Portable Water Scanner PWS

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Portable Water Scanner (PWS)

• ECE 445 - Senior Design
• Project 17
• Members Ogden Dlima Robin O
• April 28, 2005

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Overview
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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

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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

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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 gt 15 ppb
• Water is contaminated and unsafe to drink
• If lt 15 ppb, passes through body without any
  problems

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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

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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

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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

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Graphs
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Original Design
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Initial Block Diagram
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Initial Schematic for PWS
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Revised Project Build
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Revised Block Diagram
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Light Detector Circuit
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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

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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

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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

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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

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Current Boost Circuit
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Initial Drawing of Portable Device
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Portable Water-proof Box
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Functional Tests Procedures
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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 LEDs, 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)

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Test Results for Light Detection
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LCD Demonstration
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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

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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

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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

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Questions