Project final Report wireless power transfer (Autosaved) (1)
Descrição do Produto
WIRELESS POWER TRANSFER (WIRELESS CHARGER FOR A USB
CONSUMER DEVICE)
By
ALADE OLUGBENGA OLAYINKA
Student Number: 44308450
IPR401E DESIGN PROJECT IV
SEPTEMBER 2014
Mr. MABASO M.
Head of Department Electrical
Engineering
Ekurhuleni West College TVET
Project Mentor
ABSTRACT
This project describes an implementation of a wireless charger for USB
consumer devices. The smart charger is able to automatically sense the
presence of a nearby electronic device and detect its internal battery
level. When the battery level of a USB device in proximity is dropped below
a certain preset threshold, the smart charger will be initiated through an
ultrasound communication system and start to charge the device. The
charging process will be stopped automatically once the battery is fully
charged. The automated charging capability avoids excessive charging power
and makes the proposed charger eco-friendly. It is also a worry-free charge
since users do not have to plug in a charger.
DECLARATION OF OWN WORK
I declare that this report is my own, unaided work. It has been submitted
for the Baccalaureus Technologiae in Electrical Engineering in the
Department of Electrical Engineering at UNISA. It has not been submitted
before for any degree, Diploma or other examination at any other tertiary
institution.
Signed:................................
By..........................................................................
................
At ..........................................on this
......................day of ......................2007
Mentor:
Signed:................................
by..........................................................................
..............
Signed:.................................
by..........................................................................
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ACKNOWLEDGEMENTS
I would like to thank my mentor and co-workers on this project, Mr Mabaso
Meshack for his tremendous contribution with regards to his firm attitude
towards the success of this design and the programming of the IC. This
project would not have been possible without his help.
I would also like to thank the entire workshop crew of Ekurhuleni West
College Kathorus Campus for their availability and support, making the
workshop available for different experimental findings on the work.
In addition I would like to thank my Wife and Daughter for their amazing
understanding and support although.
I put up my final vote of thanks to the Electrical Engineering Department
at UNISA for the privilege to study with them.
TABLE OF CONTENTS
WIRELESS POWER TRANSFER
............................................................................
.................. CHAPTER 1: INTRODUCTION
............................................................................
.................... 1
1.1
Purpose.....................................................................
.................................................................1
1.2 Specifications
............................................................................
............................................... 1
1.3
Subprojects.................................................................
............................................................... 2
1.3.1 Battery Detection Unit
............................................................................
............................ 2
1.3.2 Communication
Unit........................................................................
................................... 2
1.3.3 Antenna Coil Unit
............................................................................
................................... 2
1.4 Background on Wireless Power Transfer Theory
................................................................... 3
1.5 Review on Previous Designs
............................................................................
......................... 4 CHAPTER 2: DESIGN DESCRIPTIONS
............................................................................
..... 4
2.1 System Electrical Specifications
............................................................................
.................... 4
2.2 Initial Design Blocks
............................................................................
....................................... 5
2.3 Design Procedure
............................................................................
............................................ 6
2.3.1 USB Battery
Detection...................................................................
..................................... 6
2.3.2 Communication
............................................................................
....................................... 8
2.4 Design Details
............................................................................
.................................................. 9
2.5 Design Calculations
............................................................................
....................................... 12
2.5.1 Antenna Coil Design
............................................................................
............................. 12
2.5.2 Power Transmission Efficiency
............................................................................
............ 14
2.5.3 System Efficiency
............................................................................
.............................. …..14 CHAPTER 3: EXPERIMENTAL RESULTS
.........................................................................
15
3.1 Design Verification
............................................................................
........................................ 15
3.1.1 USB Battery Detection
............................................................................
.......................... 15
3.1.2 Communication Testing
............................................................................
....................... 16
3.1.3 Antenna Coil Testing Results
............................................................................
............... 18
3.1.3.1 Waveform Measurements
.........................................................................
........................ 20
3.1.3.2Range Measurement
.........................................................................
............................. 22
3.1.3.3 Capacitance and Inductance
.........................................................................
................ 22
CHAPTER 4: COST ANALYSIS
............................................................................
................. 22
4.1 Cost Analysis
............................................................................
................................................. 22
4.2Part List
............................................................................
......................................................... 23 CHAPTER 5:
CONCLUSIONS
............................................................................
.................... 23
5.1 Accomplishments
............................................................................
.......................................... 23
5.2 Ethical
Considerations..............................................................
................................................ 24
5.3 Conclusions
............................................................................
.................................................... 24
5.4 Future work / Alternatives
............................................................................
........................... 25
REFERENCE………………………………………………………………………………………………………………………………………26
APPENDIX A Block Diagrams
APPENDIX B Schematics
APPENDIX C Hall Effect Sensor
APPENDIX D Picture
CHAPTER 1: INTRODUCTION
The idea of wireless power transfer originated from the inconvenience of
having too many wires sharing a limited amount of power sockets. We believe
that many people have the same experience of lacking enough sockets for
their electronic devices. Thus by creating a wireless power transfer
system, it would help clean up the clutter of wires around power sockets
making the space more tidy and organized.
1.1 Purpose
The purpose of this project is to produce a platform which can detect the
battery level of an electronic device, such as a cell phone, then be able
to automatically charge the device when the battery level of the device
drops below a certain threshold. Our project will use resonant induction
charging which can charge multiple devices at the same time as long as they
have the same resonant frequency.
Benefits include:
Safe wireless power transfer
Compatibility with USB devices
Eliminates power outlet clutter
Intuitively self-charging
Features include:
Ability to charge multiple devices
Automatic detection of battery life and the need for charging
1.2 Specifications
The project was split up into battery detection, communication, and
wireless power transfer. For each individual module specification, refer to
section 1.3.
The Hall Effect sensor detects the battery level through current in the USB
and when the current is above a certain point, meaning low battery level,
the sensor sends a signal to trigger the microcontroller. The
microcontroller then sends a signal to the transmitting ultrasound to start
the communication process. This is the battery detection part. The
receiving ultrasound is fed with 40 KHz sine wave and the wave is rectified
through a bridge rectifier and stabilized through a capacitor. This is the
communication part. The stabilized DC signal turns on the switch to start
the charging process. After the switch is on, a DC signal is fed into a
voltage divider from an AC to DC power supply to power the oscillator. The
oscillator outputs a 13.56MHz sinusoidal wave to the amplifier for greater
power. When the amplified power is fed to the transmitting antenna coil,
the transmitting antenna coil induces magnetic field to the receiving
antenna coil and the power is received by the receiving antenna coil. This
AC power is then rectified into DC voltage and stabilized through a voltage
regulator and then charge the device through USB.
1.3 Subprojects
1.3.1Battery Detection Unit
The Hall Effect sensor and the PIC microcontroller are charged through four
3V button cell batteries and lowered through a 5V Voltage regulator. The
clock oscillator is connected to the PIC for sufficient clock pulse and is
also powered by button battery.
1.3.2Communication Unit
The transmitter is an ultrasonic piezoelectric transducer with a signal
amplifier. When the battery level is low, the microcontroller turns on the
piezoelectric transducer to transmit an ultrasound signal to turn on the
charging dock. The ultrasound receiver is a piezoelectric microphone with a
signal amplifier which can convert an ultrasound signal into electrical
signal and then amplifies the signal.
1.3.3Antenna Coil Unit
The loop antenna converts an electrical current into an electromagnetic
field. In the near field region, the magnetic field dominates and therefore
electrical energy is transmitted wirelessly through magnetic field
coupling. The loop antenna is built with copper wire gauge 12 at resonance
frequency 13.56MHz. An electrical small loop is desired for our project so
that it can be fit into a cellphone form factor. A balun is connected to
the loop antenna because the output of the power amplifier is an unbalanced
signal.
The coil/loop antenna is made of an inductor and a capacitor, therefore
using the equation below to calculate its resonance.
1.4 Background on Wireless Power Transfer Theory
The concept of wireless power transfer can be traced back to 1820 when
Andre-Marie Ampere developed his law which states that an electric current
produces a magnetic field. Following the work by Michael Faraday (1830),
James C. Maxwell (1864) and Heinrich R. Hertz (1888),
Nikola Tesla experimentally demonstrated wireless power transfer in 1891
[1]. In Tesla's experiment, he designed a resonant circuit that is able to
couple a high frequency current into another resonant circuit of a similar
structure. With his circuit, he was able to power wirelessly (without any
physical interconnecting conductor) a light bulb.
The theory behind wireless power transfer is already detailed in the
Maxwell's equations,
The last two curl equations state that a time-varying magnetic flux
generates an electric field, and a time-varying electric flux generates a
magnetic field. Therefore, if a time-varying electric current can be
generated, the time-varying current will induce a time-varying magnetic
field.
This time-changing magnetic field can "somehow" be picked up and induce a
time-varying
electric field, or an AC voltage across a receiving load. Tesla's
contribution lies on the design of a circuit than can generate/receive a
time-varying magnetic field in free-space. It shall be emphasized that
Tesla's method is not based on the direct transfer of energy through the
use of propagating electromagnetic wave. Tesla's method is actually a near-
field method, whereas the use of propagating electromagnetic wave (like
transmission of microwave power through an antenna) is a far-field method.
The two methods differ by the transmission range as well as the angular
coverage of the system. Near-field method, though has a shorter range, the
energy is more confined than far-field method.
1.5 Review on Previous Designs
Although Tesla demonstrated wireless power transfer over a century ago, the
subject was not well investigated until researchers at Los-Alamos National
Laboratory developed the first passive radio-identification (RFID) tag [2].
The RFID tag is passive because the chip inside it is powered by the signal
that incidents on it. Later in 2007, as the research group at MIT
demonstrated the wireless powering of a light bulb, the research effort
into wireless power transfer got further boosted [3].
Indeed, in 2006, a senior design project group at Illinois has completed a
project entitled
"Wireless Power Adapter for Rechargeable Devices" [4], which was almost a
year ahead of the MIT group. In the project, the group successfully
demonstrated that a cell phone can be wirelessly charged.
CHAPTER 2: DESIGN DESCRIPTIONS
2.1System Electrical Specifications
Input voltage AC 110 V @ 60 Hz
Output voltage DC 4.2 V
Output current 25 mA
Wireless transfer frequency 13.56 MHz
2.2Initial Design Blocks
The system consists of three major components: battery indicator,
transducer/receiver unit, wireless power transfer unit. The battery
indicator outputs a signal when the battery level of the portable device to
be charged reaches a certain threshold value. When the battery of the
portable device is below a certain threshold, the first LED of battery
indicator will turn off and then the edge detector will detect a falling
edge. The SR latch holds the signal from the edge detector and then turns
on the switch. The signal from the switch is fed to a transducer that links
to a receiver in the charging dock. The transducer is an ultrasound
transducer that emits an ultrasound signal. After the receiver in the
charging dock detects a signal, the signal is fed into a rectifier to
convert it from sine wave to a unipolar signal. The unipolar signal will
feed into low pass filter to convert it into DC voltage. To reduce ripples
of the DC voltage, voltage regular is applied, results a flat DC voltage
which can turn on the switch. The switch turns on the power supply unit in
the dock and power is drawn from the AC wall outlet. The 60 Hz AC current
is then converted to a higher frequency that is suitable for wireless power
transfer (for example, 13.56 MHz in the ISM band). The up-converted AC
current is then fed to the wireless power transfer unit. The wireless power
transfer unit is implemented by a pair of resonant loop antenna/coil,
voltage divider, oscillator and power amplifier. After the AC-to-DC
converter transfers the AC power supply to DC voltage, the 5 volts will
then feed into voltage divider so that its output can reach to the
operating frequency of the oscillator. The following power amplifier will
amplifies the output of the oscillator. The signal is fed to the coil
antenna through the balun. The loop antenna/coil is brought to resonance by
capacitive loading and using multiple windings. The received antenna will
pick up the magnetic field and transfer it to electrical signal and then
the signal is rectified into unipolar signal by bridge rectifier. The
unipolar signal then is fed into voltage regular to convert to DC voltage.
The output of the voltage regulator is connected to the USB charging port
of the portable device to be charged. When the battery is fully charged, it
will light up the last LED in the battery indicator. This causes a rising
edge and is then detected by edge detector. This will release the latch to
turn off the switch and then turn off the Ultrasonic transmitter which will
stop charging the platform. The initial and final block diagrams are
displayed in Appendix A.
2.3Design Procedure
2.3.1USB Battery Detection
At the beginning, we designed a battery indicator for battery detection.
However the disadvantage part of this is that a wire needs to connect to
the battery to detect the voltage drops. Since the detection on USB port is
always 5V, the only choice we have is to connect a wire to the battery in
the cell phone. After testing the current change in different battery
level, we decided to use PIC microcontroller with Hall Effect sensor to
detect the current since the current change is inversely proportional to
the battery level.
Using a multimeter from the lab we calculated the current as the phone
charged. The results are shown below.
Table 1. Current, voltage, and power at different battery levels while
charging
Battery Life (%) Current (A) Voltage (V) Power (W)
> 95 0.05 5.1 0.255
95 0.3 5.1 1.53
90 0.35 5.1 1.785
75 0.65 5.05 3.2825
70 5.05 3.535
0 4.7 3.995
The above values for current in Table 2.2.1 varied as it charged, thus only
approximations. Also, the battery life was determined through a phone
application. Something that was noted during these tests was that this
battery was charging at about 5V, while our voltage regulator was set at
4.2V. This does not appear to be a problem. In this case the phone would
charge at a slightly lower rate or the current would increase through the
USB cord.
Using a Hall Effect sensor to detect the magnetic field created by the
current, we would be able to detect the current of the USB line. The Hall
Effect Sensor we chose was the ACS712 [5] which operates between -5A and
+5A outputting a voltage value between 1.5V to 3.5V. The current and
voltage was linearly related with 2.5V corresponding to 0A. However,
sensing if the battery needed charging through the current created another
challenge. This challenge was that the battery sensing would only be
possible when the device is charging, thus when the device finally stops
charging, there would be no way of sensing the battery and sending out a
signal that it needs to be charged.
The solution to this was to implement a microcontroller that could pulse a
40kHz ultrasound signal when the device needed to be charged and be able to
stop pulsing when the device no longer needed charging. When the
microcontroller detected the device no longer needed charging it would stop
pulsing the 40kHz ultrasound for one minute, then begin pulsing the signal
again to continue charging. The microcontroller would then detect if the
battery needed to continue being charged or still fully charged and act
accordingly as stated above. Due to time constraints, we chose to implement
the PIC16F887 [6] which are offered available in the lab. Using the flow
chart from Figure 1, we programmed the microcontroller.
Figure 1. MCU Flow Chart
2.3.2Communication
Another modification with respect to the old design is that we eliminated
low pass filter and voltage regulator in the charging platform. After
implementing the circuit, we noticed that the signal after the amplifier is
stable enough to turn on the switch by adding a capacitor to reduce the
ripples. The ultrasonic signal was AC coupled, amplified, fully rectified,
put through a low pass filter, and finally a voltage regulator.
Due to the microcontroller being only able to output a 5V peak to peak
square wave through its PWM function, an AC coupling capacitor of 100uF was
added in series to eliminate the 2.5VDC offset at the receiving ultrasonic
sensor. The ultrasonic sensors were then tested and found to have more than
a 16 inch reach at 5V peak to peak. Also, as the transmitter frequency
varied away from 40kHz the receivers ability to pick up the signal
decreased dramatically. Through these observations, it can be said that the
ultrasonic transmitter/receiver was acting as a bandpass filter centered
around 40kHz. At the same time, the BS270 MOSFET [7] that was going to be
implemented as the switch for the charging dock to transmit power or not
was found to need a gate voltage of 7V or more to fully allow the charging
dock to transmit power. These findings resulted in the elimination of the
low pass filter and the voltage regulator, for they were no longer needed
in the design.
Knowing that some noise would still be flowing into the ultrasonic sensor
we decided to filter out the low voltage signals by using a diode bridge to
rectify the 40kHz ultrasound signal from the ultrasound receiver. In this
case we decided to go with the 1N5817 Schottky diode because of its low
0.45V forward voltage compared to the typical 0.7V. Although diodes do
exist that have a lower voltage drop, the 0.45V voltage drop was not high
enough to affect the range of the ultrasonic sensors.
Now that the 40kHz signal was able to be read and properly filter out the
low voltage noise from the ultrasound receiver, the signal had to be
amplified above 7V to be able to turn on the MOSFET. To do this we chose to
use the LMC 6482 [8] operational amplifier to boost the signal. By placing
an amplifier, it would amplify not only the signal we needed, but random
noise from the rectifier. By taking this into account, we chose to adjust
the resistor values to a point where the gain would be enough to drive the
on signal to rail voltage, but not high enough to let random noise power on
the MOSFET to a relevant value. By amplifying the on signal to rail
voltage, we were no longer able to use the 5VDC from the wall converter to
power on the op amp. This resulted in having to power the op amp with three
CR1616 [9] in series, which are 3V button cell batteries.
2.4 Design Details
2.6.1 Battery Detection
The Battery Detection Module was designed so that we could know whether the
battery needed to be charged or not. This module uses an ACS712 Hall Effect
sensor and a PIC16F887 as its primary components. The Hall Effect current
sensor had a linear relationship with the voltage and therefore only needed
to be powered and connected to the USB through pin 1 [14]. As for the
PIC16F887, it needed to be programmed following the flow chart seen in
Figure 1. By using the Hall Effect current sensor, we associated each
current with a certain voltage value which then needed to be read by the
PIC. From the datasheet and the Hall Effect voltage input to the PIC, the
Analog to Digital Converter (ADC) needed to be set up. Since the Hall
Effect sensor was designed to operate between -5A to 5A the voltage output
between the 0A to 1A range only varied from 2.5V to about 2.7V. For this
reason, the resolution of the ADC should not be large and thus calculated
with the following equation.
(2.6.1)
With the PIC needing 5V to power on, the reference voltage was set to that
same value. Although up to 16 bits of resolution can be used, we felt that
the 10bits was sufficient for operation at 4.8828mV/bit as calculated in
equation (2.6.1). Using the resolution per bit, the digital assigned value
for each voltage could be determined with equation (2.6.2). Referring back
to Table 1 we approximated a turn on/off charging current to be around .5A
which corresponded to a voltage output of about 2.6V.
(2.6.2)
Reading the datasheet of the PIC16F887 closely, we decided to use a 20MHz
clock oscillator [15] to make the PIC more stable and accurate. This
frequency was then set up to be divided by 32 so as to maintain the speed
of the PIC within readable range.
Finally, the PWM signal needed to be set up to drive the 40kHz 5Vpk-pk
ultrasound to the ultrasonic transmitter. To do this it was necessary to
set the Timer2 register value, which the datasheet provided an equation.
Plugging in the already known values in equation (2.6.3) the equation was
reduced to equation (2.6.4). Although using a prescalar of 4 or 16 would
have also given a relatively accurate 40kHz signal, prescalar 1 was more
exact and therefore was used in the PIC code. This resulted in a Timer2
value of 124 and a duty cycle of 124/2 = 62.
(2.6.3)
(2.6.4)
The final step in operating the battery detection involved powering the PIC
and Hall Effect sensor. In this case, 4 3V coin cell batteries were
connected in series and fed through a KA7805 linear voltage regulator with
a 0.33µF capacitor to ground at the input and a 0.1 µF capacitor to ground
at the output. This output was a steady 5V which was necessary to power on
the PIC and Hall Effect sensor.
2.6.2 Communication
The Communication Module was designed to turn the MOSFET on when a 40kHz
ultrasound is detected and off when the 40kHz signal is not transmitting
and noise is present. Seeing how the microcontroller pulsed a 5Vpk-pk 40kHz
wave, a 100µF AC coupling capacitor was connected in series in order to
eliminate the 2.5Vdc offset. Due to the .9V forward voltage drop of the
diode bridge rectifier, the receiving ultrasound signal needed to be
greater than .9Vpk-pk in order for a signal to be read on the output of the
bridge rectifier.
If the ultrasonic receiver read a signal that was larger than .9V it would
then be amplified using the LMC 6482 as a non-inverting signal amplifier
with the following equation.
(2.6.2.1)
By setting R2 to 10kΩ and R1 to 51.1Ω, we were able to obtain such a high
gain. By using
this gain, we were able to increase the range of the ultrasonic sensor.
This high gain is able
to detect and amplify the signal to the necessary rail voltage of about 8V
from the coin cell batteries as soon as the voltage surpasses .93559V. In
the video posted on the web page the range can be seen to extend about a
foot and a half, which far exceeds the power transmission range. When the
ultrasound transmitter was off, the noise that was seen at the amplifier
edge appeared to be about .1V, which according to equation (2.6.2.1)
resulted in about 0.5mV noise signal.
3.6.3 Wireless transmission
After the receiver in the charging dock detects a signal, the signal is fed
into a rectifier to convert it from sine wave to a unipolar signal. The
unipolar signal is then fed into an amplifier and a capacitor which reduces
ripples of the DC voltage. The DC voltage turn on the switch and the switch
turns on the power supply unit in the dock and power is drawn from the AC
wall outlet. The 60 Hz AC current is then converted to a higher frequency
that is suitable for wireless power transfer (for example, 13.56 MHz in the
ISM band). The up-converted AC current is then fed to the wireless power
transfer unit.
Figure 2. Overview of the wireless power transfer system
As shown in Figure 2, the wireless power transfer unit consists of a pair
of resonant loop antenna, voltage divider, oscillator and power amplifier.
After the AC-to-DC converter transfers the AC power supply to DC voltage,
the 5 volts will then feed into voltage divider so that its output 2.5V for
the operating frequency of the oscillator. This oscillator converts the
input signal into a sine wave with desired frequency at 13.56MHz. The
following power amplifier amplifies the output of the oscillator and then
feed to the coil antenna through the balun to balance the signal. So that
the signal can be transferred into the loop antenna is brought to resonance
by capacitive loading and using multiple windings. The loop antenna can
convert an electrical current into an electromagnetic field. In the near
field region, the magnetic field dominates and therefore electrical energy
is transmitted wirelessly through magnetic field coupling. The loop antenna
is built with copper wire gauge 12. The received antenna will then pick up
the magnetic field and transfer it to electrical signal and then rectify
into unipolar signal by bridge rectifier. The unipolar signal then is fed
into voltage regular to convert it into DC voltage. The output of the
voltage regulator will be around 5V to charge the battery. The diode there
is to avoid current going from battery to the wireless power transfer unit.
When the battery is fully charged, the Hall Effect sensor detects a small
current. This causes a trigger from the sensor to the PIC microcontroller.
The PIC microcontroller then turns off the Ultrasonic transmitter which
will stop charging the platform.
2.5 Design Calculations
2.5.1 Antenna Coil Design
L = inductance (µH)
r = mean radius of coil (cm)
N = number of turns
l = length in cm
N = 6 turns
r = 3.5cm
l = 4cm
?L2.42μH
C = capacitance
?C 56.9pF
?
(a)
(b)
Figure 3. Fabricated antenna coil
The fabricated antenna coil is shown in Figure 3. Both the transmitting
antenna and receiving antenna are structured in the same way. Both antennas
have the same number of turns.
2.5.2Power Transmission Efficiency
Efficiency = Power at the received loop antenna X
100 % = 6.8%
Power at the transmitting loop of the antenna
System Efficiency = Power delivered to battery X 100 % = 6.6%
Power drawn from battery
2.6 Schematics
Wireless power transfer unit:
Wireless power receive unit:
CHAPTER 3: EXPERIMENTAL RESULTS
3.1 Design Verification
3.1.1 USB Battery Detection
Since we were unable to draw enough current in the USB for the Hall
Effect Sensor to be tested, using dc power supply current was varied from
0A to 1A while testing the voltage.
This graph is shown in Appendix C.1 and is similar to what is seen in the
datasheet [1].
Since the microcontroller could not be fed a voltage from the Hall Effect
sensor, we simulated a high current signal (ie., above 2.6V) and checked
the output of pin 17 to verify the 40kHz 5Vpk-pk signal as shown in
Figure 3.1.1.1. The voltage was then decreased and increased to simulate
a low current, full battery, followed by a need for charge. The PIC then
took about one minute before pulsing the 40kHz signal again. This test
along with a range test for the ultrasound can be seen on the course
website that simulates the current dropping after being high for a while,
then waiting one minute before checking if the signal needs charging
again.
When initially designed, four 3V coin cell batteries were used to power
the PIC. Looking at the datasheet of these CR1616 batteries, the capacity
for these batteries is only 55mAh. By leaving them plugged in and
operating for too long they had accidentally run low and deemed the
communication part of the demo inoperable.
Figure 3.1.1.1 PWM signal from PIC16F887
3.1.2 Communication Testing
This part of the project was easy to test by breaking it up into a series
of checkpoints and verifying the correct signal. To start, we set up the
ultrasonic sensors approximately 4 inches apart and powered on the PIC to
output the 40kHz wave. In Figure 3.1.2.1 the PWM signal from the PIC is
shown with the output of the ultrasonic receiver. While the 40kHz signal
was still on the output after the bridge rectifier showed that the
frequency had doubled to about 79.7kHz and the voltage amplitude of the
signal had dropped about .9V to about .547V as shown in Figure 3.1.2.2.
With this received signal from the bridge rectifier it was then amplified
to the positive rail voltage of the batteries powering the op amp which
is around 7V and shown in A.5. When the signal was cut off and no signal
was being read, then the output voltage was insignificant as shown in
Figure 3.1.2.3.
Figure 3.1.2.1 40kHz square wave from PWM with 40kHz output from the
Ultrasonic Receiver
Figure 3.1.2.2 Bridge Rectifier Signal from Ultrasonic Receiver
The output of the rectifier after the signal fed from Ultrasound. The two
ultrasound sends 40kHz for communication and the maximum range for two
ultrasound to communicate successfully is about 30cm.
Figure 3.1.2.3 Amplified 40kHz signal when in range
The output of amplifier after the signal fed from the rectifier. From this
graph , the ripples can be reduced by adding a capacitor and then is able
to turn on the switch.
3.1.3Antenna Coil Testing Results
3.1.3.1 Testing for Two Coil Antenna
The graph on the left shows its correspondence to the theoretical graph
since voltage has a linear relationship with magnetic field.
3.1.3.2 Resonance Frequency Testing
This graph is a measurement of peak-to-peak voltage at receive coil as the
frequency changes and it confirms the coil resonating at 13.5 MHz.
3.1.5Range Measurement
Distance between Two Coil (cm) DC Voltage to the USB (V)
Closest ~0.1 4.17
1. 2.88
2. 1.26
3.1.6Capacitance and Inductance
The measurement of the inductance of the antenna coil is around 0.8uH. The
measurement of the capacitance of the antenna coil is
CHAPTER 4: COST ANALYSIS
4.1 Cost Analysis
Part List
"Description "Part "Price "Quantity"Total "
" " "(R) " "($) "
"Charging ANNEX " " " " "
"Battery Detection " " " " "
"Ultrasonic Transmitter "400ST160 "82 "1 "82 "
"PIC "PIC16F887 "31 "1 "31 "
"5V regulator "KA7805 " 97.20 "1 "97.20 "
"20MHz oscillator "FOX1100 " "1 "97.20 "
" " "97.20 " " "
"Coin Cell Batteries "FOX1100 " 97.20 "4 "388.80 "
"USB Charger " " " " "
"Copper Wire "1ft. " "1 "54.00 "
" " "54.00 " " "
"Surface mount RF Schottky "HSMS 2828 "51.55 "1 "51.55 "
"Diodes " " " " "
"Voltage Regulator "MIC5209-4.2YS "28.41 "1 "28.41 "
"Charging DOCK " " " " "
"Communication System " " " " "
"Ultrasonic Receiver "400SR160 " "1 "97.40 "
" " "97.40 " " "
"Low Pass Filter and Full wave"LMC6482 "25.21 "1 "25.21 "
"Rectifier " " " " "
"Schottky Diodes "1N5817 " 2.07 "4 "8.28 "
"MOSFET "BS270 " " "2.05 "
" " "2.05 "1 " "
"Charging System " " " " "
"AC-to-DC Power Supply "VOF-15-5 "197.46 "1 "197.46 "
"Voltage Divider "LM2681 "31.02 "1 "31.02 "
"Oscillator "ASE2-13.500HZ-ET " "1 "51.40 "
" " "51.40 " " "
"Power Amplifier "BBA-322-A "317.09 "1 "317.09 "
"Balun "XFA-0201-1WH " "1 "200.70 "
" " "200.70 " " "
"Copper Wire "1ft. " "1 "130.00 "
" " "130.00 " " "
"Power Amplifier " 568-6212-1-N "340.00 "1 "340.00 "
" "599-1026-1-N " " " "
Total 2922.57
Grand total: R2922.57
CHAPTER 5: CONCLUSIONS
5.1 Accomplishments
The communication unit with ultrasound works in 30cm apart and the battery
detection through current can be adjusted for needed current in the
electronic devices. The Wireless transmission unit can transfer power from
annex to platform and light up an LED.
5.2 Ethical Considerations
With this responsibility, not only will we reassure that the final
product will meet its expectations, we will assure it is safe for use and
put warning labels on items deemed unsafe if tampered with
Through thorough testing of each component, we will guarantee that our
performance claims are accurate
Ideally this project will further open the door to exploration in
wireless power transfer.
5.3 Conclusions
Through the testing of the USB ports, we were able to fix the battery
detection problem in the beginning. We decided to implement the Hall Effect
sensor and the PIC microcontroller for detection so that the circuit is
able to detect the battery level through USB port which is a more
convenient way to do it. The battery detection module and the communication
unit are able to work as we designed.
We experienced some level of distortion in when the supply of voltage was
220V at 50 Hz Frequency, so we decided to make use of 110 V supply at 60
Hz.
The wireless transmission unit is not able to function as our design that
we expect to see the unit can charge a battery. However, the transmission
does transfer power the charging annex that an LED can be lighted up. The
low power transfer efficiency is due to the low current ouput at the
voltage regulator. A good way to increase the current is to add a current
amplifier after the voltage regulator so that the power is sufficient to
charge the device since the output voltage is great enough in this case
(around 4.1V). In order to charge more different devices, a good impedance
matching is recommended. We can construct an impedance matching circuit by
inserting discrete L and C elements between the balun and the output of the
final stage amplifier to achieve 50 ohms impedance.
Overall, the circuit is able to light up an LED and automatic battery
detection. We could have completed the project as we expected if our
shipping of the components did not take 3 weeks to receive all of them.
5.4 Future work / Alternatives
For the future work, there are many ways to improve the wireless power
transmission. To reduce the size of the coil, we can make a multilayer coil
which can be made planar for easy integration with device platform. We can
also load the antenna coil with ferrite to concentrate the magnetic field
so that the transmission range can be increased. For maximum power
transfer, a 50 impedance matching is needed. We can construct an
impedance matching circuit by inserting discrete L and C elements between
the band and the output of the final stage amplifier. To improve the
transmission range, we can insert more RF power amplifiers and current
amplifier after voltage regulator. For battery detection improvement, we
can try to detect from the output battery level of cell phone's operating
system.
References
[1]. Nikola Tesla, US patent No. 454,622, "System of Electric Lighting.",
1891.
[2]. http://www.transcore.com/pdf/AIM%20shrouds_of_time.pdf
[3]. http://web.mit.edu/newsoffice/2007/techtalk51-30.pdf
[4]. J. ukkar and P. H. Hirschboeck, "Wireless Power Adapter for
Rechargeable Devices", Senior Design Project Report, 2006.
[5]. Allegro Micro systems, Inc., "Fully Integrated, Hall Effect-Based
Linear Current Sensor IC with 2.1 kVRMS Isolation and a Low-Resistance
Current Conductor", [Online Document], October 2011 [cited 5 December
2011], Available HTTP: http://www.allegromicro.com/Products/Current-Sensor-
ICs/Zero-To-Fifty-Amp-IntegratedConductor-Sensor-
ICs/~/media/Files/Datasheets/ACS712-Datasheet.ashx
[6]. Microchip, "PIC 16F887", [Online Document], October 2011 [cited 5
December 2011], Available HTTP:
[7]. Agilent Technologies, "H M -282x surface Mount RF chottky Barrier
Diodes", [Online Document], May 2009 [cited 26 October 2011], Available
HTTP: http://www.avagotech.com/docs/AV02-1320EN
[8]. MICREL, "MIC5209 500mA Low-Noise LDO Regulator", [Online Document],
August 2000 [cited 26 October 2011], Available HTTP:
http://www.datasheetcatalog.org/datasheet/Micrel/mXsvxvq.pdf
[9]. CUI INC, "series: VOF-15 Description: AC-DC Power supply", [Online
Document],
September 2011 [cited 26 October 2011], Available HTTP:
http://products.cui.com/CUI_VOF15-5_Datasheet.pdf?fileID=5125
[10]. National semiconductor, "LM2681 witched Capacitor Voltage Converter",
[Online Document], January 2003 [cited 26 October 2011], Available HTTP:
http://www.national.com/ds/LM/LM2681.pdf
[11]. ABRACON CORPORATION, "2.5Vdc CMOS Compatible SMD Crystal Clock
Oscillator", [Online Document], June 2011 [cited 26 October 2011],
Available HTTP:
http://www.abracon.com/Oscillators/ASE2series.pdf
[12]. LINX TECHNOLOGIE , "BBA eries RF Amplifier Data Guide", [Online
Document], January 2003 [cited 26 October 2011], Available HTTP:
http://www.linxtechnologies.com/resources/data-guides/bba-xxx-a.pdf
[13]. RFMD, "XFA-0201-1WH 1:1 MT Transformer", [Online Document], [cited
26 October
2011], Available HTTP: http://www.rfmd.com/CS/Documents/XFA-0201-1WHDS.pdf
[14]. Access Communications PTY LTD, "U B Reference", [Online Document],
July 2007
[cited 5 December 2011], Available HTTP:
http://www.accesscomms.com.au/reference/usb.htm
[15]. FOX Electronics, "TTL Clock Oscillator F1100E", [Online Document],
1998 [cited 5
December 2011], Available HTTP: http://www.brookdale.com/Fox/f1100e.pdf
APPENDIX A: BLOCK DIAGRAMS
Figures A.1 and A.2 show the transition between our initial design and our
final design.
Figure A.1 Initial block diagram from Design Review
Figure A.2 Final block diagram
34
APPENDIX B: SCHEMATICS
B.1 Charging Platform Final Schematic
B.2 Charging Annex Final Schematic
35
APPENDIX C Battery Testing and Communication plots and pictures
Figure C.1 Hall Effect Sensor Output Voltage vs. Input Current APPENDIX D
Pictures
Picture D.1 The entire circuit with 3 major parts: battery detection unit,
communication unit and
wireless transfer unit
-----------------------
Parallel LC
Antenna coil
pair in the
system
0
5
10
15
20
25
30
35
40
0
2
4
6
8
Distance(cm)
Voltage(V)
0
50
100
150
200
250
300
350
12.5
13
13.5
14
14.5
15
15.5
Frequency(MHz)
Voltage (mV)
3.1.4
Waveform Measurements
Results and Graphs
Oscillator output:
1.77
Vpp @13.48 MHz
1
st
amplifier output:
4.44
Vpp
2
nd
amplifier output:
Vpp
12.74
T
he gain from the 1
st
amplifier output to the
2
nd
amplifier output is
dB which is
9.2
slighltly
off
form
the
typical gian
of this amplifier 13dB.
This is due to the
impedance mismatching.
This is measured by
using oscillascope
connecting to the output
o f the 2
nd
amplifier and
the ground of the circuit.
The output of the
Oscillator is not a
perfect sine wave since
we need to
add a filter
to filter the noise out.
This is tested by using
oscillascope connecting
to the out put of the
oscillator and ground of
the circuit. The gain
from the oscillator to
the 1
st
amplifier is
db
8
which is slightly
off
from
the typical gain
13
dB of t
his amplifier
since the impedance
matching is saller than
the required impedance
50
ohm
Balun output (fed to transmit coil):
33.4
Vpp
Receive coil output:
7.94
-JKLOPQij "?Ÿ ®¯°²ù , - ; < > üìÜ Vpp @13.48 MHz
Bridge rectifier output:
The balun converts the
unbalance signal to a
balance
and differential
signal. Therefore
theoutput of the balun
seems t ampliy the input
signal from the 2
nd
amplifier. Due to the
small resistance causing
the impedance
mismatching, the power
decreases signif
icantly
as the distance increase
and the grea loss of
power
makes the
receive
coil
receiving around
8
Vpp.
The bridge rectifier
rectifies the AC
signal from the
antenna coil to a DC
signal and there is a
loss during this
rectifing process.
Aprroximately each
diode in recitfier
absorbs
V from
1
the
input signal.
2.45
2.5
2.55
2.6
2.65
2.7
2.75
0
0.2
0.4
0.6
0.8
1
1.2
Voltage (V)
Current (A)
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