STRAIN SENSING AND MONITORING
STRAIN SENSING AND MONITORING
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I worked under the supervision of Professor Oh Sung Kwon and Professor Evan Bentz at the Department of Civil and Mineral Engineering from May 2021 to September 2022. My primary work involved upgrading the existing lab data acquisition system.
DAQ Configuration and Strain Monitoring
DAQ Configuration and Strain Monitoring
May 2021 - Semptember 2021
Over the summer of 2021, I worked on creating a Graphical User Interface for DAQ Configu ration and Strain Monitoring. Furthermore, I upgraded the existing lab DAQ by integrating a display to monitor strain measurements in real time.
The GUI served two important purposes:
DAQ Configuration
This included zero offset and scale calibration of the 16 strain sensors attached to the DAQ.
Strain Monitoring
The acquired data from the sensors was parsed through the serial port, stored and plotted in real time. The interface also supported mathematical operations of the acquired data in real time. The LCD could also be configured to display a tabular or graphical view of the data.
The GUI is a multi threaded program with two threads: The Main thread and Serial thread. The Main thread is responsible for handling the GUI and running it smoothly without crashing. The Serial thread handles the serial communication with the sensors on the DAQ.
Select screenshots of the GUI are shown below:
Field Deployable Strain Module
Field Deployable Strain Module
January 2022 - September 2022
The goal of this project was to develop a Low-Cost strain sensor that could be deployed anywhere with minimal installations. A wireless communications protocol with a base station was also part of the design. Power management was a big concern since the sensor was required to run for an entire year without battery replacements. The sensor is controlled by an Atmega328P Microcontroller with a 16Mhz external clock.
The final product combined five major design elements:
Latching power switch circuit
To conserve as much power as possible, a latching power switch circuit was implemented. This circuit ensures that the device turns off (effectively consuming 0Amps) when no data is being logged. The device was turned on at regular intervals with an RTC interrupt.
Strain Sensor
A quarter Wheatstone bridge converted the resistance changes of the strain gauge into voltages. These voltages were amplified and converted into digital signals prior to transmitting them to the microcontroller. The strain gauges used were thin films of wire that change resistance when subjected to mechanical strain.
GPS Module
To accurately time the data measured, a GPS module was used to update the RTC at regular intervals and mitigate any errors in its readings.
SD Card
An SD card ensured that a copy of the strain data was stored on the device locally.
Long Range Radio (LoRa)
The device was fitted with a LoRa chip to communicate wirelessly with a base station. LoRa was primarily chosen for its low cost, low power consumption and long range capabilities. Moreover, with the existing Things Network based on the LoRa protocol, the device could be connected to the internet, thus making it a robust solution. A base station with a similar architecture was designed to communicate with the device. Currently, the wireless commands are limited to receiving stored data and modifying the device configuration. More capabilities will be incorporated in the future to make it IoT compatible.
Breadboard Prototype
Strain Sensor
Receiver Module
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