hand gesture & proximity sensing using wireless power

Hand gesture & proximity sensing using wireless power transfer coil:

Analysis and application

By

Supreet kaur Juneja, B.E

A Thesis

In

Electrical Engineering

Submitted to the Graduate Faculty

of Texas Tech University in

Partial Fulfillment of

the Requirements for

the Degree of

MASTER OF SCIENCES

Approved

Dr. Changzhi Li

Chair of Committee

Dr. Brian Nutter

Mark Sheridan

Dean of the Graduate School

May 21, 2016

Texas Tech University, Supreet kaur Juneja, May 2016

ii

ACKNOWLEDGEMENTS

I would like to thank Dr. Changzhi Li, advisor and chairperson of this thesis, for his

constant support and guidance for the project. The project would not have been possible

without his technical supervision. He not only helped me technically but has always

motivated me with my work and patiently helped me with my problems.

I would like to thank Dr. Nutter for being on my thesis committee and helping me

complete my Master’s thesis. My sincere thanks to Dr. Zhiming Xiao for his co-

operation and insightful comments.

I would specially like to thank Department of Electrical Engineering for giving me the

opportunity to pursue my Master’s in Texas Tech University. I would like to thank

Jackie Charlebois for helping me with clerical work and for her constant motivation and

support.

I would like to acknowledge Lab-mates - Chenhui Liu and Yao Tang for their help and

guidance. I would also like to thank my family and friends for bearing me during this

time and supporting me throughout.

Finally, thanks to all those who knowingly or unknowingly helped me during this time.


iii

TABLE OF CONTENTS

ACKNOWLEDGEMENTS .......................................................... ii

ABSTRACT .................................................................................. iv

LIST OF TABLES......................................................................... v

LIST OF FIGURES...................................................................... vi

I. INTRODUCTION ......................................................................... 1 Background ...................................................................................................... 1

Wireless Power Transmission ......................................................................... 2

Gesture detection application using WPT coil ................................................ 4

II. PHYSICAL MODEL .................................................................... 7 Analysis of the board ........................................................................................ 7

Working on increasing sensitivity ................................................................... 11

Inductive sensing ....................................................................................... 12

Frequency of oscillations .......................................................................... 16

LDC Evaluation board ................................................................................... 19

LDC1000 IC ................................................................................................... 22

Adafruit Bluefruit EZ-KEY ........................................................................... 25

Application of the Evaluation module ........................................................... 27

LabVIEW Code Flowchart ............................................................................ 32

III. CONCLUSION ........................................................................... 34

IV. BIBLIOGRAPHY ...................................................................... 35

V. APENDIX A ................................................................................ 39 Clapp Oscillator design calculation ................................................................ 39

VI. APENDIX B ................................................................................ 41

VII. APENDIX C .............................................................................. 42


iv

ABSTRACT

After Nikola Tesla’s initial research in the field of Wireless Power transmission not

many improvements or developments were done in this field, until now when there is

increased popularity of Wireless technology. In a step ahead in the application of

wireless power transmission- Near field communication, research was done on Non-

contact human interaction using this technology. With moving hand or finger position

and gesture, the change in coil inductance was observed and using this this change

desired output operations were performed.

Initially research was conducted to improve upon the sensitivity of a differential

structure based on oscillators and mixers and to reduce the circuitry used to achieve the

desired result of using the wireless power transmission coil to not just transfer power

but act as a sensor. Later on, application was developed and bringing this to reality and

demonstrating how the WPT coils sense the presence of hand or finger and interact with

humans.

Although the sensitivity of the coil is not much, but it was successfully tested as a sensor

and was able to detect the presence of hand and display different pictures depending on

where the hand is placed. Also, by looking at the less reliable apple iPhone home buttons

and constant presence of home button icon on the screen of the phone, application was

developed to replace this with the coil sensor and perform the task same as the home

button getting rid of the icon on the screen.


v

LIST OF TABLES

2.1 Simulation result at different frequency ..................................................... 17

2.2 Register Map ................................................................................................. 21

2.3 Pin configuration .......................................................................................... 22

2.4 Pin Description .............................................................................................. 26

A.1Pin Description .............................................................................................. 41


vi

LIST OF FIGURES

1.1 Resistive analog touch screen ......................................................................... 1

1.2 Wireless power transmission concept ........................................................... 2

1.3 Block diagram of wireless power transfer .................................................... 3

1.4 Wireless charging of home appliances .......................................................... 4

1.5 Board design .................................................................................................... 5

1.6 Different coil size ............................................................................................. 6

2.1 Block diagram ................................................................................................. 7

2.2 Clapp oscillator circuit ................................................................................... 8

2.3 Mixer & low pass filter stage ......................................................................... 9

2.4 Frequency to voltage conversion ................................................................. 10

2.5 Waveform at different stages of frequency to voltage conversion

circuit ...................................................................................................... 11

2.6. Different shapes of inductive coils .............................................................. 12

2.7 Fill ratio vs inductance.................................................................................. 13

2.8 Fill ratio vs inductance.................................................................................. 14

2.9 Output diameter vs inductance .................................................................... 15

2.10 Design of clapp oscillator ............................................................................ 16

2.11 LDC1000EVM ............................................................................................. 19

2.13 Mutual inductance between human finger and coil ................................. 20

2.14 LDC1000 IC package .................................................................................. 22

2.15 SPI communication ..................................................................................... 23

2.16 Serial interface protocol ............................................................................. 24

2.17 Bluefruit EZ-KEY ...................................................................................... 25

2.18 Pin configuration ......................................................................................... 25

2.19 iPhone dummy body ................................................................................... 27

2.20 LabVIEW GUI ............................................................................................ 28

2.21 Assistive touch selection .............................................................................. 28

2.22 User input selection ..................................................................................... 29

2.23 GUI screen when finger not placed in front of the coil ............................ 30

2.24 GUI screen when finger not placed in front of the coil ............................ 31


vii

A.1 Common Base Clapp Oscillator .................................................................. 39

A.2 Read L subVI ................................................................................................ 42

A.3 Read Buffer subVI ....................................................................................... 42

A.4 L Process subVI ............................................................................................ 43

A.5 Main part of VI of reading and displaying the image according

to placement of finger ............................................................................ 43


1

CHAPTER I

INTRODUCTION

1.1. Background

There have been a great breakthrough in past couple of years in human – machine

interaction. Machines like personal computers, smartphones, automobile, etc are all

capable of doing what seemed to be nearly impossible 20 years back. The machines

today are proficient of processing and sensing human gestures and position, human

voice tonal modulation, and many such application which makes these machines super-

intelligent.

In twentieth century, inventors and researchers where trying to find a better way in

which human can interact with machines. During this time, while teaching at the

University of Kentucky, Dr. Samuel C Hurst came out with the invention of electronic

resistive screen interface and seven years after working on the interface and trying to

make it transparent and user friendly, Dr. Hurst came out with the amazing technology

which today we see almost everywhere- Touch screens. Today, the touch screens are

not only resistive but also capacitive.

Fig1.1 Resistive analog touch screen [10]

The drawbacks of the above mentioned touchscreens are, when resistive touch screen

are concerned they are not durable as they are made of flexible material which can be

easily damaged. Whereas capacitive touch screen though durable does not respond to

objects other than human fingers and are also costly. In one such effort of making the


2

interaction better, affordable and simple, this paper talks about use of wireless power

transmission in sensing and responding to humans.

1.2. Wireless Power Transmission

Nikola Tesla, first demonstrated the concept of Wireless Power Transmission in 1890.

But, it was only from past few years, that people realized the importance and benefits

of this technology with application like wireless charging. The best part about this

technology is, it is based on the simple concept of magnetic and electric field and so it’s

not only simple to implement or understand but also affordable. Wireless Power

transmission uses two coils which interact with each other when magnetic field is

generated in one coil and is induced into another coil.

Fig 1.2 Wireless power transmission concept [12]


3

As can be seen from the figure below, the transmitting side consist of a DC power

source, this source is then converted to oscillating frequency using oscillator. These

oscillations are then passed through the Drive Loop with N1 turns. Now, when transmit

coil with N2 turns is brought near the Drive loop the transmit coil transfers energy to

the Receiver coil. The oscillations generate magnetic field in the transmitting coil which

in turn induces alternating current in the receiving coil. Basically as soon as the

receiving coil is placed near the transmitting coil, the receiving coil cuts the magnetic

field of transmitting coil. Because of this a electric field is generated at the reception

side. The Load loop then receives the power from the Receive coil which is then

converted back to direct current and can now be used to drive the load.

Fig 1.3 Block diagram of wireless power transfer

DC POWER

SOURCE OSCILLATOR

TRANSMITTING COIL

TRANSMITTING SIDE

VOLTAGE

REGULATOR RECTIFIER

RECEIVING COIL

RECEIVING SIDE

LOAD


4

The concept of Wireless power transfer is therefore based on energy coupling, in this

case Magnetic coupling. Therefore, when electric current gets transferred because of

the magnetic field interaction of two coils, magnetic coupling takes place. For proper

coupling between the two coils, Resonance plays a very important role. Basically, when

two objects oscillate at same frequency, they transfer the maximum power. So, when

two coils placed next to each other oscillate at resonant frequency, maximum power

transfer takes place between the coils and the receiving coil can receive the signal at

larger distance in such case.

This technology is being used for wireless charging of cellphones, toothbrush and

researchers are also trying to use it to charge all the appliances at home or workplace as

can be seen from below fig.

Fig 1.4 Wireless charging of home appliances [13]

1.3. Gesture detection application using WPT coil

As discussed till now, coils are being used to transfer power between devices. But, if

the receiving coils is replaced with our hand, although power transmission will not take

place, but the magnetic field of transmitting coil are being cut which changes the

conductivity distribution of the transmitting coil. This change in conductivity changes

the resonant impedance and the oscillating frequency. This change of oscillating


5

frequency causes the transmitting coil to act as a sensor that can sense the obstacle

cutting its magnetic field and depending on the change of frequency from the original

oscillating frequency the transmitting coil can also sense the positioning of the obstacle.

When the change in magnetic field due to the hand placed in front of it is measured, the

amount of change on the transmitting side is very less. So, for gesture or position sensing

mere use of coils and rectifier couldn’t solve the problem. This was the reason, mixer,

buffer and some frequency convertors were used. The board was designed so that it can

detect the hand movement in X and Y direction and so a differential structure was used

with a up and down convertor to detect X and Y direction respectively.

Fig 1.5 Board design [4]

While working on the above model although it was able to detect the direction of hand

movement, but the coil was not too sensitive to detect the presence of hand until it is

placed too closed to the coil. Initially the work was done to increase the sensitivity of

the coil by working on the mixer and the oscillator and changing the frequency so as to

match it with the resonant frequency of the hand so as to detect it. Also, the coil size

was changed in order to see the effect it has on the sensitivity.


6

Fig 1.6 Different coil size

While working on the PCB, the main issue was the difference of frequency change was

not dominant enough to change it to voltage. Hence, at the output not much voltage

change was observed even when the coil size was increased. So, for this application

purpose, Texas Instruments evaluation module – LDC 1000EVM is being used. The

LDC 1000 uses the difference of frequency and rather than converting it to voltage, it

uses the frequency directly to sense the obstacle in front of it.

Coil 1 Coil 2

Coil 3 Coil 4


7

CHAPTER II

PHYSICAL MODEL

2.1. Analysis of the designed board

The basic idea behind the design of position and gesture controlling using coil was being

able to detect hand movement as change of effective field distribution around the

transmitting coil. So, when AC current flows through the coil a magnetic field is

generated and when hand is placed in front of the coil it induces eddy current which

generates its own field opposing the original magnetic field being generated by the coil.

The inductive coupling between these two transmitting and receiving fields are

proportional to both size and distance.

The change in the frequency due to Human interaction was very small, hence to detect

this small change in frequency a differential structure consisting of two oscillators and

mixer was used. Fig. 2.1 below shows the system block diagram. When the hand is

moved

Fig.2.1 Block diagram [4]

Xiao, Zhiming, Dieter Genschow, Chenhui Liu, Yan Li, and Changzhi Li. "Non-contact Human Machine Interface Based on Bio-

interaction with Wireless Power Transfer Features." 2015 IEEE MTT-S 2015 International Microwave Workshop Series on RF

and Wireless Technologies for Biomedical and Healthcare Applications (IMWS-BIO)(2015): n. pag. Web.


8

is moved in X direction, oscillation are generated and the Operational amplifier is used

to convert the single ended output of the oscillator to a differential buffer. This is then

given to the mixer which generated difference frequency signals. It is then given to the

Low pass filter, which is used to filter out the high frequency components and the low

order mixer output is then fed to the edge detection circuit via a buffer. The buffer is

used as the signal strength at consecutive stages input are not strong enough to drive the

respective stage. So, with the use of buffer before the mixer, the buffer increases the

strength of the signal in order to run the mixer. The edge detection circuit is used to

transform the mixer output into a DC voltage value which can be easily measured and

processed.

The figures (Fig. 2.2 – Fig. 2.4) shows the various stages of the differential design

circuit. The Fig. 2.2 is the Oscillator stage. As can be seen, it’s a Clapp Oscillator circuit

followed by the Low pass Active filter. The Clapp Oscillator is a Common base

configuration circuit with the base of the transistor at Virtual ground. The signal is fed

at the input of the emitter and output is obtained from the collector of the transistor. The

feedback path is from the Collector to emitter via two capacitors.

Fig. 2.2 Clapp oscillator circuit [2]


9

Also, unlike Colpitt Oscillator, Clapp oscillator uses a series capacitor with the inductor.

The purpose of the capacitor is to generate stable frequency at the output. The capacitors

used in Colpitt are variable capacitors, so, the oscillations generated at the output may

vary because of variable feedback voltage. Therefore, with Clapp Oscillator, the

capacitors are kept fixed and the capacitor in series with inductor is varied. This series

capacitor does not impact the feedback ratio, so by tuning this capacitor the feedback

ratio remains constant, thereby giving a stable oscillations at the feedback side.

Fig. 2.3 Mixer & low pass filter stage [2]

Fig 2.3 show a mixer stage followed by Low pass filter. The Mixer stage generates down

converted frequency. Basically, the frequency generated by the oscillator is in MHz

range and the difference in frequency caused due to hand movement id in KHz range.

So, in order to effectively measure the change in frequency it is necessary to down-

convert the frequency in KHz range. Also, as the Mixer uses larger input capacitance,

so in order to drive the mixer circuit buffer is used after oscillator to be able to generate

signal stronger enough to drive the Mixer. The Low pass filter is used to filter out nay

high frequency signal at the output of mixer.

Fig. 2.4 below shows the edge detection circuit, an integrator circuit is designed using

a transistor circuit along with a capacitor. Waveform ‘a’ in Fig. 2.5 is the difference

frequency generated between oscillators. This is fed to integrator circuit which gives


10

Fig. 2.4 Frequency to voltage conversion [2]

signal ‘b’ at the output which is then given to invertor, generating signal ‘c’ with

difference pulse width as it is the inverse form of the integrated waveform. The

difference frequency waveform ‘a’ is given to the inverter generating signal waveform

‘d’ of same pulse width as waveform ‘a’. These waveforms, ‘c’ and ‘d’ are fed to AND

gate generating a signal waveform which correspond to the difference in pulse width of

waveform ‘c’ and ‘d’. This waveform ‘e’ can then be used to give the value of voltage

signal which correspond to the movement of hand. The circuit till the AND gate is

therefore acting as Edge detector so that it respond to the edge at the input and process

it using integrator. The signal ‘e’ is the given to the Low pass filter which further process

the signal to remove any unwanted higher frequency component and generate a voltage

signal proportional to the input change of frequency.

Edge detection circuit

LPF


11

Fig.2.5 Waveform at different stages of frequency to voltage conversion

circuit [2]

The working of the prototype circuit was also demonstrated by designing a GUI in

LabVIEW and demonstrating the change of frequency by changing image displayed on

the screen depending on the movement of hand in front of the coil.

2.2. Working on increasing sensitivity

In order for better understanding of the model and to increase the sensitivity of the coil,

initially experiments were conducted using different types of coils and its impact on the

oscillations was observed. Later, work was done to improve the design of oscillator so

as to be able to resonate at frequency same as the hand movement. To improve the

design of oscillator initially Colpitt oscillator was replace to Clapp oscillator by adding

additional capacitor C5 as can be seen in Fig 1.6. The sensitivity increases by using

capacitive coupling.


12

2.2.1. Inductive sensing

When inductive sensing is taken into consideration, there are various factors that impact

it. And, it is necessary to study and check the impact of each one of these.

I. Inductor shape and size:

Fig. 2.6. Different shapes of inductive coils [26]

The circular coil in above Fig.2.6, is most symmetrical around the area and thus it

generates field which is symmetrical giving higher inductance. Also, because of the

edges in other three coils it causes parasitic resistance in the coils thereby reducing the

inductance.

As can be seen from the above Fig 2.6, the dOUT and dIN determine the fill ratio of the

coil or ‘𝛒’. Equation 2.1 is Wheeler’s equation [21] and it shows the relation between

the value of inductance on different parameters. So, from equation 2.1, inductance is

directly related to the average diameter of the coil but inversely related to the fill ratio.

If the coil’s fill ratio is high it means the coil is too closely packed which generates

opposing magnetic field at the center, thereby reducing the inductance.


13

L = 𝐾1µ0𝑛2𝑑𝑎𝑣𝑔𝑐1

1+𝐾2𝜌(𝑙𝑛 (

𝑐2

𝜌) + 𝑐3𝜌 + 𝑐4𝜌2) - (2.1)

where,

- 𝐾1 & 𝐾2 are geometry dependent, based on shape of inductor

- µ0 is permeability of free space

- n is number of turns

- 𝑑𝑎𝑣𝑔is average diameter of the turns = 𝑑OUT+𝑑IN

2

- 𝛒 = 𝑑OUT−𝑑IN

𝑑OUT+𝑑IN , and represents the fill ratio of the inductor

- 𝑐1,𝑐2,𝑐3,𝑐4 are layout dependent factors based on geometry

Fig. 2.7 Fill ratio vs inductance

Fig. 2.7 shows the relation between fill ratio and inductance. So, as fill ratio increases

the inductance value decreases.

The width of the coil is also important in determining the inductance. So, if the width is

less, the resistance is more thereby reducing the quality factor of the coil of the coil,

thereby reducing inductance.

∆ : Coil 1(15µH)

◊ : Coil 2(7.5µH)

: Coil 3(12µH)

+ : Coil 4(19µH)

∆ : Coil 1(15µH)

◊ : Coil 2(7.5µH)

: Coil 3(12µH)

+ : Coil 4(19µH)


14

II. Number of turns

As can be seen from Wheeler’s equation [21], the number of turns is directly

related to the inductance. More the number of turns larger will be the

inductance. Although, care should be taken about the fill ratio as it as inverse

effect on the inductance.

III. Multiple layers

Fig. 2.8 Fill ratio vs inductance [16]

If the number of layers is increased the inductance value increases. Also, the main

advantage of using number of layers is, it increases the inductance value with same size,

area and number of turns of the coil. So, application where optimization and larger

inductance is required, multiple layers is very useful. The layers should be connected in

the manner shown in the Fig. 2.8. such that the current entering the first coil goes around

the coil towards the center and then enters the center of the second coil beneath it and

then goes out, so that the current goes in one direction of the coil.


15

Fig. 2.9 Output diameter vs inductance

Fig 2.9 shows a relation between Output diameter and inductance of the coil. So,

although the inductance increases as the outer diameter of the coil increases, but for coil

4 and 2, although the diameter is same, the inductance is much larger for coil 4 as

compared to coil 2. The reason is coil 4 is designed with 2 layers connected in multi-

layer format. So, with the same size and area, the inductance value has significant

change because of the number of layers.

So, while designing the coil, it is necessary to take discussed parameters into

consideration depending upon the requirement of the application. For the application

discussed later in the application, smaller size of the coil and larger inductance was

required. So, coil 4 was used as gives good inductance value in small area.

∆ : Coil 1(15µH)

◊ : Coil 2(7.5µH)

: Coil 3(12µH)

+ : Coil 4(19µH)


16

2.2.2. Frequency of oscillations

After selecting the required coil, it was necessary to work on the frequency of

oscillations by improving the oscillator design. For better performance, clapp oscillator

was used as it has extra capacitor which does not impact the feedback ratio fed to the

amplifier, thus giving better stability to the oscillations.

Fig 2.10 Design of clapp oscillator

The above Clapp Oscillator was designed using Common Base configuration. As can

be seen the output is taken at the collector and feedback is given to the emitter and base

is grounded. The signal fed at the emitter depends on the feedback ratio (VF/VOUT) and

as can be seen in the above Fig. 2.10, this ratio is dependent on capacitor C3 and C5. So

the capacitor C4 can be tuned for frequency change keeping the capacitor C3 and C5

constant and not impacting the feedback ratio thereby keeping the frequency stable. To

further increase the design, tank circuit was improvised by using different coil size and

frequency in range 5MHz-10MHz.


17

Table 2.1 Simulation result at different frequency

Theoretical

frequency

Inductance

f = 5MHz

f = 7MHz

f = 9MHz

L1=15µH

67.61pF

34pF

20pF

Frequency when hand was not

placed

4.832MHz 6.734MHz 8.723MHz

Change in frequency when hand

was placed

4.368MHz 6.339MHz 8.311MHz

L2=7.5µH

135pF

68pF

41.73pF


placed

5.28MHz 6.912MHz 8.715MHz


was placed

5.01MHz 6.537MHz 8.22MHz

L3=12µH

84pF

43.12pF

26.08pF


placed

5.307MHz 6.77MHz 8.70MHz


was placed

5.031MHz 6.40MHz 8.511MHz


18

So, unless we increase the size of the coil we are not able to have significant change in

the value of inductance at the output if the above prototype design is taken into

consideration. Also, it is necessary to reduce the circuitry so as to able to use the design

in cellphones and in other optimized devices. Therefore, more research was done on

reducing the circuitry and finding alternate solution to frequency to voltage conversion

process. To do this microcontroller was planned to be used. On research about how to

interface microcontroller and detect the change in frequency, Texas Instruments

research work on Inductive sensing was found and although the application being

different, the design of the board was in the same line as was planned for this research

project purpose.

TI

100pF,19µH


placed

5.780MHz


was placed

5.5865MHz


19

2.3. LDC Evaluation board

Texas Instruments designed various evaluation module based on Inductive sensing. One

such board is LDC100EVM. The purpose of the board is to use inductive sensing and

detect metal object or any conductive object in the target area.

Fig 2.11 LDC1000EVM [20]

This evaluation module uses MSP430 microcontroller to process the change in

inductance value and measure the value of inductance after the object is detected at the

target. As can be seen PCB based inductive coil is used which give better accuracy to

the module. The second part is the LDC1000 IC. This IC is responsible to measure the

change in frequency of the LC tank circuit and calculate corresponding inductance

value.

Fig 2.12 Functional block diagram [20]

MSP430

LDC1000 IC

Inductive coil


20

Fig. 2.13 Mutual inductance between human finger and coil

Fig. 2.13 shows the coupling that exist between the inductive coil of the LDC1000EVM

and the finger of the user. There exists capacitive coupling between the finger and the

coil. So, even though on placing the finger reduced the inductance of the coil, the

capacitive coupling causes the total frequency reduction at the oscillator output, which

is useful in detecting the presence of the finger placed. So, if a metal is placed in front

of the coil, the inductance reduces and frequency increases. Therefore, this decrease and

increase in frequency can be very useful in determining whether a finger is placed in

front of the coil or a metal is placed.

LDC1000 uses two types of Data as can be seen in above Fig 2.12, the frequency counter

data and the proximity data. The former is used to determine the type of conductor,

depending on the type the frequency changes and is sent to the SPI interface. The latter

distance of the conductor from the coil and is basically given in the form of resistance

of the coil. Since the project deals with the change in inductance, only change in

frequency data is taken into consideration.

LDC1000 used frequency counter to calculate the value of inductance. It uses the value

in registers 0x23, 0x24 and 0x25 where content of registers are given below in table:

M

C

M: Mutual Inductance

C: Parasitic capacitance

L: Inductive coil

L


21

Table 2.2 Register Map [20]

Register Name Address Direction Bit content

Frequency counter

data LSB

0x23 RO FCOUNT LSB

Frequency counter

data Mid-byte

0x24 RO FCOUNT Mid-

byte

Frequency counter

data MSB

0x25 RO FCOUNT MSB

Sensor frequency, fsensor = 1

3* (

Fext

Fcount)*Response time

where, Fext: frequency of external clock

Fcount: value in data registers 0x23, 0x24, and 0x25

Response time: last three bit stored in register 0x04

Thus, having value of frequency we can calculate value of Inductance using formula for

resonant frequency,

fresonant = 1

2𝜋√𝐿𝐶

So, value of Inductance,

L = 1

(fresonant∗2𝜋)2∗𝐶

where, C is the capacitor parallel to the coil


22

2.4. LDC1000 IC

Fig. 2.14 LDC1000 IC package [20]

LDC1000 is 16 pin WSON package with interrupt control and SPI feature allowing easy

interface with the microcontroller. SPI interface are used in order to send and receive

the data from microcontroller using specific bus lines and clock signal. It also used Chip

Select Bar pin to select the device with which communication is to be done. The IC

operates at maximum voltage rating of 6V and supply current of maximum 2.3mA. In

order to send and receive data out of chip, the fSCLK frequency of maximum 4MHz is

used. The description of the pins of the IC is as follows:

Table 2.3 Pin configuration [20]

Pin

Number

Pin Name Description

1 SCLK Clock out/clock in data from/into the chip

2 CSB To select the device with which communication is to be

done

3 SDI Slave Data In

4 VIO Digital IO supply

5 SDO Slave Data Out


23

6 DGND Ground

7 CFB Filter capacitor

8 CFA Filter capacitor

9 INA External LC Tank

10 INB External LC Tank

11 GND Analog ground

12 VDD Analog supply

13 CLDO LDP bypass capacitor of 56nF

14 TBCLK External time base clock

15 N/C No connection

16 INTB Interrupt control

Fig 2.15 SPI communication

As mentioned earlier, LDC1000 is a SPI device. It acts as a slave and the microcontroller

acts as a Master. In order to initiate the conversation, the CSB line is which is by default

is at HI state is pulled LOW. Also, before after the 16th clock pulse of SCLK, the CSB

line must be brought back to default state. If not at the 16th clock pulse, it must be

initialized to default at every 8*(N+1) clock cycle.

SCLK

MOSI

MISO

SS

SCLK

MOSI

MISO

SS

SPI

MASTER

SPI

SLAVE


24

Fig. 2.16 Serial interface protocol [20]

As can be seen in Fig. 2.16, communication between the Master and Slave takes place

in bytes. The first bit of the MSB byte signify whether the data is to be read or written,

with 0 signifying data write operation and 1 signifying data read operation. The next 7

bits are used to signify the address of the register. The LSB byte is the 8-bit data field.

At the rising edge of the SCLK pulse, data is sampled and at the falling edge data is

received by the Master. And, at the end of 16th clock pulse the CSB is set to default.


25

2.5. Adafruit Bluefruit EZ-KEY

Fig. 2.17 Bluefruit EZ-KEY [14]

Bluefruit is a Bluetooth controlled keyboard device with default values given to the keys

and these values can also be modified according to the application. There are 12 input

pins and the module works from 3-12V. So, when the key is pressed from the Bluefruit,

it sends the command to the computer which displays the key pressed.

Fig. 2.18 Pin configuration

Bluefruit

EZ-key HID


26

Table 2.4 Pin Description

Pin Assignments Default Values/Description

0 UP arrow

1 DOWN arrow

2 Left arrow

3 Right arrow

4 Return

5 Space

6 Number ‘ 1’

7 Number ‘ 2’

8 Letter ‘ w’

9 Letter ‘ a’

10 Letter ‘ s’

11 Letter ‘ d’

TX This is UART output. It is 3V logic level

output

RX This is UART input. 3-5V TTL logic,

9600 baud

L1 Indicates if the key is pressed

PB Pair button pin. It is used

L2 Extra pin to indicate the pairing of

device.

RS Reset pin to reset the module. Does not

affect pairing.

3V Power supply pin

G Ground

Vin Power supply pin

Ground Ground

Ground Ground

Ground Ground

For the purpose of showing the Home button feature on the iPhone, a push button switch

was used. This switch was connected to pin no. 6 of Bluefruit EZ-key, so every time a

key is pressed, the Bluefruit module send Number ‘1’ to the paired device, in this case

a computer was used. The value from the Bluefruit module was accepted in LabVIEW


27

using AcquireInputData.vi. This VI accepts and displays the data received from the

paired keyboard. Depending on the data received from the Bluefruit module, the ‘key-

press’ is indicated using a LED on the front panel

2.6. Application of the Evaluation module

The Home button of iPhone suffer from wear and tear even if it is used cautiously.

Although a touchscreen icon is provided by Apple on the iPhone or iPad, it is not so

convenient to use your cellphone or tablet feature with the icon always present on the

screen. Therefore, in this application, a module was successfully designed to replace the

icon on the screen of the iPhone/iPad by using a coil with the home button. So, if the

home button is not working, placing a finger in front of the button would display the

home screen.

In order to interface with the computer and check the feature, LabVIEW was used to

create the GUI. Also, to be able to check the function of the button Adafruit’s Bluetooth

device Bluefruit EZ-KEY HID was used.

(a) (b)

Fig 2.19 iPhone dummy body (a) exterior of the iPhone (b) Inside circuitry for

apple iPhone


28

Fig 2.20 LabVIEW GUI

The GUI was designed using NI LabVIEW and NI VISA session was used to interact

with the USB port. As can be seen from the GUI, by default the feature of the coil

sensing is switched off. Users are given option to select if they wish to select Assistive

touch at the top right corner

(a) (b)

Fig. 2.21 Assistive touch selection (a) When Assistive touch is pressed (b)

When assistive touch is not pressed

If the Assistive touch (6) on the top right corner is not pressed, the GUI waits for the

Bluetooth module’s signal and by default the iPhone coil is not activated. The push

1 2 3 4 5 6 7 8 9

4 6 7


29

button on the iPhone is connected to the Bluetooth module’s 6th pin which will send

digit ‘1’ when the push button is pressed. So, when the push button on the iPhone is

pressed, the bluefruit sends digit ‘1’ to the paired device. At the GUI end, when the

LabVIEW receives this digit, it will lit the LED display (7) .Also, it can be seen from

Fig 2.21 (b) that (4) displays digit ‘1’, this is nothing but output showing the signal

being received from the Bluetooth module. The data is being collected in the form of

array. So, from the GUI, it can be seen that the first element received is digit ‘1’. When

the user selects Assistive touch option (4), as can be seen from the Fig 2.21 (a), the

button OK is disabled signifying that the key was pressed.

(a) (b)

(c)

Fig. 2.22 User input selection (a) when COM port not selected (b) when COM port

selected (c) When start streaming pressed

When the Assistive touch button on the front panel of the GUI is pressed, the GUI waits

for the user to press Start Streaming and select the port at which the LDC1000EVM is

connected. Initially the LED display (11) shows ‘Disconnected’ and ‘Stop streaming’

button is disabled signifying that the LDC1000 EVM is not connected. The ‘Cap’ value

(12) by default has value of 100pF which is also the capacitor value connected in parallel

with the coil on the tank circuit of the LDC1000EVM. This can be changed in case the

tank circuit is modified depending upon the frequency requirement. When the LDC

1000EVM is connected at the suitable COM port (10) from the drop down list is

selected, the LED display on the front panel shows ‘Connected’ as can be seen from

Fig.2.22 (b).Also, as soon as the COM Port is selected and the Start streaming’ button

10 11 12


30

the front panel is pressed, the data starts streaming and as can be seen from Fig. 2.22

(c), the ‘COM’ port selection (10), capacitance selection ‘Cap’ (12) and the ‘Start

streaming’ button are disabled so that the data streaming operation is not impacted by

any random selection errors.

Fig. 2.23 GUI screen when finger not placed in front of the coil

Fig.2.23 shows the screen when user presses the ‘Start Streaming’ button. The graph (8)

on the screen shows the value of inductance of the coil in graphical representation. Also,

(5) in the Fig. 2.23, displays the home screen as can be the screen of apple iPhone. (2)

displays the actual inductance of the coil.

2 8 5


31

Fig. 2.24 GUI screen when finger not placed in front of the coil

When the data is streaming, the coil acts as a sensor and check for the finger to be placed

near it. After detecting the presence of finger in front of it, it displays the home screen

(5) giving three options: Music, Photos and Home. So when any of this button is

selected, the GUI redirects to the respective location on the local drive. The third option,

‘Home’ will take back to Home screen. The field (1) shows the path of the local drive

at which the GUI redirects the USER on selecting respective button on the screen.

1 5


32

2.7. LabVIEW code flowchart

START

Assistive

touch? Wait for keyboard input

Lit the LED on front panel

Wait for Port Selection

Wait for User to Start Streaming

Form a cluster of input data

Pass the cluster to ‘Read-L’ VI

NO

YES

De-queue the ‘All Data’ queue

from ‘Read Buffer’ VI

Process the data in ‘L process’

VI

Plot the inductance chart

Process the inductance

value

A


33

Was the

finger placed?

NO

YES

A

Give the option to select

desired folder

Redirect to folder of choice

Stop

streaming?

Keep the default screen

selected

NO

YES

STOP


34

CHAPTER III

CONCLUSION

The objective of this project was to analyze, improve the sensitivity and reduce the

circuitry of the already designed prototype board for non-contact human interaction

using Wireless Power transmission coil. Also, it was desired to build an application to

replace the home screen button on Apple phones so as to have alternate solution because

of the problem caused by wear and tear of the buttons.

Although coil was successfully detecting hand movement but the change in frequency

due to the hand was not very significant. Efforts were taken to improve the sensitivity

by working on different frequency, different coil size and oscillator. With increase in

coil size the sensitivity improved a little, but using larger coils will only add to the

already big circuitry. Research was done to be able to detect the frequency and use

microcontroller to detect this change and display it for human interaction. For this

purpose, Texas Instruments – LDC1000 evaluation board was used.

The application for Apple phones was successfully developed using LabVIEW and

using hardware circuit – TI-LDC1000EVM and Adafruit Bluetooth module.


35

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39

APPENDIX A

1. Clapp Oscillator Design Calculation

Fig.A.1 Common Base Clapp Oscillator

V=12V

Assuming collector current, IC to be 5mA and β to be 100

Therefore, IB = IC

β =

(5∗10−3)

100 = 50µA

Also, current through resistor R1 and R2 is 10 times the base current. So, the current

through these resistors is 0.5mA

The voltage at the collector is half of the supply voltage for better sweep, so it is

assumed to 6V and voltage at the emitter is assumed to be 1.3V

Therefore, R4 = (𝑉−𝑉𝐶)

𝐼𝐶 =

(12−6)

(5∗10−3) = 1.2KΩ

R3 = 𝑉𝐸

𝐼𝐶 =

1.3

(5∗10−3) = 260Ω


40

R1 = (𝑉−𝑉𝐵)

(5∗10−4) =

(12−2)

(5∗10−4) = 20KΩ

R2 = (𝑉𝐵)

(5∗10−4) =

2

(5∗10−4) = 4KΩ

The frequency of operation is 5MHz and value of inductor is 7.5µH so the capacitor

value can be calculated by following equation:

fresonant = 1

2𝜋√𝐿𝐶𝑇

The value of CT comes out to be 135pF. The value of capacitors, C3, C4, C5 are

selected such that.

1

𝐶𝑇 =

1

𝐶3+

1

𝐶4+

1

𝐶5

𝐶3 = 270pF, 𝐶4 = 270pF, 𝐶5=170pF


41

APPENDIX B

1. Transistor Configurations [27]

Table A.1: Pin Description

Common Emitter configuration

CE small signal model

Common Base configuration

CB small signal model

Common Base configuration

CB small signal model


42

APPENDIX C

SUB-VI

Fig.A.2 Read L subVI

Fig.A.3 Read Buffer subVI


43

Fig.A.4 L Process subVI

Fig.A.5 Main part of VI of reading and displaying the image according to placement of

finger

hand gesture & proximity sensing using wireless power

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