Iowa State University

Smart Civil Infrastructure Monitoring Design Final Report

(May 12-26)

EE 492

Project Client

Laflamme Simon

Faculty Advisor

Randall Geiger

Project Team:

Xianbo Tao (Electrical Engineering)

Kun Zhang (Electrical Engineering)

Guoyan Kai (Electrical Engineering)

Table of Contents

Section 1: Planning………………………………………………………………………………3

1.1 Requirements/Specification:

1.1.1 Problem Statement ………………………...... 3

1.1.2Concept Description ………………………………………...... 3

1.1.3Concept Diagram ……………………………………………...... 4

1.1.4Operating Environment……………………………………...….….4

1.1.5User interface Description…………….……………………..……..4

1.1.6Functional Requirements…………………...………………………5

1.1.7Market / Literature Survey…………………………………..……..5

1.1.8Deliverables………………………………………………...………5

1.2Project Plan:

1.2.1 Work Breakdown………………………………………..………….6

1.2.2Resource Requirements…………………………………………….6

1.2.3Project Schedule……………………………………………………7

1.2.4Risks………………………………………………………………..7

Section 2: Design…………………………………………………………………………………9

2.1 System design:

2.1.1 System Requirements………………………….……….….…………9

2.1.2 Functional Decomposition………………………...…………………9

2.2 Detailed design:

2.2.1 HW/SW Specifications…………………………………..…………10

2.2.2 I/O Specifications…………………………………………...………11

2.2.3 User Interface Specification……………………………………..….12

2.2.4 Test Plan…………………………………………………………….12

2.2.5 Simulation / Prototyping……………………………………………12

Section 3: Implementation/Testing…………………………………………………………….18

3.1 Prototype:

3.1.1 Build………………………………………………………..……….18

3.1.2 Test Results………………………………………………………....21

3.2 Project Closure:

3.2.1 Conclusions / Lessons Learned……………………….…………….23

3.2.2 Future Work……………………………………………..………….23

Section 4: Appendix: Operational Manual…………………………………………….25

Section 5: Team Member Information ……………………………………….…...….30

1. Planning

1.1 Requirements/Specification

1.1.1Problem Statement

There is considerable concern about the long-term safety of the aging civil infrastructures in the country. This concern relates to bridges, buildings, public transportation and public utility systems such as conventional and nuclear power plants. Monitoring or inspection to identify potential problems and prevent catastrophic failures is one way to help mitigate the growing concerns.

In this project we will focus on the development of a smart civil infrastructure monitoring system. This system will use state of the art stress sensors and wireless communications to provide real-time stress data to a WEB-accessible database that can be regularly monitored to detect potential problems. This project will be supervised by Professor Randy Geiger in consultation with faculty members in the Department of Civil and Construction Engineering who are working on the development of new sensors and their application in smart civil infrastructure modeling.

One sensor that will be used is a soft capacitive membrane sensor that was recently introduced by Dr. Simon Laflamme as part of his doctoral work at MIT prior to joining the faculty at Iowa State University in the CPrE Department. Strain-gage type sensors will also be considered. In addition to applying these sensors to physical members in structures such as bridges, application of sensors to the blades of wind turbans will be considered. In this latter application, energy harvesting will be considered as a means of powering a wireless communications interface that transmits stress data to an intermediate node which will subsequently use wireless transmission for connection to the WEB-accessible interface.

1.1.2Concept Description

The entire system is made up by an array of capacitors, wireless communication transmitter, a receiver such as cell phone. The array of capacitors which is attached to is designed to detect the stress of the bridge.

Our project’s goal will mainly on the use of these capacitors to collect data. Each capacitor will compare with its neighbor by subtraction when it encounters stress; and the delta-capacitor function is determined by its intrinsic property from manufacture, temperature, and stress.

Instead of approaching to a bridge, we will set up an equivalent model in lab to test the stress-capacitor function. 200pf capacitor will be used and a switch connected to 2pf capacitor as delta-capacitor due to stress by just turning on or off the switch to make same effect as the capacitor encounters stress. When the capacitor changes too much that exceed stress the bridge undertakes, thiscircuit will output a voltage varied with the capacitor change. The voltage change will be transmitted to ArduinoDuemilanove; then a computer will store the data and send voltage data to user’s cell phone wireless.

1.1.3Concept diagram

1.1.4Operating environment

  • A bridge to work with
  • Make all the equipment in same moisture, sunshine, temperature.
  • Accessibility to supply power
  • Computer signal accessible

First of all, our project main goal is to ensure the safety of the bridge, so we must have a bridge to complete our project.

Secondly, some capacitors, resistors and some other equipment are highly dependent on the temperature or environmental factors. So, if they are not in the same situation, the data we get will not accurate.

Finally, we need a supply power to make sure the circuit works. In most places, we will have Wi-Fi signal for sure.

1.1.5User interface description

The user provided with a cell phone will be informed of the current condition of the bridge, voltage data.The user interface side of the system was split into the programs running on the Arduinoin user’s computer and Logmein in user’s phone and computer.The Arduino was responsible for both capturing the output of both voltage sensors,and sending the measured data with in real time over the wireless connection to the base station. Thebase station was responsible for reading the data from the Arduino, converting the raw data intovoltage information. Finally the user can access to real-time data from the cell phone. Logmein should be installed on both computer and cell phone. This software is used for cell phone to remote control the computer to get voltage data.

1.1.6Functional requirements

  • Different types of routers will not affect the entire communication.
  • The interface is supposed to require little technical experience which makes common people to operate.
  • Capacitive sensors shall overcome the interruption of other natural force such as wind and rain just collecting data from condition of bridge.
  • The wireless network should be reliable and stable to send data to the user constantly.
  • The transmitter shall have sufficient defense to protect itself working in an urban and rural environment. The weather change will not affect its function.
  • Some factors such as its intrinsic property from manufacture, temperature, and stress will affect the value of capacitors
  • The duration of the transmissionfrom user’s computer to cell phone should be synchronized.

1.1.7Market / Literature Survey

It’s just a new born detection in our research field. our products can be marketed to the normal citizen and research place. Also, our device can be used by the state government some real estate, they can set our device into their buildings or bridges, detect the flaw, and make sure the safety.

1.1.8Deliverables

This product can be used by the bridges and even buildings that get a long age. Then we can detect the specific place where the bridges or other things’ inner structure changes that can cause the bridges crash. So we can find out the bridge which has the flaw in time, and make the decision.

1.2 Project Plan

1.2.1 Work breakdown

1.2.2Resource Requirement

1.2.3 Project Schedule

First Semester:

Week 1-3:

Build a website for our senior design project. Make an appointment with advisor and client to talk about the contents of project, and go to the place where we will use our project, then we get known with teammates, and set up weekly meeting time with advisor and teammates.

Week 4-9:

Construct a certain concept for the project, we basically have two main parts, one is circuit design, and data transmit. Divide task into each group members.

Week 10-13:

Realize the structure based on the concept. Find problems existing for each stages of the concept and solve them.

Week 14-15:

Prepare for the presentation, finish the design document, project plan, and set the goal for second semester.

Second Semester:

Week 1 -4:

Choose the best design from several designs proposed by last semester, make design circuit into realistic circuit, and test the circuit, and figure out problems for the realistic circuit.

Week 5 – 11:

Because all of us three are EE students, we need to take some time to deal with the basic material and knowledge of data transmits using the microcontroller.

Week 12 – 13:

Fix small problems, and make the circuit more stable, hoop up to microcontroller to display output signals showed on computer screen, and remote control byan iPhone.

Week 14 – 15:

Prepare for the final presentation, report, and demo.

1.2.4Risks

Our circuit is measuring the difference of the capacitances, and our circuit is hooked under the bridge, so when cars are driving through, this can affect the capacitances, so it may affect our measurement, and we have to care about this issue.

2. System Design

2.1. System design

2.1.1 System requirements

The smart civil infrastructure monitoring system is used to detect whether the crack or broken point happened on the bridge or not.The small capacitance measurement circuit is able to the voltagedifference of two capacitors in very small changes, like 0.1 pf. These voltagedifferences reflect the stress of the bridge undertaking.Additionally, the input to the circuit is supposed to be sine wave, so the design another circuit that provides sine ware is required. AWien Bridge Oscillator and AGC circuit satisfies this need. In order to detect the peak value of output sine wave, a peak detect is added to the small capacitance measurement circuit. A microcontroller will store the stress data and analyze the data which will send touser’s computer.A receiver such as a smart phone will pick up the signal by Wi-Fi. The smart phonecan get the stress data of the current condition of the bridge. Through the phone, professional bridge constructors can remote control the computer to access updated data.When voltagevalue exceeds thethreshold voltage, 0.21V for 180pf capacitor, the bridge should be shut down and constructors would go to the bridge to fix it where crack happened.

2.1.2Functional decomposition

  • Many pieces of soft capacitors are stickled under the bridge. If there is crack existing on the bridge, it will stress the soft capacitors so that the capacitance of some stages will change somehow.
  • The circuit designed for capacitive sensors has a function to take subtraction of capacitors so that the location of the capacitors changed can easily be found. Differential amplifiers play an essential role in the design.
  • AWien bridge oscillator and AGC circuit provides stable sine wave with frequency 1578Hz for input of the small capacitance measurement circuit.
  • The real-time stress data reflect delta function of capacitance, which will be analyzed by a microcontroller. A program is made to deal with the data and interface with hardware.
  • Since the Arduinoboard fails to detect the peak voltage of the small capacitance measurement circuit at output terminal. A peak detector should be passed by before the Arduino. The detector should successful measure peak values.
  • TheArduinoboard reads peak values from its analog input at pin 0.It will convert analog signals to the digital.
  • The Arduino software can convert the digital back to the original so that real-time stress voltage can be stored in computer.
  • Asmart phone will pick up the signal by radio. And computer will get the stress data of the current condition of bridge. Also, the iPhone can remote control the computer. For the control, LogMeIn is good software to make the need meet. Some professional bridge constructors will go to the bridge where crack happened.

2.2. Detail design

2.2.1 HW/SW specifications

Hardware

  • Small capacitance measurement circuit

The main function of the circuit is to measure capacitance change based on voltage change. Relavantciruitssuch asWein bridge oscillator, AGC and peak detectorare required to make this circuit successfully function.

  • ArduinoDuemilanove

The Duemilanove is a self-contained USB development board centered on an ATMega328P. For this project, the 9V DC battery was used for power. The voltage circuit connects to the Arduino board through analog pin 0. This allows the Arduino to sample the output voltage from the current measurement circuit with the ATMega328’s 10-bit ADC. The USB connection on the board was used for programming the chip and getting serial output for troubleshooting. The interface between USB and the ATMega328’s UART was provided by the Arduino’s built in USB to serial converter chip. The device showed up as a virtual COM port on the host PC, and could be interfaced with any program capable of reading and writing to a serial port.

  • WiShield

The WiShield contains an 802.11b compliant wireless module that handles the network, data link, and physical layers of the design’s wireless connection. The board came preassembled from AsyncLabs, thus no major hardware assembly was required for the wireless portion of the circuitry. Female headers with male leads underneath were included on the board, so that the WiShield was inserted into the Arduino main board’s female headers with no soldering required.

Software

  • The software side of the system was the program running on the Arduino on the base station. C language is required. The Arduino was responsible for both capturing the output of both voltage sensors, and sending the measured data with time over the USB connection to the base station. The base station was responsible for reading the packets from the Arduino, converting the raw data into voltage information, and presenting it to the user in a clear fashion.

2.2.2 I/O specifications

The input to the Wien Bridge Oscillator is DC voltage of 15 V. AGC circuit can generate a table output sine wave with frequency of 1578 Hz and 1V-Vpp. We need to provide bias voltage of 15 V for all amplifiers we use. The output of the small capacitance measurement circuit is a sine wave. The peak detector can figure outpeak values from the of the small capacitance measurement circuit, so its output is a dc voltage which is expected to be proportional to capacitance changes.

2.2.3 User interface specification

The user interface isLogmein whichprovides software as a service-based remote connectivity from smart phone and computer. It should be downloaded on both smart phone and computer from Apple applications.smart phone and computer should be in the region of Wi-Fi coverage The user can get in and go with remote access from Logmein to work from anywhere by accessing desktop of PC.To setup the software, the user should input user name and password of his/her computer to the software as a log-in account. After that the software will automatically get access to desktop of PC through Wi-Fi network. All the data on PC are available to users.

2.2.4 Test plan

First of all we design the small capacitance measurement circuitthat can accurately measure small capacitance changes in the function of voltage. These output voltage should be consistent with our theoretical analysis. Specie is a good tool to plot the theoretical sine outputs which are closed to the outputs of the board circuit measurement from scope. Then we tested stable sine wave outputs of Wien bridge oscillator and AGC. The Arduino board works well from transmission of analog data to computer. Finally, iPhone displays voltage value of the peak reflecting stress of the bridge.

2.2.5Simulation / prototyping

This is the schematic of the small capacitance measurement circuit. The simulation is done in OrCAD Capture. The input is sine wave with frequency of 1578Hz.

Capacitors we tested are 179.3pf, 179.47 pf, 178.57 pf, 179.44 pf, 180.36 pf, 180.58 pf, and 181.94 pf. The differences of each two capacitors are calculated in the table below. The corresponding simulated voltage outputs are recorded. For simulated graphs, red curves are input sine wave, and green curves are outputs.

179.3p- 179.47p simulated vaule: 0.198939V

179.3p-178.57p simulated vaule 0.856517V

179.3p-179.44p simulated vaule 0.163845V

179.3p-180.36p simulated vaule: 1.2378V

179.3p- 180.58p simulated vaule: 1.4935V

179.3p – 181.94p simulated vaule: 3.0684V

179.47p – 178.57p simulated vaule: 1.0554V

179.47p – 179.44p simulated vaule: 0.035094V

3. Implementation/Testing

Abstract: Since we come up with some concepts and ideas to figure out the solution that our project addressing on, we have to implement and test the result practically. The prototype is divided into two parts; one is how to build the system; secondly, whether the testing result matches what we expected based on concept.

3.1 Prototype

3.1.1 Build

The purpose of our project is to detect the small capacitance change between two stages (two soft capacitor sensors). We divided out measuring system into four stages: Wien Bridge Oscillator, AGC circuit, small capacitance difference measurement circuit, and precision peak detection circuit. Overall structure showed following:

Small Capacitance Difference Measurement Circuit

Two blocks represent two soft capacitors sensor. We hook up the soft capacitor under the bottom of the bridge. The capacitance will change if the crack happens on the bottom of the bridge, because it will stress the soft sensor. It will cause the voltage difference of the input of two buffers. Furthermore, it will have output voltage difference at the point A. Based on the transfer function of small capacitance difference measurement circuit; we can easily to manipulate the output change based on the input change. The transfer function showed following:

The limitation of this circuit

We have to concert about the bandwidth of the operational amplifier. Also we need to consider about the enough gain to clearly catch the small output voltage change based on small capacitance change.

How to get a fixed AC input for this circuit.

How to collect the output and transmit into a microcontroller.

Wien Bridge Oscillator and AGC circuit

This is a brilliant solution to solve the limitations from previous part. We design a Wien Bridge Oscillator and AGC circuit. The purpose is in order to get an AC signal at a fixed frequency but unstable amplitude based on the equation: