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Building Spectrometer

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Building Spectrometer Powered By Docstoc
					Building a Spectrometer
                 Robyn Badon
               Michael Barnes
                   Terrell Black
              Ryan Bloodworth
                Robyn Mackey
Lecture Outline
   Introduction
    › What is a Spectrometer?
    › How it works/ Project relevance
 Spectrometer Design Overview
 LED Geometry
 Hardware
 Software
 Summary
                   Introduction
   What is a spectrometer?
    › Optical instrument to automatically measure
      light intensity/ detect color changes
   What are we using it for?
    › Urinalysis
    › More accurate than human eye alone
       The urinalysis test strip is compared to
        predefined samples by color
         Computer can eliminate human error
Overview of Project Relevance
   Medical screening device with 5
    modules
    › Thermometer
    › Blood Oxygen Saturation
    › Blood Pressure
    › ECG
    › Urine Glucose SPECTROMETER
   For safety urine is sampled
    › Reduce risk of disease transmission
    › Much more sanitary
              How it works…
 Collect sample using test strip
 Light reflects off the colored strip
 Light intensity is picked up by the
  photoresistor
 Different reading for each LED
    › Based on concentration of glucose in urine
     sample
Light… back to Physics...
   Human perception of color
    › Composition of light an object reflects
   A quick example:
    › If an object appears red, the red light is
     reflected while all other colors are absorbed
Trivia
   If an object appears to be white, what is
    happening?
                               Light




Figure 3. Electromagnetic radiation. The visible wavelength range
              extends from approximately 350-700nm.
       Image source: http://www.andor.com/library/light/
Our Spectrometer
                      Reflectance
                       spectrometer
                      Intensity
                       measured by
                       photoresistor
                      Interpret
                       results
Photoresistor
   A photoresistor or LDR is an
    electronic component whose
    resistance decreases with
    increasing incident light
    › made of a high-resistance
      semiconductor intensity.
    › If light falling on the object is high
      enough, electrons get energy to jump
      into the conduction band
    › The resulting free electron and its’
      hole conduct electricity, therefore
      lowering resistance
Application
        Glucose
         concentration
        Human analysis by
         color matching
    Basic Reflection Spectrometer Design

 Three LEDS; blue, green and red.
 LEDs are controlled by the PIC
 Each LED is turned on one at a time
 LED is reflected down on the
  photoresistor causing the resistance
  value to change
 The voltage value is read in by PIC
 Data sent back to PC and compared
Basic Reflection Spectrometer Design




       Figure 4. Block diagram of mini
          reflectance spectrometer
             LED geometry
 LEDs are arranged at a 30° angle
 The light is directed in a narrow beam
  towards the sample
 Prevents light from entering photoresistor
  directly, which would obscure the true
  signal
 The entire circuit is put in an opaque box
  to preventing interfering light from
  entering
                                               Spectrometer geometry




                             Variety of LEDs

Boxed in green is most typically used, estimated at 80% of world production
            Boxed in red is the LED used for our spectrometer
           Powering the LEDs
 Red and Green powered by PIC
 Resistors used as voltage dividers




   Blue LED needs more power
                 Blue LED
   Transistor used as switch to power blue
    LED
Spice Analysis of
Transistor and Diode Voltage
             The detector
 NSL-6110 photoresistor
 Change is voltage is very small
 Must be amplified
 Run through 2 stages
 Voltage divider
 Non-inverting Amplifier
The detector
        Controlling Software
 PIC code for reading reflectance
 GUI
 KNN Algorithms
     Central Unit: the 18F4520
 Input/Output port
 A/D conversion
 Adaptation for RS232 communication
             PIC Code
 PIC must activate LEDs and read in
  Voltage from the photoresistor
 Set port D, pins 0-2 to output
 Loop program until RX interrupt
 Run functions based on char received
             MeasureR()
 Turn on red LED, turn off green and blue
 Wait short time
 Read in voltage
 Convert analog to digital
 Divide by 256, multiply by 5
 Save value
 Turn off red LED
            GUI Software
 Using Visual Basic
 Button and text box for each LED
 Button sends char to PIC
 PIC returns data which gets displayed in
  text box
Controlling Software




 Figure 8. Example Visual Basic GUI
    Color Matching Software
 Training phase
 Classification phase
             Training Phase
   Create sample data by scanning known colors
   Urinalysis Strips with known concentrations
         Classification Phase
   Compare current sample to test data by
    computing distance




 Create a list of K closest training values
 Take the average to find concentration
Summary
 Our spectrometer has been designed to
  read urine glucose strips
 However, it is versatile enough to be
  used in any application where color
  detection is needed
 It can be adapted to be used for
  anything from protein concentration to
  pregnancy tests
Questions?

				
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