UNIVERSITY OF LOUISVILLE
Two Electrode Potentiostat
System Requirements Specification
Lucas Bennett
Professor: Dr. Dozier
Sponser: Benjamin Willaims via Dr. Harnett
11/9/2011
Revision 1
This is the System Requirements Specification for the Two Electrode Potentiostat that is to be developed
for use by the University of Louisville’s Electrical and Computer Engineering Department.
ECE 599
Two Electrode Potentiostat
Team 0
0.2 Table of Contents
0.2 Table of Contents .................................................................................................................................... 2
1.
Purpose of the System .......................................................................................................................... 3
2.
Background Information ....................................................................................................................... 3
3.
Operational Concept ............................................................................................................................. 4
4.
System Description ............................................................................................................................... 4
4.1 Major Components ............................................................................................................................. 5
4.1.1 Data Display Management System .............................................................................................. 5
4.1.2 Arduino Development Board ....................................................................................................... 6
4.1.3 Daughtercard ............................................................................................................................... 6
4.2 Functional Requirements .................................................................................................................... 6
4.2.1 Data Display Management System .............................................................................................. 6
4.2.2 Arduino Development Board ....................................................................................................... 7
4.2.3 Daughtercard ............................................................................................................................... 7
4.3 External Interfaces .............................................................................................................................. 7
4.3.1 PC with USB Connection .............................................................................................................. 7
4.3.2 Power Connection ........................................................................................................................ 7
4.3.3 Electrodes..................................................................................................................................... 7
4.4 Internal Interfaces ............................................................................................................................... 7
4.4.1 USB Connection............................................................................................................................ 7
4.4.2 Digital to Analog Convertor (DAC) ............................................................................................... 8
4.4.3 Digital Potentiometer (POT)......................................................................................................... 8
4.4.4 Digital Relay Control Module ....................................................................................................... 8
4.5 Design Constraints .............................................................................................................................. 8
4.5.1 Cost of system must be under $100 ............................................................................................ 8
4.6 System Requirements ......................................................................................................................... 8
4.6.1 Develop an inexpensive Potentiostat for use in a lab setting...................................................... 8
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4.6.2 Document firmware for ease of use and later modification ....................................................... 8
4.6.3 Document Potentiostat so it can be produced by unskilled users .............................................. 8
4.6.4 Log Data for later analysis ............................................................................................................ 9
4.6.5 Provide an Intuitive GUI for user ................................................................................................. 9
4.6.7 Make recommendations for expanding Two Electrode Potentiostat to a three electrode
configuration ......................................................................................................................................... 9
5.
Works Cited ........................................................................................................................................... 9
1. Purpose of the System
The Two Electrode Potentiostat will be designed so that it is easy to reproduce and cost effective in
comparison to the current alternatives. The system will be used in by graduate and undergraduate
students in a laboratory. The purpose of the system is to allow the students to measurements redox
chemistry.
2. Background Information
Dr. Cindy Harnett of The Electrical and Computer Engineering (ECE) Department of the University of
Louisville has the need for several potentiostats in her classroom’s laboratory so students can research
the chemical redox reactions of fuel cells and other devices. Current alternatives lack the optimized
Pontentistat functionality and cost at least a $1,000 to produce. A high quality Pontentiostat for
research could potentially cost well of $10,000 [1].
According to Williams final report, a Potentiostat is a control and measuring device capable of keeping
the potential of a working electrode constant with respect to a reference electrode. It accomplishes this
by adaptively adjusting the voltage output from the Voltage Output Digital to Analog Convertor and the
resistance of the Digital Potentiometer to control the voltage across the CELL.
The Two Electrode Potentiostat system is continuing project from previous semester’s groups of the ECE
department’s ECE 599 ‘Capstone’ classroom. At the time of the project hand off, there were two
previous semesters worth of contribution to the system.
The original student group found open source project materials for the creation of a Two Electrode
Potentiostat device. This open source project, “Ardustat,” was created and implemented as designed
(http://steingart.ccny.cuny.edu/ardustat) by the first semester’s group of students. This system was
developed by Dan Steintgart at the City College of New York (CCNY). Unfortunately, very little
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documentation was provided with this system and thus reverse engineering was required to develop the
system. While some beneficial progress was made from the group, there were errors that left
functionality limited and somewhat inoperable.
A second semester produced another attempt at the creation of the Two Electrode Potentiostat system.
Ben Williams, a graduate student of the ECE department made several successful contributions to the
system. Williams found the misuse of a resistor in the systems board layout. Additionally, Williams was
able to improve the documentation and source of the system’s firmware.
At the current time, the system has been handed off for a third semester’s enhancements. The Two
Electrode Potentiostat is operated by a user via the usage of a Data Display Management System
(DDMS) running on a Personal Computer. The DDMS is accessed by a subpar Graphical User Interface
(GUI). The GUI is cumbersome and unintuitive. Since the measurements of chemical redox reactions are
a very complex procedure, the need for an enjoyable research experience is a necessity.
Simultaneously, there is another group in the ECE 599 class working on a Three Electrode Potentiostat
system. It is the hopes of the class that the two systems can be ran against the same constraints so that
a comparison between the configurations can be made.
3. Operational Concept
The user of the Two Electrode Potentiostat will access the controls of the system via the GUI of the
DDMS. Once in the GUI, the user will have the ability to connect, calibrate and send measurement
configurations to the processor. While the system is taking measurements, they will be relayed on
screen to user. Upon completion of the measurement process, the user will be able to export a CSV file
which can be manipulated by the user to create meaningful graphs.
4. System Description
The Two Electrode Potentiostat is used for the characterization of various devices over voltage, current
and load ranges. There are three major components that form the system: 1) A DDMS running on a PC
operated by a GUI, 2) an Arduino Development Board for firmware execution, 3) A Daughtercard for the
housing of electrical control components.
The DDMS will allow connection, calibration and configuration of measurement testing. Once
connected, the DDMS will communicate with the Ardunio Development Board. In the GUI of the DDMS,
the user will specify the measurement of a cyclic waveform as well as other parameters such as
maximum voltage or current for operating a Two Electrode Potentiostat. While executing the specified
measurements, the results will be displayed to the user on the GUI. Upon completion, the user can
review logged measurements in a CSV file for easy manipulation. The DDMS connects to the Ardunio
Development Board through a Universal Serial Bus (USB) connection.
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According to Williams report, the Arduino will use its onboard Analog Inputs to measure the voltage of
the power source and the voltage across the Digital Potentiometer (POT) and the Digital to Analog
Power Output (DAC). This will allow the Arduino to adjust the resistance of the POT and the voltage
output of the DAC, thus adjusting the output of the power source.
4.1 Major Components
The system is composed of three major components: Data Display Management System and a
Processor.
Figure 1: System Block Diagram
4.1.1 Data Display Management System
4.1.1.1 System Control
The DDMS will control the Arduino Development Board. The DDMS allows the user to specify
certain conditions that are considered when measuring Devices Under Testing(DUT).
4.1.1.2 Data Logging
The DDMS provides the means of logging and storing measurement results of the Two Electrode
Potentiostat for the user. The data will be written to a CSV during testing so that memory
requirements of system are never a threat to the computer, so long as hard drive space is
available.
4.1.1.3 Data Display
During the DUT testing, all current measurements will be displayed to the user live on the GUI
(4.1.1.4) of the DDMS.
4.1.1.4 DDMS Graphical User Interface
The three previous subcomponents of the DDMS will be controlled by a user operating the GUI.
The GUI should provide intuitive means for configuring the routines of the Arduino
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Development Board which in return will provide the user with on-screen live measurements as
well as measurements for a specified amount of time.
4.1.2 Arduino Development Board
The second major component of the Two Electrode Potentiostat is an Arduino controlled
processor system. The main purpose of this component is to manage the data communication of
the entire system. The component will capture configuration information from the DDMS and
specify how the Daughtercard will capture measurements of the DUT. The DDMS
communication is managed through Universal Serial Bus(USB) connection. Upon the
measurements return from the Daughtercard to the Arduino Development Board, this
component will package data up for retrieval by the DDMS.
4.1.3 Daughtercard
The final component of the Two Electrode Potentiostat system is the process of capturing
current measurements across DUT’s by utilizing a two electrode configuration.
4.2 Functional Requirements
4.2.1 Data Display Management System
4.2.1.1 Gathering Input Parameters
For proper measurement of DUT’s, users will need to specify maximum voltages, currents and
loads. For a user to accomplish this, the GUI will entail text field areas for specifying these items.
In addition, the user will also need the ability for specifying the amount of time to run the
measurement process in the DDMS.
4.2.1.2 Transmit Configuration to Arduino Development Board
Once the parameters are specified they will need transferred to the Arduino through a USB
connection.
4.2.1.3 Starting Measurement Process
There will need to be a button to signify to the controller that the measuring process has begun.
4.2.1.4 Exporting Raw Data
There recorded results will need to be exported into a Comma Separated Valued (CSV) format
file. To accomplish this, the need for an export button with in the GUI is a necessity as it will
provide the user with a mindless yet autonomous method for obtaining data in a manipulatable
format.
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4.2.2 Arduino Development Board
4.2.2.1 Capture Configuration
The Arduino Development board will receive the testing configuration from the DDMS and
convert it to executable commands that will be sent to the Daughtercard.
4.2.2.2 Report Results of Measurement Set
The Arduino Development board will need to send received Daughtercard results back to the
DDMS through the USB connection in a readable format.
4.2.3 Daughtercard
4.2.3.1 Execution of Measurement Set
When the Daughtercard received the execution instructions from the Arduino it will need to
execute measurements across the DUT utilizing the two electrode configuration and return
results to the Arduino.
4.3 External Interfaces
4.3.1 PC with USB Connection
This interface will is essential is it provides both a connection between the DDMS and the rest of
the Two Electrode Potentiostat system as well as the proceeding external interface (4.3.2). The
PC itself will provide the means for executing the Graphical User Interface portion of the DDMS
and thus specify and record particular measurements which will be transmitted to the rest of
the system.
4.3.2 Power Connection
Due to the electrical complexity of measuring chemical redox reactions, as well as the inclusion
of electrical components in the system, the need for electrical power is a must. The power for
the Arduino and Daughtercard components will be fed though a USB connection with the PC.
4.3.3 Electrodes
According to Williams report, this board is designed to have one set of leads, a (+) and a (-),
connected to an Analog Input on the Control Board. This connection plugs into the 2.5mm
headphone jack on the Daughtercard.
4.4 Internal Interfaces
4.4.1 USB Connection
The Two Electrode Potentiostat system specifies how the Daughtercard is to measure a given
DUT. Two accomplish this, a system internal USB connection is required. This will allow for the
data configuration and transferal of response signals between the major components of the
system.
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4.4.2 Digital to Analog Convertor (DAC)
According to Williams report, the Control Board communicates to the DAC via a SPI bus, and a
control digital output pin. The DAC can output 0V – 5V, depending on the requests of the
control board.
4.4.3 Digital Potentiometer (POT)
According to Williams report, the Control Board communicates to the POT via a SPI bus, and a
control digital output pin. The POT can set the resistance between a pin and wiper between 0Ω
and 50kΩ, depending on the request of the control board.
4.4.4 Digital Relay Control Module
According to Williams report, the Control Board communicates to the Relay Control Module via
a digital output pin, allowing the Control Board to connect and disconnect the DAC.
4.5 Design Constraints
4.5.1 Cost of system must be under $100
Dr. Harnett’s lab will require that several devices be utilized and thus the need for a cheap
system exists. Since most standard research Potentiostat devices can cost several thousands of
dollars this system will be designed at an affordable cost.
4.6 System Requirements
4.6.1 Develop an inexpensive Potentiostat for use in a lab setting
As mentioned before, commercial potentiostats can cost in the price range of $5,000 to
$10,000. This generally prohibitive researching factor must be avoided. William’s report
concludes this requirement will be satisfied.
4.6.2 Document firmware for ease of use and later modification
According to Williams report, all firmware must be documented at a level that a new user can
come in and modify parameters or add new functionality without having to go through detailed
circuit analysis, or program analysis. William’s report concluded that this requirement has been
satisfied.
4.6.3 Document Potentiostat so it can be produced by unskilled users
According to William’s report, the potentiostat boards must be able to be easily assembled by
unskilled users, such as first or second year electrical engineering students. This will allow for
many boards to be built for laboratory use, while allowing such students to gain circuit
experience. With the materials provided within William’s report, this requirement should be
satisfied.
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4.6.4 Log Data for later analysis
Since the Two Electrode Potentiostat will be used in a classroom setting, data logging is a
necessity. The current GUI running on the DDMS will provide a means for this and thus this
requirement has already been satisfied.
4.6.5 Provide an Intuitive GUI for user
At the time of the project handoff, the GUI will function in a very meticulous manner that an
untrained user will not be able to grasp. The need for a cleaner interface is a must since this
system will be used in a classroom environment.
4.6.7 Make recommendations for expanding Two Electrode Potentiostat to a three
electrode configuration
Upon reviewing the final testing data of the Two Electrode Potentiostat, it is possible the
recommendation for system to have the need to be upgraded to a three configuration model.
5. Works Cited
[1] Rowe AA, Bonham AJ, White RJ, Zimmer MP, Yadgar RJ, et al. (2011) CheapStat: An Open-Source, “DoIt-Yourself” Potentiostat for Analytical and Educational Applications. PLoS ONE 6(9): e23783.
doi:10.1371/journal.pone.0023783
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