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STUDY ON WIRELESS BATTERY-LESS COMPUTER MOUSE ADILA BT MOHAMED KHALIDI UNIVERSITI TEKNOLOGI MALAYSIA “I hereby declare that I have read this report and in my opinion this report has fulfills the scope and quality for the award of degree of Bachelor of Engineering (Electrical)” Signature : ___________________________ Name of Supervisor : EN. ALIAS BIN MOHD YUSOF Date 7th MAY 2011 : STUDY ON WIRELESS BATTERY-LESS COMPUTER MOUSE ADILA BT MOHAMED KHALIDI A project submitted in partial fulfillment of the requirements for the award of degree of Bachelor of Engineering (Electrical) Faculty of Electrical Engineering Universiti Teknologi Malaysia MAY 2013 ii I declare that this thesis entitled “Study On Wireless Battery-less Computer Mouse” is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree. Signature : Name : ADILA BT MOHAMED KHALIDI Date : 7th MAY 2013 iii Specially dedicated to my beloved parents, brother, sisters for their loves, support and encouragement. iv ACKNOWLEDGEMENT First and foremost, the greatest thanks and grateful to Allah S.W.T with all His Majesty, for giving me a good health while finishing this thesis. A special thanks to my family members for contributing ideas, and giving a full support on this project. Without my family, it would be hard for me to accomplished. I also would like to express my sincere appreciation to my supervisor En.Alias Bin Mohd Yusof for his supervision during completing this project. Last but not least, thousand thankful to my beloved one and to my all friends that giving me support physically and mentally in which their assistance helped along the way. v ABSTRACT This project was conducted to study about wireless computer mouse which using a standard USB power supply and eliminates the use of batteries completely. The system uses a soft switched current-fed push-pull converter for DC to AC conversion. The AC current which flows through a disk coil embedded in a mouse pad were providing a time varying magnetic field that transfer power to a power pick-up coil located within the computer mouse, through magnetic induction. This power which was tuned-up and regulated by an advanced voltage control methoddynamic detuning control, has proven to be able to provide sufficient power to drive a wireless battery-less computer mouse. vi ABSTRAK Projek ini telah dijalankan untuk mengkaji mengenai tetikus komputer tanpa wayar yang menggunakan bekalan kuasa USB standard dan menghapuskan penggunaan bateri sepenuhnya. Sistem ini menggunakan “soft switched current-fed push-pull converter” untuk penukaran DC ke AC. Arus elektrik AC yang mengalir melalui gegelung cakera yang terletak dalam pad tetikus telah menghasilkan medan magnet yang berbeza masa di mana memindahkan kuasa kepada kuasa pick-up gegelung yang terletak di dalam tetikus komputer, melalui induksi magnet. Kuasa ini yang ditala dan dikawal oleh kaedah kawalan voltan maju – kawalan detuning dinamik, telah terbukti mampu memberikan kuasa yang mencukupi untuk menggerakkan tetikus komputer tanpa wayar tanpa pengunaan bateri. vii TABLE OF CONTENTS CHAPTER 1 2 TITLE PAGE DECLARATION ii DEDICATION iii ACKNOWLEDGEMENTS iv ABSTRACT v ABSTRAK vi TABLE OF CONTENTS vii LIST OF TABLES ix LIST OF FIGURES x LIST OF SYMBOLS xi LIST OF APPENDICCES xii INTRODUCTION 1.1 Problem Statement 1 1.2 Objectives of Project 1 1.3 Scope of Project 2 LITERATURE REVIEW 2.1 A Perspective of Contactless Power Transfer 3 2.2 Introduction to IPT Power Supplies 5 2.2.1 Basic Structure and Operating Principle 6 2.2.2 General Features 7 2.3 An Introduction to Litz Wire 8 2.3.1 Principle of Operation 9 2.3.1.1 Skin Effect 9 viii 3 2.3.1.2 Proximity Effect 11 2.3.2 Effectiveness 11 2.3.3 Applications 12 METHODOLOGY 3.1 Introduction 13 3.2 General Summary of The Proposed IPT Computer Mouse 4 5 13 3.2.1 System Configurations 13 3.2.2 Design Requirements 14 3.3 Primary Implementation 16 3.3.1 Resonant Converter 16 3.3.2 Primary Track Configuration 18 3.4 Secondary Pick-up Implementation 21 3.4.1 Dynamic Detuning Control 21 RESULTS AND DISCUSSION 4.1 Introduction 23 4.2 Primary Track 23 4.3 The Secondary Pick-up 24 CONCLUSION AND RECOMMENDATION 5.1 Conclusion 26 5.2 Recommendation 27 REFERENCES 28 APPENDICES 30 ix LIST OF TABLES TABLE NO. TITLE PAGE 2.1 Electric power transfer options 4 3.1 Estimated power consumption of wireless Computer mouse 14 x LIST OF FIGURES FIGURE NO. TITLE PAGE 2.1 Basic structure of a typical IPT system 6 2.2 The twisted or woven strands of LItz wire 8 2.3 Litz wire made out of 8 thinner isolated copper wires 9 2.4 Disassembled induction cooker showing litz wire coil 12 3.1 The configuration of a wireless computer mouse 14 3.2 Design flowchart 15 3.3 The self-sustained current-fed push-pull resonant converter 17 3.4 Spiral coil configuration 19 3.5 Magnetic distribution of a spiral coil distribution 19 3.6 The disk coil configuration 20 3.7 Magnetic field distribution of the disk coil Configuration 20 3.8 Dynamic Detuning Control circuit diagram 21 3.9 The relationship between tuning capacitance and parallel compensated pick-up output current 22 4.1 The primary track 24 4.2 The secondary pick-up xi LIST OF SYMBOLS μo - Permeability εo - Permittivity ωo - Nominal Frequency Lp - Primary Track Inductance Rp - Track Resistance Qp - Primary Quality Factor ZVS - Zero Voltage Switching Hz - Hertz kHz - Kilo Hertz MHz - Mega Hertz mW - Mili Watt V - Voltage mA - Mili Ampere Mm - Milimeter μm - Mikrometer AC - Alternating Current DC - Direct Current USB - Universal Serial Bus RF - Radio Frequency xii LIST OF APPENDICES APPENDIX TITLE PAGE A MC 34063A - IC 30 B CORDELESS OPTICAL MOUSE USER’S MANUAL 31 1 CHAPTER 1 INTRODUCTION 1.1 Problem Statement For a better future friendly environmental, the usage of battery is no longer needed in a wireless computer mouse because the disposals of batteries are exposing the environment and water to a lead and acid. There are many toxic chemicals inside a battery such as cadmium, mercury, lead and nickel. Therefore, it would be ideal if the batteries can be eliminated. 1.2 Objectives of Project i. To built a wireless battery-less computer mouse device. ii. To design and understand about the circuits that will be used by using Multisim 11.0. iii. To utilize the usage of Inductive Power Transfer (IPT) system for a low power consumptions at mW. 2 1.3 Scope of Project i. Design a wireless battery-less computer mouse using IPT system ii. Simulate the circuits design using Multisim 11.0 software and apply it to a PCB board. iii. Validate and testing both designed circuits which is Self-sustained currentfed push-pull resonant converter circuit and Dynamic Detuning Control (DCC) circuit. 3 CHAPTER 2 LITERATURE REVIEW 2.1 A Perspective of Contactless Power Transfer There are many ways to achieve contactless power transfer. Table 2.1 outlines the possible options for electric power transfer in electromagnetic forms. In addition to conventional systems with direct electrical contact and contactless power transfer can be obtained theoretically via inductively, capacitively or electromagnetic waves. Conductive power transfer is based on a closed circuit that allows for direct power flow along the conductors. The closed circuit is normally formed with hard wiring connections which are using typical techniques, cables and contacts. Contactless power transfer can be achieved inductively or capacitively depending on whether it is via magnetic field coupling or electric field coupling. For the closely coupled versions, theoretically the transformer and capacitors can transfer the power without direct electrical contacts, but practically, both of techniques are not suitable for delivering power to moving objects since the magnetic or electric field in the these components have to be confined within iron cores or electrolytic media. The closely coupled versions are suitable for electric machines which allow more freedom of mechanical movement especially the linear motors. The power efficiency and power factor of a linear motor are very low and 4 its expanded stator are very costly, therefore it is only suitable for transferring power over a very short distance, e.g. within a machine tool. Table 2.1 : Electric power transfer options DIRECT CONTACTLESS CONTACT FEATURES TYPES BASIC THEORIES CONDUCTIVE INDUCTIVE CAPACITIVE WAVE Hard wiring, Closely Loosely Closely Loosely Electromag- moving contact Coupled Coupled Coupled Coupled netic waves Electric circuit, Magnetic Electric arc & Circuit, AC contact circuit theories theories TYPICAL Cables and TECHNIQUES Contacts Distributed magnetic field, Power electronics Confined electric field, AC circuit Distributed electric field, Power Wave Propagation electronics Wave guides, Transformer IPT Capacitors CPT Parabolic antennas, etc. ILLUSTRATION Transferring power from the primary to secondary of a transformer is nearly impossible at low frequencies such as 50Hz or 60Hz if its coils are separated far apart without maintaining a tight magnetic coupling. However, by refer to the basic concept of Inductive Power Transfer (IPT), if the operating frequency is increased to a very high value, then the fast changing rate of magnetic field will cause a much stronger induction effect between the two coils. Practically, the power jumping across the air gap will becomes feasible. Another way of transferring power contactless is via Capacitive Power Transfer (CPT) which is analogous to IPT theoretically. In a CPT system, the two plates of a capacitor can be set apart, forming a large air gap for the power to jump across. One of the capacitor plates is mechanically free to move so that power can be transferred from a static frame to a moveable objects by combining two or more of such capacitors in a circuit. The distributed electric field in CPT system will serves as a power flow passage, consequently, the voltage, instead of the current as in an IPT system where a distributed magnetic field offers a power flow channel. 5 A high frequency is also a beneficial to the power flow via the air gap of a split “capacitor”. Therefore, high frequency power conversion may also be a major issue, with power electronics being the enabling technology. CPT is simply a new concept to serve as a counterpart to IPT. CPT has problems with high electric field intensity exceeding 30kV/cm in air and very low permittivity εo (8.854 x compared with the permeability μo (4π x ) ) which makes it 10 times more difficult. Moreover materials with relative permeability greater than 100,000 also contribute to the fact that IPT is more practical than CPT. For the wireless signal communication, the power transfer can be achieved via electromagnetic waves. However, transferring a large amount of power over a long distance in the open air using traditional wave guides or parabolic antennas can be very difficult for normal use due to the complexities involved in the power flow control [1]. This study is about Inductive Power Transfer (IPT) power supplies which are the most feasible contactless power supplies using modern power techniques. 2.2 Introduction to IPT Power Supplies IPT is a technology that using power transfer system based on magnetic coupling which is sometimes called as Inductively Coupled Power Transfer (ICPT). IPT can be described as a loosely coupled power supply system using modern power conversion, control, and magnetic coupling techniques to achieve contactless power transfer from a static frame to a moveable objects. 6 2.2.1 Basic Structure and Operating Principle Fig. 2.1 shows the basic structure of a typical IPT system. There are two electrically isolated parts in IPT system. The first part consists of a power converter and a primary conductive path which can be elongated “track” or lumped “coil”. The main function of the power converter is to supply a constant high frequency AC current (normally a 10-100kHz current with a sinusoidal waveform) along the track loop, this part often referred to as the track power supply. The second part consists of a pick-up coil and a power conditioner. Due to the mutual magnetic coupling between the primary track loop and the secondary pick-up coil, an inductive electromotive force is induced in the pick-up coil which forms a voltage source for the secondary power supply. Since the magnetic coupling is loose, which is low compared to normal transformer, the induced voltage source is usually unsuitable to be used by the equipment directly. As such, a power conditioner is required to regulate the power into the form required by the load, such as a motor controller or a lamp. Fig. 2.1 : Basic structure of a typical IPT system A high quality track current generated by the power converter is essential for proper operation of the whole IPT system. This current affects the performance of all other parts of the system (such as the magnetic coupling and the pick-up conditioning), and hence the general power flow from the static power supply to the pick-up coil. In fact, the track power supply accounts for the majority of the system cost. Normally, in order to make a full use of the track power supply, multiple pickups are attached to a single track loop. 7 2.2.2 General Features When compared with the conventional power supplies, an IPT system has the following features [1]: 1. Freedom of mechanical movement. The pick-up can move along the track loop while allowing some lateral displacement from the track centre, because of the loose coupling between the primary and secondary of IPT system. This freedom makes it possible to deliver power to moveable equipment without direct electrical contact. This is one of the outstanding characteristics of IPT and differentiates it from a traditional transformer. 2. Safe operation. There is no direct electrical contact in the path of the power flow, so it is spark free and no open live wires, thus the possibility of accidental electric shock is eliminated. IPT supplies also enhance the insulation between the primary and the secondary sides, further improving the safety level to personnel and devices. 3. Reliable and robust. There is no direct friction in an IPT system so that mechanical wear and tear, and electrical erosion are eliminated. Plus, chemical erosion of the conductors is essentially nonexistent because the electrical components can be completely enclosed. Consequently the system is very reliable and robust, requiring almost no maintenance. 4. Environmentally friendly. Its operation is not affected by dirt, dust, water, or chemicals because IPT has two independently enclosed parts. Therefore it can work in very harsh environments. Furthermore it does not generate carbon residues, as is the case with traditional sliding contact system using carbon brushes, and has no harmful effects on surroundings. 8 2.3 An Introduction to Litz Wires Litz wire is a type of cable used in electronics to carry alternating current (AC). The wire is designed to reduce the skin effect and proximity effect losses in conductors used at frequencies up to about 1 MHz [15]. It consists of many thin wire strands, individually insulated and twisted or woven together, following one of several carefully prescribed patterns often involving several levels which is groups of twisted wires are twisted together and etc. This winding pattern equalizes the proportion of the overall length over which each strand is at the outside of the conductor. The term litz wire originates from Litzendraht, braided/stranded wire or woven wire. Fig. 2.2 : The twisted or woven strands of Litz wire German form 9 Fig. 2.3 : Litz wire made out of 8 thinner isolated copper wires. 2.3.1 Principle of Operation Litz wire reduces the impact of the skin effect and the proximity effect. 2.3.1.1 Skin Effect The resistance of a conductor at DC (0 Hz) depends on its cross sectional area. A conductor with a larger area has a lower resistance. The resistance also depends on frequency because the effective cross sectional area changes with frequency. For alternating currents (AC), the skin effect causes the resistance to increase with increasing frequency. For low frequencies, the effect is negligible. For AC at frequencies high enough that the skin depth is small compared to the conductor size, the skin effect 10 causes most of the current to flow near the conductor’s surface. At high enough frequencies, the interior of a large conductor does not carry much current. At 60 Hz, the skin depth of a copper wire is about ⅓ inches (8.5 mm). At 60 kHz, the skin depth of a copper wire is about 0.01 inches (0.25 mm). At 6 MHz, the skin depth of a copper wire is about 0.001 inches (25 µm). Round conductors larger than a few skin depths don’t conduct much current near their axis, so the central material isn’t used effectively. When larger conductors are needed, tricks are used to minimize the skin effect. The goal is to increase the conducting surface area. One trick is to use a hollow conductor with a wall that is about a skin-depth thick. It is essentially a large diameter wire with the non-current interior deleted. It is bulky but it saves copper. To combat the skin effect, litz wire uses lots of thin conductors (strands) in parallel. Each thin conductor is less than a skin-depth, so an individual strand does not suffer an appreciable skin effect loss. The strands must be insulated from each other – otherwise all the wires in the bundle would short together, behave like a single large wire, and still have the skin effect problems. Futhermore, the strands cannot occupy the same radial position in the bundle (the electromagnetic effects that cause the skin effect would still disrupt conduction). The bundle is constructed so the individual strands are on the outside of the bundle and provides low resistance for a time, but also reside in the interior of the bundle where the EM field changes are the strongest and the resistance is higher. If each strand provides about the same average resistance, then each strand will contribute equally to the conduction of the entire cable. The weaving of twisting pattern of litz wire is designed so individually strands will reside for short intervals on the outside of cable and for short intervals on the inside of the cable. These allow the interior of the litz wire to contribute to the cable’s conductivity. Another way to explain the same effect is the magnetic fields generated by current flowing in the strands are in diresctions such that they have a reduced tendency to generate an opposing electromagnetic field in the other strands. 11 Thereby, for the wire as a whole, the skin effect and associated power losses when used in high frequency applications are reduced. The ratio of distributed inductance to distributed resistance is increased, relative to a solid conductor, resulting in a higher Q factor at these frequencies. 2.3.1.2 Proximity Effect The proximity effect will cause losses in cases involving multiple wires, or multiple turns, such as windings in transformers and inductors. The losses of proximity effect are to increase at high frequency even sooner and more rapidly than does skin effect. 2.3.2 Effectiveness The frequency of Litz wire is very effective below 500 kHz but it is much less effective if the frequency is above 2 MHz. Litz wire can be used at thicker cable sizes eventhough litz wire has higher impedance per unit cross-sectional area. So litz wire can reduce or maintain the cable impedance at higher frequencies [16]. 12 2.3.3 Applications High frequency application such as inductors and transformer are using Litz wire. This is because the skin effect is more pronounced and proximity effect can be an even more severe problem. Disassembled induction cooker that are using litz wire is shown in Fig. 2.4. Fig. 2.4 : Disassembled induction cooker showing litz wire coil. 13 CHAPTER 3 METHODOLOGY 3.1 Introduction For the implementation of this project, the design IPT system concepts and methodologies have been employed and need to be understood thoroughly. This chapter covers the overall theory of Inductive Power Transfer. 3.2 General Summary Of The IPT Computer Mouse 3.2.1 System Configuration The IPT primary circuit and the wireless receiver module were located together to form a single integrated mouse pad solution as shown in the configuration of IPT wireless computer mouse in Fig 3.1. Then the mouse pad will be connected to a standard USB port which will provide the power and the communication channel from the computer. The architecture of this wireless computer mouse was built on top of a commercial battery powered wireless 14 computer mouse. The primary track was design based on a standard mouse pad which is to provide a magnetic field distribution over it. Lastly, the wireless transmitter and the pick-up which are located within the wireless computer mouse. Fig. 3.1 : The configuration of a wireless computer mouse 3.2.2 Design Requirements The design requirements are to produce sufficient power at the pick-up for the load. The power demand according to the specification of the original wireless computer mouse is shown in Table 3.1. Table 3.1 : Estimated power consumption of wireless computer mouse Active State Stand-by State 3.3 V x 50 mA = 165 mW 3.3 V x 33 mA = 108.9 mW This estimated power demand does not take into account of the wireless receiver module which is the losses in the power converter, primary track and the rectifier. This design is quite challenging by considering the available power of a standard USB is only 0.5 Watt for 100 mA in low power mode and 2.5 Watt for 500 mA in high power mode at 5V. The power pick-up circuit and the power converter for high frequency magnetic field generation have to be very efficient to make the system work. The appropriate converter, track material and secondary voltage regulation will be discussed in the preceding section. 15 Determine an approriate converter topology Form primary track. Measure Lp Chooose a ωo. Calculate Cp. Measure Isc and Voc. Therefore determine power induced at the pick-up. Sufficient power induced? Choose approriate secondary tuning topology Connect pick-up/ tuning circuit to rectifier/ voltage regulator Test system performance with load Fig. 3.2 : Design flowchart It is a complex process in designing and implementing the IPT systems which involving with many parameters. The design flowchart shown in Fig 3.2 showed steps of rational flow of the project work. 16 3.3 PRIMARY IMPLEMENTATION 3.3.1 Resonant Converter Resonant converters are more efficient due to its ability to achieve Zero Voltage Switching (ZVS). Before this, controllers and zero point detectors were required to assist the set-up of the oscillation and control the commutation of the switches on the two branches of the resonant converter, such that the oscillation can be sustained and ZVS achieved [1]. For this project, a self-sustained current-fed push-pull resonant converter with no additional controllers [1] has been developed. This converter will largely reduced the complexity, power budget stress and the overall cost of the system. Fig 3,3 showed the structure of the current-fed push-pull resonant converter. As shown in Fig 3.3, the circuit comprises a current-fed push-pull inverter with parallel compensation. There is exception in this circuit which is that each switch obtains its switch driving signal from the input of the alternative switch. The switching instances will occur at the zero crossing since the switching is fully controlled by the resonance and ZVS is achieved. The current is also in phase with the voltage since the direction of current is reversed when the switches exchange its on-off state. Only real power, P is delivered to the resonant tank, this means that zero phase angle (ZPA) operation is achieved. 17 Fig. 3.3 : The self-sustained current-fed push-pull resonant converter. The primary quality factor, Q must be upper a critical value to achieve selfstarting and ZVS. The primary quality factor is defined as : Lp is the primary track inductance, Rp is the track resistance and ωo is the nominal (oscillating) frequency. According to “Critical Q analysis of a current-fed resonant converter for IPT applications” [14] and “Dynamic ZVS Direct On-line Start up of Current Fed Resonant Converter Using Initially Forced DC Current” [10], the minimum Qp for self-starting and ZVS is 2.54 and 1.86 respectively. Various resonant frequencies associated with a series loaded parallel resonant tank have been defined. Based on a thorough theoretical analysis, it has been found that ZVS frequency reduces at low Q values and operation cannot be sustained below a Q of 1.86. These figures are significant with IPT systems where low Q values are economically preferable. In practice, Q is load dependant and therefore should be designed larger than 2 to ensure safe operation [1]. 18 The maximum equivalent load for ZVS start up corresponds to a quality factor Q of about 2.54. By considering the ramp up delay of a practical DC power supply, complete direct on-line overshoot free start up is achieved by starting point the inverter at lower DC voltage levels. Compared with other control methods, this method not only improves the system reliability and efficiency, but also reduces the system cost as a very simple controller can be used and no additional starting equipment is required. This circuit will be constructed and tested to check whether it able to start up and shut down automatically. 3.3.2 Primary Track Configuration The distribution of the magnetic fields will be determine based on the primary track physical configuration which has a great effect on the power transfer efficiency. The relationship between Voc, magnetic field strength and distribution are defined as : N is the number of turns of the pick-up coil, B is the magnetic flux density component that cuts perpendicularly through A and A is the area enclosed by the pick-up coil. This equation showed that the primary track configuration should have a field distribution such that it is cutting perpendicular through the area enclosed by the pick-up, at any location on the mouse pad. Two configurations have been considered which is the spiral and the disk coil configuration. 19 (a) Spiral coil (b) Cross-sectional view of a spiral coil Fig. 3.4 : Spiral Coil Configuration (a) Surface magnetic fields (b) Different pick-up coil windings Fig. 3.5 : Magnetic field distribution of a spiral coil distribution. The flux in the vertical direction is cancelled out by neighbouring wires for the spiral configuration. This will lead the flows of magnetic field within the horizontal plane or along the surface of the mouse pad. Fig 3.4 (a) showed the flow direction in the horizontal plane by the arrows. Fig 3.5 (b) showed the pick-up that will have to be rotated on different parts of the spiral coil to achieve maximum power transfer with this field orientation while another possibility is to use two pickups. By considering the limited space available in a wireless computer mouse, both of these options are not practical. 20 Fig. 3.6 : Disk Coil configuration (a) Magnetic field direction (b) Pick-up coil winding Fig. 3.7 : Magnetic field distribution of the disk coil configuration Fig 3.6 showed that a disk coil configuration has a simpler magnetic field distribution as shown in Fig 3.7. The angle between the pick-up and the field direction would be more optimal on different parts of a disk coil by having the enclosed plane of the pick-up perpendicular to the vertical axis. This is where the disk coil was adopted. 21 3.4 SECONDARY PICK-UP IMPLEMENTATION The parallel pick-up compensation can increase open circuit voltage, Voc by a factor of Qs and this is where the parallel tuning was adopted as discussed in section 3.2.2. But, this will lead to another problem which is a parallel compensated pick-up is behaving like a current source and the supplied voltage changes with the load. If the tuned voltage exceeding the maximum voltage of 3.6 volts, there is probability danger will occur. This danger can be avoid by using a smart voltage regulation method that has been used to regulate the output voltage to be constant which is the Dynamic Detuning Control (DDC). 3.4.1 Dynamic Detuning Control Fig. 3.8 : Dynamic Detuning Control circuit diagram Fig. 3.8 shows that Ct is the detuning capacitor and Cf is a voltage stabilizing capacitor. The Capacitor Switching Control circuit will switches ON S when the load voltage VL exceed a limit threshold which will completes the connection of Ct by changing the overall tuning capacitance to (Cs+Ct). This changes the amount of tuned pick-up current output, and also VL. 22 Fig. 3.9 : The relationship between tuning capacitance and parallel compensated pick-up output current. This experiment will face two possible tuning schemes, under-tuning and over-tuning schemes. As shown in Fig 3.9, the under-tuning scheme, Cs+Ct is equal to the resonance capacitance, which gives the maximum tuned pick-up output current. The maximum point should provide a VL of 3.3 volts in this application while for the over-tuning scheme, Cs is set to the resonance capacitance and Ct is set such that (Cs+Ct) will reduce the tuned pick-up output current to an appropriate level. This conclude that to provide the needed power under heavy loads, the undertuning scheme need to switch ON more while when there is an excess power, the over-tuning scheme will switch ON. The advantage of this circuit is, the unused power will dissipate as heat because it is regulated by detunes the power pick-up. This control mechanism is much more efficient than Zener diodes or linear regulator. 23 CHAPTER 4 RESULTS AND DISCUSSION 4.1 Introduction This chapter presents the results obtained from the used methodology. Then the discussion on the results obtained is done. The results and discussion obtained from the measurements on the primary track and secondary pick-up. 4.2 Primary Track The estimated power consumptions of wireless computer mouse in active state is 165 mW. The results showed that the maximum power which is 165 mW that required by the pick-up for the load has been met in most locations on the mouse pad. Multi-strands Litz wires were used in the primary track helps in reducing the AC power losses because it has a lower AC resistance. Fig. 4.1 showed the insight of primary track. 24 Fig. 4.1 : The primary track. 4.3 The Secondary Pick-Up Fig. 4.2 : The Secondary Pick-up 25 Fig 4.2 showed the Secondary Pick-up circuit board that has been connected with the origin circuit board of wireless mouse. As the circuit was constantly switching to provide sufficient power to the load and power was lost in this constant switching process, the results showed that the under tuning schemes has produced less power which is 140 mW. While when there are excess power, the over-tuning scheme will switched ON. A power output of 193 mW was obtained while the switching loss was much smaller. The voltage across the wireless computer mouse input, VL was successfully controlled at about 3.3V. 26 CHAPTER 5 CONCLUSION AND RECOMMENDATION 5.1 Conclusion The objective of this study is to built wireless battery-less computer mouse device, to design and understand about the circuits that will be used by using Multisim 11.0 and lastly to utilize the usage of Inductive Power Transfer (IPT) system for low power consumptions at mW. From the obtained results and observations, the analysis of the system performance was done and suggestion for the enhanced system has been provided. After the completion of the study, the objectives of this project were achieved. Wireless Battery-less Computer Mouse is finally built as planned. A prototype driven by a standard USB power source have been successfully designed eventhough the prototype does not working properly. It has found that the IPT power supply can successfully delivered the required power at all locations within the disk oil. 27 5.2 Recommendations For the recommendation, the study can be enhanced by developed the usability of the proposed mouse system such as the movement limitation of the IPT wireless computer mouse. An intrinsic limitation of the IPT technology is the limited power transfer range between the primary and the pick-up. The movement is only allowed within the mouse pad, this would be inconvenient in situations where the mouse is required to move away from the mouse pad, for examples, when it is for presentations or computer gaming. 28 REFERENCES 1. Hu, A.P.: ‘‘Selected resonant converters for IPT power supplies’’, PhD thesis, Department of Electrical and Computer Engineering, University of Auckland, Oct 2001 2. Yungtaek Jang, M. M. 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