ChemSense - A Portable and Affordable Mid-Infrared Chemical Detection Sensor


University: The University of Texas at Austin
Team Members: Travis Brannen, John Elson, Steven Prickett, Kaarthik Rajendran, Aaron Treptow, Parker Wray
TI Parts Used:

  • TM4C123GH6 (2)
  • TPS73633 (3)
  • OPA320

Project Description

ChemSense is a portable, mid-infrared chemical sensor system that has applications in national security and industrial safety. Current infrared chemical detection technologies are bulky and costly. Utilizing Dr. Ray Chen’s lab-on-chip QCL/QCD, our challenge was to design, build, and test a portable, affordable mid-infrared chemical detection sensor. 

Our design solution takes traditional, benchtop spectroscopy components (pulse generator, laser driver, and lock-in detector) and shrinks them to fit on a custom-designed printed circuit board (PCB). Thanks to our unique PCB design and use of digital signal processing (DSP) detection, our solution addresses key design requirements in portability (<2 lbs), real-time detection (within 100 ms), and power consumption (2 W).

ChemSense provides a fully customizable, lightweight, and low power solution to the need for mobile broad spectrum chemical detection. ChemSense is composed of a dual mode laser driver, quantum cascade laser (QCL) and detector (QCD), digital lock-in amplifier, user interface (onboard touch screen and/or android app), and power electronics. These elements are integrated on a custom printed circuit board (PCB) weighing less than 2 pounds and requiring less than 2 watts of power.

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Features
  • High-fidelity chemical detection utilizing the mid-infrared chemical absorption spectra. 
  • Tunable Postive and Negative Laser Drivers
  • BlueTooth LE Wireless Connectivity with a dedicated Android App
  • On-board LCD Touchscreen
  • Under 2 W Power

Resources

Please visit our website for more information.

User's Guide

ChemSense senses chemicals by absorption spectroscopy, a method of chemical detection where light of a particular wavelength passes through the chemical of interest and is attenuated based on the chemical’s absorption of light at that wavelength. A detector then collects the light and the attenuation is used to infer chemical concentration.

ChemSense’s laser driver can provide either positive or negative voltages in either continuous or pulsed mode, depending on the application. In providing these options, we attempt to provide a laser driver that can operate most solid state lasers on the market today. When the user sets a laser modulation frequency and duty cycle, this information is sent to the DSP MCU. The DSP MCU generates a sequence of pulse triggers, which are used as the control signal for the laser driver. The laser driver then sends high voltage and current pulses to drive the laser.

ChemSense provides the option to interface with the sensor either through an onboard 7” touch screen to interface with the user as well as a wireless Android tablet. The idea of the onboard touch screen is to provide full control and immediate data analysis directly from ChemSense, without out the need for external equipment or interfacing. The Android application provides external control and analysis. This allows the user to attach ChemSense to a robot to analyze dangerous chemicals in environments not safe for people. Additionally, if the user desired to monitor an area for a prolonged period of time, they could leave ChemSense running and check the Android application periodically. Using an external UI has the added benefit of reducing the power needs of the device itself.

The user interface is run by ChemSense’s dedicated UI MCU. This processor handles all user requests, ensures the requests are sent to the proper subsystem, and manages all communications with ChemSense’s android application. The processor also performs all concentration calculations and updates a concentration versus time graph for the user every 100 ms. The user can also define a concentration set point at which an onboard alarm will sound. This feature is also mimicked on the tablet. Written in Java, the app allows the user to perform all of the same functions with a wireless tablet as with the on board user interface as well as the ability to export recorded data. Utilizing the onboard memory and processing power of the tablet, ChemSense’s Android app can record up to one hour of sensing data (36,000 samples) and wirelessly email this data to an address of your choosing. This allows for additional post processing, if desired.