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Portable Water Scanner ( PWS )

Portable Water Scanner ( PWS ). ECE 445 - Senior Design Project # 17 Members: Ogden Dlima & Robin O April 28, 2005. Overview. Introduction. Water Contamination is a big issue all around the world More than 2,500,000 die each year from unsanitary water conditions

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Portable Water Scanner ( PWS )

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  1. Portable Water Scanner(PWS) ECE 445 - Senior Design Project # 17 Members: Ogden Dlima & Robin O April 28, 2005

  2. Overview

  3. Introduction • Water Contamination is a big issue all around the world • More than 2,500,000 die each year from unsanitary water conditions • Water testing is very expensive and time consuming • Sample is taken from water source to the laboratory • Present water testers only check for generalized contamination • Unable to name contaminant and give concentration • If contaminated, water is treated using a generalized purifier • Unable to predict reaction with unknown contaminants

  4. Initial Design Idea • PWS will check for specific contaminant and concentration in ppb • Will be able to treat only for the specific contaminant • Will be able to treat based on the observed concentration • Takes testing from the laboratory directly to the water source • Quick, inexpensive and accurate results • Portable device will be able to withstand all weather conditions • Platform for detection of all types of contaminants • Idea could be extended to other types of liquids • Choose “LEAD” as the contaminant for our design • Major issue with current drinking water sources

  5. The Contaminant “Lead” • Highly toxic to humans, especially young children • Nervous system damage can lead to learning disabilities, coma, and death • Causes anemia, kidney failure and hypertension • Reproductive system effects include stillbirths, miscarriages, male infertility and neurological impairment in the fetus • Heavy metal, can be detected using a lead sensor • Does not exist freely in nature, only as Pb2+ • EPA regulation: > 15 ppb • Water is contaminated and unsafe to drink • If < 15 ppb, passes through body without any problems

  6. Product Features • Identifies the presence of lead • Quantifies results to ppb and displays on LCD • Offers portability and long life via two 9-V alkaline batteries • Offers small and compact design for on-site testing • Offers waterproof and robust casing to prevent damage to inner circuits • Provides slot for water sample and air-tight capping • Box is completely sealed off to prevent any light from entering in

  7. Product Benefits • Educates users of the presence of lead in water • Reduces health risks due to consumption of contaminated water • User-friendly device • Universal ability to check for water contamination at the source • Quick treatment of water based on contaminants detected • Portable device due to compact design and long battery life • Base platform for detection of a whole range of contaminants

  8. DNA based Bio-Sensor for Lead • Initial idea was to design our own lead sensor • Prof. Yi Lu and the Lu Group develop DNA based biosensor to detect divalent lead • Two DNA strands: substrate and the catalytic DNAzyme • RNA present in substrate • DNA strands are broken in presence of Pb2+ and there is fluorescence “glowing state” • DNA strands can be engineered to be specifically sensitive to any such metal ions • Fluorescent intensity proportional to lead concentration

  9. Graphs

  10. Original Design

  11. Initial Block Diagram

  12. Initial Schematic for PWS

  13. Revised Project Build

  14. Revised Block Diagram

  15. Light Detector Circuit

  16. Software Flowchart Pseudo Code Initialization/Reset State Initialize and begin LCD Display start sequence Define default calibration value in one 8-bit word Clear old 8-bit ppb value Go to First Wait State Scan State Begin voltage regulation sequence Begin ADC sequence Read 8-bit output of ADC Determine 8-bit subtraction of calibration value from ADC output Compute and convert result into three numerical values for ppb readout Go to Display State Display State Enable three corresponding characters for ppb value Display “ppb” Go to Second Wait State First Wait State If scan switch is set, then go to Scan State Else go to First Wait State Second Wait State If scan switch is set, then go to Scan State If reset switch is set, then go to Reset State Else go to Second Wait State

  17. 5v Regulated DC Power Supply • Two 9v Alkaline Batteries in series as input • +5v regulated DC output • LM7805C – 3 Terminal Positive voltage regulator • SPST On/Off Switch to prevent draining the battery • LED lights up when power is supplied to the circuit

  18. +18v Battery Monitor • R3(potentiometer) controls the trip-point of the circuit • When the voltage falls below the trip-point, the LED lights • The trip-point for the +18v battery is set at +8v • Below +8v, the 3 terminal positive voltage regulator will not function properly

  19. Over-voltage Protection Circuit • Protects the micro-controller and LCD from excess DC regulated voltage • Can switch off the output should the input voltage raise above 5.6v • Max. current circuit can handle is 1 Amp • 1N4734 - 5.6v Breakdown zener • BC108 -- Low power NPN Transistor • BFY51 – NPN transistor capable of switching

  20. Current Boost Circuit

  21. Initial Drawing of Portable Device

  22. Portable Water-proof Box

  23. Functional Tests & Procedures

  24. Testing Procedures • Tested output voltage of initial photocell/photoresistors • Results showed not enough sensitivity to relevant wavelength range (520 – 565 nm) • Tested output voltage of photodiode to be sent to A/D converter • With one LED, found a less consistent and linear relationship between brightness and photodiode output voltage • With two LED’s, found a more consistent and linear relationship between brightness and photodiode output voltage • Replaced testing of DNA with Fluorescein for light detection circuit • DNA is too expensive and time consuming to produce • Tested output of power supply using oscilloscope • Showed minimal variations from expected 5 volt output (~30mV)

  25. Test Results for Light Detection

  26. LCD Demonstration

  27. Power Supply Output • X-axis: 100µs/div • Y-axis: 1.00v/div • Output Voltage: 5 volts • X-axis: 2.00µs/div • Y-axis: 20mv/div • Ripple: + 30mv

  28. Successes and Challenges • Succeeded with design of portable power supply • Succeeded with design of the light detection circuit • Succeeded with finding linear relationships between light intensity and photodiode output voltage • But could not detect enough light from Fluorescein to produce noticeable voltage change • Succeeded with LCD controls using PIC controller • But could not obtain input from A/D converter • Did not succeed with A/D converter

  29. Engineering Solutions • To overcome Shortcomings in design • Use a photodiode more sensitive to needed wavelength (520 – 565nm) • Resolve complications with A/D converter using PIC controller • Apply linear relationship determined by earlier tests using PIC • Calculate and convert lead content in terms of ppb to LCD display

  30. Questions

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