THE BICYCLE-POWERED SMARTPHONE CHARGER bicycle riders, such as commuting cyclists, may have use for

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  • THE BICYCLE-POWERED SMARTPHONE CHARGER

    A Thesis

    presented to

    the Faculty of California Polytechnic State University,

    San Luis Obispo

    In Partial Fulfillment

    of the Requirements for the Degree

    Master of Science in Electrical Engineering

    by

    Chris Arntzen

    June, 2013

  • Page ii

    © 2013

    Chris Arntzen

    ALL RIGHTS RESERVED

  • Page iii

    COMMITTEE MEMBERSHIP

    TITLE: The Bicycle-Powered Smartphone Charger

    AUTHOR: Chris Arntzen

    DATE SUBMITTED: June, 2013

    COMMITTEE CHAIR: Dr. Lynne Slivovsky, Associate Professor

    Electrical Engineering Department

    COMMITTEE MEMBER: Dr. Bryan Mealy, Associate Professor

    Electrical Engineering Department

    COMMITTEE MEMBER: Dr. Taufik, Professor

    Electrical Engineering Department

  • Page iv

    ABSTRACT

    The Bicycle-Powered Smartphone Charger

    Chris Arntzen

    This thesis entails the design and fabrication of a smartphone charger that is

    powered by a bicycle dynamo hub. In addition to the design and validation of the charger

    prototype, this thesis involves the testing and characterization of the dynamo hub power

    source, the design and construction of specialized test equipment, and the design and

    prototyping of a handlebar-mounted case for the smartphone and charging

    electronics. With the intention of making the device a commercial product, price,

    aesthetics, and marketability are of importance to the design. An appropriate description

    of the charger circuit is a microcontroller-based energy management system, tailored to

    meet strict power demands of current smartphones. The system incorporates a switched-

    mode power supply, lithium polymer battery, microcontroller, and specialized protection

    circuitry. Prototype testing confirms that the circuit meets the charging requirements of

    the smartphone at bicycle speeds ranging from 7 miles per hour to as high as 55 miles per

    hour.

    Keywords: DC Converter, Switched Mode Power Supply, Bicycle, Dynamo Hub,

    Energy Harvesting, Energy Management

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    ACKNOWLEDGMENTS

    I would like to thank my advisor, Dr. Slivovsky, for encouraging me to pursue

    graduate school and providing me with an interesting thesis project. I would like to thank

    Dr. Taufik and Dr. Dolan for providing me with a background in power electronics. I

    would also like to thank Dr. Mealy for supporting my decision to pursue graduate school

    and helping me reconnect with Cal Poly. I give thanks to Dr. Freed and Patrick Goebel

    of the Cal Poly Industrial Manufacturing Engineering Department for making the case

    design portion of this thesis a reality. I would not have been able to accomplish this

    MSEE Degree without the support of my family, including the Vogler side. I would

    particularly like to thank Ed and Patricia Arntzen, Dan and Heidi Arntzen, and Roger and

    Nancy Vogler.

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    TABLE OF CONTENTS

    Page

    List of Tables ..................................................................................................................... ix

    List of Figures ......................................................................................................................x

    Chapter

    1. Introduction ..............................................................................................................1

    1.1 Scope of the Project ....................................................................................1

    1.1.1 Problem Statement .............................................................................1

    1.1.2 Price Point ..........................................................................................2

    1.1.3 Ergonomics ........................................................................................2

    1.1.4 Speed Considerations .........................................................................3

    1.1.5 Case Design .......................................................................................3

    1.2 Background .................................................................................................7

    1.2.1 Hub Background ................................................................................7

    1.2.2 Cycling Power Considerations ...........................................................8

    2. Design Requirements .............................................................................................11

    2.1 Initial Testing ............................................................................................11

    2.1.1 Preliminary Test Fixture ..................................................................11

    2.1.2 Types of Hubs and Wheels ..............................................................12

    2.1.3 Preliminary Test Results ..................................................................12

    2.2 Design Equations and Considerations ......................................................15

    3. Product Design .......................................................................................................20

    3.1 Circuit Design ...........................................................................................20

    3.1.1 System Level Design .......................................................................20

    3.1.2 Input Section ....................................................................................20

    3.1.3 DC/DC Converter Topology Selection ............................................26

    3.1.4 Microcontroller Selection ................................................................32

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    3.1.5 Voltage, Current, and Temperature Sensing ....................................34

    3.1.6 Battery and iPhone Cable Selection .................................................35

    3.2 PCB Design ...............................................................................................36

    3.2.1 Size, shape, and layer considerations ...............................................36

    3.2.2 Layout Considerations .....................................................................38

    3.3 Firmware Design .......................................................................................39

    3.4 Final Testing .............................................................................................40

    3.5 Prototype Revisions ..................................................................................43

    3.5.1 Topology Revisions .........................................................................43

    3.5.2 Input Protection Revisions ...............................................................44

    3.5.3 Other System Revisions ...................................................................47

    4. Results…… ............................................................................................................50

    4.1 Simulation Results ....................................................................................50

    4.1.1 SEPIC Simulation Results ...............................................................50

    4.1.2 Component Rating Simulation Results ............................................54

    4.2 Standard Test Bench Results ....................................................................54

    4.2.1 SEPIC Performance .........................................................................54

    4.2.2 System Functionality .......................................................................58

    4.3 Custom Test Fixture Results .....................................................................59

    5. Conclusion .............................................................................................................62

    5.1 Meeting the Design Requirements ............................................................62

    5.1.1 Description of Criteria Met ..............................................................62

    5.1.2 Cost Analysis ...................................................................................62

    5.2 Future Improvements ................................................................................63

    5.2.1 Hardware Improvements ..................................................................63

    5.2.2 Compatibility ...................................................................................64

    5.2.3 Extended Testing .............................................................................64

    5.2.4 Firmware ..........................................................................................65

    5.3 Future Opportunities .................................................................................66

    5.3.1 Patenting ..........................................................................................66

  • Page viii