1 Micro-processor Controlled Potentiostat -Full Report- By Chris Benton Prepared to partially fulfill the requirements of CSU ECE 402 Department of Electrical and Computer Engineering Colorado State University Fort Collins, Colorado 80523 Project Advisor: Dr. Jorge Rocca Approved by: Dr. Jorge Rocca
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1
Micro-processor Controlled Potentiostat
-Full Report-
By Chris Benton
Prepared to partially fulfill the requirements of
CSU ECE 402
Department of Electrical and Computer Engineering
Colorado State University
Fort Collins, Colorado 80523
Project Advisor: Dr. Jorge Rocca
Approved by: Dr. Jorge Rocca
2
Abstract
I conducted my senior design at the Colorado State University Engineering Research
Center (CSU ERC) under Dr. Jorge Rocca. One of the experiments being conducted at the center
is the Generation of Bright X-ray Sources by Femtosecond Irradiation of Vertically Aligned
Nanostructures, and this is the research group that I worked with. A potentiostat is an
electrochemical device essential to the production of the nickel nano-wire targets used in the
experiment. In order to improve the current production process, I was assigned to design and
build a custom potentiostat for our exclusive use in the lab. The final result of my senior design
was a multi-channel potentiostat that has the necessary features and capabilities for us to grow
nano-wire targets independently at the laboratory, with a cost significantly less than that of
purchasing a commercial potentiostat.
The potentiostats commercially available have many more capabilities than are necessary
to our operation, so the one that I have designed and constructed has only the features necessary
for our experiment. These features include being an enclosed and portable unit, multi-channel
simultaneous operation, and real-time current measurement. I began with the simplest form of a
potentiostatic circuit (a single op-amp design) and planned out how to improve it to operate as
desired. I then added the necessary circuitry to enable it to perform to specification. I stabilized
and refined the design using simple sheet nickel to copper electroplating as an analog for the
electrolytic cells. Following successful demonstrations of stability and performance, I created a
product grade electrical assembly and basic chassis to extensively test the unit design on actual
targets for use in the experiment. I also developed a graphical user interface (GUI) program in
order to control, and receive live feedback from, the unit. With experimentally sound target
production established, a final unit was constructed for permanent use with the lab.
Using these techniques, I successfully designed and built a multi-channel potentiostat
system. The device correctly operates as a potentiostat and has been shown to operate stably,
consistently, and accurately during target growth. It has been verified that the system provides
accurate live feedback on the operation of the cell accurate to 10 microamperes, allows direct,
independant control different potentiostat channels, and can display live data from the device,
plotting trends in current measurement as they occur. The device and interface constitute a nano-
wire growth system that meets all demands of the experiment and is comparable to commercial
units. Thus, the cost of a commercial grade potentiostat was avoided, and two of my units are
currently being used in production of targets for research.
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Table of Contents
Part 1: Introduction
Part 2: Design and Features
Part 3: Development and Stabilization
Part 4: Prototyping and Construction
Part 5: Graphical User Interface and Arduino Code
Part 6: Testing and Target Production
Part 7: Final Units and Continuation
Appendices
4
List of Figures
Figure 1 Experimental Setup
Figure 2 Simple Potentiostat
Figure 3 Block Diagram
Figure 4 Circuit
Figure 5 Current vs. Time Plot
Figure 6 PCB Top Layer
Figure 7 GUI Display Capture
Figure 8 SEM Image 1
Figure 9 SEM Image 2
Figure 10 SEM Image 3
Figure 11 Photo of Complete Unit
5
Part 1: Introduction
At the Colorado State University Engineering Research Center (ERC), one of the
research groups is the National Science Foundation Center for Extreme Ultra-Violet Science and
Technology. The center is exploring the development of compact coherent extreme ultraviolet
(EUV) sources and their applications in challenging scientific and technological problems. The
summer prior to working on my senior design project, I participated the Research Experience for
Undergraduates (REU) program at the center. I decided to continue my experience at the ERC by
conducting my senior design there with Dr. Jorge Rocca, the center director, as my senior design
project advisor.
My time at the laboratory over the summer gave me experience with the tools and
resources available at the ERC, as well as introducing me to the experiment I ultimately worked
with for my senior design project, Generation of Bright X-ray Sources by Femtosecond
Irradiation of Vertically Aligned Nanostructures. This experiment consists (as the name
suggests) of shooting nano-structure targets with a high contrast femtosecond laser and taking
diagnostics of the X-rays emitted (see figure 1). The experiment is dependent upon the
continuous production of the nanostructure targets. These targets are nickel nano-wire arrays
which are grown by electrochemical deposition. The overall motivation for my senior design
project is to better the nano-wire growing operation and to make it an independent process which
can be performed at the laboratory.
The experiment
was being run by
the graduate
students Reed
Hollinger and
Clayton Bargsten.
At that time, the
production of the
targets was
conducted at the
chemistry building
on campus,
utilizing much of
their equipment.
Specifically,
potentiostats.
Potentiostats are
devices used in
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electrochemistry and are essential to the production of the nano-wire targets used in the
experiment. One of the goals of the experiment is to rely less on the use of the equipment owned
by the chemistry department. However, commercial potentiostats can cost in the range of 10,000
to 15,000$. As such it was impractical to purchase one for this experiment alone. The significant
cost comes primarily from the exceptional performance and range of supply values demanded by
certain advanced chemistry applications. However the needs of the potentiostat for nanowire
growth are fairly limited, and so it was decided that we should construct our own. This
potentiostat became the primary focus of my senior design project.
Potentiostats are relatively simple in concept, but must be extremely precise and stable in
operation in order to produce good wires. In the target production process, the potentiostat is
what is used to deposit the nickel and grow the wires. Simple nickel electroplating only utilizes
two electrodes, the anode and cathode. The anode charges the solution and the nickel is
deposited onto the work which is connected to the cathode. Applying a voltages results in the
current through the solution which deposits the nickel. However, the electrolytic cell is a
dynamic environment, with changes in conductivity and variations in current flow that results in
poor production when growing precision structures like nano-wires. As such we use a
potentiostat to grow our wires. A potentiostat in its simplest form (see figure 2) has three
electrodes, the counter, the reference, and the work. The cathode connected to the work is the
same as for regular electroplating. The potentiostat uses a third electrode called a reference
electrode to measure the potential of the plating solution. The potentiostat then regulates the
voltage applied to the
counter electrode in order to
keep the reference at a
constant potential. This is
most often accomplished
through a feedback circuit to
an operational amplifier. The
input voltage is what the
reference electrode is
matched to, and determines
the rate of deposition. Figure
2 depicts a very simple
potentiostat and electrolytic
cell.
In this document, I explain
the process I went through in
creating a potentiostat and support system for the experiment, as well as my methods and
reasoning for design choices. In part two, I show and justify the modifications and improvements
I made to the figure 2 design in order to make a potentiostat suited to our purposes. There were
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many design requirements that had to be met, but following the design phase, I conducted
extensive testing a revision on my circuit. It was necessary to establish an extremely stable mode
of operation for all amplifiers in the design. Any oscillations or large ripples in output during
operation had to be stabilized. The process of testing the circuit and correcting for instabilities is
discussed in part three of this report. Following the completion of a stable and working
potentiostat, I expanded the single potentiostat into a four channel system where each channel
can be controlled independently, and the entire unit can function without assistance from
laboratory supply. Having a single portable unit is necessary to provide a device comparable to
commercial products. In part four, I discuss the process of designing the printed circuit board
(PCB) and the construction of a complete unit. The graphical user interface (GUI) was another
significant part of making the unit a complete working system. The interface was designed in a
software called “Processing,” to run on a personal computer alongside the device. The software
allows for the direct control of the unit, and for live feedback to the operator. The arduino also
had to be programmed to control the unit and communicate with the user interface. The
development of the interface and arduino code is discussed in part five. In part six, I will discuss
the testing procedure performed on the complete prototype, and how the results verified the
device. Extensive operation of the prototype demonstrated that it was time to develop it into its
final form. The final unit, along with its features and performance are discussed in part seven.
Possible future work on the project is also discussed in that section. Multiple appendices are
included for reference and for proper use of the device.
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Part 2: Design and Features
Commercial potentiostats have a wide supply range for a variety of uses in advanced
electrochemistry, however the potentiostat I designed needs to only operate in the supply ranges
we use when growing nano-wire targets. It was also necessary to include significant margins in
order to allow for testing procedures that operate at different values than actual growth
parameters. The many design features I eventually went with come from seven primary design
requirements.
● 4 independent channels
● Control reference voltage and run time
● +/- 5 volt (minimum) reference voltage range
● <1mv ripple stability in output and regulation
● Up to 10 mili-amperes current supply per channel
● Current measurement with 10 micro-ampere resolution
● A single unit that operates independently of external devices
● A PC based user interface to control and observe operations
These design specifications were the guide for all design decisions made for the project. Where I
had a choice in methodology, I would generally choose to emulate the performance of a
commercial potentiostat where practical. I also chose technologies that I could easily learn about,
or that I already had experience with. In this way, I always knew that the project was within my
ability to complete. This was my guide to the design decisions I faced throughout the project.
While a potentiostat circuit itself is relatively simple, it requires a voltage input signal
that can be set depending on the rate of growth you desire. It also requires some way to read and
observe the current measurements. These are all things that can be handled by a microprocessor.
I decided to utilize products from Arduino for this role. Arduino products are praised for their
ease of use, the large amount of community support, and reliability for projects such as these.
Given the extensive resources available for them, they were the obvious choice for my
microprocessor. In addition, many of my peers have or are currently using arduino processors in
their own projects. This meant that I would have immediate help if problems arose during my
work on the project. I eventually chose the arduino mega, as it has enough digital and analog
communications pins to support all four channels of the potentiostat, as well as possible extra
features to add on later.
The challenge with most any microprocessor is how to easily interface with them. The
simplest solution was to connect the arduino with a personal computer. This is the same
technique used by the commercial potentiostat we use at chemistry. From the personal computer,
you can implement a graphical user interface (GUI) that will allow you to control reference
voltage, run time, and display a moving window of the current vs. time plot. The use of a
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personal computer led me to my overall block design of the potentiostat system (figure 3)
The user inputs into the computer the desired run time and voltage which sends the data
to the arduino. The arduino communicates through serial to a digital to analog converter (DAC)
which supplies the reference voltage to the potentiostat that runs the cell. The potentiostat is
connected to the arduino, so that the arduino can measure the current in the cell and passes the
data back to the computer. The computer displays a real time plot on the monitor for the user to
observe during the run. Combined together, these elements allow for a potentiostat and control
system comparable to that of a commercial potentiostat.
While the control systems are essential, the heart of the potentiostat is the amplifier
circuit which regulates the voltage of the counter electrode in the electrolytic cell. The amplifier
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circuit is what actually grows the wires, while everything else is simply a support system. The
rest of the system can only be developed and tested following the completion of the amplifier
circuit. As such, the amplifier circuit was the first objective. In figure 4, you see my design for
the amplifier used in the
potentiostat.
The red circuitry is the
core of the circuit: the
potentiostatic amplifier. This is the
amplifier that actually maintains
the reference voltage to the signal
and is a stabilized version of the
circuit seen in figure 2. The
amplifier is an OPA228, and was
chosen due to the extremely small
(10 microvolt) offset voltage, and
for its rating of up to 45 mA
supply range.
The blue circuitry is
hereafter referred to as the
“puller” circuit. For a potentiostat
to operate correctly, the working
electrode must maintain a zero
potential, but this makes it difficult
to make a current measurement in
this series circuit. As such, I
implemented another OPA228 that
creates a negative voltage across a
measuring resistor, and maintains
a virtual ground at the working electrode, “pulling” current flowing in the cell through the
resistor. In this way, I have a known resistance and measured voltage with which I can calculate
the current through the cell.
Unfortunately, the arduino on board analog to digital converter (ADC) can only measure positive
voltages with a ground reference. As such I built the green circuit, an analog inverter using a
simple 741 op-amp and matched resistors. The output of this circuit can be read by the arduino,
and a current measurement calculated.
By using different size measuring resistors, and by changing the internal reference that
the arduino uses for the ADC, I can change the range and resolution of the current measurement.
However, the best size for measuring during nickel wire growth is 150 ohms. Using the 10bit
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ADC and a 1.1 reference voltage will provide 7.16 micro-amp resolution to the current
measurement, and a range of up to 7.3 mili-amps. The inverting circuit resistors are 1kohm with
an error of .01% making them superbly matched to provide an accurate inversion of the analog
signal.
This circuit design is the final form of the potentiostat, and has been shown to operate
correctly. It was duplicated three more times in order to form the four channel potentiostat which
was the goal of this project. However, the amplifier had to undergo significant development and
testing before being duplicated.
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Part Three: Development and Stabilization
The development and refinement of the circuit took a significant amount of time. This is
because the stability and operational requirements of the potentiostat are extremely strict.
Finding a power supply smooth enough to provide rail voltages is difficult in and of itself. Given
that the resolution goal of the current measurement requires millivolt level accuracy, and that the
reference voltages vary by 10’s of millivolts, a sub millivolt level stability is required in all parts
of the circuit. As such, extensive stability testing and repair was necessary, and a significant
amount of time was dedicated to this.
I conducted the testing process by starting with only a single potentiostatic amplifier (the
blue circuit in figure 4), and slowly adding components and building the circuit larger, stabilizing
the sections as they are added. One of the challenges of testing a potentiostat circuit, however, is
finding an appropriate load for it to act on that will demonstrate correct or incorrect operation. I
began with simple series resistor networks that operated as a voltage divider to provide a
reference voltage. While it does not simulate the capacitive and dynamic nature of an electrolytic
cell, it does show if the op-amps are already in need of stabilizing capacitors. After stabilizing
the circuits operating on resistor networks using capacitors, I used a simple nickel to copper
electroplating process. The actual electroplating solution accurately models a nano-wire growth
run, changing impedance and adding a capacitive quality to the load. Testing was done on the
electroplating solution rather than wire templates due to the cost of the templates being in excess
of 20$.
Initial testing was done at the ERC under the supervision and guidance of Mark
Woolston, who advised on the general placement of stabilizing capacitors. Using his suggestions
I was able to gradually begin to develop my circuit. At this point in time, my circuit required a
minimum of 3 DC power supplies and an oscilloscope in order to perform a test run. Due to low
availability of supplies at the ERC, I used resources in the labs on campus for most of my
stability testing. Using the electroplating solution and Marks advice, I was able to determine
where I needed stabilizing capacitors in the circuit as well as on the power supplies I was using. I
was eventually able to minimize all ripple values to under 1 millivolt in magnitude and was able
to effectively plate nickel to the copper sheets I was testing with.
With a working amplifier circuit, the next stage in the project was to obtain a current
measurement using the arduino, and compare the magnitude and trends with the expected value
given the commercial potentiostat. Eventually this will be done automatically and the arduino
will export the data to be displayed on a computer. As it is, I instruct the arduino to perform 100
analog reads per second, and export them to a serial monitor. I then wrote the values from the
monitor to a data file and imported it into a data analysis program. This cumbersome method
13
demonstrated proof of concept for the current measurement. By using current density and area
calculations, I estimated that the current while electroplating should be about 4.4 mA per square
centimeter. Below is the post processed plot showing current versus time for one of my runs that
ran for 120 seconds (figure 5).
Figure 5
The approximate size of the metal strip I was electroplating to for this test was
approximately one square centimeter. The data show approximate currents of 7 mA. Given the
rough nature of the calculations, the data shows a good correlation to the current density
expected. The trend of the plot is almost identical to the trends observed during actual nano-wire
growth. All of this supports the correct operation of the circuit, with accurate current
measurement.
At that time, the circuit is build on a breadboard with the arduino connected using test
leads. Using laboratory voltage supplies is impractical for a final unit. The next step of the
project was to design complete prototype unit that could operate independently, and be used for
thorough testing of the design.
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Part Four: Prototyping and Construction
The core most any electrical unit is a printed circuit board upon which most of the
electrical components are placed and soldered. Using a breadboard (as had been done up to this
point) is unacceptable in any professional unit, and eliminating it was the first step. The PCB I
designed holds the DAC’s, the four potentiostat circuits, power routing, and acts as a shield for
the arduino. I used the software a fabrication house of ExpressPCB for the design and
manufacturing of the PCB. It is a relatively user friendly software and allows for fast
manufacturing at a low price. The design of the board focused on some key aspects:
● Minimize cross talk between all measurement lines
● Provide clean and organized routing of all traces
● Keep all outputs separated from power distribution
● Minimize board size while keeping components adequately spaced
● Provide mounting for arduino and reliable connections
● Provide labeling for easy reproduction and population of board
● Allow for feature addition with access to unused arduino pins
The schematic and design of the potentiostat transferred to the PCB with no mistakes,
and population of the board went smoothly. The vast majority of the board was designed with
through hole components, such that if testing revealed an issues with a component value, it could
be easily replaced. An image of the top layer of the board can be seen in figure 6.
Figure 6
15
In order to minimize the noise present inside the unit, I decided to use a linear +/- 12 volt
power supply. A linear supply, while more expensive provides a cleaner output, and puts out
minimal RF compared to a switching supply. It was also necessary to include a small board with
low power signal relays. Due to the intrinsic potential of the plating solution to the electrode,
simply setting the reference voltage to zero will not stop the plating process. In order to truly
“turn off” the potentiostat, it is necessary to physically disconnect it from the cell. Relays are
placed in line with the counter electrode output, and when a run is finished, the relay is simply
switched off. This also assigns a binary on or off value to whether or not the cell is running.
The rest of the prototype unit is the hardware consisting of fuses, clip leads, power
sockets, and indicators. All of the electronics and hardware were assembled and mounted inside
of a small project box. With the construction of the prototype unit complete, the only thing
necessary for final testing was an interface to operate the device.
16
Part Five: Graphical User Interface and Arduino Code
In order to make the system complete and user friendly, it was necessary to implement a
GUI to be run on a companion personal computer during operation. A software called
“Processing” allows for easy development of on screen drawings and interaction, as well as
serial communication via USB ports. The coding environment of Processing and that of arduino
are very similar. Using a custom serial communications protocol, I established a method of
communication between the arduino and the interface. The interface would consistently update
the arduino with the state of the run for each channel, while receiving cell current data from the
ADC’s on board the arduino. In this way, the interface had active control over the unit, while
receiving live data on the deposition process.
The arduino only performs a limited set of operations. It receives the values via USB at
which to set the reference voltage for each potentiostat circuit. It then passes along these values
to the DAC’s which send an analog signal to each circuit. It then takes a reading on the value of
the voltage across each measuring resistor and compares that voltage to an internal reference of
1.1 volts. The arduino then sends the data back to the PC via the same USB cable. The arduino
also operates the relays that connect or disconnect each cell, depending on the instructions
received from the GUI.
Figure 7
17
The appearance of the graphical user interface is seen in figure 7. The interface has a
much more complex operation than the arduino. For each channel of the potentiostat, the
interface has an edit button and display for the run time and reference voltage, as well as a start
and stop button. The interface also displays a moving window plot of the currents in the cells,
along with an average of the values displayed and an instantaneous read out of the values being
received. The interface also displays timers to indicate how long a cell has been running, and
how long until completion of the run. The GUI keeps track of the values being sent to and
received from the arduino, as well as boolean state for the operation status of each cell. Much of
the code is devoted to the implementation of buttons that are activated with mouse clicks. The
buttons have active response to indicate whether a value is being edited or not, and even prompts
the user with how to enter data. Due to the setup of the buttons you can edit multiple entities
simultaneously, start separate cells at different times, and even update the deposition parameters
mid run. The code regularly updates the unit with current values and constantly receives current
measurements from the unit. All of this provides for a clean and easy to use interface.
All code for the arduino and the GUI can be found in the appendices.
18
Part Six: Testing and Target Production
The most basic testing of the unit was carried out immediately after completion and
covered basic power up, extended power on periods, extended idle periods, and basic function of
potentiostats on dummy resistor networks.
In particular, measuring the heat buildup in
the unit over extended operation was
extensively investigated to determine if
ventilation was required. However, the
minimal power usage of the device showed
that heat was a non-issue. Outputs of the
power supply and electrodes were also
observed on oscilloscope and were shown
to be within ripple tolerances. With basic
functionality tested, and with previous
electroplating tests showing correct
behavior, it was decided that the unit was
ready to be tested on actual target
templates.
At the time that the prototype unit
and user interface were completed and
initially tested, target production for the
experiment was being performed on
borrowed commercial potentiostats. The
commercial devices were only capable of
running one cell at a time, and production
was under great strain. The two units to
which we had access were being run late
into the night in order to keep up with target
production, as a single deposition can take
multiple hours. After a target is grown and
treated, it is inspected by scanning electron
microscope to verify high quality wire.
Even with commercial devices not all targets
meet requirements, so all targets must be
inspected. Due to the pressure on production, the testing of the prototype unit was conducted by
immediately trying to grow actually targets for the experiment. There was no risk to the
experimental accuracy because any target produced by the unit would be inspected before use.
Figure 8
Figure 9
19
The SEM images of other target had been thoroughly characterized by the researchers to
establish characteristics of high quality targets. The ultimate evaluation of the potentiostat was if
it could produce targets that would pass inspection by SEM.
The demand for targets at that time
include a wide range of potentials and run
times, which would test the limits and
capabilities of the unit. Running the four
channel unit alongside the other two
borrowed units tripled the production of
targets during that week of testing, and
helped to ease the demand of target. All
targets produced by the custom unit were
prepared and evaluated using the SEM,
and they were found to be comparable to
those produced using the commercial unit
and viable for use in the experiment.
Figures 8, 9, and 10 show example SEM
images used to verify the quality of the
wires. The success of those trials indicated that the system was ready for a final version and that
the design was sound and reliable. The prototype unit continued to be used to aid in target
production, while a final version with cosmetic changes was being constructed.
Figure 10
20
Part Seven: Final Unit and Continuation
With the prototype device
operational and tested, I was asked to
construct a second unit, as target production
was still under strain. Building a second unit
allowed me to make cosmetic changes to the
initial design to make it more professional
and reliable. This included adding LED
indicators to each channel on the unit for
extra feedback on the operational status of
the unit, as well as installing more aesthetic
power indicators and labeling. It also
allowed for more organized wiring inside of
the unit, as well as the use of IC cradles for
easy replacement of operational amplifiers
on the board. The two units are functionally
identical, ensuring consistent target
production from both the final and the
prototype unit. The final system was tested
in a similar manner to the first unit, and it
was verified that it too produced good
targets for use in the experiment. A picture
of the completed unit can be seen in figure
11.
Both the final and the prototype units are currently in parallel use producing targets being
used in the experiment, capable of running eight simultaneous depositions. The experiment has
transitioned from nickel to depositing other materials as well, requiring a variety of plating
potentials. Aside from minor trouble shooting, they have both operated consistently for over six
months. Other groups at the research center have also expressed interest in the units, as normal
electroplating is commonly desired, and potentiostats facilitate controlled growth.
Future work on this project would most likely consist of the construction of yet another
unit. Given the PCB files, code, and this report, it should be relatively easy to construct
additional units. If there is ever a need to plate with higher currents, the devices could be
modified by using high current rated amplifiers, and adjusting the internal reference of the
arduino. As for the GUI, there are several modifications that could be made. Some possible
options for improvement are listed below:
Figure 11
21
● Include a feature that allows for exporting the history of a run into a data file
● Allow for two units to be operated from a single PC
● Include active scaling of the plot window in order to view data more closely
● Include auto-turn-off protocols for unusual behavior in cells
● Impose limitations on possible input values to prevent misuse
While there are small improvements one could make to the system, it fulfills all
requirements set out at the beginning of this project. The system is currently being used in
conjunction with the research center experiment, and it has been shown to operate comparably to
a commercially bought system in that context. The final cost of development was also shown to
be significantly lower than that of a commercial solution. Should there be a continuation to this
project, it would be to meet entirely different or expanded criterion.
22
Appendices
Appendix A: Abbreviations
● CSU: Colorado State University
● ECE: Electrical and Computer Engineering
● EUV ERC: Extreme Ultraviolet Engineering Research Center
● REU: Research Experience for Undergraduates program
● LCD: Liquid Crystal Display
● GUI: Graphical User Interface
● DAC: Digital to Analog Converter
● ADC: Analog to Digital Converter
● SEM: Scanning Electron Microscope
● RF: Radio Frequency
● LED: Light Emitting Diode
Appendix B: Budget
The list below contains an itemized cost of a single potentiostat unit.
Part name Part number Cost
Unit enclosure RMCS19038BK1 $78.96
Measuring Resistor x4 Y0785-1.0KA-ND $14.92
Potentiostat amplifier x8 OPA228PA-ND $3.33
Inverting amplifier x4 LM741 $0.70
DAC x2 MAX5322EAI $12.15
Filter capacitors x32 399-9775-ND $0.33
Stabilization capacitors x8 478-5097-ND $0.73
Stabilization capacitors x4 399-9714-ND $0.79
Stabilization capacitors x4 399-9771-ND $0.40
Disconnection relays x4 306-1251-ND $1.63
Power Switch 451-1182-ND $3.65
Relay breadboard V2010-ND $7.33
Linear power supply 179-2305-ND $52.66
23
Neon power indicator 1091-1101-ND $4.32
Channel LED indicators x4 350-2794-ND $2.20
Power cable 839-1179-ND $5.35
USB feedthrough MUSB-D511-00-ND $9.36
USB cable 1175-1413-ND $3.22
AC power connector Q335-ND $0.78
Cell clip leads x8 501-1332-ND $4.34
Cell clip leads x4 923835-GN-ND $14.15
Capacitor x8 493-5956-ND $0.25
Printed circuit board Custom PCB $69.28
Total cost of 1 unit 478.13 not including shipping. The goal of producing a unit for less than $500.00 was met
Appendix C: Past Version of Timeline
*Written Sept 2012*
Timeline Overview: The Potentiostat that is the subject of my senior design is to be used with
an experiment at the CSU Extreme Ultraviolet Research Center. The experiment that I am
working with requires the creation of nanowire targets. The production of these targets uses
a potentiostat to grow the nanowires. The focus of my senior design for the first half of the
year will be the design and construction of a potentiostat for growing these targets. Following
the completion of the potentiostat, I will move on to one of the other long term projects for the
experiment.
First Semester Timeline: September 2012
September:
● Amplifier circuit component selection process
● Component ordering and shipping
● Breadboard testing of amplifier circuit
October:
● Revision of amplifier circuit and project boxing
● Initial Arduino research and familiarization
● Analog and digital interface component selection and ordering
● Acquire components for multiple amplifier circuit channels
November:
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● Arduino development with digital/analog interfaces
● Construction of all four channels of amplifier circuits
● Arduino testing with amplifier circuits
December:
● Development of arduino user interface and PC communication
● Testing and boxing of all components and channels
January:
● Revisions and improvements on potentiostat design
● Add features and more control options to potentiostat
● Begin planning on possible follow up projects to occupy remainder of semester
Second Semester Timeline: January 2013
December:
● Establish a moving window in the GUI
● Transfer the prototype amplifier circuit to a soldered breadboard
● Duplicate the prototype as three additional channels
● Find and purchase all components for rail voltage supplies and DACs
● Perform nano-wire growth and use SEM to absolutely verify good growth
January:
● Implement the DAC as a signal voltage source
● Implement run time and voltage control into the GUI
● Begin work on enclosure box and rail voltages
February:
● Install circuitry and microcontroller in unit with fuses and indicators
● Add features such as LCD current display
● Make improvements on GUI and finalize product
March:
● Possibly begin reproduction of final potentiostat or add features to existing model
Appendix D: Calculations
Current Measurement Resolution:
voltage resolution=reference voltage/(2^ADC bit count)
1.1/(2^10)=1.07mV
current resolution=voltage resolution/Rm value
.00107/150=7.16 uA
Current Density:
total current/(area of exposed target*porosity)=current density
0.005/((pi*0.55^2)*0.12)=4.38mA/cm^2
25
Expected current:
expected electroplating current=current density*plating area