LOW POWER TIRE PRESSURE MONITORING SYSTEM A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Sravanthi Goparaju December, 2008 LOW POWER TIRE PRESSURE MONITORING SYSTEM Sravanthi Goparaju Thesis Approved: Accepted: __________________________ __________________________ Advisor Department Chair Dr. Nathan Ida Dr. Jose A. De Abreu-Garcia __________________________ __________________________ Committee Member Dean of the College Dr. James Grover Dr. George K. Haritos __________________________ __________________________ Committee Member Dean of the Graduate School Dr. George Giakos Dr. George R. Newkome __________________________ Date ii ABSTRACT Power management is considered to be an important aspect in designing battery operated Tire Pressure Monitoring Systems (TPMS) as it helps to prolong the lifespan of the battery. There are several methods that can be used to design a low power tire- pressure and service monitoring system. One of the most common methods for power reduction is the duty cycle method. This thesis suggests an idea of implementing the TPMS in combination with a separate Radio Frequency Identification (RFID) circuit, especially a very low power (active or passive) RFID whose sole purpose is to detect the interrogating signal. This RFID circuit which can operate at a typical frequency of 125 kHz is used to turn ON a higher power transmitter which is initially in SLEEP state and soon after entering the active state performs the communication, updating, etc. Once the desired task is completed, the high power transmitter returns to SLEEP state or is turned off until the next interrogation. The implementation of SLEEP mode to minimize power consumption is discussed in detail and the currents consumed by the microcontroller in SLEEP and ACTIVE modes are measured and recorded. The microcontroller in SLEEP mode consumed a current of 17µA which reduced the overall average current consumed by the microcontroller and the pressure sensor. Furthermore, this method promises an improvement in the battery iii life and the calculations showing this improvement are discussed with the example of an AA battery with 2800mAh battery life. iv DEDICATION Dedicated to my family, teachers and Kalyan Kaladhar. v ACKNOWLEDGEMENTS I would like to thank the committee members Dr. Nathan Ida, Dr. George Giakos and Dr. James Grover for their guidance and support throughout my Master’s program. I would like to specially thank Dr. Ida for giving me the freedom of thought and expression while performing my research. I would also like to thank the Department of Electrical and Computer Engineering at the University of Akron for giving me a chance to pursue the Master’s degree by providing financial support. In this context, I would like to express my sincere thanks to Prof. Kult for making my teaching experience in Circuits I and II Labs enjoyable and memorable. Thanks to Erik Rinaldo, and Greg Lewis for providing me with the entire necessary infrastructure needed to complete my research work. I express my heartfelt gratitude to our department secretary Gay Boden who never hesitated to extend her helping hand with a sweet smile right from the day I started my Master’s program. I owe my sincere and heartfelt regards to my Mom, Dad, Brother and Kalyan who always supported and guided me. Without them, I would not have come so far. I also take this opportunity to thank my other family members and cousins who helped me in making my stay in USA a comfortable one indeed. I thank Divya and Srutha for everything. You both are really wonderful. Finally I would like to thank all my seniors and friends for their invaluable support and cooperation. vi TABLE OF CONTENTS Page LIST OF TABLES............................................................................................................ xii LIST OF FIGURES ......................................................................................................... xiii CHAPTER I. INTRODUCTION .........................................................................................................1 1.1. Goal of Research.....................................................................................................1 1.2. Major Focus............................................................................................................2 1.3. Thesis outline..........................................................................................................5 II. FUNDAMENTAL THEORY........................................................................................7 2.1. Definition of Tire pressure monitoring system.......................................................7 2.2. Evolution of TPMS.................................................................................................8 2.3. TPMS concepts.......................................................................................................8 2.3.1. Types of TPMS............................................................................................9 2.3.2. Direct Versus Indirect TPMS.....................................................................10 2.3.3. Operation of TPMS....................................................................................10 2.3.4. Applications and architectures of Tire pressure monitoring system..........11 2.4. Design challenges of TPMS.................................................................................13 vii 2.5. Power management in TPMS ...............................................................................14 2.6. Definition of RFID ...............................................................................................17 2.7. Components and Operation of RFID....................................................................17 2.7.1. Definition of RFID tag...............................................................................18 2.7.2. Definition of RFID reader..........................................................................18 2.7.3. Classification of RFID tags........................................................................18 2.7.4. Operation of RFID .....................................................................................20 2.8. Communication in wireless applications..............................................................21 2.8.1. Transmission and reception of data in wireless applications.....................21 2.8.2. Encoding schemes......................................................................................21 2.8.3. Modulation.................................................................................................24 2.8.4. Modulation techniques...............................................................................24 2.9. Conclusions...........................................................................................................26 III. BACKGROUND AND RELATED WORK ...............................................................28 3.1. Power sources for TPMS......................................................................................28 3.2. Current consumption in a TPMS module .............................................................30 3.2.1. RF transmission .........................................................................................31 3.2.2. CPU execution ...........................................................................................31 3.2.3. Motion detection ........................................................................................32 3.2.4. Power down current ...................................................................................33 3.3. Power management...............................................................................................33 3.3.1. Data management and strobe oscillator .....................................................35 3.3.2. Wake-up and sleep schedules ....................................................................38 viii 3.4. RFID device wake-up methods ............................................................................38 3.4.1. RFID communication system ....................................................................39 3.4.2. Method to reduce power consumption of an active tag .............................41 3.4.3. A better method to reduce power consumption of an active tag................42 3.5. Tire pressure monitoring systems on current market ..........................................44 3.5.1. TPMS based on vehicle speed ...................................................................45 3.5.2. An integrated chip to monitor tire pressure ...............................................45 3.6. Energy harvesting .................................................................................................46 3.7. Hardware and software concepts of TPMS ..........................................................48 3.7.1. Inside the tire..............................................................................................48 3.7.2. Outside the tire...........................................................................................49 3.8. TPMS functionality ..............................................................................................51 3.8.1. TPMS Transmitter .....................................................................................51 3.8.2. RF generator...............................................................................................52