the user could cycle through the different screens. These screens were: Battery Efficiency, the amount of power on each battery as well as its efficiency percentage, the current drive mode, temperature in Celsius, temperature in Farenheit, and finally the buck converters efficiency itself as it performed voltage step down. By holding down ‘B1’ the user could select among 3 drive modes: Eco mode(maximizing range), Standard Mode (where the cart behaved as normal while keeping a battery in reserve), and

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Performance Mode (where all power was routed to the motor to maximize acceleration). If both keys were held then the user could set the screen to automatically cycle each data page associated with ‘B0’ while still being able to select drive mode as before. Later we included a forth vehicle mode called charge where the vehicle charged both batteries but could still move, despite the intended output being unrealistically slow considering our goals.

Figure 3.26: Simple Example of Dashboard Mounted User Interface

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4. Project Hardware and Software Details

The primary focus of this area is how we went about establishing the methodology for the designs in section 5. Some ideas were not implemented on the final design. However all were vital to the design process.

4.1 Initial Design Architecture and Related Diagrams

As seen in figure 23 from before the project was divided into 6 major portions: Panels, Converter, Batteries, Motor, Microcontroller, and Display. This was reorganized into what would become our primary tasks of our project which became Photovoltaic Optimization, The Drive Circuit, and User Interface which were to be divided among the team members in an overlapping manner. This system in addition to adding flexibility, allowed for each circuit to respond in real time as oppose to at the end of each third instruction such as in simpler, linearly constructed work.

4.1.1 Photovoltaic Optimization Photovoltaic optimization focused primarily on how solar energy was handled and delivered to the cart. Solar technology is not constant such as one might expect from a normal power source. Depending on the load placed across the circuit, PV cells can either dissipate low current at high voltage or vice versa. The only constant is wattage. As a result we designed a maximum power point tracking circuit in which sensors read the energy coming off the panels and then digitally manipulated the load seen by the panel via a digital buck converter of our own design. In this manner we achieved the optimal output for the current conditions of the cart such that the cart would be able to minimize charge time.

The primary concern for this portion of the project was the wattage of each panel. Though the panels only output 250 Watts, when adjusted to 18 volts, the current began to increase up to 12 Amps. This became a problem not only due to how it affected the components, but by the fact that it required us to custom build a device rated for these ranges. Modern products went no higher than 5 amps and had to be manually adjusted. Luckily through reviewing much documentation we were able to design a converter that used rapid switching across a MOSFET to manipulate output in the manner expressed in the end of section 3. The only limitation was that the accuracy of our sensors greatly reduced the efficiency of our final model.

4.1.2 Drive Circuit In the section 3.4.1 we made note of how our project used a multitude of relays, and high current circuits to drive the motor. This constituted our dynamic drive circuit. Similarly to the previous representation, the circuit was manipulated by a series of high current relays that in turn were manipulated by step up relays. The

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relays provided a logical way to use minimal I/O from our microprocessor to power our cart in the various modes associated with this portion of our design. These modes would allow for the cart to behave in the unique way that set our project apart by being able to charge while driving, as well as power the motor. This part of the project can be best described as the combination of all portions of our project including PV optimization and user interface.

In this portion of our design, power dissipation in the cart was again an issue. We had to ensure that the lines could handle the high current passing through them without melting or causing feedback. We had to ensure that each drive mode could be dynamically controlled. But most importantly we had to ensure that no matter what happened to these lines it would not affect our microprocessor or the carts ability to perform.

To that end the design called for the cart to be able to charge and dissipate using a series of relays that would fail before damage to the electrical line could occur so that any issue could be easily repaired, Luckily the motor was isolated from the rest of our project, and a series of fuses ensure no mistake on our part would damage the motor. In case of a failure in the switching the cart defaulted to the standard drive mode to ensure normal operation. And of course, to ensure no power dissipation in the relays would affected our microcontroller we used a series of step up relays to isolate the systems. Finally we included sensor integration so that should there be an issue of any sort on the vehicle, the cart would be able to react without human intervention preserving both it, and the users safety.

4.1.3 User Interface This portion of our design incorporated the microprocessor, relays and sensors. The primary focus of this portion was to give the users as much control as possible while still leaving primary oversight of the cart to the onboard computer. As described prior, the main options left to the user were permit the user to choose what is displayed, allow the user to select drive modes, and help the user find the optimal angle for panel positioning when parked. Though we had hoped to make the cart more aware in order to make the best decisions itself, to less burden the user; we feel our end product is more than intuitive enough for the average user to infer its functionality and use it effectively. The one major drawback of this project was a desire for Bluetooth integration. Though an interesting future to have had, and moderately simple to implement, we had also intended to make it so that the phone side application would allow the user to work get more from the information sent to their phone. However due to time constraints and lack of teammate availability this feature was left out.

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4.2 Solar Array

For the solar array solar modules use light energy from the sun to generate electricity through . The majority of modules use wafer-based cells or thin-film cells based on or silicon. Most solar modules are currently produced from silicon photovoltaic cells. These are typically categorized as monocrystalline or polycrystalline modules, though monocrystalline modules have the higher rated performance ratings. The structural (load carrying) member of a module could either be the top layer or the back layer. The SPOC vehicle was tuned for maximum range and energy efficiency using the power from solar energy provided by our monocrystaline array. This system was a combination of two 250 Watt photovoltaic cells which followed a standard 12x8 cell configuration across the surface of each panel These photovoltaic cells were mounted on the roof of the vehicle as well as the rear via 3 hinges, and were positioned so that the cables from each could easily go down the side of one of the supports to the battery compartment where the buck converter was housed. In figure 4.1 you can see how the positioning of the junction box affected our component placement considering that cables included with the panels do not actually run the full length of the panel. Not to mention it is ideal to have as few loose wires as possible on any motor vehicle for the safety of the users.

Figure 4.1: Motor, Battery, Charger I/O Integration

By placing the panels here we were able to benefit the project in several ways. First and foremost, the top of the cart is where we would receive optimal sunlight exposure for a fixed panel. This then allowed the second panel to be maneuvered in a way to compliment the first. Second, the position of the first panel took the place of the original roof itself, this meant that despite adding two large solar panels to our project, the cart itself did not experience that much additional weight. Finally the placement of the panels, while ideal for absorbing sunlight, was also able to be cooled while moving so as to help improve overall performance. [37]

Despite these points there are several things to be kept in mind about solar panel technology that was key to why we chose it, one of which is more efficient in

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terms of how the silicon is able to absorb solar energy and convert it at what is considered a high rate for the purpose of electrical output. Monocrystalline solar cells can achieve 21% efficiency whereas other types of less expensive cells including thin film and polycrystalline are only capable of achieving around 10% efficiency. Few solar charger companies use monocrystalline solar panels because of the higher cost to produce the solar cells, although these higher efficiency products are starting to have greater consumer demand in the market place due to their efficiency.

4.3 Cart

Using the chosen “classic golf cart” system associated with our model vehicle our cart subsystem layout was simplified somewhat, compared to more high end models made by this manufacturer. Below in figure 4.2 is an electrical schematic of the “EZ Go” cart system associated with our vehicle when it was purchased. As you can see six Trojan T105 batteries are placed in series to power the motor, when current enters the positive terminal the vehicle charges, and when it exits the positive terminal power dissipates to the motor.

Figure 4.2: Motor, Battery, Charger I/O Integration of a standard E- Z_Go TXT Freedom model ’05 Golf Cart

Understanding the basic design of the cart was paramount to how we went about modifying it for the purposes of our project. It should be noted that our primary manipulation of these power circuits only called for taking three batteries on one side of the bank, out of series with the three on the opposite side. No

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actual components from our project directly affected the vehicle motor, but instead limited the energy being passed to the motor through the batteries. [38] Some components to help with this include very large diodes to insure energy flows linearly.

4.4 Power Control Subsystem

From our various power sources (battery reserves and solar cell array panel), the power was distributed to the controller from the panels to be optimized and allocated to the electric motors. The power distribution from the panel was manipulated by the microcontroller via the buck converter influencing the amount of power dissipated to the batteries from the batteries and solar array go to and from the microcontroller. Power allocation controllers within the microcontroller powered the motors and during times of inactivity recharge the battery stores. In figure 4.3 a rudimentary mock up of this standard for how power dissipation from solar energy was to be distributed to high draw electrical components became the foundation for understanding our relay drive system. At various loads the electric motors would absorb and dissipate power at these dynamic rates leading to our selection of the dynamic drive control. [39]

Figure 4.3: Power Allocation to and From the Various Controllers

For our SPOC design, we had three specific components providing power output and drawing power input: the solar array panel, the batteries stores, and the electric motors. In order to facilitate power regulation between the three components, a network within the control as mentioned before, distributed this power in the various modes. These modes became eco mode, in which one of the two 18volt banks worked with a panel to drive the cart, while the other panel charged the other bank. Then there was standard mode where the car used a single battery and the two panels to mimic its normal drive mode to the user, thus improving the vehicle range. And finally the performance mode which dissipated all the energy in parallel to achieve maximum current at nominal voltage for the fastest acceleration. These drive modes distributed the power to the various cart components in the rudimentary manner represented by figure 4.4 below.

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Figure 4.4: Power Allocation In the Various Drive Modes

4.5 User Interface Subsystem

In order to facilitate some degree of user-machine interaction and to increase the user’s knowledge of the current status of the cart, we decided to implement a simple user interface. This interface used several basic hardware components, in addition to some background software, to present the user with useful data about the cart and the components within, as well as aid in tuning the cart for optimal performance.

4.5.1 Hardware Components The user interface for our cart included several components, listed above in section 3.3.3. The components linked together to create the rudimentary user interface that we felt, best met the user’s needs given our limited time constraints. For our interface we used the normal I/O from an atmega328 to drive an external OLED 16-character 2-row display that was used as the primary form of data output to the user. Additionally, the data displayed on this controller allowed for control via two buttons on the user display as shown below in figure 4.5 where buttons could be positioned ina multitude of locations based on the designers desire. Though we had many fine options we chose to go with the corresponding placement of buttons 3 and 4 as this fit best on the board and made for the cleanest look for our project. It should be noted that this U/I represents a board that is 3 inches tall by 4 inches long though it is hard to characterize in this simplistic mockup.

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Figure 4.5: UI Layout

It was important that our final design be both inexpensive but also extremely durable in order to ensure that the components could function properly when exposed to the elements but also be easily replaceable should the worst have happened. Since our primary design focus was on sustainable transportation over an overly aesthetic user interface, we felt this minimalist approach best suited us. Each of our interface components had been selected to fulfill this series of constraints based on low cost and high energy efficiency, and in the end all components could be dedicated to the atmega itself. To this end, it was judged that the power savings and high visibility of an OLED display was worth the tradeoff over a more pixilated screen such as the more expensive alternative models that were also available to us, and would have required significantly bulkier code to use. Additionally, those components would have had a higher power cost and been harder to integrate in to many facets of the project. Not to mention the potential for them to be accidentally damaged due to their sensitive nature only served to reinforce why we couldn’t use them.

Based on the design specs of the WEH001602A OLED 16x2 Character component, we could use a multitude of different methods for porting output to the screen. The display supported a series of commands with parallel data streams, used for sending specific commands to the onboard display controller. All of which were supported by intuitive and easy to read libraries. Alternatively, we could have also used the serial data method for sending these commands to the display’s onboard controller. However due to the I2C integration that would have already have had to have taken place at that point would already be too demanding on what was to be our master atmega for the purposes of microprocessor component integration.

In addition to the built-in controller, there was a secondary option available to us for outputting data to this screen. The controller supported an auxiliary input method for “Graphic input”. This mode gave us more freedom for building the interface, as the graphic input mode allows for full control over the individual pixels on the display. Through a combination of these two methods, we created several simple yet highly descriptive displays for relaying information to the user, while allowing for dynamic choosing of the information by the user.

The user will have a means of input to the cart through the additional input components of this user interface. This input will be facilitated by the inclusion of a series of buttons located adjacent to the display. These buttons will be labeled

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by either the user interface or a series of physical labels, which will be determined when we actually implement the interface.

These buttons and the display were connected to the atmega328 by ribbon cable so as to allow communication for both input and output while accommodating the extensive number of I/O ports. Once properly connected, the software running on the atmega328 appropriately modified the display output and operational configuration of the electrical cart. This let the user interact with the cart according to their preferences as well as increasing the effectiveness and marketability of the cart.

Another feature that was crucial to the UI was that the project allow for manipulation of the rear panel for the purpose of adjusting and holding the panel in particular positons. This was achieved by having the user lift and the slide the rear panel along a pole while holding the button attached to the pole. Once the sensors on the rear panel detected the optimal sunlight angle the microprocessor would cause the buzzer to go off alerting the user. This way the user could find the best angle without worrying about any sort of visual queues. If the buzzer did not go off that meant that the ambient light out made the angle negligible to begin with.

4.5.2 Stretch Goals Over the course of the project there were many different design ideas. But due to the nature and timetable for SPOC the implementations became somewhat limited. Here we focused on what parts would be preferable had we had the time to add them to our project, as well as why it was difficult to implement in our current design.

One of our primary stretch goals were a fully articulated Photovoltaic cell mount. For the purpose of maintaining optimal photovoltaic absorption it was ideal to implement a mounting system with at least two points of articulation. The mount would rotate along the x-axis (Up and down) at up to 80 degrees of freedom. While the final project did include this feature, it would have been nice to have it in an automated fashion that could do it without user input, and even greater sensitivity.

Another primary stretch goal for the project was implementation of GPS. There are many GPS enabled microcontrollers and Arduino GPS adapters and shields. By adding accurate, functional GPS, SPOC could have optimized travel patterns over terrain. It would have also allowed the vehicle to maintain travel data so that it could inform the user when it was dissipating more energy than it would need for a return trip.

The limitation for this goal is that it is inefficient for SPOC to implement GPS on any of the currently intended Arduino Uno models. This is due to the computational overhead of persistently tracking vehicle position. It also requires

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the use of I/O pins that will be accommodating a host of other components that are far more important for proper vehicle functionality. The alternative to these limitations is to acquire another microcontroller that is dedicated to GPS tracking which was possible using I2C but not practical for this project.

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5. Design Summary of Hardware and Software

This section focuses on how components from the project were actually integrated as a whole. The primary components of this system are the Photovoltaic cells connection to the battery assembly. The remainder was battery connection to the motors, and finally the microcontroller overlay. The microcontroller sensor connections were also an important aspect of the overall maintenance of the vehicle but not as crucial as these 2 primary components. Other points of interest were User interface. This includes the LCD integration designs. Finally this section also covered the basics of vehicle design and usage modeling. This includes the vehicles expected performance mode and also a brief look at the performance boundaries affected our vehicle.

5.1 Solar Cell Charge System

The solar cell charge system transfers the power from the array of photovoltaic cells in one of two possible directions. The solar charging system can transfer power to the electric motors during use in transportation or the converted solar power can be delivered to the batteries to recharge them during period of system rest. This system will be regulated by two of the microcontrollers working in tandem with each other to ensure efficiency while maintaining safe functioning of the cart and associated systems. [40]

Figure 5.1: Solar Cell Charge Diagram

The simple system shown in Figure 5.1 above was designed to easily charge the batteries using the power generated by the solar cells. This charging circuit was controlled by two of the programmed ATMega328 microcontrollers working in tandem, one to efficiently convert power and one to control the distribution of this power after generation. The distribution-focused microcontroller allocates power from the solar panel to the electric motors during the performance-focused drive modes and allocates power to the battery banks during the recharge-focused drive modes.

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5.1.1 Buck Converter As outlined in section 3.4.2, a buck converter was implemented to load-match each of the PV panels, thus allowing for greater optimization of power output. The buck converter had to be able to withstand up to 35V and 8A on the solar panel side, while sustaining output voltages of 14-24V and corresponding currents of 15-10A. These extremely high-powered requirements placed strong limits on the parts available for use, as well as dramatically increasing the associated costs.

Shown below in Figure 5.2 is labeled picture of the final realization of the circuit as it was implemented on SPOC. It is clear that some changes were made to the simple design shown in section 3.4.2, as additional complexity was required for this application.

Figure 5.2: Labeled Final Buck Converter

The converter was constructed around a pre-drilled perforated circuit board, with some of the holes widened by usage of a dremel tool. Once the parts were properly laid down on the board, a combination of 14AWG and small-gauge wire was used to connect the components properly. A P-channel MOSFET designed for high power applications handled the switching portion of the buck conversion process. However, driving the MOSFET properly without exceeding tolerances

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required the inclusion of a secondary circuit on the board to ensure that the MOSFET was triggered appropriately.

One of the benefits of utilizing a buck converter is the ability to dynamically alter the ratio of input to output voltage by changing the duty cycle being supplied to the MOSFET that controls the overall flow of current. For an ideal buck converter, the duty cycle directly corresponds to the input / output voltage ratio, but with non-ideal components small inefficiencies creep in and reduce the output voltage below this ideal level. This ratio control will become very important in the next section for the implementation of maximum power point tracking.

As shown below in Figure 5.3, the Timer1 Arduino library was utilized to generate a clock signal at 14.93kHz with a variable duty cycle based off of the position of a potentiometer. This was utilized primarily for testing, and the potentiometer control was going to be phased out in favor of a dynamically automatic adjusted pulse width, as decided by the microcontroller.

Figure 5.3: Generation of Clock Signal

5.1.2 Maximum Power Point Tracking (MPPT) The primary driving force behind the inclusion of the buck converter was to enable the independent tracking of each PV panel’s power point. Because of the underlying physics behind the operation of photovoltaic cells, they most effectively produce their rated wattage under highly specific loads. By implementing current and voltage sensors on the solar panel, it is possible to alter the conversion characteristics of the buck converter to maximize the power output of the solar panel.

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As shown in the previous section in Figure 5.3, a common Arduino library was utilized to allow for dynamic adjustment of the clock pulse width by the microcontroller. This pulse width modulation, or PWM, forms the groundwork for tracing out the I/V curve that the solar panel follows. At the knee of this curve, power is maximized, so in order to find the maximum power the microcontroller simply has to slowly adjust the pulse width in the direction of increasing power.

The steady pattern of adjustments followed by measurements is known as “perturb and observe” and is the primary algorithm utilized by most of the MPPT systems on the market today. Additional research was carried out to find other potential options for this algorithm, but in the interest of simplicity and time the P&O model was eventually selected. Some of the successful results of this implementation are seen in figures 5.4 and 5.5. Here the duty cycle of the converter is varied in order to display how power dissipation across this unit works. In figure 5.4 the duty cycle I shorter resulting in a lower load voltage (shown in turquoise) when compared to input (purple). However as the signal is manipulated to a longer cycle the voltages move to meet each other. One of e the most remarkable facets of this project was that this was achieved via a square wave off an atmega 328P-PU.

Figure 5.4: Generation of Clock Signal as oscilloscope output. Shorter duty cycle lower voltage

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Figure 5.5: Generation of Clock Signal as oscilloscope output. Longer duty cycle less voltage

That means that realistically any hobbyist could make an Atmega Buck converter with enough research and the right parts. This is not to under play the project. To find the components shown in the above figure took many months of searching and redesigning.

5.1.3 Panel Mounting and Adjustment To reiterate the SPOC utilized two sets of solar panels to achieve optimal power absorption in order to meet the design requirements. In figure 5.6 below, there is a side by side comparison of the before and after and how the carts profile changed once these components were mounted. As shown the cart will clearly pick up some wind resistance due to this change in profile however this is negligible considering that this cart will not exceed 10 miles per hour under optimal conditions. Here you can also see how the canopy has been replaced by PV cells. This actually proved more beneficial than the previous design because the panels better protect the cabin of the vehicle form the elements, and from more angles helping better protect sensitive parts of the vehicle.

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Figure 5.6: Original Cart Profile (left) Modified Cart profile (right)

In figure 5.7 there is a close up look at the panel adjustment mechanism that can barely be seen behind the seat in figure 5.6’s modified profile. In figure 5.7 the left image depicts the carts rear panel in a partially extended position at roughly 30 degrees to parallel with the ground. On the right is the image of the handle used to adjust the rod from the previous picture. On the handle, in the dark region is a button that when held, can alert the user as to when they reach the optimal angle via the buzzer mounted directly adjacent to it. While not aesthetically pleasing these components needed to be wrapped in tape to help protect them from the elements considering their position.

Overall this implementation was quite simple as seen in the code in figure 5.8. The primary focus of the code was to detect if the button used for adjusting the panel was being pressed. If not then the microprocessor did absolutely nothing allowing it to remain in a low power mode. The moment the user interacted with the project the atmega knew to start listening for values off the Photo resistors. You may note that the analog read for these resistors was partially truncated at read.

This was so that the threshold was low enough that practical comparisons could be made in real-time since the platform was intended to move while measuring. Once these values matched while the button was pressed the buzzer adjacent to the button went high. The buzzing represented an angle ideal for charging. The best part about this implementation was that it also accounted for light entering at an angle but did not make it the point of primary focus since the panel could only rotate on one axis, but received light from multiple directions. Overall the project implemented simple code like this in parallel to maximize efficiency.

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Figure 5.7: Cart with real panel partially extended (left) Cart adjustment rod with mounted components (right)

Figure 5.8: Buzzer code representation

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5.2 Battery Motor Integration

The battery motor integration was standard to the cart used for the final implementation of SPOC. Since this was the manufacturer's design it was impossible to interact with the motor directly. As a result SPOC has an extensive array of 30 Amp relays running throughout its battery compartment for this express purpose. In figure 5.9 the relay drive circuit is shown with the integrated atmega328. The container represents a self contained black box that is able to drive the vehicles relay components via a series of step up relays. These relays then drive large 30 Amp relays placed throughout the battery compartment.

Figure 5.9: Relay driver housing (left) Secondary relay controller (right)

The large black rectangle is the primary 12 volt battery module responsible for powering the larger relays that was intended to be replaced by a direct connection to the batteries later on. In figure 5.9 on the right there is the secondary mode selector which allows for manual mode selection should the normal I/O fail for any reason. This is mainly a safety precaution since the primary screen is always exposed to the elements and could be damaged. On the secondary controller drive modes are changed by holding down the toggle witch. When the green LED is on it is in eco, when red it is in performance, and when both are on it is in standard. That being said the final version of the project included a park mode where neither LED is on representing that both batteries are charging.

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Figure 5.10: Setup code snippet for Relay Driver

This is reflected in the code snippet from figure 5.10. Here the code shows the different relays that are associated with the project. Each one of the outputs corresponds to one of the eight low voltage relays from figure 5.9 as seen in the black box. These values were than manipulated to produce the three different drive modes shown in figure 5.11. In the following figure all three drive modes are represented as simple digital writes with their corresponding LED combinations to ensure that the mode displayed is accurate.

In the following figure 5.11 the code is shown in the order standard, performance, eco and charge. Though the first three are drive modes, the fourth is actually a last minute variant intended to boost energy absorption when the cart is stationary. Note that this code does not switch between batteries in real time because that was to be handled by additional code from the buck converter which spoke to the relays using I2C.

The labels for the code are fairly straight forward but you will note that setStand (which is standard mode) has no output lines going high. This is to ensure that should the worst happen and the cart not be able to dynamically change mode for any reason, the components reflect the standard drive mode and can behave as such so that the user is not completely left at a loss. The primary reason for choosing standard though was that is required the least manipulation for components to work in that fashion.

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Figure 5.11: Relay drivemodes: Eco Mode (top Left), Performance Mode(Top Right), Standard Mode (Bottom Left), Charge Mode (Bottom Right)

5.3 Sensor Integration

For our project monitoring project components was cruicial for tracking energy dissipation, temperature changes in the components, solar intensity, and direction. As a result the final version had 2 primary types of sensors we intend to use for data collection. They are photo detectors, and thermistors. While voltage and current sensors were also part of the project they were not included here due to their lack of use in the final project. Through the use of these sensors it was possible to accurately collect all data necessary to keep up to date statistics on things such as battery life while maintaining vehicle longevity.

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5.3.1 Photodetectors The project utilized 2 GL5528 CdS Photoresistors. The vehicle used these 2 resistors for tracking light intensity, and by extension the position of the sun. The two photo detectors were placed on opposite sides of a divider along the lateral portion of the rear panel as depicted in figure 5.12. The purpose for positioning them in such a manner was to track light intensity in order to determine when the panel received direct, or near direct sun light. By determining the brightness of the light being taken in from the sun, the onboard computer could calculate the rate of energy absorption of the vehicle. Using this information the computer compared these values against each other to determine if this met the optimal solar exposure angle for the rear panel.

Figure 5.12: GL5528 Photo resistors mounted on custom housing for optimal incident angle of light detection

Referring back to the stretch goals, another reason for the appeal of these light detectors is that they will allow the computer to track the position of the sun even when the user is absent. The implications being that it would have been outstanding to include an autonomous energy collection system for the rear panel to maximize energy intake when parked, even if only over a few degrees. In this way a dedicated Atmega328 would improve the solar intake of the vehicle by statistically significant margins. [41]

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5.3.2 Thermistors In order to adequately track thermal dissipation from the batteries, this project used 4 DS18B20’s. These are standard three prong thermistors with a range of - 55 to positive 125 degrees Celsius covering the Trojan T105’s entire operational range. These are low profile thermistors that could be easily integrated into the design of the project while remaining modular. An electrical systems temperature can greatly impact a devices overall efficiency, this is even more true when dealing with solar energy and high intensity light sources. As a result SPOCs sensor array was trained to track these values to ensure that none of the components exited there area od acceptable operation.

The four thermal sensors were to be attached to each battery following the manner displayed is figure 5.13. the image shows 4 thermostats resting in between each gap in the batteries to get an average of temperatures and report them to the user. In the diagram all the primary lones come from a central hub which then snake down in to their respective areas, the reaming lines return to the microcontroller. That fact that these thermostats have such high precision for Digital I/O signals and could be easily replaced and read added to its benefits. [42]

Figure 5.13: 4 DS18B20 Thermistors distributed throughout the battery compartment of the vehicle

5.4 User Interface

The user interface consists of a series of hardware modules used for input and output, as well as some software designed to run on the MSP430 microprocessor. For the project all the components were connected to a perf board and then mounted on the vehicle. The display appears as it does in the image in figure

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5.14. As demonstrated there are two buttons attached to a single 16x2 OLED screen for the purpose of displaying data. The figure itself shows button ‘B1’ being pressed allowing for the change of drive mode with a short descriptor. However should anything go wrong, the controller variant shown in figure 5.14 is still available. Figure 5.15 shows the how each button executes, as well as what the combination does.

Figure 5.14: 16x2 OLED Display Integration

Figure 5.15: Button combinations associated with figure 5.14

The components were dash mounted as shown in figure 5.16 because this was thought to be the simplest and most accessible location for a user to access

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these controls. Additionally the screen would display data while driving that pertained to vehicle performance, therefore it would be best if the driver could easily view this data without becoming distracted from vehicle operation.

Figure 5.16: User Interface positioning

Before moving on a quick code review of how helpful spark fun and Adafruit libraries are, would prove beneficial. In figure 5.17 the code shows all the necessary pin assignments in order for the code to display data. This takes literally three lines of code: Import the adafruit libraries for the component (line 1), Assign the digitalWrite pins (line 3), and finally initialize the lcd screen for 16x2.

User interface consists of a series of hardware modules used for input and output, as well as some software designed to run on the MSP430 microprocessor. For the project all the components were connected to a perf board and then mounted on the vehicle. The display appears as it does in the image in figure 5.14. As demonstrated there are two buttons attached to a single 16x2 OLED screen for the purpose of displaying data. The figure itself shows button ‘B1’ being pressed allowing for the change of drive mode with a short descriptor. However should anything go wrong, the controller variant shown in figure 5.14 is still available. Figure 5.15 shows the how each button executes, as well as what the combination does.

This is significantly more light weight than any other method found to display I/O to users. It was three lines of code, took up little to no on board memory so that more could be allocated to other functions. Above all it represented near full

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control over the LED board. The ease is further reflected in the write commands for the screen shown in figure 5.18. Here the code follows a simple format. Set cursor to X,Y coordinate, erase what was there before, set cursor again, and print. It made displaying multiple things on a single screen significantly easier as can seen from the previous figure 5.14

Figure 5.17: User Interface positioning

Figure 5.18: OLED print method

5.5 Microcontroller

For the project a dedicated circuit board was designed as seen in Appendix B, and fabricated to a board design in Appendix C. The board represented the originally desired microprocessor for this project, the atmega 2560. The board shown in figure 5.19 was the final product of countless hours of labor incorporating both a 2560, as well as high power components. However due to a minor lab mishap some of the components were damaged and the entire Printed Circuit Board became unusable. This is partially reflected in figure 5.10 in how the repairs were attempted. The solution was to go back to our originally intended microcontroller.

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Figure 5.19: 2 Layer PCB for atmega 2560

In figure 5.20 was the contingency plan for the PCB for SPOC. 3 perfboard fabricated atmega 328 processor boards with 28 pin sockets ready for programming. Each board cost less than $10 to fabricate and proved a significantly better component due to its modularity. Using I2C these components were able to be easily retrofitted for the varying tasks. And shifted around or dedicated to whatever function.

Figure 5.20: 3 Perforated circuit boards modeled after the Arduino Uno R3 to accommodate atmega328

To program the atmega328s, a USB powered arduino UNO was used as the serial debugger. It allowed code to be sent to the 328 which was mounted adjacent to the Aduino. The programmed chip was then moved to one of these 3 microprocessor housings. The ultimate beauty of these perforated board microprocessors was that they allowed the user to code in Arduino IDE but still export to a different platform. The assembly, in addition to being relatively cheap, was also very easy. A novice electrical engineer with minimal soldering knowledge could assemble one in an hour.

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The only drawback to using these microcontroller boards over printed circuit boards was that they remained mostly exposed. As short on one of these could be catastrophic to the proper execution of the previously discussed code which is integral for vehicle operation. As such many measure were taken to ensure that once finished, the processors would be secure and not move around despite the SPOCs movements.

5.6 Vehicle Modeling

This phase was still in its preliminary design phase early on but once so we have no actual code since we still need all necessary components to demonstrate the environment and actual I/O control. However the intent for the modeling modes was to produce three different drive settings: Performance mode, Standard mode, and Eco mode. All these worked off the internal computer in the vehicle and affecting different aspects of the vehicle such as range, top speed, and power dissipation as described before in the battery motor integration section. Our hope was to have all these facets working with Bluetooth and GPS integration. This way both the user and the vehicle were able to keep the most up to date statistics on the vehicles performance and when components may need to be replaced.

5.6.1 Normal Mode Normal mode was just as it suggests. In this instance all vehicle components behaved as they normally would in the absence of any supervising software. For normal mode the on board computer simply managed functions that are integral to the carts operation; these include: energy dissipation oversight, energy collection oversight, and top speed control. The purpose of overseeing the energy dissipation and collection was to ensure that the carts components were operating efficiently and within tolerable standards.

As stated before a common danger with electric vehicles is poorly supervised energy transfer. Unregulated, this behavior can drastically affect the vehicles performance over the course of its lifetime. It can also put the cart in danger of overheating and catching fire. The other aspect (limited top speed) simply limits vehicle speeds to what would typically be expected of the cart by its manufacturer. This way the cart is operating within expected norms so the risk for the priory stated dangers is at a minimum but can still be present when dealing with such a dynamic system.

5.6.2 Performance Mode

In performance mode the vehicle’s monitoring no longer limited acceleration Here the goal was how to deliver the optimal amount of energy to the motors as efficiently as possible. The on board computers focused on guiding all this

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energy into the motors while staying within tolerable limits. To reiterate this meant that the only limiting factor was the temperature of the components. Should a case arise where the vehicles energy output was causing too much heat production, the on board computer took the necessary precautionary measures such as limiting the top speed, or cutting power to the motors all together. Thankfully during testing no such situation occurred otherwise power to the system would have been disabled entirely.

Since the vehicle did still need to perform properly with decent remaining charge, it was intended that a limiter be included in the UI that would switch the performance mode back to normal mode. Ideally this was an adjustable percentage so that the user could select how hard they wish to push the system. With a baseline of 25% to ensure that there is ideally enough charge for the return trip since it would be preferred to make it home. However due to time constraints they could not be implemented and the feature had to be removed.

5.6.3 Eco Mode In Eco (economical) mode the vehicle’s entire functionality based solely around traveling as efficiently as possible. The original model called for the computer to calculate the most energy efficient top speed so that the vehicle could achieve maximum range. For practical purposes it was intend to implement a low end for this mode that limits speed to no lower than 6 mph. Referring back to the desired GPS implementation, GPS could drastically improve the vehicles drive ability by calculating the distance it had to travel between its current location and its desired location. This way the cart could be set to calculate the desired top speed so that it can reach the target destination while using maximum power dissipation. It would also communicate with Bluetooth devices (ideally gps enabled phone) to determine the optimal path for mapping and getting to the destination. Again the system was a desirable as it would need at least on board bluetooth and possibly on board GPS to work properly. The end result became an Eco Mode that used nothing more than solar energy and intuitive relay switching to distribute power. The primary panel (one with greatest output) worked with one set of three batteries to power the motor, while the second panel trickle charged the other batteries. By using the least current possible, trickle charging would improve longevity of the Trojan Lead Acid batteries. It was intended that this system choose between which battery and panel were arrange d in what way based on real time values, while achieved the entire system called for multiple delays interdispersed between line switches to preserve the relays and prevent ringing.

5.6.4 Safety Measures

The final concern of this section was safety of both the passenger and the vehicle. The resulting drive modes were the result of all these systems and designs working in tandem. For the relays, current limits for the line and motor became a primary priority, so fatigue points were placed through out each line so

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that should there be any sort of feed back or power spike, no actual damage would come to cart components. Furthermore the shutoff circuits guaranteed that power auto dissipate to ground in case of this prior issue.

To guarantee that the lines did not get too hot the design incorporated 8AWG, and parallel 10AWG thick insulation electrical cable to guarantee that load did not effect the vehicle, and that the battery compartment not heat up as a result of thermal energy through those line. Additionally high current diodes were placed on all the outlines to guarantee that current be flowing in the proper direction. This ensured that if components did fail, no shorts would occur damaging the internal systems. The only modification that was not able to be made was the addition of two fans that would have used energy from the batteries to flow air through the compartment. This way the batteries and all adjacent electronics would remain at a constant temperature in the absence of heat collection.

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6. Part Acquisition and Bill of Materials

Table 6.1 below shows a breakdown of the costs associated all major components of the vehicle. This is the primary body, which was purchased with the Trojan batteries already installed. We used one Grape Solar 250 Watt Monocrystalline Photovoltaic panel as the roof of the vehicle, as well as a secondary PV panel mounted on the rear of the cart. We also acquired an Adafruit OLED screen with simple I/O; this was mounted on the vehicle dash. And finally we purchased several ATMega328 Microcontrollers to modularly handle all onboard calculations, computations, and energy tracking. The modular layout keeps our design complications to a minimum, as well as aiding in ease of testing.

Table 6.1: Primary Component Costs for Project Budget

Component Model Description Cost

Cart E-Z-Go TXT Standard outdoor electric 2- $1,600.00 seater club cart.

Battery x12 Trojan T105-RE Long lasting lead acid battery $0.00 Signature Line Flooded intended for outdoor use. Deep Cycle 6V Battery Included in purchase of cart.

Photovoltaic Grape Solar 250-Watt High efficiency Photovoltaic $374.99 Cells x2 Monocrystalline Silicon solar paneling. Photovoltaic Module

Screen Adafruit Blue Character Small energy-efficient display $27.95 OLED with excellent readability in 16x2http://www.adafrui direct sunlight. t.com/products/1287

Controller x3 ATMega328 P-PU with Low power embedded $5.50 Optiboot microcontroller. Designed for efficient vehicle control and power monitoring.

Printed Circuit 4PCB, various SMD Single layer board with SMD $185.30 Board manufacturers components.

Cost of Primary components: $2579.73

Table 6.2 is a breakdown of the components that are of significance but not as integral. These include the various sensors that allowed for active optimization of cart energy distribution. Additionally, this includes the DC-to-DC converters described in section 5.1, as well as the relays and diodes used to implement the

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drive modes. Additionally, a hobby kit with many wires and testing components was used for initial prototyping of the many systems on the cart.

Table 6.2: Sensor and Peripheral Electronics Costs for Project Budget

Component Model Description Cost

Thermal TMP36 - Temperature Standard hobbyist thermal sensor $1.50 sensors x6 Sensor used for tracking heat of cart components for efficiency statistics and preventing overheating

Photodetector GL5528 CdS Simple photovoltaic sensor meant $1.50 (light sensor) Photoconductive cell to measure light intensity for x2 tracking PV cell absorption efficiency and PV cell positioning

Hall Effect HMS 10-P Current sensor designed around $15.25 Current Sensor Hall Effect principle, used in MPPT x4 and buck converter designs

Buck Converter Self-built from Switching mode buck converter $31.49 x2 individual components described in section 5.1

SPDT x8 AGT 30/40A SPDT Single-pole double throw relays $13.95 Relays used to control energy dissipation in each drive mode

High Voltage IN250B Used in tandem with above SPDTs $3.00 Diode x8 to control energy flow

Assorted wires Flex - Arduino starter Assorted cables, mini breadboard, $59.95 and cables kit wires, sensors, and buttons for testing purposes

Cost of cables, sensors, and buttons: $331.53

Overall Total: $2911.26

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7. Project Prototype Testing

This section covered how we went about designing tests for the project, it also focused on what content needed to be tested and the best way to measure these changes. The goal was to see how much of an improvement SPOC had over its rivals. Primary testing worked all on facets, from UI, to stress testing, to code.

7.1 Hardware Test Environment

Since there are a variety of factors involved in the testing of our various parts as well as our final prototype, we now specify the environment and conditions our parts were tested in. Some parts needed specific individual testing, including the cart, the batteries, and the solar panel. These tests were evaluated independently of the prototype testing to calculate various specifications. For the design of the power optimization unit as well as the user interface, specific understanding of the cart specifications was required along with the solar array performance and storage capabilities of the deep cycle batteries used. Various factors were tested to ensure the reliability, safety, and proper functionality of the finished prototype.

7.1.1 Location Because of the size of our project, we required a place to store and test the cart. The loading dock outside of the Engineering 1 building was used because of its proximity to the lab in which we tested all of our major components. Directly following cart acquisition, the cart was moved to this location for storage and testing. Here the cart was safely kept and tested on the large sidewalks that connect the UCF campus together. Because of the difficulty of transportation of the cart, we did not move the cart very much during the design, testing, and troubleshooting phases. We used our access to a trailer for occasional long distance transportation of the cart. One specific issue with our location is the Florida weather; while we struggled with bad weather, humidity, and warm conditions, our cart did not experience severe cold weather conditions. The location chosen for our parts and prototype testing was more than acceptable, and allowed for easy testing and implementation.

7.1.2 Ground Environment For the testing of the initial cart acquired and the later prototype, several different ground environments were observed in their relationship to the level of performance on each test. With our selected location, we had a variety of different ground environments with which to test our carts. This variety of ground environments helped us evaluate the fluctuating power consumption of the motor based on the softness of the ground, as well as the various levels of steepness. For the energy optimization of our final project, the particular performance of the carts tires, motors, batteries, and optimizing unit was evaluated with respect to

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these varying conditions. Less than ideal ground conditions have the potential to cause additional strain on the electrical components, which in turn can result in overheating and dangerous electrical fires. This danger was mitigated by the inclusion of our temperature sensing network, as well as our emergency shutoff software protocols. In the northeast corner of the university campus, we have access to various terrains: road, off road, as well as various levels of steepness which gave us a variety of conditions under which we designed, tested, and recorded performance data.

7.1.3 Weather Conditions For the testing of the initial acquired cart, other components, and the later prototype, various weather conditions were experienced throughout the course of the designing process. This spectrum of conditional testing assured the overall stability, safety, and part functionality of the components and project as a whole. As the creation and testing of the project took place in the University of Central Florida region, humidity and heat, as well as severe storms are obvious weather factors that we tested. Our design will not have to be particularly tolerant of cold weather, due to seasonal and time constraints.

One of the issues inherent in warm climates is the possibility of electrical components overheating and melting or causing electrical fires. Excess humidity can also short electronics via corrosion and rust, wreaking havoc on delicate electrical components within our design. For this reason, our design was built to be as sturdy as possible while also limiting any performance fluctuations based on heat and humidity. Additionally, we included a temperature-monitoring network that helped to mitigate the risk of electrical fires or other temperature- based damage.

In addition to the weather-based stress testing that we put the cart through, we also tested the output of the solar panels under a variety of conditions. The output of a PV panel is of course dependent on availability of sunlight, but output also varies inversely with temperature. Because of these dependencies, we had to test the panels under a variety of different weather conditions and temperatures. This testing allowed us to better understand the performance characteristics of the solar panels, thus allowing for better optimization of the power output from the panels under widely varying conditions.

As shown in Table 7.1 below, a specific set of environmental conditions were isolated to determine and predict potential problems before they arose. These categorized environmental conditions are each associated with a few concerns that pertain specifically to the listed condition. By ensuring that each concern was handled properly, it was guaranteed that SPOC was able to successfully perform under all outlined environmental conditions.

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Table 7.1: Environmental concerns

Environmental Test Specific Concerns Within SPOC Design Conditions

Off Road Terrain -Electric motor overheating due to increased stress -Airborne debris interfering with improperly protected electrical components

Steep Grades -Electric motor overheating due to increased stress -Unstable conditions can cause issues with circuitry and with the efficiency of the solar array.

Hot Weather -Decreased efficiency of the photovoltaic cells within the solar panel causing overall energy throughput drop -Electronics might malfunction due to higher levels of heat; electric motor is also more likely to overheat during prolonged periods of use in warm climates

High Humidity -Possibility of electrical shorts due to heavy humidity and condensation build-up on unprotected electrical components within the designed SPOC -Condensation on and in solar panels can easily cause drastic reduction of PV cell efficiency

Overcast Skies -Decreases the amount of sunlight incident on the solar panel of photovoltaic cells -Decreased sunlight results in decreased power output and a drop in the range extension usually provided by the use of the solar array system

7.2 Hardware Specific Testing

With a number of different subsystems and components, the possibility for error was very high with the individual parts and the interactions between them. To design and code our power optimization framework, the core of the project, we had to know and understand the performance of our various components with a minimized amount of error. Under various weather and daytime conditions, the solar panel performs at different levels of performance, so our team tested the solar panels under each of these conditions. The electric cart was tested before and after design modifications to accurately adjust and calculate the adjustments of the speed and range of the electric cart. Under various heat and speed conditions, the performance of the energy optimization was positively affected due to increased knowledge of the performance characteristics. We observed the performance of the included deep-cycle Trojan batteries to determine the effects of various environmental conditions. To this end, charging and discharging cycles were implemented to test the performance of the batteries. Finally, after the

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design and implementation phases of the project, our team conducted a series of tests on the prototype before integrating all components together. Several rounds of troubleshooting and additional testing followed this integration testing phase; these allowed the team to enhance the project for optimization of metrics such as range, speed, component temperatures, and user interfacing.

7.2.1 Solar Panel Testing The performance of the chosen solar panel was directly affected a variety of different factors. The varying performance was evaluated to design the rest of the systems and calculate the SPOC’s ability to reach the desired goal specifications. Atmospheric conditions were the main contributor to solar panel inefficiencies which is why positioning was so significant. We had hoped to have an apparatus similar to that of figure 7.1 for the SPOC but feel that the current variation was adequate given the time frame. Since photovoltaic cells work best when the sunlight is orthogonally incident on the substrate of the panel. This rarely occurs in real world applications, so the effect of the angle of incidence on the panel efficiency is highly important to the design. [43]

Figure 7.1: Panel Adjustment Reference Design

Days of partial sunlight directly affected the performance of the solar panels, as clouds and smog obscured the available sunlight, creating an environment unfriendly to solar power production or optimization. In some cases, humidity caused condensation in and around the panels, which consequently limited the absorbed light, while excessive heat directly decreased the efficiency of the individual photovoltaic cells. These different environmental factors helped to prove the beneficial effects of hinging panel mechanisms to maximize the available sunlight on the rear solar array panel.

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7.2.2 Electric Cart Testing From our acquired cart, several performance characteristics required evaluation to calculate energy optimization specifications for our desired goals. The top speed safely reached by the cart was measured with multiple different weight loads on the cart, as well as varying passenger counts. Power drawn by the electric motors at various speeds and levels of acceleration was measured and analyzed to calculate the most energy efficient speeds of travel, as well as optimal acceleration characteristics for the designed SPOC. [44]

Additionally, on various surfaces and grades, the power drawn from the batteries was measured to gain an understanding of the average load exerted by the electric motors under different conditions. Electric cart testing included multiple phases of speed evaluation, voltage loading, effect of carrying capacity, effect of terrain, and average range of the vehicle as acquired.

7.2.3 Battery Testing The two primary metrics for measuring battery health are charge time and rate of discharge. The Trojan deep-cycle batteries were tested under a variety of conditions to determine health both before and after modification. The battery discharge rate was tested under a variety of loads to test the durability and longevity of the battery with and without stress. [45]

The batteries were also tested for their recharge times in two specific ways. The chosen Trojan batteries should have their recharge times measured when recharged by outlet. The recharge rate from the solar cell panel should also be recorded for comparison. With these performance values, the necessary calculations were made to optimize the use of the energy drawn from the batteries and from the solar panel. With this data, we set up specific constraints on vehicle ranges and speeds that could be practically reached.

7.2.4 Microcontroller Testing Microcontroller testing can be performed on a number of levels. Various input and output signals can be measured to assure the functionality of the microcontroller and its communication to various components such as the light sensors, power controls, Bluetooth components, GPS functions, temperature controls, and user interface input and output. [46]

The proper function of the controller can be tested under a number of environmentally adverse conditions such as heat, humidity, motion, and even other electrical/ magnetic fields. Microcontroller coding can be tested as well under various software testing conditions as details in following sections. Table 7.2 reflects how these concerns related to elements of the SPOC.

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7.2.5 Component Performance Table

Table 7.2: Component Performance Table

Individual Component to be Tested Performance Values To be Tested

Solar Panel -Efficiency at various times of day -Efficiency in adverse weather conditions -Efficiency in prolonged high heat

Electric Cart -Top Speed -Power Draw at various speeds -Power Draw on non-ideal surfaces -Average range of the acquired cart

Deep Cycle Batteries -Recharge Time from Outlet versus -Recharge Time from Solar panel -Extended Battery Life

Microcontroller -Turnon voltages -Proper functionality in non-ideal conditions such as heat & humidity -Communications with various sensors

7.2.6 Prototype Testing After the integration of the designed components and features into a rough prototype, our team enters the testing and troubleshooting stage of the design process, where we test various situation and features of the design to see if the designed SPOC functions as we had hoped and planned it to. In this stage, we put our prototype through its paces in our attempts to polish and smooth out the rough edges on the initial design. Speed and range will be tested using the various modes relying on the different modes of power supply from the batteries and the solar panel.

The various optimization modes can be tested and adjusted to meet our desired specifications. The “eco mode “ will minimize the drain on the batteries while maximizing the range and energy efficiency of the SPOC. The “power mode” will maximize the speed of the cart while providing a steeper drain on the batteries and solar array of the cart. The “normal mode” of the cart will leave the operation of the cart unchanged in its use of electric motors and battery reserves. The various outlet and solar panel based recharge times can be tested as well. The overall functionality of the cart can be optimized with small adjustments being made to the layout of the user interface. Table 7.3 reflects the primary points of this testing as was follo9wed in what became the final design of the project.

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Table 7.3: Prototype Testing Table

Prototype Feature Tested Various Conditions Tested Under

Range -Different weather and terrain conditions -Range at different speeds -Range in eco mode vs. power mode

Speed -Different terrain conditions -Speed in power mode vs. eco mode -Safe maintenance of speed at all times

Optimization Modes -Eco mode really does maximize range -Power mode really does maximize speed

Charge Times -Outlet recharge vs. solar panel recharge time -Solar panel charging capabilities under various non-ideal weather and daytime conditions

User Interface Simple and intuitive controls and layout Sturdy and bug-free design withstand abuse

7.3 Software Test Environment

Software testing for our project will be conducted in the MSP430’s Optimized C/C++ Compiler v 4.2. The primary focus for this testing is USer interface and the MSP430’s ability to handle data tracking and mode switching. MSP430’s can only run on the physical microcontroller with which the code is intended for ensuring that the system operates on the actual deployment hardware.

The primary software test will to load the base energy tracking software on to the bootloader. We will then perform simple I/O circuit tests by applying different currents to the lines normally intended for the solar panel, batteries and motors. We will also do the same testing across the different types of sensors. The focus of this testing is ensuring software will shut off at certain ranges to prevent overload.

Another focus for testing is the Bluetooth. We will be installing a Bluetooth shield on out atmega328P-PU. To this end we intend to test simple communication between the atmega328P-PU and a device running compatible Bluetooth capable software. Ideally this will be a simple test since the majority of firmware, and Bluetooth functional protocols are already embedded in our RN-42. As a we will have the device ping our microcontroller, and vice versa, to see what limitations we have in our communication between the two modules. Table 7.4 reflects primary desired components that were to have been tested with Bluetooth integration had we had time.

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Table 7.4: What we expect to test strictly regarding Software communication and I/O solely on the atmega and RN-42 pin assignments

Software Feature Tested Various Conditions Tested Under

Different simulated -We will run different currents on the voltage in Photovoltaic inputs lines intended for the PV cells to ensure shut off in case of extremely high or extremely low voltage

Temperature Sensor -Send high thermal reading from thermal sensor line to determine if battery is in danger of overheating -Send high thermal reading from display to determine if display is in danger of thermal damage. -Send fluctuating thermal reading from thermal sensor on PV cell to determine if the MSP430 will suggest angle alterations.

Bluetooth connectivity -Will the RN-42 send a signal to the paired device -Will the RN-42 recieve a signal -How much data can we transmit with minimal overhead

7.4 Software Specific Testing

Software specific testing will focus on different drive modes and data tracking. Over the course of this testing the primary focus will be to achieve three differently tuned vehicle drive modes by determining how the code will limit the I/O on the PINs. The first mode is normal mode. Here our code will limit the top speed to manufacturer standards and monitor all system sensors to ensure collection and dissipation are within acceptable norms. The next is Performance mode, here we want to ensure that the microcontroller correctly monitors sensor data to ensure the vehicle suffers no damage, and to ensure that when it calculates a given remaining battery percentage it switches back to normal mode. The final mode is economical mode. Here the code will take in the data we send it and determine an optimal top speed and performance to determine efficient energy dissipation. This final mode was currently being redesigned since it requires one consolidated computational algorithm that we are still working on. It was subject to change since we had not completed a real world model due to limitations in the part acquisition process. However table 7.5 reflects the primary testing methodologies that would have accompanied the modeling statistics had the time allotted for it.

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Table 7.5: Testing methodology for the strictly computational aspects of the atmega328 in regard to collecting and relaying statistics on energy expenditure and metadata

Software Feature Tested Various Conditions Tested Under

Normal Drive mode -Will the system behave normally to changes in sensor data? -Can the system properly maintain charge dissipation limiting top speed using I/O PINs

Performance mode -How well does the system respond to differences in readings from thermal sensors? -Can it properly calculate the energy left in the batteries? -Will it disable the motors when differing percentages are reached? (no lower than 15%)

Economical mode -How efficient is our algorithm compared to other algorithms used commercially? -Would projected values increase or decrease over extended periods of time? Is a limitation in vehicle hardware improving or hindering overall performance?

Data statistics -Is the onboard computer properly tracking the changes and flow of energy? -Do simulated values match the test input -Can the system accurately calculate the longevity of components? -Can the system accurately calculate the functionality of subsystems via metadata? -How efficiently can the microcontroller relay this data without causing computational overhead?

The other focus of Software specific testing for our project was data tracking similar to that which was mentioned above. In the course of our project we need to ensure that our microcontroller maintains up to date data about all components. It needs to track energy dissipation, and component longevity. These usage statistics helped to optimize the vehicles lifespan and keep energy tracking and efficiency as high as possible. The data included how components were functioning, flow of energy, and what expected values for thing such as solar intake and charge transfer should be.

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The code would then output this data and use it to optimize vehicle performance calculations. In the same manner it could determine if a component or system does not operate within acceptable standards. ideally this type of testing would explain how efficiently the onboard controller could track the integrity of subsystems with minimal outside input from sensors or hardware. Overall more testing was necessary but what was achieved in the allotted time given the available man power was considerably adequate.

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8. Administrative content

This was preliminary oversight of the projects. What goals and mile markers were set. When were certain portions of the project to be completed. Most importantly Did the project meet the requirements on time. This was the measure of our success in terms of scheduling.

8.1 Milestones

The project will be organized according to a series of milestones. These milestones will help serve as the timeline used to gauge the overall progress of the project. Each milestone, or phase, symbolizes transition from one specific state of functional completion to another. The phases are arranged so that we can start with the most basic design goals and work up through more complex design states to reach the final state of the project, as well as allowing for additional improvements as we finish each state.

Phase 0: Cart For tracking purposes, Phase 0 is included as the starting point of the design portion of the project. This Phase is marked by the acquisition of the golf cart, and is the most basic functional stage of the design implementation. At completion of this phase, the cart will be functional, though entirely dependent on periodic recharging. This phase represents the completion of the initial phases of design and acquisition, though it requires very little in the way of implementation time and effort. It also requires the largest degree of funding.

8.1.1 Phase 1: Energy Acquisition speed for the solar array will strongly affect the time required for completion of Phase 1. At completion of this phase, the solar array will be linked to the battery for passive charging, much like a portable version of the standalone power stations already in place in some areas for use by electric vehicles. This portable solar charging apparatus will likely be connected through the charging circuit already present in the golf cart, easily modified for variable solar power input instead of steady cycle mains power. This stage of project implementation completion will mark the initial transition away from a dependence on externally supplied mains power to internally supplied solar power for the purposes of charging the vehicle’s battery pack, thus satisfying a primary project goal of sustainability. However, at this point the project is still mostly dependent on an external power source, as the solar energy will only be utilized while the cart is in an idle or inactive state. Additionally, the cart at this point does not have in place any means of energy management or other associated functions.

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8.1.2 Phase 2: Control After the solar panel has been integrated to charge the cart at rest, there is still a great deal of room for improvement. These optimizations will be implemented through an onboard microcontroller. This control device will collect a great deal of information on the many different systems and sensors present in the cart. This data will then be used to increase the overall efficiency of the system. At this point, the system will be locked into a specific mode of high efficiency use, which will effectively maximize the range of the cart. The next phase of project completion will add an additional layer of functionality to this element of control by allowing for user input.

Maximization of efficiency will only be possible through a great deal of testing, as well as highly effective programming through the microcontroller. Because of this dependency on testing, it is vital that the solar panels be tested during this stage of implementation in parallel with the integration of the microcontroller. This will allow us to begin the programming of the microcontroller as soon as it has been integrated into the overall system.

8.1.3 Phase 3: User In accordance with the design goals of this project, the previous phase’s maximum power-optimization mode will not be the only option available to users of the cart. In order to facilitate the changing of operational modes, a User Interface will be implemented. This user interface will utilize a monitor in tandem with a series of buttons to present the information gathered by the control device implemented in Phase 2. This information, such as range, current power output, battery charge, etc., will also help the user decide which of several running modes to choose from. These modes will each favor to some extent either performance or efficiency, furthering the goal of power optimization and increasing market feasibility.

8.1.4 Phase 4: Possible Project Component Extensions During the project, we will undoubtedly arrive upon more ideas for potential implementation and improvement options. These ideas will be recorded as they are created, so that they may be implemented if time and funding allow in this final stage of the project. There are many potential ideas available for implementation within the scope of this project, but time and money are both limited on this project. As a result, ideas must be judiciously chosen based on careful analysis before integration into the final project. While creating this initial design document, we have already found several options for further project extension that do not properly align with the initial design scope for our project, as well as some options that may prove unfeasible because of time or other constraints. These options are further explored in various sections above.

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8.1.5 Phase 5: Testing & Troubleshooting As the project reaches its final stages, we will be testing and recording the performance of our design to maximize its power, range, and efficiency. Some of this testing will require brute force trial and error testing to perfect the implemented design. Range, speed, and optimization modes will be tested. During this stage, we will find our various bugs and have to troubleshoot issues in our hardware and software designs to optimally meet our design specifications within the time allotted to our team for the SPOC completion. We must expect the worst and leave plenty of time to reformat components to meet any serious errors that we find in our design. This phase is the most dangerous in the level of unknowns going into it. The last month of our calendar time period should be primarily allocated to this key stage of prototype production.

8.1.6 Projected Phase Calendar To prepare for the level of work needed throughout the next five months, we have designed a preliminary calendar of dates to prevent any egregious misuse of our time during design and production. The first phase of cart acquisition ends during the first week of the Spring 2014 semester. Phase 1 of energy design includes the first month of the Spring 2014 semester. Phase 2 will include working on the Power optimization components which will include the largest portion of code work and hardware/software integration. Because of the level of work, we allocated over a month of time to Phase 2. Phase 3 includes the design of the user interface which is one of the simpler design subsystem components within our prototype; this phase has been allocated approximately three weeks for completion. Phase 4 is the “least necessary” of the phases, including any additional extensions or desirables to our original design. Because of the superfluous nature of this phase, we allocated approximately two weeks for this phase. Lastly, a sturdy three weeks was allocated for the final testing and troubleshooting phase of our project design. All this data is organized in table 8.1 however the final project did not stick as closely to this timeline due to issues with time and resources available for each phase.

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Table 8.1: Projected milestones

Phase of Completion Dates of Phase Period

Phase 0 12/16/2013 - 1/10/2014

Phase 1 1/6/2014 - 2/7/2014

Phase 2 2/3/2014 - 3/7/2014

Phase 3 3/3/2014 - 3/28/2014

Phase 4 3/24/2014 - 4/4/2014

Phase 5 4/7/2014 - 4/25/2014

8.2 Budgeting

The budget of the program is shown above in Section 6. The following sections will break down the sources of the funds required by the bill of materials.

8.2.1 Outside Funding Duke Energy covered the majority of this project’s expenses. These expenses are broken down in Section 6, and total to $2,674.79. Within this funding, there is a small amount of flexibility depending on price fluctuation for each part or subsystem.

8.2.2 Personal Thanks to Duke We would like to thank Duke Energy for their sizable contribution of $2,674.79 to our project. This money was fundamental in helping us acquire the best parts, to make the most energy efficient vehicle possible. Though this is just a foreshadowing of things to come we believe that the SPOC speaks strongly to Duke Energy’s philosophy of energy conservation. Our product is a step up from conventional fossil fuel vehicles achieving similar speeds and range in suburban settings, with zero emissions. Further more the fact that it is solar powered means that it puts no stress on a city's power grid, and can even serve as an auxiliary power source for a user’s energy needs.

It is our hope that the SPOC will bring about a paradigm shift in urban human transit. By presenting cities with an easy to maintain, reliable, and conventional electric people carrier we can change the way people travel in their day to day commute. However, our product is not simply limited to personal transport vehicles. We believe that with the proper technology and opportunity our project could be scaled to accommodate more passengers, making for public transit that can run reliably with minimal maintenance or cost. Additionally our novel energy

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tracking software and hardware could bring about improvements in how electrical systems interact when using high power or requiring frequent charging.

By working with the largest energy company in the United States we believe we have a real chance to improve people’s lives by changing how they commute. It is our hope that our work will also contribute to Duke Energy’s legacy of providing sustainable, affordable, reliable, clean energy.

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Appendix A (Bibliography)

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[5] "University of Central Florida Zenn". RetrievedOctober , 2013 Available: http://www.sailingtexas.com/SPEV/Cars/UCFZenn/ucfzenn.html

[6] Cronin, I , "New release". RetrievedOctober , 2013 Available: http://www.zenncars.com/press_rel/04_09/ZENN_under_10000.pdf

[7] "SOLFEX Primos 600 Digital Solar Thermal Controller". RetrievedOctober , 2013 Available: http://www.evoenergy.co.uk/solar-thermal/our- technology/controllers/

[8] "Smile". RetrievedOctober , 2013 Available: http://starev.com/images/pdfs/brochures/sep/g%20smile%20e%20brochure_ small.pdf

[9] Bullis, K , "Forget Battery Swapping: Tesla Aims to Charge Electric Cars in Five Minutes". RetrievedOctober , 2013 Available: http://www.technologyreview.com/news/516876/forget-battery-swapping- tesla-aims-to-charge-electric-cars-in-five-minutes/

[10] "Grape Solar 250-Watt Polycrystalline Grid Tied PV Solar Panel". RetrievedOctober , 2013 Available: http://www.globalindustrial.com/p/electrical/renewable-energy/solar- panels/grape-solar-280-watt-polycrystalline-grid-tied-pv-solar-panel

[11] "Grape Solar : PhotoFlex-100W Solar Panel". RetrievedOctober , 2013 Available: http://www.grapesolar.com/images/pdf/small-off-grid- manuals/PhotoFlex-100W.pdf

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[12] "Rhyno-500". RetrievedOctober , 2013 Available: http://www.grapesolar.com/portable-products/portable-chargers/rhyno-500- detail.html

[13] Dionysios Aliprantis PSERC Webinar

[14] Pesaran, A , "Sustainability: The future of transportation". RetrievedOctober , 2013 Available: http://www.nrel.gov/vehiclesandfuels/energystorage/pdfs/42469.pdf

[15] Evanczuk, S , "Designing a High-Efficiency Solar Power Battery Charger". RetrievedOctober , 2013 Available: http://www.digikey.com/us/en/techzone/energy- harvesting/resources/articles/designing-a-solar-power-battery-charger.html

[16] "Products". RetrievedNovember , 2013 Available: http://arduino.cc/en/Main/Products

[17] "Arduino BT". RetrievedNovember , 2013 Available: http://arduino.cc/en/Main/ArduinoBoardBT?from=Main.ArduinoBoardBluetoot h

[18] “How to connect Multiple Arunino Microcontrollers with I2C” Retrieved April http://hacknmod.com/hack/how-to-connect-multiple-arduino-microcontrollers- using-i2c/

[19] “Star EV ‘Smile’ Car” Retrieved November 2013. Available http:// starev.com/images/pdfs/brochures/

[20] “Polaris GEM Cart” Retrieved October 2013. www.polaris.com/EN-US/GEM-ELECTRIC-CAR/Pages/Home.aspx

[21] “Polaris GEM Cart” Retrieved October 2013. Avaialble from: www.polaris.com/EN-US/GEM-ELECTRIC-CAR/Pages/Home.aspx

[22] ”Classic Club Car Design” Retrieved november 2013. Available from : http://www.clubcar.com/commercialbusiness/transport/pages/villager4.aspx

[23] ATMega328 Reference sheet https://www.sparkfun.com/datasheets/Components/SMD/ATMega328.pdf

[24] ATMega328 optiboot Arduino Uno Reference Sheet https://www.sparkfun.com/products/10524

[25] “Blue Character OLED 16x2” Retrieved December 2013. Available from: http://www.adafruit.com/products/823

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[26] Mini Toggle Button Switch, January 2014. https://www.sparkfun.com/products/97

[27] Radioshack Piezo Element 1500-3000Hz Buzzer http://www.radioshack.com/product/index.jsp?productId=2062402

[28] “Trojan Battery Array” retrieved November 2013. Available from: http://fosterscramalotinn.com/ci_interior.html

[29] "Premium Flooded Batteries... optimized for ". RetrievedNovember , 2013 Available: http://www.trojanbatteryre.com/products/products.html

[30] ‘Trina Solar Panel Specs and Picture” Retrieved December 2013. Available from http://www.solarhome.org/trinasolartsm- 240pa05240wattssolarpanelmc4.aspx

[31] “Specs and Pic for Power Film Flexible Solar Panel” Retrieved November 2013. Available from: http://www.powerfilmsolar.com/products/oem- comparison-chart/

[32] ‘Specs and Pic for Grape Solar 390 W panel.” Retrieved November 2013. Available from: http://www.grapesolar.com/250w-mono-gs-s-250-fab5.html

[33] “Solar panel electrical wiring and network” Retrieved November 2013. Available from :http://www.grapesolar.com/250w-mono-gs-s-250-fab5.html

[34] “Microcontroller Integration” Retrieved November 2013. Available from: http://www.eit.uni-kl.de/koenig/gemeinsame_seiten/projects/ROSIG.html

[35] Perferation Board Arduino Schematic and Design, January 2013. http://www.instructables.com/id/Perfboard-Hackduino-Arduino-compatible- circuit/

[36] Wikipedia Buck Conversion Operation, March 2006. http://en.wikipedia.org/wiki/File:Buck_operating.svg

[37] ‘Solar Panel Architecture”Retrieved November 2013. Available from: www.solarpanel-manufacturer.com

[38] “Golf Cart Electrical Schematic’ retrieved October 2013. Available from: http://binatani.com/ez-go-golf-cart-wiring-diagram-electric-system/

[39] “Power Subsystem Diagrams” Retrieved November 2013. Available from: http://hpevs.com/Site/

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[40] “Solar Charge System Simple Design’ Retrieved December 2013. Available from: http://homemadecircuitsandschematics.blogspot.com/2011/12/how-to- build-solar-panel-voltage.html

[41] "CdS Photocell Photoconductive Cell GL5528". RetrievedDecember , 2013 Available: https://www.bananarobotics.com/shop/CdS-Photocell-GL5528- (5%20pack)

[42] "TMP36 - Temperature Sensor". RetrievedDecember , 2013 Available: https://www.sparkfun.com/products/10988

[43] “Solar Panel Testing Diagram” Retrieved November 2013. Available from: http://www.testfei.com/solar-photovoltaic-cell-test-equipment.html

[44] “Electric Cart Testing” Retrieved December 2013. Avaiable from: http://visforvoltage.org/forum/solar-vehicles/1835

[45] “Battery Testing Diagram’ Retrieved December 2013. Available from: www. sandiegocart.com/

[46] “Microcontroller Testing Diagram” Retrieved December 2013. Available from: www. electronicsweekly.com

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Appendix B (Intended PCB Schematic)

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Appendix C (PCB Board Layout)

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