2. 2
Executive Summary
The objective of this senior design project comprised the development of a portable electric field
sensing system that can read data from fields produced by a transmission line. It will be
accomplished by merging two systems; a 3axis analog circuit capable of sensing the electric
field, and a digital data logger that will be able to record the 3axis electric field data. The scope
also includes constructing a sine wave generator circuit that is able to output a 60Hz signal with
low distortion used with a lock in amplifier. The analog system needs to be able to measure and
manipulate the signals from the electric fields and provide power for the digital system, all while
trying to minimize space weight and power consumption. The data logger system should have
the capability to remotely turn on and off when mounted on an unmanned aerial vehicle (UAV).
It must also be able to create a new data file remotely without the user manually creating the file
beforehand. Most of the code for this project was written in C using the Energia development
environment. To design the sine wave generation circuitry, the AD9833 module from Maxim
will be used to generate a sine wave. Testing was done in stages throughout the design process
resulting is a fully successful field test. Overall, the goal to complete the 3axis electric field and
data collection system by the end of December 2015 with as small a budget as possible was
accomplished. The current budget for the analog portion of this project was approximately
$293.34, and the budget for the digital portion of this project was approximately $238. This
comes to a total of $534.34. However it is important to note that this total does not included costs
for what was gifted from previous teams.
3. 3
Table of Contents
Executive Summary1
Introduction5
Preceding Work5
Analog Front End
1. Introduction6
2. Design Approach6
3. Added Circuitry8
3.1 5V Reference Generation10
3.2 Reference Signal Interface10
3.3 1.25V Reference Generation11
3.4 Output Signal Interface11
3.5 Terminal Blocks and Test Points12
4. Testing12
5. Budget15
Digital Front End
6. Introduction15
7. Remote Activation16
7.1 Requirements16
7.2 Implementation16
7.3 Interface with Digital Front End17
8. Sinewave Generation17
8.1 Requirements17
8.2 Implementation18
8.3 Interface with Analog Front End18
9. Analog To Digital Conversion18
9.1 Requirements18
9.2 Timer Interrupt19
9.3 ADC Setup19
9.4 Time and Space Tradeoff19
9.5 Problems and Solutions20
10. Data Acquisition21
10.1 Background of Petite FAT File System21
10.2 FAT File System and Implementation21
4. 4
10.3 Problems and Solutions22
11 Program Flow22
12 PCB Board23
13 Results24
13.1 Spring Semester Achievements24
13.2 Fall Semester Achievements24
14 Budget25
Field Tests26
Recommended Improvements27
Conclusion28
Appendixes29
References40
5. 5
List of Illustrations
1 Schematic of 1D lockin circuitry (Figure 1)7
2 Assembled PCB (top view) (Figure 2)7
3 Assembled PCB (bottom view) (Figure 3)8
4 3Axis Schematic (Additional Circuitry Highlighted) (Figure 4)8
5 Layout of 3D lockin circuitry (Figure 5)9
6 5V reference for MSP430 power supply (Figure 6)10
7 Reference signal interface (Figure 7)10
8 1.25V Reference for shifting circuit (Figure 8)11
9 Shift/Scaling circuit for MSP430 input (Figure 9)11
10 Terminal Blocks and Test Points (Figure 10)12
11 Lab Testing Setup (Figure 11)13
12 Integration with digital team MSP430 (Lab Testing) (Figure 12)13
13 Linearity Plot (Perpendicular sensor 62mm from top capacitor plate) (Figure 13)14
14 Linearity Plot (Perpendicular sensor 3mm from top capacitor plate) (Figure 14)14
15 Analog Front End Budget (Table 1)15
16 Layout of the MSP430F5529 (Figure 15)16
17 Turnigy Receiver (Left) and Receiver Controlled Switch (Right) (Figure 16)17
18 AD9850 (Previous Design) (Figure 17)18
19 AD9833 (Current Design) (Figure 18)18
20 ADC measurements of 60Hz sine wave when ADC clock is 25MHz (Figure 19)20
21 ADC measurements of 60Hz sine wave when ADC clock is 5MHz (Figure 20)20
22 MicroSD Card Module (Figure 21)21
23 Program Flow Diagram for the Data Logger System (Figure 22)23
24 PCB board design (Figure 23)23
25 Circuit used for successful remote activation (Figure 24)24
26 Generation of sine wave from AD9833 (Figure 25)25
27 Power consumption of the data logging system (Table 2)25
28 Digital Front End Budget (Table 3)26
29 Test site with 500kV transmission lines (Figure 26)26
30 Electric field strength of three axis from power line (Figure 27)27
6. 6
Introduction
Modern society heavily depends upon power transmission. Malfunction can occur in segments of
any network due to natural disasters or man made errors. This can bring the activity of a
community to a sudden halt. The ability to monitor and identify the breakpoint in the
transmission line will help to restore power to the community quickly. This, in turn, will reduce
resources and money necessary to maintain a functioning power grid.
The objective of this project is to design a system that will determine the voltage of a power line
by measuring the electric fields. This report will illustrate the design of a system that measures
the X, Y, and Z planes of the electric field. This project was managed by two separate teams with
independent focuses. The first team focused on the analog system. This consisted of designing a
3axis system as well as minimizing the overall size of the analog design. The focus of the
second team was to design a digital data logger system and sine wave generator circuit that will
enable data acquisition from the 3axis analog system. This project is a continuation from the
efforts of past teams who have assembled key components such as a 1axis design. Recently, the
project has seen some important success in collecting actual data from a powerline during field
testing. The final objective of this design project is to incorporate both the digital and analog
components onto a UAV and to demonstrate that electric field can be reliably recorded. All of
these objectives will be combined with efforts to further reduce space, weight, power, and cost.
This report will consist of two primary sections. Each of these sections will illustrate the work
accomplished by each team respectively.
Preceding Work
This project was initiated by Dr. Allee in the Fall of 2013 in collaboration with the US Army
Research Lab. From this work, Dr. Allee was able to demonstrate the linear relationship between
the voltage from a conductor and the output voltage from the lockin amplifier using a Ddot
sensor. From the basis of this work, the first team commenced the project in Fall 2013 and
Spring 2014 to replicate the data collected by Dr. Allee. Their work focused on miniaturizing the
lockin circuitry to take electric field measurements from the transmission line, building a basic
data logger system using the MSP430F5529 to record the electric field on a SD card module, and
constructing an UAV to carry the circuitry that would take the measurement. So far, the first
team has demonstrated a working prototype that gave reliable readings of the electric field. The
second team that finished up during the spring of 2015 focused on expanding the measurement
capability to magnetic field, while maintaining the same level of accuracy and precision
measurement in the electric and magnetic fields.
7. 7
Analog Front End
1 Introduction
As a continuation of a multiyear project, this team will improve upon the single axis electric
field design that was previously developed. The primary focus will be to implement three
dimensional detection as well as reducing space, weight, and power (SWAP) of the current
design. This section details the preceding work, the projects goals, design approach and testing
as well as the budget required to successfully achieve these goals.
2 Design Approach
The miniature lockin amplifier will consist of various electronic components ranging from
resistors to IC chips. The design incorporates four major sections which includes voltage
regulation circuitry, six lock in channels, transimpedance amplifiers and a Pulse Width
Modulator (PWM) to sine converter. The single axis design from the previous group can be seen
in Figure 1. The Ddot sensor is a metal conductor that supplies the input signal to the miniature
lockin amplifier. Electric flux will induce a current on the Ddot sensor which will then be
amplified by the transimpedance amplifier. There will be two channels per axis which will
multiply two sinusoids at a target frequency using an AD630. The first channel is an in phase
representation of the product of two sinusoids, one of which is the signal induced on the ddot
sensor and the other is a created reference signal. The output will yield a signal with both a DC
component and one at twice that frequency. Passing this analog signal through a low pass filter
will eliminate the higher frequency and will then be processed using a digital signal processor.
The second channel will output the same sinusoid, but will be 90 degrees out of phase. The
magnitude of these two channels will be processed within the AD630 and give a pure DC value
that’s proportional to the electric fields. The 3axis version has been designed and implemented
in PCB123’s software. Fabrication of the board has taken place over the summer. In Figures 2
and 3 the assembled 3axis version of the design can be viewed. The board is setup in a way such
that it can easily interface with the digital back end that our peer senior team has designed. Upon
integration of the analog and digital circuity, noise reduction features will be added to the design.
13. 13
Figure 9, the signal is shifted above zero into the positive range that is necessary for ADC. This
portion of the circuit uses the OPA4227 as well as 100kΩ potentiometers.
3.5 Terminal Blocks and Test Points
Figure 10: Terminal Blocks and Test Points on PCB board
In order to keep the circuit cleaner two terminal blocks were added for convenience when
connecting input or output wires; where TB1 contains input signals and TB2 contains output
signals. Adding terminal blocks helped to ensure that wires would not become lose during testing
and create any false data acquisition.
In addition to adding terminal blocks in the layout, test points were also added in order to verify
the right signal was being output at crucial points throughout the circuit. The five blocks located
at the right most corner of Figure 10 are all of the test points available on the board. Going from
right to left the first test point (V_s) is for the voltage shift where the voltage is brought to 1.25
V, and (V5_V) is the 5V reference voltage coming from the board. The next two blocks (V_90
and Vref+) are the reference signal and the reference signal after having gone through the 90
degree phase shift. The last two blocks are the test points for the voltage rails. The smallest
terminal block (TB3) is the input for the reference signal from the MSP430 to the board. There is
also an output for the PWM reference signal created on board that can contain a jumper wire to
the input reference signal point if the internal reference signal wants to be used.
4 Testing
Testing was performed to validate the implementation of the new design. A 20 V peak to peak
sine wave was applied to two copper plates to produce an electric field. To prevent interference
from surrounding equipment, a sinusoidal voltage at 97 Hz was used to create an electric field
across a parallel plate capacitor. For testing in the lab, transimpedance feedback resistors were
set to 200 MΩ. This provided for maximum gain while avoiding clipping of the output signal.
Lab testing successfully validated the new design implementations. In Figures 13 and 14 we
show the linear relationship of the board’s output vs Efield strength. Testing was then
performed to verify the system integration between our board and the digital analysis circuitry
designed and built by another team, which can be seen in Figure 12. Tests confirmed the
successful integration of the analog and digital circuitry. A cube was 3D printed to hold the 3 d
15. 15
0.010 0.100 1.000 10.000 100.000
Voltage Generating E‐Field (V)
0.01
0.1
1
10
Output Voltage (V)
Linearity Plot
Z‐Axis Y‐Axis X‐Axis
Figure 13: Linearity Plot (Perpendicular sensor 62mm from top capacitor plate)
As can been seen in Figure 13, the output has a linear correlation to the voltage that is generating
the electric field. However, the sensors are recording the same data independent of their
orientation. In theory the sensor that is perpendicular to the electric field should be linear while
the other two sensors that are parallel to the electric field should be constant across all input
voltages.
0.010 0.100 1.000 10.000 100.000
Voltage Generating E‐Field (V)
0.01
0.1
1
10
Output Voltage (V)
Linearity Plot
Z‐Axis Y‐Axis X‐Axis
Figure 14: Linearity Plot (Perpendicular sensor 3mm from top capacitor plate)
17. 17
digital and analog components onto a UAV and to demonstrate that electric field can be reliably
recorded. All of these objectives will be combined with efforts to further reduce space, weight,
power, and cost.
Figure 15: Layout of the MSP430F5529
7 Remote Activation
7.1 Requirements
One major issue with the current design is power consumption. As of now, the process of
collecting data with the MSP430 uses 9V batteries, allowing it to run approximately 3040
minutes. In addition, the only way to collect data is to manually activate the process. This is,
however, inefficient when multiple samples are needed consecutively in a short amount of time.
The actual data collection doesn’t take more than 1 minutes, so much of the battery power is
wasted during setup, manual activation, and take down time. One way to conserve battery power
is to install a remote activation feature which allows the MSP430 to be powered on remotely.
This means multiple samples could be taken quickly, allowing the batteries to be used only when
data is ready for collection.
7.2 Implementation
This solution will be implemented through the use of a receiver which relays the signals sent
from the controller to the flight control module. The receiver being used is from the Turnigy 9X
series (seen in Figure 16), which comes with eight relay channels for communication with the
UAV via the flight controller. Four of these channels are dedicated to each of the four motors
powering the propellers. By connecting a fifth channel, we gain the capability of incorporating a
switch from the flight controller to add the needed functionality of an activation switch. Once the
flight controller was programmed to the appropriate switch, we were ready to connect our signal
18. 18
circuit. The Turnigy Receiver Controlled Switch (RCS) (seen in Figure 16) was used to convert
the signal sent to the receiver into an on/off switch. Then, the voltage source was connected to
one end of the switch and the active high pin of the MSP430 to the other end. With this switch
functioning, the MSP430 merely needs to be programmed to receive the signal and respond
accordingly.
7.3 Interface with Digital Front End
Once the RCS was functioning as expected, a large scale test was implemented, involving the
analog front end team. With the MSP430 properly programmed and the analog board ready, all
the necessary connections between the two boards were made. With the RCS connected to the
MSP430 wakeup pin, and with everything else properly connected, the overall tests were
conducted. First we powered on the MSP430, which immediately went into low power mode as
it was programmed to do. In this low power mode (LPM4) the MSP430 consumes 180nA/MHz
instead of the constant 300μA/MHz it would normally consume. The wakeup signal was then
sent to the receiving pin on the MSP430 via the RCS and confirmed that the MSP430 fully
powered up. In addition to waking up, the MSP430 successfully collected meaningful data from
the analog board as it was programmed to do.
Figure 16: Turnigy Receiver (Left) and Receiver Controlled Switch (Right)
8 Sinewave Generation
8.1 Requirements
A clean sinusoidal signal is necessary for this application because such a signal will be used in
the signal processing procedure to separate meaningful measurements from environmental noise.
As noted by the first team in their previous work1
, minimal frequency difference between the
field and reference voltage can cause the output to have ripple. Specifically, when the frequency
difference is greater than 0.1Hz, the resulting ripple is noticeable from the background noise.
Therefore the signal generation circuit must be able to tune to the desired frequency with the
resolution of less than 0.1Hz. Moreover, the new signal generation circuit must consume less
19. 19
than 200mW, the power consumption of the Arduino, in order to prolong the data acquisition
time and improve power consumption.
8.2 Implementation
The previous implementation of the portable sinewave generation used the AD9850, shown in
Figure 17, to produce the reference sinusoidal waveform. Although the module has good
frequency resolution, its power consumption is too high as compared to the theoretical values
specified by the data sheet. When in active mode, the module consumes about 188mW,
compared to the 88mW used when in idle mode. This is probably because the module uses a
125MHz clock. To optimize power consumption, the AD9833, shown in Figure 18, will be used
in the design. This model consumes around 24mW when active and 9.9mW when idle. The
significant reduction in power is due to the fact that the AD9833 implements a lowpower
architecture and uses lower clock speed, 25MHz as compared to 125MHz. Moreover, the
AD9833 at 25MHz can achieve the frequency resolution of 0.1Hz by using a 28bit
programmable frequency registers. This satisfies the requirement that was discussed previously.
Higher frequency resolution of 0.004Hz can be achieved by lowering the clock speed to 1MHz.
Figure 17: AD9850 (Previous Design) Figure 18: AD9833 (Current Design)
8.3 Interface with Analog Front End
Since the signal coming out of the AD9833 module is only positive, a voltage shifter circuit will
have to be created in order to center the sinusoidal waveform about the 0V level. A phase shifter
circuit will also be needed to obtain a sinusoidal output that is 90o
out of phase with the original
waveform. These two circuits will be implemented using simple op amp circuit configurations
and created by the analog frontend team in order to achieve better integration with the analog
circuitry.
9 Analog to Digital Conversion
20. 20
9.1 Requirements
Data coming from the analog front end must be digitized and stored into a SD card to allow
further analysis. To achieve this objective, the analog and digital conversion (ADC) module of
the MSP430F5529 will be used. This module must be able to achieve the minimum sampling
rate of 1kHz with adjustable means to allow the module to run at different sampling rate. The
ADC should utilize the highest possible resolution in order to capture accurate data and be able
to capture analog data on six analog channels.
9.2 Timer Interrupt
Energia IDE has a builtin function that allows users to easily delay the program by a specific
amount of time. However, this method is not ideal for obtaining an accurate sampling rate since
it introduces a delay to the whole system, thus wasting CPU resources that can be used for
something else. In order to overcome this problem, the timer module is used to precisely tell the
ADC module when a new sample should be taken. This is accomplished by loading a value into
a 16bit register of the timer. Whenever the timer increments to this value, a signal is sent to the
ADC module to signal collection of another round of analog data. Decreasing the value in the
timer increases the sampling rate and the same can be said in reverse. Timer utilization to trigger
the ADC module has two advantages: first it allows precise timing to obtain a precise sampling
rate, and second, it allows the whole program to flow without delaying the CPU to obtain analog
data.
9.3 ADC Setup
In order to obtain maximum performance from the ADC module, setup of the ADC module must
be configured appropriately for a given application. Energia IDE has a builtin function to allow
the user to easily obtain analog data from any given analog channel. For this given application in
which sampling rate can be high, calling the builtin function to obtain analog data introduces a
lot of overhead because the builtin function reinitializes the ADC module every time the
function is called. This is made worse since we have to sample six analog channels while trying
to obtain the minimum delay between each channel. To overcome this challenge, the ADC
module will be initialized to take analog data from a sequence of channels at the beginning of the
program flow. When the timer triggers the ADC module, the module will run through each
channel in sequence and collect one sample from each channel in order to minimize the delay
between channels.
9.4 Time and Space Tradeoff
In order to have the fastest sampling rate, data from the ADC module must be stored to a
temporary buffer so that it will not be overridden by new data that comes into the ADC. This is a
problem due to the fact that the time it takes for data to be written into the SD card is an order of
magnitude slower than the sampling rate. One way of storing this data is to store it into the RAM
buffer since RAM has the fastest access time. However, the MSP430F5529 only has around 8kB
of RAM memory on it. This could limit the amount of sample data that we wish to take. To solve
21. 21
this problem, flash memory can be used as a buffer instead. While the MSP430FF5529 has
128kB of flash memory on it, the access time for this memory is significantly slower than the
RAM. This will reduce the maximum sampling rate that we can achieve with the MSP430F5529.
We will use RAM as our buffer since the sampling rate is higher priority.
9.5 Problems and Solutions
One of the problems facing the team when developing the ADC system was overclocking the
ADC module. The initial plan was to clock the system with the maximum clock speed, which is
25MHz, in order to minimize the time delay between channels as much as possible. However
overclocking the ADC module at this speed results in distorted measurements at half the range of
the reference voltage. The results are shown in Figure 19 for the input of a 60Hz sinusoidal
wave. To rectify this problem, the ADC module is configured to run at 5MHz clock speed, the
maximum clock speed recommended by the datasheet. This reduction in clock frequency results
in much smoother and accurate measurements in all six channels as shown in Figure 20. Another
potential problem that the team faced is the fact that MSP430 can be powered through the ADC
channels if the voltage on those channels exceed 3.3V. In this case, disconnect the ADC channels
so that power consumption does not fry the MSP430 and make sure that the voltage is between
0V and 3.3V.
Figure 19: ADC measurements of 60Hz sine wave when ADC clock is 25MHz
22. 22
Figure 20: ADC measurements of 60Hz sine wave when ADC clock is 5MHz
10 Data Acquisition
10.1 Background of Petite FAT File System
In order to collect data from the MSP430 microcontroller, the Petite FAT file system was
implemented to allow seamless transfer of data between the microcontroller, SD cards, and the
general computer. This architecture of data storage requires minimal amounts of memory
storage; however, the file system only allows appending new data to an existing file, not creating
new files on the fly. This limitation greatly diminished the ability of the UAV to take multiple
segments of data without overwriting the old data in flight. The ability to create new files to store
different measurement blocks will greatly enhance the readability of the data.
10.2 FAT File System and Implementation
The plan to acquire data will be accomplished by interfacing the MSP430 microcontroller2
with a
Secure Digital (SD) card using a FAT16 format and a microSD card module as shown in Figure
21. The SD card is a type of flash memory card designed as a removable storage device with a
Figure 21: MicroSD Card Module
9pin interface. There are three different modes of operation: Serial Peripheral Interface (SPI),
onebit SD, and fourbit SD. SPI will be the mode of operation chosen. The plan is to upgrade
from the Petite FAT file system to the FAT file system to provide more features, such as
appending an existing file, creating a new file, etc. This file system will allow the
23. 23
microcontroller to create a new file every time it is instructed to record data using a switch on the
flight controller.
In order to implement the FAT file system, the team has adopted using one of the FAT file
system libraries created for the Arduino platform. The reasons for this implementation are first,
similarity between the MSP430 platform and the Arduino platform reduces the development
time, and second, the encapsulation of the hardware specific functions allows developers to focus
on the software functionality. Since the MSP430 platform shares much similarity with the
Arduino platform, only slight modifications are needed in order to make the library work with
the MSP430 microcontroller. These modifications include changing the hardware pin so that it
matches with the MSP430 SPI pin layout and deleting header files that are specific to the
Arduino platform. Moreover, this library implementation hides away the intricate complexity of
the working of the SD card and the FAT file system. Functions like open() and close()
automatically recognize the current directory where a new file should be created as well as
naming, formatting, and closing the file on the fly.
10.3 Problems and Solutions
Since the MSP430F5529 has one SPI module, this forces the team to tie the sinewave generator
AD9833 and SD card to the same common pins on the microcontroller board. A test was carried
out in the lab to determine whether or not sharing the same SPI module would affect the
functionality of either the AD9833, or the SD card, or both. It was determined that the initial
configuration of both peripherals went smoothly. However, when the communication is switched
to the SD card during midoperation, the microcontroller was unable to detect the SD card. This
is a problem since field testing will require the microcontroller to switch between the AD9833
and the SD card. In order to rectify the problem, other digital pins are used to simulate SPI
communication with the AD9833. Although using other digital pins that are not designated to be
used in SPI communication results in lower communication speed, it is not a concern in this
application. We only wish to turn on and off the AD9833, not see how fast we can communicate
with it.
11 Program Flow
The program flow of the whole system is shown in Figure 22. The program starts out initializing
all the variables necessary for the process. These include sampling rate, pin configurations, data
buffer, and file names. The process will subsequently put the microcontroller into sleep mode in
order to conserve energy. While in the idle mode, a remote switch can wake up the
microcontroller through an interrupt process. The interrupt will then disarm itself so that it does
not trip itself during the main process. The program flow will then proceed to enable the
AD9833 (the portable sinewave generator mentioned above) together with the timer peripheral
and create a new file on the microSD card. Then the system enters the main loop where it will
check for new data to be put into the SD card. Inside this loop, the timer interrupt can start the
24. 24
writing process in order to collect ADC samples at regular intervals. After all data has been
collected and written into the microSD card, the program proceeds to disable the AD9833, the
ADC module, and the timer interrupt. It will then rearm the remote switch interrupt and go back
into the sleep mode.
Figure 22: Program Flow Diagram for the Data Logger System
12 PCB Board
Various components such as the AD9833, MSP430, SD card and GPS are all required to
complete the proposed design. However, connecting these components proved to be challenging
and messy. To remedy this complication a PCB board was designed, this board can be seen
below in Figure 23. This board helps resolve a few problems, the first of which is wiring. It
would be devastating to the system if a wire got caught in a propeller or disconnects due to
turbulence. In addition the PCB design also aids in making the overall system compact. All of
the components have been incorporated into this board and will allow for a clean stacked design.
25. 25
Figure 23: PCB board design
13 Results
13.1 Spring Semester Achievements
During the semester a lot of headway was made for the project. There were two main goals to be
achieved this semester and the group was able to accomplish both. The first task as stated above
was the remote activation. This task was accomplished by splitting up the work into two
sections, the MSP430 and the receiver for the wireless controller. First the MSP430 was
programmed to stay in sleep mode then when it receives an external signal it will interrupt the
sleep mode and run the program. From here the receiver and receiver controlled switch
combination enables the signal from the controller to reach the MSP430 and trigger the external
interrupt. The group was able to successfully test this design and Figure 24 below shows the
circuit used for the remote activation. In addition to the success of the remote activation the sine
wave generation was also tested and solved with the aid of the AD9850 board. The team was
able to program the AD9850 board to generate a sine wave signal. Not only was it a success but
the sine wave it generates is accurate as well. The wave generated was within a range of +/
0.01Hz when set to 60Hz.
13.2 Fall Semester Achievements
In the second semester, the team decided to switch to the new model AD9833 after testing with
the AD9850 revealed that the old model consumed too much energy. FAT file system and ADC
module were implemented in order to collect analog data and store it to the microSD card. Steps
were taken in order to ensure that the program flow was smooth and flexible in a way that it
allows others to change the sampling rate or the output of the sinusoidal frequency with
minimum modification to the main code. Shown below is also the table detailing the power
consumption of the system.
27. 27
MSP430 0.99 24.75
Total 11.22 185.7
14 Budget
Throughout the semesters there were a few purchases that need to be included in the budget.
First, two separate AD9850 boards were purchased for the purpose of the sine wave generation.
Dissatisfaction with the AD9850 forced the team to purchase AD9833. The second item is the
switch used for the remote activation. The third item purchased by the team is a set of
rechargeable 9v batteries. These will be used to power the boards. The fourth and final item
purchased is the PCB board. This board will be used to simplify the combination of all the
components used in the design. There are a number of other parts also used in the design that
were previously purchased. Table 3 shows a budget of the various parts including the extra
AD9833 board.
Table 3. Digital Front End Budget
Item Quantity Total Price($)
AD9833 2 14
MSP430F5529 Microcontroller 1 10
SD card booster pack 1 7
9V Rechargeable battery 4 25
APM 2.6 1 60
Switch adapter 1 12
PCB board 2 110
Total 238
Field Tests
Field tests were conducted in order to test the validity of both the analog and digital parts under
real world application. The tests were conducted in an open dirt field with the testing apparatus
situated midway between two power line poles to avoid any electric field line anomaly. A stake
was driven to the earth in order to establish the most stable ground for the whole entire system.
Picture of the test site is shown in Figure 26. Data points were taken 5m apart for the total of 10
data points. Field data was then analyzed and graphed in MATLAB. The results are shown in
Figure 27. From the graph, voltage of all three axis are proportionally inverse with varying
distance. However, magnitude in the x axis is significantly less than the magnitude in the other
axes. This should not be the case since lab results indicated that all axes must have roughly the
same magnitude. Future improvements to the project must understand, and be able to eliminate
this problem.
29. 29
PCB. This way the whole design can be flat and narrow. Thus distributing the weight on the
quadcopter and simplifying the circuit.
When looking at the digital side specifically, there are two methods of taking data from the ADC
peripheral and passing it through to the microcontroller RAM. The first is to explicitly write the
code to take the data from the ADC and pass it through to the RAM buffer. Another approach is
to use Direct Memory Access (DMA) in order to transfer data from the ADC peripheral to the
specific location in the RAM. Due to limited time on the project, the team chose to go with the
first method due to its simplicity. However, it is recommended that the second approach be
implemented in the future. This is because DMA does not require the microcontroller processing
time in order to transfer data to the RAM. Instead the DMA peripheral bypasses the
microcontroller and transfers data directly into the RAM. This method requires less time as
compared to the first method and potentially reduces the latency between measurements from
each ADC channel.
In addition, the team found that it would be desirable to know the location where each
measurement was acquired in the field. This can be done through implementation of a Global
Positioning System (GPS). In addition to the writing transmission line data to the SD card, the
team recommends that GPS data also be written to the SD card to show where the transmission
line signal was measured.
Even though the team was able to scale down the power consumption of the MSP430 hardware,
power consumption of the MSP430 Launchpad hovered around 50~60mA. This can be explained
by the fact that the Launchpad also includes an eZFET onboard. This peripheral allows a
programmer to debug the MSP430 through USB connection without using a JTAG device. In
final production, a custom circuit should be built in order to eliminate unnecessary peripherals
that increase the overall power consumption. However, at this testing stage, we encourage any
future endeavor to use the Launchpad out of sheer convenience and a custom circuit should only
be built when everything is finalized and ready for production.
Conclusion
The overall purpose of the project consisted of two primary tasks; to build an analog circuit that
can sense electric field from the power line in three dimensions and to build the digital circuit
that is capable of storing 3D electric field information to an SD card using the MSP420F5529.
We have demonstrated that the whole system works in the lab as well as in the field by showing
that the electric field is inversely proportional to distance. However, there is much more work to
be done in the future in order to bring the system to manufacturing stage. These include building
a customized circuit that houses both the analog and digital parts in order to improve cost,
weight, and power, incorporating GPS into the system in order to accurately pinpoint the location
