DESIGN OF ENVIRONMENTAL MONITORING SYSTEMS PH SENSING Marc Prat Xarpell Department of Electrical and Computer Engineering University of Alberta Supervisor: Dr. Petr Musilek Edmonton, May 2014 Abstract This document explains the design process and methods of a pH sensor and data logger. It shows how taking advantage of the unique spectral properties of a polymeric membrane, a circuit can be conceived to measure the acidity of a solution within a specific pH range. It also goes through the testing of said circuit and its embedding into an already built CO 2 monitoring device, as well as a basic programming code to make it work properly. The project focuses on finding out whether this pH monitoring technique can be used as a cheaper alternative to classic methods, making use of already existing tools and the artificially synthetized membrane. It eventually proves as a high potential instrument for pH sensing, with large scope for improvement at an inexpensive cost, thus making it highly useful for unmanned environmental monitoring processes. ii Table of Contents Chapter I: Introduction ..................................................................................................... 1 Chapter II: Background ..................................................................................................... 3 pH ................................................................................................................................. 3 Definition .............................................................................................................. 3 Measuring systems and techniques ..................................................................... 4 Etalon ........................................................................................................................... 8 Overview ................................................................................................................ 8 Synthesis and preparation ................................................................................... 8 Spectral properties ............................................................................................. 10 Development tests ............................................................................................. 11 Wireless gas monitor and data logger ....................................................................... 13 Overview ............................................................................................................. 13 Basic functions .................................................................................................... 14 Chapter III: Main objectives ........................................................................................... 16 Hardware design .......................................................................................................... 16 Design validation .................................................................................................... 16 Embedding ............................................................................................................. 16 Programming.......................................................................................................... 17 Software validation ................................................................................................ 17 Chapter IV: Hardware design ......................................................................................... 18 Overview and requirements ........................................................................................ 18 Functionality ....................................................................................................... 18 Size and price ...................................................................................................... 19 Light source .................................................................................................................. 20 Red LED ................................................................................................................ 21 Red/Green LED ..................................................................................................... 23 Red Laser Diode ................................................................................................... 24 Summary .............................................................................................................. 26 Driver ................................................................................................................... 27 iii Measuring circuit ........................................................................................................ 27 Phototransistor ................................................................................................... 29 Photodiode ......................................................................................................... 32 Selected hardware ....................................................................................................... 34 Chapter V: Design validation .......................................................................................... 36 Equipment .................................................................................................................... 36 Methodology and procedure ....................................................................................... 37 Results .......................................................................................................................... 38 Red LED ................................................................................................................ 38 Green LED ............................................................................................................ 39 Red Laser Diode ................................................................................................... 40 Useful range ......................................................................................................... 40 Chapter VI: Embedding ................................................................................................... 42 Schematic ..................................................................................................................... 42 PCB ............................................................................................................................... 43 Chapter VII: Programming .............................................................................................. 44 Overview ...................................................................................................................... 44 Algorithm ..................................................................................................................... 44 Chapter VIII: Future work ............................................................................................... 47 Project completion ....................................................................................................... 47 Device optimization ..................................................................................................... 47 Chapter IX: Conclusion .................................................................................................... 49 iv List of Tables 1. Etalon irradiance at peak wavelength ................................................................. 12 2. Red LED main technical data ............................................................................... 22 3. Dual LED main technical data .............................................................................. 23 4. Red Laser Diode main technical data .................................................................. 25 5. Technical data summary for different light sources ........................................... 26 6. Hardware summary ............................................................................................. 35 7. pH and current ideal matching ............................................................................ 41 v List of Figures 1. pH to [H+] relationship .......................................................................................... 4 2. pH indicator color chart ......................................................................................... 5 3. Typical commercial pH meter ................................................................................ 6 4. pH meter diagram.................................................................................................. 7 5. pH measuring systems price and accuracy............................................................ 8 6. Etalon sample ........................................................................................................ 9 7. Development tests setup .................................................................................... 11 8. Etalon irradiance and pH decreasing relationship .............................................. 12 9. Wireless Gas Monitor and Data Logger ............................................................... 13 10. Hardware block diagram ..................................................................................... 18 11. Original conditioning board ................................................................................. 19 12. Red LED picture and circuit schematic ................................................................ 22 13. Dual LED picture and circuit schematic ..............................................................