Project_ReportTBelle(1)

Kinetic Energy Harvester
Third Year Project
Final Report
Tyler Belle
Supervisors: Dr. Gianluca Marcelli &
Mr. Stephen Kelly
08– 04 – 16

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i. Acknowledgements
As with all major projects and milestones it could not have been completed without the help
and support of various peers along the way. This section is devoted to thanking and recognizing
those who would have assisted and been partially responsible for this project reaching this point
of success.
Deepest thanks must be extended to my family who never stopped believing in me from
beginning to end and provided the mental support required to overcome times of hardships.
My supervisors, Dr. Gianluca Marcell & Mr. Stephen Kelly, have been staples with the smooth
running of this project from start to finish and I extend honest gratitude to them for their hard
work and wise advice with all of my project related issues.
Special thanks is extended to Andy Brookman & Harvey Twyman of the School of Engineering
& Digital Arts technical for their hands-on assistance and technical advice for debugging and
correcting hardware problems discovered along the course of this project.
Finally, there are no words to accurately exemplify my appreciation of my friends, both British
& Barbadian, who offered constant support both technical and mentally uplifting, reminding
me never to give up and giving me the strength to achieve the project objectives in a timely
and efficient manner with special mention of:
 Cyndi Marshall
 Hadiya Squires
 Jalea Best
 Joel Earps
 Lakshmi Kanumuru
 Marissa Headley
 Pooja Balaji

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ii. Declaration
I certify that I have read and understood the entry in the School Student Handbook on
Plagiarism and Duplication of Material, and that all material in this assignment is my own
work, except where I have indicated with appropriate references.
#Signed: ................................ Date: 2016 – 04 – 08

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iii. Summary
Alternative and renewable sources of energy are one of the main trending topics of discussion,
research and innovation in this technological era. As time moves on, devices already associated
with this discipline are becoming more efficient and more desirable for large and small
applications. This can especially be noted in the conceptualization of “wearable technologies”,
which add a sense of portability to energy harvesting systems. The intended project was based
within these disciplines and its main aim was to design and create a functional wearable kinetic
energy harvester.
This manufactured circuit was expected to be worn on a user’s arm and convert its movement
into usable kinetic energy through the utilization of magnets within a coil, a practical
implementation of Faraday’s Law of electromagnetic induction. The induced signal will
undergo amplification processing before storage in a suitable battery cell. This stored energy
can then be discharged to through a USB interfaced device to charge it.
Tests conducted and results documented confirm the implementation of this system was a
success. The employed circuit was deduced to be fully in line with the expected functionality
and technical requirements outlined at the commencement of this project as an efficient and
cost effective kinetic energy harvester. Final assembly and testing is to be carried out within
the weeks following the completion of this report.

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Table of Contents
i. Acknowledgements ................................................................................ 1
ii. Declaration............................................................................................. 2
iii. Summary ................................................................................................. 3
1. Introduction .............................................................................................. 6
1.1 Aims & Objectives ......................................................................... 6
1.2 Literature review .............................................................................. 8
1.3 State of the art............................................................................... 12
1.4 Technical requirements.................................................................. 13
2. System Description & Implementation.............................................. 14
2.1 Induction ......................................................................................... 15
2.1.1 Correlation of Faraday’s law to Kinetic Energy.................................... 17
2.1.2 Achieving Faraday’s Law Parameters .................................................. 18
2.1.3 Problem discovered and their solutions................................................ 22
2.2 Electrical Signal Management........................................................ 25
2.2.1 Operation of LTC3108 .......................................................................... 26
2.2.2 Problems associated with electrical signal management...................... 28
2.3 Internal Battery Charging ............................................................... 28
2.3.1 `Operation of LTC4071......................................................................... 29
2.3.1 Lithium Polymer Battery........................................................................ 31
2.3.2 Problems Associated with internal battery management ...................... 33
2.4 Discharging ..................................................................................... 33
2.4.1 Pololu 5V step-up Voltage Regulator S7V7F5...................................... 34
2.4.2 USB socket........................................................................................... 34
2.5 PCB Implementation ....................................................................... 36
2.5.1 PCB Design.......................................................................................... 36
2.5.2 PCB Manufacturing .............................................................................. 37
2.6 Enclosure ........................................................................................ 38
2.7 Rigging ............................................................................................ 40
3. Test Results & Discussion.................................................................... 41
3.1 Induction Coil Testing..................................................................... 41

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3.1.1 Discussion of Induction Coil test Results.............................................. 45
3.2 Bridge Rectifier Testing.................................................................. 46
3.2.1 Discussion of Bridge Rectifier Results.................................................. 48
3.3 Testing of Amplification Circuitry................................................... 48
3.3.1 Discussion of Amplification Circuit Results:.......................................... 50
3.4 Testing of Battery Storage Circuitry.............................................. 51
3.4.1 Discussion of Charging Circuit Test Results......................................... 52
3.5 Testing of Discharge Circuitry........................................................ 53
3.5.1 Discussion of Discharging circuit results:.............................................. 55
4. Conclusions........................................................................................... 57
4.1 Summary of findings ....................................................................... 57
4.2 Work to be completed..................................................................... 57
4.3 Developmental Considerations....................................................... 58
5. References............................................................................................ 59
Appendix A.................................................................................................. 61
Appendix B.................................................................................................. 62
Appendix C.................................................................................................. 63
Appendix D Figure 1.................................................................................... 64
Appendix D Figure 2.................................................................................... 65
Appendix E.................................................................................................. 66
Appendix F .................................................................................................. 67
Appendix G.................................................................................................. 68
Appendix Ha................................................................................................ 69
Appendix Hb................................................................................................ 70
Appendix I................................................................................................... 70

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1. Introduction
The technological world is progressing at an ever increasing rate of development. Each passing
day heralds the reformation of past scientific discoveries and applications. Particular interest
has gone into alternative sources of energy especially those of the environmentally friendly or
renewable nature. Energy is the foundation of most, if not all, forms of matter and electrical
systems. It gives the ability to move and carry out tasks. Fossil fuels are used to provide power
to most vehicles and even generators for entire countries. They are, however, non-renewable
and finite in nature and for that reason research has gone into more renewable sources of energy
such as wind energy, hydroelectricity and kinetic energy. The process of collecting this latent
environmental energy and transforming it into usable electricity is known as energy harvesting.
Benefits of energy harvesting include:
 Improved Efficiency: Waste heat and latent is collected as useful energy thus
increasing effectiveness of the energy originally put in.
 Battery-less: The function of an energy harvester to create its own energy. Due to this
fact, most energy harvesters do not require their own power supplies.
 Environmentally-friendly: The sources of energy targeted by energy harvesting are
usually renewable and green in nature as they exist readily in our environment(e.g.heat,
wind movement, solar panel).[1]
Large scale energy harvesters can be used to supplement industrial level machinery and
electronics. On a small-scale, devices with energy harvesting capabilities are valued as light-
weight secondary power sources. The foundation of this process is rooted in the discipline of
kinetic energy harvesting as well as incorporation of energy harvesting into “wearable
technology”. In the form of wearable technology, this project will prove to be a commercially
viable, environmentally friendly and portable source of power for consumers from all walks of
life.
1.1 Aims & Objectives
The provided definition of this project was outlined as follows: Energy harvesting is the
process employed to extract energy from external sources (e.g. radiation, wind energy and
kinetic energy) - the energy is stored and then used to power small appliances. The project will
consists in designing and building a wearable device capable of converting kinetic energy into

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electricity, which is stored and then used to power body-worn appliances such as mobile
phones.
Based on the information provided, the intended aim of this project was the design and
implementation of a wearable system which would be able to harvest the kinetic energy or
movement of its wearer into usable electrical energy. The harvested electricity must be able to
be stored and repurposed to power small electronics such as mobile phones. This aim was then
used to specify objectives for this project.
Objectives
 Create a circuit which transforms kinetic energy to electrical energy.
 Final System must be able to suitably output enough power to charge small electronics.
 Device must be enclosed in an appropriate casing with suitable rigging, allowing it to
be worn comfortably.
In addition, based on the nature of the project, the following characteristics are expected to
present in the final product to make it more appealing to users.
 Comfortably worn on the arm whether the user is stationary or in motion.
 Lightweight, should feel as close to weightless as possible for ease of carrying by the
user (Optimum weight: <= 1.5 kg).
 Compact, the entire size of the device should not be bulky as large objects on the wrist
tend shake around more in motion due to lack of even support across its base. This
jittering can prove to be uncomfortable and obstruent for the wearer (Optimum
dimensions: 20 cm length x 12cm width x 7 cm or smaller).
 Suitable internal rigging need to be put in place so that motion by the user does not
cause damage to the circuitry.
 The circuit casing should be water-proof.
 Should be able to charge small portable electronics via USB.
 The overall product should be cost-effective and efficient in nature.
The deliverables provided at the conclusion of this project are thus to be:
 A working kinetic Energy harvesting circuit
 An enclosure for the built circuit and rigging allowing the entire system to be worn
 Final Report documentation summarizing the project

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1.2 Literature review
Many techniques were researched before the discovery of an appropriate method for this
project. Past studies have proven that there are many methods in which kinetic energy
harvesting can be achieved. These include the use of piezoelectric material, electromechanical
generators and electromagnetic induction. Each of these techniques were accompanied with
their respective pros and cons in relation to implementation within this project.
Piezoelectric devices are transducers which convert the force exerted on them to an electrical
charge. Khaligh et al[2] explains that these devices can be used to capture the kinetic energy
from vibrations present in industrial environments such as the engines of motor vehicles. Based
to the information discovered, piezoelectric devices were not heavily considered due to the
points stated by Khaligh et al[2]. A very important functional requirement of this project is a
suitable level of efficiency. As stated by Khaligh et al.[2], in the case of a 68 kg person walking
at a speed of 2 steps per second, an estimated 67 watts(W) of power is generated. Due to the
structure of piezoelectric material, the mechanical and electrical power losses result in an
estimated harvesting of 1.265 W. This estimation gives a conversion efficiency of less than
2%. The output was suitable for electrical storage and repurposing for this application,
however, more research was undertook to find methods which were more conservative and was
capable of harvesting more of a wearer’s input energy.
Researchers at Simon Fraser University were very successful in the implementation of a
biomechanical energy harvester device in the form of a knee brace.

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Figure 1: 3D rendering of Biomechanical energy harvesting knee brace [3]
This device consists of a rotor and mechanical generator. The rotor spins as the wearer steps
and, in turn, this spins the generator and generates electricity. The operation of this system can
be likened to that of regenerative braking where the stopping force of a vehicle is harvested
into electrical energy. The brace can be configured to harvest energy on both swings of the leg
or only on the back swing. The reason for this is due to the extra input required for acceleration,
resulting in a decreased efficiency associated with the system’s operation. In order to
counteract this, Donelan et al[3] implemented the alternate mode where the knee brace would
assist with deceleration of the knee and harvest only on this swing. This device was tested on
students walking on a treadmill at a pace of 1.5ms-1
. It was found that subjects generated 7 ±
0.7 W of power with an extra 18 ± 24 W of metabolic power required for proper movement
with the device in continuous generation mode. In regenerative braking mode, 4.8 ± 0.8 W of
electricity was generated with an increased metabolic cost of 5 ± 21 W.

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*COH stands for cost of harvesting. This is the rate at which metabolic power must be put into a system to achieve a
particular change in electrical power. High COH denotes low efficiency.
A) The average power output of the swing of a person’s leg
B) The average power generated in continuous generated mode
C) Figure illustrating the average power output from regenerative braking mode
Figure 2: Illustrations of the average power generated under various conditions
It is evident that the main disadvantage of this system is its inefficient nature due to the added
work to overcome the weight and movement of the stiff rotor. Johnston [4] further states that
the 1.5 kg device requires 60 W of power to carry the generator alone without it generating any
power. As one of the main requirements of a wearable system, as well as efficiency, is being
light-weight, this knee brace was considered to be unfit for this implementation. A more
efficient and light-weight method of implementation was required.
Amirtharajah et al[5] explains the use of an inertial based electromechanical generator. This
device operates under the logic of Faraday's Law.

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Figure 3: A generator mechanical schematic[5]
Voltage is generated when the housing is shook. The movement of the mass in turn moves the
wire coils cutting the magnetic flux lines of the permanent magnet, B. In accordance with
Faraday's law of electromagnetic induction, a voltage will be induced within the coils with a
magnitude that is directly proportional to rate at which the magnetic field lines are cut by the
wire coils. The following output was measured under the conditions of the natural frequency
oscillation by the mass, m.
Figure 4: Output of electromechanical generator after displacement and release (natural
oscillation frequency = 94 Hz)[5]
Outputs of almost 200 millivolts were able to be attained from just a small displacement. It was
theorized that even larger voltage peaks would be attained under the large amplitude
movements of the human body. The knowledge provided by this experiment provided a very
solid foundation for this project. The method of electromagnetic induction was chosen as
appropriate for the application of this project for two reasons. These reasons are energy
conversion efficiency and scalability. Due to the near frictionless rigging of the magnet, it can
be assumed that, were a user to shake the electromechanical setup, most if not all, of the kinetic
energy provided would be transferred to the magnet. The range of movement would only be

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limited to the length and rigidity of the spring. This allows for greater efficiency of kinetic
energy to induced electricity. The second benefit of electromagnetic induction is its ability to
be scaled. As noted by Amirtharajah et al[5], increasing the number of coils is a method of
increasing the possible maximum peak output voltage. The lightweight and flexible nature of
copper wire allows for a great number coils to be made without a compromise of overall weight
or volume of the system. It was decided, however, that other methods of carrying out this effect
would be researched. As the project is meant to be wearable in nature, it was determined that
the shifting mass in the electromechanical rigging would prove bulky and uncomfortable for
users.
1.3 State of the art
Based on information researched, electromagnetic induction was determined to be the most
appropriate energy harvesting method for this project. A different way of achieving this affect
was required to allow for the ability of the device to be worn. This wearable structure concept
was based on two state-of-the-art electromagnetic energy harvesters. These are the shaker
flashlight and AMPY, the motion-charger. These devices have similar means of operations.
AMPY and the shaker flashlight both consist of stationary coils encompassing a free moving
magnet. As a user moves the device, the internal magnets will pass through the coils, causing
an electromagnetic induction of current. Faster movement denotes a larger input of kinetic
energy and thus more induced current. This induced current is then stored in an electrical
storage device like a capacitor or battery until this energy is required.
Figure 5: Schematic of a shaker flashlight[6]
Shaker flashlights utilise capacitors as their energy storage component [6]. These allow for
quick charging and discharging. The discharge time of capacitor and its capacity, however, are
what make the use of capacitors inappropriate for this project. One of the main objectives of
this project is the charging of mobile phones. It is known that mobile phones charge at a rate
of around 5 V/1 A. This charging criteria must be applied to a phone's battery over a period of
time for the proper build-up of power. The quick discharge and low power capacity of

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capacitors prevent them from being practical for this project. Super capacitors are more
powerful alternatives to capacitors which could have been used. They are still, however, much
weaker in terms of capacity and power as compared to a conventional battery. Additionally,
super capacitors can be very bulky and expensive.
Figure 6 : Internal layout of the AMPY motion-charger[7]
AMPY uses an 1800 milliamp-hour(mAh) Lithium-ion battery as its electric storage
component of choice. This is capable of fully charging an IPhone 6. The AMPY system weighs
about the same as a mobile phone and is the size of a deck of cards [7]. Lithium-Ion batteries
are light-weight and compact, allowing for high power density without a compromise of space
or comfort in wearable technology applications. Users are capable of discharging the harvested
electrical energy via a USB port. In addition to the basic function of kinetic energy harvesting,
AMPY also provides a user feedback system in the form of LEDs. These LEDs indicate the
magnitude of charge currently being stored on the motion charger. The information acquired
from the analysis of the AMPY product was very helpful and important in the design and
implementation of this project. The final AMPY product is a very commercial, user-friendly
and cost-effective project.
1.4 Technical requirements
Building on the data attained from research into energy harvesting techniques, various
technical requirements were defined as guidelines for the optimum project. The functionality
of prototypes made, as well as the final product, would be collated against these requirements

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to confirm the success of the project. The following stipulations are expected of the final
product:
 Generation of power due to movement(Application of Faraday's Law)
 Retention of harvested kinetic energy using suitable power storage(Lithium Polymer
Battery)
 Discharge of electrical energy to charge small electronics via USB(Current rating of
500 mA/ Voltage Rating of 5 V)
 Appropriate internal rigging to protect PCB from damage due to movement
 Appropriate external rigging to allow entire system to be worn
2. System Description & Implementation
Figure 7: Block Diagram illustrating the functionality of the kinetic energy harvester System
The kinetic energy harvester's operation can be summarised as follows:
 The user will wear the enclosed energy harvester on their forearm.
 The user will move their arm.
 Internal conversion circuitry will convert the kinetic energy of the user's forearm into
electricity by Faraday's law of electromagnetic induction.
 Converted electricity must be amplified, processed and regulated before storage.

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 Converted and processed electrical energy is stored in the on-circuit lithium
polymer(li-po) battery.
 Step up and regulate the discharge voltage and current of the lithium polymer battery
to 5V/500ma respectively.
 Discharge through a USB socket to charge connected small electronics
The techniques to execute these stages will be explained in further detail in the following
sections.
Following Figure 7, it can be seen that this device's functionality can be segmented into four
main stages to summarize its overall operations. These stages are electromagnetic induction,
electrical signal management, internal battery charging, and discharging. It should be noted
that due to time constraints, this entire circuit has not been fully assembled and tested by the
submission of this document. The methods intended to be used in the continued work will
however be explained.
2.1 Induction
As previously mentioned, the operation of this device follows the application of Faraday's law
of electromagnetic induction. Jackson [8] states that, in 1831, it was observed by English
scientist, Michael Faraday, that a transient current is induced within a circuit when (a) a steady
current within an adjacent circuit is turned on and off, (b) the adjacent circuit with a steady
current flowing is moved relative to the first circuit, (c) a permanent magnet is thrust into or
out of the circuit. . This phenomenon was determined to be a result of the changing magnetic
flux in the environment of the circuit. Changing flux was found to induce an electric field
around the circuit, mathematically integrating these field lines results in the derivation of the
induced electromotive force (EMF). This force can be likened to a voltage, following Ohm's
law,
𝑉𝑜𝑙𝑡𝑎𝑔𝑒 = 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 × 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒
Where a voltage acting on a resistive load results in the flow current within the present
circuit.
(1.0)

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Figure 8: Illustration of electromagnetic induction observed by Michael Faraday [8]
According to Jackson, if a circuit, C, is bounded by an open surface, S, with unit normal, n,
and a magnetic field strength , B, the magnetic flux, F, of a circuit can be defined by the
equation:
(1.1)
Equation 1.1 was further utilized by Faraday to derive the law of induction,
𝜀 = −𝑘
𝑑𝐹
𝑑𝑡
Where ɛ is the induced e.m.f, -k is the constant of proportionality and
𝑑𝐹
𝑑𝑡
is the rate of change
of magnetic flux with respect to time.Equation 1.1 states that induced e.m.f is directly
proportional to the rate of change in magnetic flux in the environment of a circuit. The negative
sign serves to indicate that the induced current is generated in such a way as to oppose the
change of magnetic flux which is occurring through the circuit. This is a phenomenon outlined
by Lenz' law which states that the direction of induced current within a wire loop will oppose
the change in magnetic flux which caused it, in an attempt to keep the magnetic environment
of the wire loop constant[9]. In the context of this project, the constant of proportionality, k, is
representative of the number of coils of wire being affected by magnetic flux.
𝐹 = ∫ 𝐁 ∙ 𝐧 𝑑𝑎
𝑆
(1.2)

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2.1.1 Correlation of Faraday’s law to Kinetic Energy
The formula for kinetic energy of an object is defined as follows:
𝐾𝑖𝑛𝑒𝑡𝑖𝑐 𝑒𝑛𝑟𝑔𝑦 =
1
2
× 𝑚𝑎𝑠𝑠(𝑘𝑔) × 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦2
As the mass parameter would tend to be constant in most applications, it was deduced that the
correlation between kinetic energy and induction of current by Faraday's law lies in the time
and velocity variables of their equations. Large velocity will denote the movement of an object
over a small time period resulting in a large kinetic energy value. This means to "capture" the
kinetic energy input to the system, a method of causing a change of magnetic flux in relation
to a change in input energy must be implemented. This implied the involvement of a moving
part whose speed is proportional to a change in magnetic flux.
The findings of Faraday confirm that there were 3 ways of implementing of his law. These
are listed as follows:
 Movement of a coil relative to a stationary magnetic source.
 Movement of a magnet relative to a stationary set of coils.
 Varying of a magnetic source's flux within the environment of a set of coils through
the use of an adjacent variable current source.
Given the definition of this project, the third implementation was determined to be impractical
as it does not involve the use of motion or kinetic energy. The first implementation, although
sound in theory, was determined as inappropriate for this project due to the possible problems
its design and implementation would be associated with. This implementation would utilize a
large stationary magnet within the environment of a small coil of wires. This coil would be free
to move relative to the magnet, under the influence of movement by the user, resulting the
induction of current. The speed of the coil as it interacts with the magnetic environment would
determine the induced current magnitude. As previously mentioned, this project is expected to
be light-weight, cost-effective and energy efficient in nature. The following problems were
expected to occur if this implementation was chosen.
 Large magnets can be very expensive, decreasing the cost effectiveness of the device
 A large magnet would constitute a large addition of weight to the overall system
(1.3)

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 The large magnet would have large extraneous magnetic field lines which could have
a negative impact on circuitry internal and external to the system.
As the type of copper wire used would remain constant, the cost and weight factor of the wire
was not considered in this comparison. It was found that a large magnet (15x10x75mm) had a
price of £11.99[10] as compared to the cheaper and more compact (15 x 15 x 30 mm) magnets
priced at £3.52[11]. The use of smaller magnets would prove to be the more cost-effective
choice thus establishing the employment of Faraday's second implementation of his law of
induction as the technique of choice for this project.
Analysis of Faraday's law reveals that there are 4 ways in which a large induction of current
can be achieved through exploitation and manipulation of the parameters of the equation.
These are:
 The use of a large magnetic field strength(B)
 Utilizing a coil with a large cross-sectional area (A)
 The use of a large number of coils of wire(k)
 Fast rate of change of magnetic flux, constituting a small time parameter(t)
2.1.2 Achieving Faraday’s Law Parameters
1. Large magnetic field strength: Neodymium is the strongest commercially available
magnetic substance in the world. They are very magnetically dense as less than a cm2
block of neodymium is capable of lifting 1.7 kg [12].The Tesla (T) is the unit of
magnetic field strength. Neodymium magnets have a strength of 1.25 T which is a
relatively large value as ultra-strong magnets such as medical magnetic resonance
machines have field strengths of around 1.5 to 3 T [13]. Small neodymium magnets
were chosen as they would provide a large magnetic field strength without a
compromise of overall weight and volume of the system.
2. Large cross-sectional area of coil: A large coil was chosen not to be used in this project.
It was determine that this would result in a larger and bulkier final system to
accommodate the size of the coil. In addition, studies by Rfy et al.[14] show that
magnetic field strength decreases exponentially with distance. This was taken into
consideration in coil size selection as Faraday's law applies for a constant magnetic
field.

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Figure 9: Graph of magnetic field strength of neodymium materials over increasing
distance [14]
Analysis of the figure 9 graph revealed that most neodymium affiliated objects had a
significant reduction of magnetic field strength at a distance of 2 cm or more. As the
magnets intended to be used are very small in diameter (10 mm) and electromagnetic
induction works best at high field strengths, it was determined the coils would be
formed by wrapping the wire around an insulating pipe whose internal diameter is close
to 10 mm. This will limit the degradation of the magnetic field due to empty space. This
size would facilitate effective use of the peak magnetic field strengths found in close
proximity to the neodymium magnets.
3. Large number of coils: The original implementation of the coil consisted of the
continuous wrapping of 17 SWG wire. This wire was 1.422 mm in diameter which is
much thicker than wires used for average electrical applications. The reasoning for the
use of thick wire was to limit the internal resistance which would increase the current
generated by electromagnetic induction.
𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 =
𝜌𝐿
𝐴
=
𝑟𝑒𝑠𝑖𝑠𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝑤𝑖𝑟𝑒 ×𝑙𝑒𝑛𝑔𝑡ℎ
𝑐𝑟𝑜𝑠𝑠𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑤𝑖𝑟𝑒
Equation 1.3 outlines the formula for the resistance of wire. It can be seen that a
larger cross sectional area will result in a small internal resistance.
𝐶𝑢𝑟𝑟𝑒𝑛𝑡(𝐼) =
𝑉𝑜𝑙𝑡𝑎𝑔𝑒(𝑉)
𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑅)
Derivation of Equation 1.0, gave rise to the above equation which is the current
derivation of Ohm's law. Analysis reveals that components with large resistances will
result in a smaller current. Following this logic, it was originally speculated that wire
with a large cross sectional area should be utilized for this application. Testing of the
17 SWG wire against thinner wire (0.711 mm diameter) proved however that thinner
1.3

20
wire allowed for a much larger power output. The results of this test are discussed
further in section 3.1.
4. Small time parameter: The time parameter of the system will be decided by the time
taken for the magnet to pass from one point to another within the coils. The magnets
were chosen to be small and light for this purpose. This would allow them to be easily
moved under the force of the user's movement. A small weight will facilitate little loss
of kinetic energy due to overcoming inertia which would in turn decrease kinetic energy
to electrical energy conversion efficiency.
With these variable implementations in mind, the following components were utilised.
Figure 10 : Coil of wire used for Kinetic Energy Harvesting Project(22 SWG/0.711mm
diameter)

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Figure 12 : 9 Neodymium Disc magnets(10mm x 3mm each)
The 22 SWG wire was used to wrap an 11 mm internal diameter insulating pipe a numerous
times. Given the parameters of the coil, the number of turns can be calculated as follows:
Length of entire coil: 11cm = 110mm
Diameter of wire: 0.711mm
Therefore an estimated
110
0.711
≈ 155 𝑡𝑢𝑟𝑛𝑠 𝑝𝑒𝑟 𝑙𝑎𝑦𝑒𝑟
Number of layers of coil: 8 and a half 11 cm in length
Therefore there is an estimated 155 𝑡𝑢𝑟𝑛𝑠 𝑝𝑒𝑟 𝑙𝑎𝑦𝑒𝑟 × 8.5 𝑙𝑎𝑦𝑒𝑟𝑠 = 1315 𝑡𝑢𝑟𝑛𝑠 𝑖𝑛 𝑡𝑜𝑡𝑎𝑙
The insulating pipe diameter was chosen to be as close as possible to the diameter of the magnet
being used as the strength of the magnetic field affecting the wire decreases exponential with
distance away from the magnet. The coil was made to be 11 cm long to keep the overall device
compact. The intention is for the neodymium magnet block to be placed inside of the coil
wrapped pipe and positioned perpendicular to the wrist inside of its enclosure. As the user
moves their arm back and forth, this will move the internal magnet through the coil. The
movement of the magnet will cause an induction of e.m.f proportional to the speed of the
magnet. In this way, the kinetic energy of the user can be harvested and transformed to
electrical energy.

22
2.1.3 Problem discovered and their solutions
The need for DC: It is a well-known fact that the batteries of all kinds are charged and
discharged using DC. They are unable to be charged by an AC voltage. Figure 12 illustrates
how the use of Faraday's law and Lenz' generates an AC voltage.
Figure 12: Illustration of the various instances of induction via Faraday's Law [15]
As previously mentioned, Lenz' law states that the direction of induced current within a wire
loop will oppose the change in magnetic flux which caused it, in an attempt to keep the
magnetic environment of the wire loop constant. This means the current generated through the
passing of a magnet from one side of a coil to the other will not be constant but instead fluctuate.
An approaching north pole of a magnet will have the same effect as a retreating south pole. In
the same way, a retreating north pole will have the same effect as an advancing north pole. It
can be seen, in reference to figure 12, that the former results in a flow of current in the
downward direction whereas the latter results in an upward current flow. These events
occurring consecutively will result in an AC voltage.
Solution: Rectification is one of the main methods of converting an AC signal into a DC
signal. A diode is a component which only allows the flow of current in one direction is
commonly used for rectification purposes. Originally, it was reasoned that a bridge rectifier
would be an effective solution to this problem. As illustrated by figure 13, a bridge rectifier is
a component consisting of four rectifier diodes in a particular formation which allows for full-
wave rectification.

23
Figure 13: Illustration of operation of bridge rectifier [16]
It can be seen that, bridge rectifiers are much more efficient than using singular diodes as they
capture both the positive and negative curves of oscillating voltages as compared to singular
diodes which only capture one. The use of regular diodes within the bridge rectifier was soon
disregarded however due to the voltage drop associated with signal diodes. Most signal diodes
have a voltage drop of 0.7 V [17]. This means that in the case of one path of a bridge rectifier
circuit, there will be a voltage drop of 0.7 x 2 = 1.4 V. Therefore in a low voltage application
such as this project, the induced current would be unable to pass through these diodes as their
peak voltages would be in the measure of a few hundreds of mV. In addition, in cases of high
input peaks where the input voltage peak is greater than 1.4 V, this would be dropped along
the bridge rectifier, significantly reducing the efficiency of the overall system.
For this reason it was decided that a bridge diode would be created from the formation of 4
Schottky diodes in a similar bridge rectifier layout as illustrated n figure 13. Schottky diodes
are special rectifying components which have a low voltage drop in the range of 0.2V. In terms
of the total voltage drop across any particular path in a bridge rectifier, this will equate to 0.2
x 2 = 0.4 V.
Low power generation: Test results show that the output of the inductor coil when the
magnet is falling under the force of gravity is very low. These will be discussed further in the
test results section of this report. Analysis of Faraday's equation shows that increasing the
number of turns to a great value is the only way of compensating for the low power output.
This is because the magnetic field strength is fixed by the chosen magnets. This can be
visualised with the computing of a voltage based on possible real life parameters of Faraday's
law.
Using Equation 1.2 and the following values,
k/Number of coils = 1315 turns

24
Magnetic Field Strength (B) = 3 T (Magnetic Field Strength of Neodymium)
Cross sectional Area inner-most coil (A) = π x (
11×10−3
2
)2
= 9.5 x 10-5
m2
Time over which magnet was moving = 0.5 seconds
The Voltage induced can be calculated to−1315 ×
3 ×9.5 ×10−5
0.5
=
−0.74955 𝑉𝑜𝑙𝑡𝑠 𝑖𝑛𝑑𝑢𝑐𝑒𝑑 𝑎𝑡 𝑜𝑛𝑒 𝑝𝑜𝑖𝑛𝑡 𝑖𝑛 𝑡𝑖𝑚𝑒 .
It can be seen that the output of the coil is extremely small (<1V). This energy must be stepped
up if it is to have any substantial use in charging of electronics at 5 V especially if it was to be
rectified which could result in a large fraction of the input energy being lost through the voltage
drop of the bridge rectifier.
Solution: As noted in previous sections, a lithium polymer battery is expected to be charged
by the induced electrical energy. Research into the charging of lithium polymer batteries
showed that they have a very particular method of being charged for efficient use [18]. This is
illustrated in figure 15. Disregard for this charging method could result in permanent damage
to the battery, explosion or spontaneous combustion [19].
Figure 15: Charging profile of a 1Ah 3.7V lithium polymer battery [18]
The breakdown of this charging algorithm will be covered in the internal battery charging
aspect of this system implementation segment. Figure 15, however, shows that an input of 1A
at 4.2 V is required for efficient charging as well as the adjustment of these values over time
for the constant current/increasing voltage and constant voltage/decreasing current segments
portions. As test results revealed a maximum input of 500 mV DC, a method of stepping up
the voltage and implementing the charging algorithm was required. Research into possible

25
solutions led to the discovery of the LTC3108 and LTC4071 integrated circuits for use in
voltage magnification and lithium polymer battery charging respectively. These chips will be
discussed in section 2.2 & 2.3.
2.2 Electrical Signal Management
This section will give a breakdown of the research and components associated with the
electrical signal processing of the project. The need of larger voltage inputs to charge the
lithium polymer battery merited the requirement of amplifying circuitry to carry out this
process. Originally, a seemingly suitable solution to this problem was the use of a boost DC-
DC switching regulator. This component would take a low input voltage and magnify it to a
level of choice. In theory, it was thought that this would allow the output of a regulated 4.2V/1A
signal. Characteristics of low input switching regulators found via research debunked this
theory. In all cases of switching regulators discovered, it was found that none of the
components were capable of stepping up a voltage as low as the levels generated in this project.
This can be illustrated in the specifications of the lowest input step up regulator found, the
TPS6122xlow input voltage switching regulator (Refer to Appendix A for datasheet extract).
The TPS6122x series is considered a "low-input" step-up voltage regulator, allowing the
magnification of voltages as low as 700 mV. The peak DC voltage after rectification of
harvested electricity was in the range of 500 - 600 mV which is still below the lowest input
value of the component, disallowing proper operation. In addition, supposing that the user
moves fast enough to generate 800 mV DC voltage, it is impractical that the device would only
allow for battery charging when high velocity movement is present as that is not how the
average consumer would move the device during day to day activities.
Following the disproving of the use of switching regulators, the use of operational amplifiers
were researched. The example used for explanation in this project is TLV232x series (Refer to
Appendix B for datasheet extract). This integrated circuit is capable of stepping up very low
input voltages (Range of -300mV to 8V) to a larger output level (Range of -8V to -7V). The
main disadvantage of this component is the need to be powered. As this project is meant to be
renewable energy and the discipline of energy harvesting, it was determined to be inappropriate
to include the need of external power sources such as batteries for the device to function.
The final resolution to solve the low power problem was determined to be the LTC3108 energy
harvesting circuit (Refer to Appendix C for Datasheet extract). The LTC3108 is an integrated

26
ultralow input DC to DC converter capable of accepting voltage inputs as low as 20 mV and
output one of four programmable regulated output voltages.
Figure 16 : Lithium Ion Battery Charger implementation of the LTC3108[20]
2.2.1 Operation of LTC3108
Figure 16 shows the application of the LTC3108 to be used. This integrated circuit works in
conjunction with an external step-up transformer (LPR6235) to create an ultra-low input step-
up DC-DC voltage regulator. An internal MOSFET switch acts as a resonant step-up oscillator
to transform input DC into high frequency AC, usually in the range of 10 kHz to 100 kHz. The
frequency of the output AC is determined by the turn’s ratio of the compact transformer. In this
application, the 1:100 ratio transformer will be used to allow the conversion of inputs as low
as 20 mV. The transformed high frequency AC is boosted and rectified using an external charge
pump capacitor (C1 pin) and the internal rectifiers of the chip. The rectified signal sends current
to the VAUX pin to charge the connected capacitor. This capacitor is used for powering the
internal active circuits of the LTC3108. The main output voltage pin (VOUT) begins to charge
when the VAUX capacitor exceeds 2.5V. The VS1 and VS pins are used to program the VOUT
output voltage. Table 1 outlines the programmable VOUT configurations.
Table 1: Regulated Voltage Using Pins VS1 and VS2[20]
VS2 VS1 VOUT
GND GND 2.35 V
GND VAUX 3.3 V
VAUX GND 4.1 V
VAUX VAUX 5 V

27
4.1 V was the chosen programmed output of choice for this application as it is as close to the
optimum charging voltage (4.2V) for lithium polymer cells. The 5 V output was considered
but this output would have to be regulated to 4.2 V for charging efficiency and safety thus
decreasing the energy efficient nature of the project.
Table 2: Pinout and Connections of LTC3108 implementation
Pin name/Number Connected Component Functionality
1 - GND Ground Component Ground Component
2-VAUX 1 µF electrolytic capacitor Output of internal rectifier
Circuit and power supply of
LTC3108
3 - VSTORE 220 µF electrolytic capacitor Acts as a backup power
source for chip when
external input power is not
present, charges after VOUT
pin is charged to regulation
4 - VOUT Output Capacitor (1000 µF) Main output of the
converter(4.1 V
programmed output)
5 - VOUT2 Not connected(Left floating)
) )(Note 1)
Logic 1V output capable of
being enabled by
VOUT2_EN pin
6 - VLDO Connected to VAUX pin as
it is unused(Note 1)
Low dropout Linear
Regulator output of 2.2V for
powering external
processors (Note 1)
7 - PGD Not connected(Note 1) Power Good Output. Pulled
high when VOUT pin is
within 7.5% of its
programmed value. Pulled
low when VOUT drops 9%
below programmed value
10 - VS2 Ground Component Voltage Select Pin 2. Used
to program output voltage of
chip (Refer to table 1)
11 - VS1 VAUX Voltage Select Pin 1. Used
to program output voltage of
chip(Refer to table 1)
12 - VOUT2_EN Not connected(left
floating)(Note 1)
Enable pin for VOUT2.
VOUT2 pin activated when
this pin is pulled high
13 - C1 1 nF ceramic Capacitor to
secondary winding of
transformer
Charge pump and
rectification circuit for the
AC of the secondary
transformer winding

28
14 - C2 470 pF ceramic Capacitor to
secondary winding of
transformer
Input to the gate of the
internal MOSFET oscillator.
Turns internal gate on and
off at high frequency.
15 - SW The primary winding of the
compact transformer
Drain of the internal
MOSFET oscillator.
Converts DC signal to AC.
Note 1 : Deemed unnecessary for this application
2.2.2 Problems associated with electrical signal management
Abiding by the charging algorithm of Lithium polymer cells: The use of the
LTC3108 will allow for the regulated output of a 4.1 V signal from the harvested low inputs.
The chip, however, fails to execute the proper method of charging required for the lithium
polymer cell. The determined solution for this problem was the implementation of the
LTC4071 lithium battery charger. The operation of this chip will be further explained in the
following section.
2.3 Internal Battery Charging
Circuitry was required for carrying out a safe lithium polymer battery charging algorithm for
effective use of the battery cell. The LTC4071 (Refer to Appendix D figure 1 for Datasheet
extract) battery charger system was chosen due to its compatibility with the LTC3108 which
was already being implemented in this project.
In addition to implementing an efficient and reliable trickle charging solution, the LTC4071
boasts a high performance battery protection circuitry to prevent over-discharge damage to the
cell being monitored. This feature is known as low battery disconnect wherein if the battery
voltage falls below the programmed low battery disconnect level, the chip will cut off the
charging current to the cell thus protecting it.

29
2.3.1 `Operation of LTC4071
Figure 17: Block diagram of internal circuitry of LTC4071 [21]
As shown in Figure 17, an input supply charges the battery through the body diode of the
internal P-channel MOSFET, MP1, until the battery voltage rises above the low battery connect
threshold (VLBC_VCC). This threshold was programmed to be 3.6 V as the alternate choice,
4.19V, will never be reached by the input voltage from the LTC3108 which is 4.1V. This
threshold is programmed by connecting the LBSEL pin to the VCC pin. Once the battery is
reconnected to VCC the charge rate is determined by the following equation:
𝐶ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 =
𝐼𝑛𝑝𝑢𝑡 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 − 𝐵𝑎𝑡𝑡𝑒𝑟𝑦 𝑉𝑜𝑙𝑡𝑎𝑔𝑒
𝐼𝑛𝑝𝑢𝑡 𝑅𝑒𝑠𝑖𝑠𝑡𝑜𝑟 𝑉𝑎𝑙𝑢𝑒
It is stipulated that the suggested charge rates of lithium-ion batteries are 0.5 C to 1C [19]. In
the case of the 1000 mAh battery cell used in this project, this represents a charging rate of
500mA to 1000 mA. Due to the delicate nature of lithium polymer cells, the lower boundary
of charging was the selected maximum charging current. This charging level should occur
when the battery is at its lowest voltage level (2.7V). The resistor value to be used was
calculated as follows:
𝐼𝑛𝑝𝑢𝑡 𝑅𝑒𝑠𝑖𝑠𝑡𝑜𝑟 𝑉𝑎𝑙𝑢𝑒 =
4.1 𝑉 − 2.7𝑉
0.5𝐴
= 2.8𝜴
As the voltage on the battery approaches the programmed float voltage (4.1V), current is slowly
shunted away from the charging stream thus reducing the charging current. The float voltage
(1.4)
(1.5)

30
is programmed by the internal 3 state decoder connected to the ADJ pin. The HBO pin is driven
high when VCC rises within 40 mV of the programmed float voltage. It is driven low when
VC falls by more than 140 mV. The following table outlines the configurations of the ADJ
pins.
Table 3: Float Voltage Configurations
Pin connected to ADJ Float Voltage
GND 4.0 V
Floating 4.1 V
VCC 4.2 V
The 4.2V float voltage was unable to be chosen as the highest voltage input to the system at
any given time would be 4.1V thus disallowing the charging of the battery to voltages higher
than this. The low battery threshold at which the charger disconnects the battery from
discharging is programmed via configuration of the LBSEL pin. Connection of the LBSEL to
VCC will cause the battery to be disconnected when its voltage falls to 2.7V, whereas
connection to GND will incur disconnection at a battery voltage of 3.6V (Refer to Datasheet
D figure 2 for datasheet extract). The former was chosen as it allows for maximum run time
of the battery and thus optimum efficiency of harvested power as compared to the latter which
allows for extended shelf life of the battery but does not efficiently use all of the energy stored
in the cell.
Table 4: Pinout and Connections of LTC4071 implementation
Pin name/Number Connected Component Functionality
1- NTCBIAS Not
Connected(Floating)(Note 1)
Used in conjunction with
the NTC pin to monitor the
temperature of the battery
being charged
2 - NTC Connected to VCC Input to the Negative
Temperature Coefficient
thermistor monitoring
circuit. Reduces float
voltage if battery
temperature is too high

31
3 - ADJ Floating Float Voltage Adjust Pin.
Configured in various ways
to choose the float voltage
of the battery being
charged(Refer to Table 3)
4 - HBO Connected to LED for user
feedback
Driven high to indicate that
the battery is almost fully
charged.
5 - LBSEL VCC Programmable low battery
Disconnect Pin. Connect to
GND to disconnect battery
at a voltage of 3.2V.
Connect to VCC to
disconnect battery at a
voltage of 2.7V
7 - BAT Positive terminal of lithium
polymer battery
Charge current flows
through here to charge
lithium Polymer Battery
8 - VCC System load Input current Charges the
lithium polymer Cell as well
as controls the discharge of
the battery
Note 1: Deemed unnecessary for this application
2.3.1 Lithium Polymer Battery
A 1000mAh capacity lithium polymer cell is used as the power storage element in this project.
This means this cell is capable of providing 1 A of continuous current before it is completely
discharged. The lithium polymer battery is one of the most excellent choices of battery for
portable electronics applications due to its light-weight and energy dense characteristics. With
an approximate weight of 20 g and compact size, while still having the capability to output a
great deal of power.(Refer to the Appendix E for li-po datasheet),, the use of lithium polymer
cells was determined to be the most appropriate approach for the selection of an internal battery
for the circuit. Extra care was taken however in the handling of this component due to its

32
destructive nature if mistreated. As previously mentioned, the LTC4071 is capable of safely
charging a lithium polymer battery, preventing damage due over discharging and over
discharging. There were, however, more hazardous possibilities to consider and prevent.
2.3.1.1 Safety Concerns Regarding Lithium Polymer Charging/Discharging
 Battery cells must not be charged above their maximum voltage(4.2V)
 Battery cells must not be discharged below their minimum voltage(3.0V)
 Battery cells must not be charged by a current larger than 1C(1000 mA in the case of
the battery in this application)
 Battery cells must not discharge a current larger than 1-2C(1 - 2A in the case of the
battery in this application)
 Battery cells must be charged between 0 and 50 degrees [18]
Further to the use of the LTC4071's battery disconnect feature, the first four safety problems
are also handled by the protection circuitry of lithium polymer cells which is illustrated in
figure 18.
Figure 18: Identification of the Lithium Polymer protection[18]
This protection circuitry is effective at overcharge and under-voltage protection. There was
determined to be no need for protection against damage due to high temperatures during
charging as this occurs in the case of high current charging whereas the LTC4071 uses a trickle
method of charging which will not incur high temperatures from large currents.
2.3.1.2 Safety Concerns Regarding Lithium Polymer external influences
Along with being sensitive to extreme temperatures, li-po's are especially susceptible to
physical damage due to piercing or blunt force. The operational environment with which the
battery is going to be working is associated with a high degree of motion which could
inadvertently cause damage to the cell, rendering it a hazard to users. For this reason the Li-

33
po has a special casing which will be screwed and securely fastened to the base of the
systems enclosure.
These safety precautions were deduced to be of the utmost importance during the
implementation of this system as failure to abide by these guidelines could result in
malfunctioning of the device or damage to user via fire or explosion of the battery cell.[18]
2.3.2 Problems Associated with internal battery management
Battery voltage too low for charging electronics: As stipulated by the objectives and
technical requirements, the required charging output for connected electronics is 5V/500 mA.
Under normal conditions, however, a fully charged lithium polymer battery will provide 4.2 -
2.7V at 1- 2 A. For this reason, a method of magnifying the voltage of the battery cell at any
time between fully charged and fully discharged to 5V as well as regulating this voltage and
its corresponding current was required.
Solution : The Pololu S7V7F5 was found to be the most appropriate step-up voltage
regulator for this issue.
Figure 19: Pololu 5V Step-up/Step-Down Voltage Regulator S7V7F5 [22]
This component is capable of outputting 5V at 500 mA over a range of voltages. This will be
discussed in further detail in section 2.4.
2.4 Discharging
After kinetic energy has been harvested from the user, it is the discharging section of electronics
which ensures that the user is able to safely connect a USB cable to the system and charge their
connected device. This segment of the circuit consists of only two main components as well

34
as a resistor array. These are the Pololu 5V step-up Voltage Regulator S7V7F5 and a basic
female USB socket.
2.4.1 Pololu 5V step-up Voltage Regulator S7V7F5
This component, as seen in figure 19, was required for regulating the output of the internal
system battery to 5V. Using the boost technology of the TPS63060 (Refer to Appendix F for
datasheet extract), this circuit is capable of accepting input voltages from 2.7 V to 11.8V and
output a regulated 5V output. This switched-mode power supply efficiently delivers up to
around 1A when stepping down an input voltage and 500 mA when stepping up to 5V[22].
Observation of the characteristics of this component showed that it has beneficial features
applicable to this project in addition to its main function of stepping up and regulation. These
include thermal shutdown, short-circuit protection , low inactive current(> 0.1 mA) and its
light-weight and compact nature.(9 x 12 x 3 mm, 0.4g)[22].These characteristics allow for the
protection of connected devices as well as the internal battery without having a substantial
negative impact on the overall weight or size of the system. The input of this regulator is
connected to the VCC pin of the LTC4071 as stipulated by the respective datasheet. The
range of voltages expected of the lithium polymer cell at any given time is within range of
acceptable input voltages of the regulator, allowing a 5V regulated output at all times. In the
discharging aspect of the li-po, as it is 1Ah, it will be able to comfortably discharge 500 mA
when fully charged for 2 hours continuously. The average battery capacity of two modern
mobile phones, the Samsung Galaxy S6 and Iphone 6, are 2800 mAh[23] and 1810 mAh[24]
respectively. This means a discharge of 500 mA will fully charge these phones between 3.5
to 5.6 hours.
2.4.2 USB socket
It is a well-known fact that the USB is used as the interface of choice for power and data for
most hand held electronics. It stands to reason that the USB would be the most efficient and
appropriate choice of interface for this project. A USB socket based at the output of the
previously mentioned S7V7F5 Voltage regulator will allow for the discharge of the regulated
5V/500 mA output to connected devices. Research into the USB interface revealed there are
two types of USB structures to choose from. These are illustrated in Figure 20 as Type A and
Type B and their associated pin descriptions in Table 4.

35
Figure 19: USB Type A & USB Type B receptacle [25]
Table 4: Pin descriptions of USB receptacles [25]
Pin Number Name Description
1 VCC +5V DC
2 D- Data-
3 D+ Data +
4 GND Ground
As the USB B receptacle was found to usually be employed for the interfacing of large
computer peripherals such as scanners and printers [26] and the USB mini receptacle is usually
found on smaller electronics which are receiving power, a 4 pin USB type A receptacle was
procured for use in this project.
Originally, it was speculated that the data lines would be unneeded for this application as the
main concern of the project is the transfer of power. Test results proved that this was found to
be true to an extent for Samsung branded mobile phones but not for Apple based phones. The
results of this test and the resulting implementation and theory will be discussed in section 3.5.
This concludes the circuit design and component selection aspect of this project. A printed
circuit board (PCB) was required to be designed and manufactured in order for these
components work together as a whole system. Section 2.5 outlines the processes conducted
from design to fabrication of the PCB board.

36
2.5 PCB Implementation
2.5.1 PCB Design
The final circuit schematic of the project was created using the PADs logic computer aided
design (CAD) software package (Refer to Appendix G for Schematic). It should be noted that
male pin headers were placed at various points throughout the circuit to allow for easy testing
after fabrication and soldering. This software allows the mapping of connections between
components which will be interfaced with each other on the board. Each element in the
schematic has an associated footprint which represents the space used by that particular
component as well as the way it is to be soldered to the board. There were some components
used which were not in the default libraries and thus their associated decals or footprints had
to be created based on the recommended dimensions found in their respective datasheets.
Once this design was completed and verified for correctness, the design was transferred to the
PADS layout CAD software package where the elements of the circuit are correlated into their
respective decals for routing. Routing is the process of drawing copper tracks between
components in the same way as they are interconnected in their schematic. The board cut-out
was chosen to be a compact 10x10cm square as this would allow for its enclosure within a
small and light-weight casing. Based on the measuring of a wrist’s width, a 12 cm width
enclosure was found to be suitable for the housing of the PCB to be made without a compromise
of comfort for users wearing it. This housing will easily fit a 10cm by 10cm board. Following
the establishment of the virtual board dimensions and appropriate placements around the board,
the routing process was carried out on the two-layer PCB(Refer to Appendix Ha & Hb for Top
and bottom layout).Routing and component placement were bounded by the following design
rules :
 Surface mounted devices are to be placed on the top layer of the PCB
 Tracks drawn from the pins of surface mounted components must be drawn directly
from the pin horizontally outwards
 Surface mounted tracks are 0.015 inches in thickness
 Through-hole component's tracks are 0.030 inches in thickness
 Ground Tracks are 0.060 inches in thickness
 Tracks connected to pin headers are drawn on the bottom layer
 All tracks must have a minimum of 0.007 inches in clearance distance between them

37
Thin tracks were required for efficient routing of the small pins of surface mounted devices to
provide short circuiting and clearance errors. Thicker tracks were chosen to limit the effect of
internal resistance of the copper as outlined in equation 1.3. Tracks were drawn on the
underside of the board for reference points as the plastic coating of pin headers prevent them
from being reached by soldering irons on the top half of the board.
2.5.2 PCB Manufacturing
Subsequent to clearance and connectivity error checking, verification and correction, the top
and bottom black and white negative layout of the board was printed and stapled together,
ensuring that the layers are properly aligned. A blank 12 cm x 12cm PCB was aligned
between the negatives and taped down to ensure it would not shift during the printing
process. It was then placed within an ultraviolet light box for 130 seconds on each side and
scrubbed with photo developer, as shown in figure 20.
Figure 20: Showing the use of the photo-box and the resulting printed pattern
This board is then etched with copper resulting in the final board, shown in figure 21, which
can be drilled and soldered.

38
Figure 21: Final etched and fabricated PCB
Subsequent to the drilling of via holes and component pin holes, the various sections of the
circuit are to be soldered to the board gradually and tested individually. Any faults discovered
are to be documented and, if necessary, the layout of the PCB circuit is redesigned and
fabricated to correct this. This method of incremental assembly prevents the propagation of
errors throughout the circuit, thus avoiding unforeseen errors becoming much more costly to
amend as the project circuit is developed. The results of fault finding, component testing and
circuit analysis will be logged and discussed in further detail in section 3.
2.6 Enclosure
The previous sections explained the intended design and implementation of the functional
aspect of the kinetic energy harvesting project. These address the first two main objectives of
the project but neglect the final aspect regarding the ability of the project to be worn. There
were two materials considered to be appropriate for the enclosure of the project PCB. These
are metal and hard plastic. Each of these have their own respective benefits and disadvantages
meriting or discrediting their suitability for use in this project. Table 4 outlines these pros and
cons which were analysed and compared against in the selection of the most suitable material.

39
Table 4 : Comparison of characteristics of metal and hard plastic enclosures
Material Enclosure
considered*
Price Pros Cons
Metal Hammond
Diecast
Enclosure
1590CE
Natural (120
x 100 x
64mm)[27]
£7.40  Sturdy
 Very weather
resistant
 Limits damage to
internal and
external circuits
from
electromagnetic
interferences(EMI)
 Can act as a heat
sink
 Expensive
 Heavier
Hard
Plastic(ABS**)
Hammond
1591USGY
Multipurpose
GPABS
Enclosure
120 x 120 x
59 Grey
£4.27  Relatively Sturdy
 Light-weight
 Less expensive
 Can be made
resistant to EMI
with conductive
paint
 Relatively
weather-proof
 Effectively
insulates users
from circuit
 No
protection
or control
of EMI
 Not as
strong as
metal
*Enclosures were chosen to be the minimum available volume capable of housing the 10 cm
by 10 cm to keep the project a slight and compact as possible
**ABS stands for Acrylonitrile butadiene styrene, a special plastic polymer utilized for its
toughness and ease of machining.[29]

40
Analysis of these advantages and disadvantages
revealed the ABS hard plastic casing to be the more
suitable housing for this project. The lighter and
economical characteristics of the ABS enclosure
compensate for the fact that it is not as sturdy as metal.
Additionally, the casing can be made resistant to EMI
by painting the insides and outside with conductive
paint, thus effectively disproving this reason as a
disadvantage. Consequently, the ABS enclosure,
shown in Figure 22, was chosen as the casing to be
used for this project. The PCB is to be fastened to the
base of the enclosure by four 3 cm PCB spacers each situated in the four corners of the board.
This will make room for the casing housing the li-po to be placed and fastened by screws
underneath the board. The final expected enclosure layout is illustrated in Figure 23.
Figure 23: Projected Layout of Kinetic Energy Harvester Enclosure and internal Circuitry
2.7 Rigging
The final design consideration of this project is the method by which the entire system is to be
worn to achieve the latter half of the final project objective. In choosing this approach, user
comfort and stability of the system during motion was paramount. The use of hook and lead
Velcro straps is the intended approach to this matter as they are one of the most commonly
used forms of easy securing for both technical and non-technical applications. Two to three
holes are to be made along the base of the enclosure on either side. Through each hole, a single
Figure 22 : 120 x 120 x 59 mm ABS
Enclosure [28]

41
200 mm x 20 mm double sided hook and loop Velcro strap will be passed through from one
side to the hole directly opposite to it. Two flat-head screws will be fastened into the base of
the enclosure, piercing the Velcro straps and fastened with nuts. These are put in place to
reinforce the holding strength of the straps as well as ensure that they remain stationary during
movement. Flat-head screws are used as, once they are screwed into the enclosure through its
base, they will sit flush against the casing, and thus will not be felt by users wearing them.
3. Test Results & Discussion
This section will outline the testing carried out along the course of the project as well as the
theory associated with the relevant components, the results, analysis of the results and finally,
how these results affected the development of the project.
As noted in the Figure 7, this project functions in a similar way to the waterfall method, where
the accurate functionality of each circuit segment is heavily dependent on the proper operation
of the segment preceding it. For this reason, testing was carried out gradually, progressing and
testing each section as it correlates to the blocks in the Figure 7 block diagram, ensuring
functionality and accuracy. In order to further clarify the breakdown of the budget as well,
there will be a running breakdown of the monies spent at each stage of testing and why this
spending occurred. In order for the surety of system functionality, tests were carried out in the
following order:
1. Testing of inductor coil
2. Testing of rectifier circuit
3. Testing of Amplification segment(LTC3108 step-up voltage regulator & LPR635
transformer)
4. Testing of Charge Storage circuit(LTC4071 battery charger &Lithium polymer cell)
5. Testing of discharge circuit(S7V7F5 +5V voltage regulator & USB receptacle)
3.1 Induction Coil Testing
Table 6: Table showing the components procured and money spent in the first stage of testing
Components Procured Cost(£)
Enamel Copper Wire 17SWG 12.96

42
3m Rigid White Conduit(20 mm internal
diameter)
1.59
Neodymium Magnets 10 x 3 mm 7.83
Total Money Spent 22.83
The aim of this test is to confirm the induction of current from the movement of a magnet
within a coil of wire.
Expected Results: Passing a magnet through a coil causes the induction of an alternating
voltage
For this trial, the 3 metre conduit was cut to much shorter and manageable segments 15 cm in
length. A single conduit was segment was chosen and a 12 cm length was marked out on it
using electrical tape. Subsequent to this, the 17SWG copper wire was wound around the
conduit a large number of times. The free end and a section of the unwound wire was sanded
to remove the enamel insulator and an oscilloscope was placed across these ends. The
neodymium bar magnet was then allowed to fall under gravity through the conduit. This
arrangement and its output is shown in Figure 24.
a) 40SWG Induction Coil b) Test Results of 17 SWG induction coil
Figure 24 : Testing of the 40SWG Induction coil
It can be seen that the employment of Faraday's law was successful and a 73 mV peak-to-peak
AC was achieved from the coil. The amplitude of the root mean square (RMS) voltage was,

43
however, too minute for use in the bridge rectifier circuit. RMS is the equivalent DC magnitude
of an AC voltage. It can be recalled that a minimum of 0.4 V input is required for proper
rectification due to the voltage drops of the two diodes in either rectification path.
It was decided that a slightly smaller gauge of wire would be used for the coil. This would
allow for a greater number of turns in the given area without a compromise of weight. It was
observed that the internal diameter of the conduit was very large relative to the diameter of the
magnets, thus leaving a degree of empty space. Information gathered from the literature review
showed that magnetic field strength decreases exponentially with increasing radial distance.
For this reason, a pipe with a smaller internal diameter was used allowing for the coils to be in
closer proximity to the stronger magnetic strengths in the magnets near field. It was noted that
the use of thinner wire and thinner pipe would have both negative and positive effects on the
output of the induction coil.
Positive impacts of thinner 22 SWG wire:
 Larger number of turns can be made within a given volume, resulting in an increase
in induced voltage magnitude, without a negative impact on the overall mass of the
system
Negative impacts of thinner 22 SWG wire:
 Larger number of turns will result in longer lengths of wire being used, which will
increase the internal resistance of the wire
 A smaller insulating pipe denotes a smaller cross sectional area of the coil for the
magnet to pass through
 Thinner wire will have a smaller cross-sectional area, thus increasing the wire's
internal resistance
The main disadvantage of the new wire and pipe implementation is the negative effect on
output current due to the increase of the internal resistance of the wire. The newly wound coil
was created using a mechanical lathe instead of hand-winding in order to save time. An
estimated 1315 turns were made in this way. It was then connected to a multimeter and its
resistance was measured so as to see how much of an impact the new gauge of wire would
have on the current output.

44
From the measurement carried out, as seen in Figure 25,
the minute 2.55 ohms(Ω) resistance of the wire was not
considered to have an exceptionally negative effect on
current output. This was further confirmed with the
connection of the coil to an ammeter and an oscilloscope
and the testing conditions of Figure 24 carried out
repeatedly in a given time frame. The ammeter gave
readings which oscillated between ±100 mA and the
waveform shown in Figure 26 was observed.
Figure 26 : Voltage Waveform of neodymium magnet falling through coil under gravity repeatedly
It was observed that a much larger voltage output was induced using the 22 SWG wire.
Subsequent to this, it was necessary to determine how efficient the conversion process of the
induction coil was. This could be found through the calculation of the ratio of input kinetic
energy of the magnet and output electrical energy. The formula for power dissipated across a
load in an AC circuit is given by,
Figure 25 : Measuring of internal
resistance of coil

45
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑃𝑜𝑤𝑒𝑟 = ∫
𝑉2
(𝑡)
𝑅
𝑑𝑡
𝑇
0
Where T is the length of time over which a pulse has acted, V(t) is the representative expression of the
voltage signal(in this case, it would be the equation of a straight line) and R is the resistance through
which the power is being dissipated across. In order to determine the power output of the induction
coil for a given passing of the magnet, the coil was arranged in parallel with a 10kΩ resistor which
acted as a load. An oscilloscope was used to monitor the voltage across the resistor. For accurate
calculations, the sampled values of the waveform recorded was imported to MATLAB for computing
(Refer to Appendix I for MATLAB script). The resulting waveform for one passing of the magnet
through the coil.
3.1.1 Discussion of Induction Coil test Results
The average power within a 0.238 second period was found to be 0.0543 W. The formula for power
output is described as ,
𝑃𝑜𝑤𝑒𝑟 =
𝐸𝑛𝑒𝑟𝑔𝑦
𝑡𝑖𝑚𝑒
𝑊
Therefore, given the calculations, the energy within the extracted time period is estimated at
0.0543 × 0.238 = 0.013 (to 3 significant figures) Joules(J).
The conversion efficiency of the coils can be found by calculating the output electrical energy as a
fraction of the input kinetic energy. As gravity is the force of movement for this experiment, the law
Figure 27 : MATLAB rendering of induced voltage waveform of one passing of the
magnet through the coil
1.7
(1.6)

46
of conservation of energy was used for the calculation of the kinetic energy. This law states that the
output energy of any system will be equivalent in magnitdue to its input. The placement of the
magnets at the top of the coil gave it a degree of potential energy. Any kinetic energy gained from
the droping of this magnet will be equivalent or less than this value of potential energy. This can be
summarised using the following equation :
𝑚𝑔ℎ =
1
2
× 𝑚 × 𝑣2
Where the left expression is gravitational potential energy , m is the mass in kg, H is the height of the
body in metres, and g is the gravitational field strength of Earth(9.8 Newtons/kilogram). For this
calculation,energy losses due to air friciton was considered negligible and it was assumed that the
velocity of the magnet was constant as it was passing through the magnet.
Using a scale, the mass of the magnets were found to be 0.0177 kg. The height is represented by the
length of the coil (10 cm = 0.1 m). The energy contained in the magnets was then calculated to be
(0.0177 x 9.8 x 0.1) = 0.017346 J.
Given the electrical energy and having calculated the kinetic energy input into the coil, the coil can
then be computed to be
𝑜𝑢𝑡𝑝𝑢𝑡 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦
𝑖𝑛𝑝𝑢𝑡 𝑘𝑖𝑛𝑒𝑡𝑖𝑐 𝑒𝑛𝑒𝑟𝑔𝑦
× 100% =
0.013
0.017346
× 100% = 74.5 % efficient. This
calculation proved excellent efficiency of the inductor coil as a kinetic energy transducer. No Further
testing was carried out on this aspect of the project and the induction coil was deemed successfully
funcitoning as expected.
3.2 Bridge Rectifier Testing
The aim of this test is to confirm the functioning of the bridge rectifier. For this experiment,
the induction coil was connected across a bread-boarded bridge rectifier as shown in Figure
27a. Figure 27b shows this test as a circuit diagram for ease of interpreting.
Expected Results: An input AC voltage to the bridge rectifier will have a DC voltage output.
The output of the rectifier was placed across a 10kΩ load for testing purposes. The magnet was
then allowed to repeatedly fall back and forth through the coil under the influence of gravity
and the resulting waveform was recorded. The input AC voltage was monitored on the
oscilloscope as well. The waveform illustrated in Figure 28 was observed during this
experiment.
1.8

47
a) Testing of Bridge Rectifier b) Circuit diagram illustrating Bridge Rectifier Test
Figure 27: Implementation of Bridge Rectifier Test
Figure 28: Ch1 – waveform output of inductor coil, Ch2 – waveform output of bridge
rectifier diode
As seen in Figure 28, the input AC voltage was successfully rectified to DC with negligible
losses of voltage magnitude due to voltage drop across the rectifier. It was postulated that the
rest of the system’s functionality would be optimized if smoother DC was utilized as the
input instead of waveforms with large ripples such as in Figure 28. In order to decrease the
ripple of the rectifier output, a polarized 220 µF capacitor was put in place parallel to the

48
10kΩ load. The experiment was then repeated under the same conditions, resulting in the
waveform shown in Figure 29.
Figure 29: Waveform showing smoothed rectified AC voltage
It was observed that as the magnet oscillated within the coil, the charge voltage on the capacitor
built up slowly. Increasing the speed of the magnet caused the charging speed to rise as well.
Once oscillation ceased, the capacitor’s voltage slowly dropped as it discharged.
3.2.1 Discussion of Bridge Rectifier Results
The test results proved the successful functionality of the bridge rectifier for use in this
project as an AC to DC converter. The input AC voltage was converted to smooth DC
without heavy voltage losses which would decrease its efficiency.
3.3 Testing of Amplification Circuitry
Table 7: Table showing the components procured and money spent in the third stage of
testing
Previous Total Expenditure 22.83
LTC3108 Ultra low Step-Up Voltage
Regulator
5.45
LPR6235 1 : 100 turns ratio compact
transformer
4.35

49
Expected Result: Movement of Magnet within Coil/Input of DC voltage shall result in a
regulated 4.1V output from the LTC3108
The aim of this test was to confirm the functioning of the amplification circuit which consists
of the LTC3108 and the LPR6235 compact transformer. As these were surface mounted
components, they were soldered to the fabricated PCB board for testing. In order to isolate the
testing to the amplification circuitry, leads were soldered to the respective ground pins of the
components being tested so as to allow for the simulation of a ground line without having to
solder the entire circuit. Each of the four ground pins of the LTC3108 as well as the ground pin
of the LPR6235 transformer were grounded and a 200 mV DC signal from a power supply was
introduced into the input pin of the transformer. In addition, a 1000 µF polarised capacitor was
placed at the output as stipulated by the LTC3108 datasheet. The output of the LTC3108 was
monitored by a voltmeter. The test board and its accompanying output is shown in Figure 30.
a) Amplification Testing circuit b) Amplification Circuit Output
Figure 30 : Testing of Amplification Circuitry
It was observed that the output of the LTC3108 quickly grew from 0 to 4.1V. At the 4.1 V
mark, the output would oscillate between 4.0V and 4.1V. This was considered to be effective
functionality of the regulator. The results gained from this test were satisfactory in proving
the correct functioning of the LTC3108, however, it was necessary for real life test
applications to be conducted in order to ensure the circuit can be used to meet the technical
requirements of the project. The use of the power supply in this was deduced to be dissimilar

50
to the application intended for this project as, the power supply voltage is constantly being
input to the system whereas kinetic energy input to the system is expected to be intermittent.
In order to conduct a practical test, the inductor coil was connected to the arrangement as
shown in Figure 27 was setup, replacing the 10kΩ load resistor with the input of the
LPR6235. In this way the rectified harvested energy becomes the input of the amplification
circuitry. It was noted that the LTC3108 is powered by charging a 1 µF capacitor connected
to the VAUX pin. The charge on the VOUT pin slowly and incrementally charges up while
the chip is being powered. To monitor and observe this effect, an oscilloscope was placed in
parallel to the 1 µF VAUX capacitor to record the magnitude of charge built up as the magnet
is allowed to pass back and forth between the inductor coil. In addition, the secondary
channel of the oscilloscope was used to monitor the output of the IC. Figure 31 shows the
resulting waveforms of this test.
Figure 31 : Ch1 – Regulated 4.1V output of LTC3108, Ch2 - Waveform showing the
charging and discharging of VAUX capacitor
3.3.1 Discussion of Amplification Circuit Results:
Based on the results of the practical testing, as shown in Figure 31, it can be deduced that the
oscillation of the magnet within the coil causes the capacitor to oscillate between being fully
charged (2.5V) to flat quickly. During this oscillation, the LTC3108 powers up and the VOUT
pin’s voltage increases slightly. A faster rate of voltage induction causes the VOUT pin to reach

51
its point of regulation (4.1V) quicker. No further testing was conducted with the amplification
circuitry and it was considered to be operating correctly.
3.4 Testing of Battery Storage Circuitry
Table 7: Table showing the components procured and money spent in the fourth stage of
testing
LTC4071 Battery Charger 3.95
Lithium Polymer Cell (3.7V, 1 Ah) 4.68
The aim of this test was to confirm the functioning of the charging segment of the circuit to
charge the on-board lithium polymer cell. This trial was carried out utilizing both constant input
voltage from a power supply as well as the intermittent power supply from the inductor coil,
which becomes regulated DC through the use of the previously tested amplification circuit. For
this trial, the LTC4071 was soldered to the circuit board and a wire lead soldered to its ground
pin so as to directly ground the chip and isolate testing from other aspects of the board. In
addition, leads were soldered to the HBO and BAT pins of the LTC4071. This allowed the
board to be interfaced with components on a breadboard before final soldering took place. A
4.1 V DC power supply was connected to the VCC pin of the battery charger to simulate input
voltage. The HBO pin was connected to a green LED which would be used to indicate the
battery cell being at full capacity. The BAT pin leads were connected across a lithium polymer
cell which was connected to the breadboard. The voltage magnitude on the lithium polymer
was monitored by a voltmeter and the charge current was monitored by an ammeter. Figure
32a illustrates this experiment arrangement and Figure 32b shows the test results of the
monitoring of the current.
Expected Results: The charger IC shall control the influx of charge current to the battery as it
approaches the programmed float voltage of 4.1V. Once the battery is fully charged, the HBO
pin will be set high, causing the green LED to glow.

52
a) Charging circuit testing arrangement b)Ammeter Results of charging circuit test
Figure 32: Illustration of the Charging circuit test arrangement
It was observed that the battery began at a
voltage of 3.6 V and grew to 4.1V at which point
it was noted that the power supply short circuit
indication LED was lit. The ammeter showed a
steadily decreasing charging current reading of
23.46 mA and, as can be seen by Figure 33, the
green LED was lit. These events indicated that
the input current was being shunted to ground as
the battery reached the programmed float voltage. This test was subsequently repeated with the
regulated energy harvested DC of the inductor coil as the input to the charger. Similar results
were observed once the output of the LTC3108 reached regulation. It was noted that the
charging current of the battery slowly decreased once the kinetic energy input was removed.
In addition, as stipulated by the LTC4071 datasheet, no charging current was present when the
input DC voltage dropped below 3.6V. The temperature of the battery cell was monitored
during the conducting of both of these trials as a sudden large increase in temperature would
indicate the malfunctioning of either the circuit or the battery.
3.4.1 Discussion of Charging Circuit Test Results
Test results proved that the LTC4071 was capable of safely and efficiently charging the li-po
cell without causing damage to the cell’s internal circuitry due to over-charging. No further
Figure 33 : HBO pin indication LED signalling
the battery was close to full capacity

53
testing was carried out and the charging segment of the circuit was deemed to be correctly
operational.
3.5 Testing of Discharge Circuitry
Table 8: Table showing the components procured and money spent in the fifth stage of testing
Pololu +5V Step-up Voltage Regulator
S7V7F5
3.21
USB Type A Receptacle 0.34
The aim of this test was to confirm the functioning of the discharging segment of the circuit.
This testing encompassed verification of the proper functionality of the 5V step-up regulator
as well as the USB as a power interface for mobile phones. The voltage regulator was to be
tested for the full range of possible input voltages it would be exposed to. These are the low
voltage and full capacity voltages of the li-po cell(2.7 V and 4.1 V respectively). The voltage
regulator was connected to a breadboard via male pin headers. The positive lead of the battery
cell was connected to the VIN pin and the ground pins were grounded. A jumper wire, which
acted as a probe, was connected to the VOUT pin of the regulator and subsequently connected
to a voltmeter. The voltage reading on the VOUT pin was monitored for the 4.1V li-po as an
input as well as a 2.8 V input from a DC power supply, in order to simulate the behaviour of
the S7V7F5 in low battery situations.
Expected Results: Output of Voltage Regulator shall be between 5 V and 5.2 V as stipulated
by its accompanying documentation.
As shown in Figure 34, it was observed that the
step-up voltage regulator performed as expected
outputting a +5V voltage with a 0.2 volt discrepancy
over the entire range of practical inputs.
The next discharging circuit test to verify the
adherence to the project technical requirements was
the confirmation of the maximum output current
being 500 mA. This test was conducted through the placement of an ammeter in series with
the output voltage pin of the regulator which was connected across a 10 Ω resistor. The
Figure 34 : Outputs of 2.7V and 4.1V
input to Step up voltage regulator

54
resistive load was chosen using ohm’s law(Equation 1.0) as the current output is dependent
on the resistance. In order to find the resistance required for a 500mA current, with a given
voltage of 5 V, the voltage was divided by the desired 500 mA current. This resulted in a
chosen load of
5 𝑉
0.5 𝐴
= 10Ω.
Expected Results: The measured current will be≤ 500 𝑚𝐴.
The resulting measured current output of 479 mA in
Figure 35 verifies the expected functionality of the step-
up voltage regulator and its adherence to the objectives
of this project.
The final aspect of the discharge circuit testing is the
confirmation of the circuit to charge a mobile device
using the energy stored in the on-board battery cell. For
this trial, the battery cell was connected to the BAT pin
of the LTC4071 via soldered wire leads. This arrangement was made so as to also test the
functionality of the LTC4071 as a controller of the battery’s discharge rate. As stipulated by
the LTC4071’s datasheet, the load (in this case the discharge circuit) was to be connected to
the VCC pin of the chip to achieve discharge control. A Samsung Galaxy mobile phone was
connected to the board via USB cable to be charged.
Expected Results: The phone will indicate that it is charging.
It was observed that the mobile phone did not register an output voltage or current to be charged
by. Connection of a voltmeter along the VCC path of the USB revealed that the voltage of the
battery was not present at any point past the step-up regulator. It was concluded that the battery
disconnect function of the LTC4071 was incompatible with the step-up function of the
S7V7F5. This was confirmed through the connection of the positive lead of the battery cell
directly to the VIN pin of the step-up regulator via jumper wire resulting in the phone
recognizing the presence of a charging current, as shown in Figure 36.
Figure 35 : Measured output of
step-up voltage regulator through a
10 Ω load.

55
a)Direct connection of battery cell via wire b)Screenshot of battery being charged
Figure 36: Testing and Results of USB charging test
Further testing is to be carried out to determine the behaviour of the lithium battery cell over
extended periods of time to assure the safety and correct operation of the system at low
voltages. It is expected that the built in protection circuitry of the lithium polymer cell can be
used to protect the cell in place of the LTC4071, which would only be used to control the
charging current of the circuit.
3.5.1 Discussion of Discharging circuit results:
Based on the results of the experiments, the USB receptacle as well as the step-up voltage
regulator were found to be fully capable of charging a mobile phone using harvested and stored
kinetic energy. Unfortunately, more testing will be required to determine the optimum layout
of the discharge circuit to accommodate the interface between the LTC4071
charging/discharging as well as discharging through the use of the step-up voltage regulator.
It was discovered that the circuit was incompatible with Apple based products such as IPhones.
Researching into this issue, it was discovered that a special resistive circuit is implemented on
the data pins of the USB as a form of “handshake” between charger and device [30]. This
handshake is an electrical means of a device detecting what type of charging current can be
allowed from the given charging port. Referencing the schematic of the circuit reveals the use
of this resistive circuit so as to make the device more universal in nature. The 500 mA
implementation, as shown in Figure 37, was used as it coincided with the expected current
output of the system.

56
Further testing is to be carried out in discharging
circuit to determine the effectiveness of the
implementation of this circuit.
This concludes the documentation of the results
gathered and the theories drawn based on these results
for these projects. Due to time constraints, these tests
could not be conducted and documented before the
creation of this report but will be carried out in the
weeks to come. The final aspect of the project to be
tested is its ability to be worn and function from
practical inputs from a user wearing the system on
their arm.
120mm x 120 mm x 60 mm ABS enclosure 4.27
200 mm Velcro Strap 0.34
Additional Spending due to component
replacement
9.80
For this reason, the following components were purchased and will be used to house the
circuit at a later date.
In addition, the following tests carried out for documentation and determination of the
project’s overall project:
 Overall functioning of all components working together as a system
 Determination of the energy required to fully charge the on-board battery from being
flat
 Overall efficiency of the system based on total energy input required to charge the
lithium polymer cell to full capacity from being 0% capacity
Figure 37 : 500 mA output resistive
circuit for USB charging[30]

57
4. Conclusions
4.1 Summary of findings
1. At this point a working kinetic energy harvester has been manufactured. It is capable
of storing harvested energy and charging mobile devices through a USB interface.
Test results reveal that thus far the project circuit board has efficiently met all
prescribed aims, objectives and technical requirements with the exception of those
regarding the enclosure and ability of the system to be worn. Various time consuming
setbacks regarding the wrapping of the coils and of the IC were responsible for the
project not being fully completed at this point. Overall, the budget spent for this
project amounted to £59.22, leaving a further £35.78 for use in future work. In
addition, to being cost-effective, test-results show that power efficiency was measured
and calculated to be a 74.5%, thus rendering the circuit’s conversion capabilities as
very efficient in nature. Overall, after observation of the circuit’s operation, this has
been considered a success. Final and further testing of the end product will be
conducted in the following weeks.
4.2 Work to be completed
Figure 38 shows the circuit which has
been implemented thus far. Upon the
requisition of the enclosure and relevant
straps, this circuit will be secured within
the housing and the straps will be fastened
to the base of the box in a layout similar to
that of Figure 23. Subsequent to this
assembly, the entire system will be
weighed and tested once more to verify
abidance with its functional specification
and technical requirements.
Figure 38 : Implementation of Kinetic Energy
Harvester Circuit

58
4.3 Developmental Considerations
During the course of the design and implementation of this system, various possible upgrades
were considered but never implemented due to the required time and budget lying outside the
boundary of this project. These design ideas are mostly concerned with the bettering of the
energy harvesting efficiency and capabilities of the system. Possible efficiency upgrades to the
device include:
 The increase of the number of coils used, thus increasing the generated electrical
energy for the same amount of kinetic energy
 The use of a stronger grade of neodymium magnet, thus constituting a larger magnetic
field strength and area of effect
 The use of another induction coil and magnet. It should be noted that the selection of
these components must be carried out with due care to avoid making the overall
device exceptionally heavy
 The inclusion of other energy harvesting components such as wind-turbines,
photovoltaic cells and thermoelectric generators for various forms of energy
generation
In addition to the improvement of the energy generation efficiency of the system, there are
various extra circuitry which could be added to better the desirability of the device as product
for consumers. These include the implementation of voltage monitoring components such as
the LM3914 IC which would be capable of displaying the voltage magnitude of the li-po cell
at any given time in the form of lit LED’s. This would be an effective way of a user feedback
implementation as the device by itself gives no information back to the user in its “black-
box” form. Furthermore, adding the ability to transfer harvested energy data over Bluetooth
to be displayed in a user-friendly format would develop the device as a desirable and
commercial product.
The techniques used in the implementation of this project and its possible upgrades are but a
few of the practicable methods which could be used to employ and achieve the pre-defined
goals of this project. It is believed that there is no real end to the possibilities and new heights
of renewable energy and energy harvesting which could be reached utilizing the information
gathered in this project as well as the already available results of other schemes within the
discipline.

59
5. References
[1] "Energy Harvesting", IOP Institute of Physics, IOP Publishing, (Accessed online on
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