Proposal-Presentation by pengtt

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									     ECE 480 – Team 6
Capacitive Rain Sensor for Automatic Wiper Control
               In Order of Presentation:
                    Ishaan Sandhu
                      DannY Kang
                     Arslan Qaiser
                       Eric Otte
                   Anuar Tazabekov
                  Agenda
• Introduction
• Background
• Design Specifications
• Conceptual Design
• Proposed Design Solution
• Hardware Specifications
• Reflection
                     Introduction



                                            GPS
  Ipod/MP3




In-Dash DVD Player
                       Satellite Radio   Safety
                         Background

              Optical Rain Sensors


• Transmits/Receives IR Beams
• Expensive
• Inaccurate (False Readings)
• Uneven Sensing Area
                           Background

                  Why Capacitive?

• Higher Accuracy – Less False
Positives
• Smaller Size – Sleek Design
• Cheaper
• Fewer Components – Less
Complex
                           Background

   Basics of Capacitive Sensors
• Three Main Types:
   • Displacement
   • Accelerometer
   • Pressure
• Capacitance
• Fringe Fields
• Dielectric differences
                Design Specifications

• FUNCTIONALITY                          • COMPATIBILITY
   • Sense water through windshield         • Fit in existing housing (1250 mm2)
   • Communicate with microcontroller       • Mount via adhesive
   • Control Wiper System

• ACCURACY                               • COST
   • Differentiate between various          • Cheaper than optical sensor
   objects
                                            • Overall cost < $12
   • Differentiate varying rain levels
                         Conceptual Design

                    Sensor Traces

• Not Your Typical Capacitor!
• Sensing Area – Copper Traces
• Designed for Base Capacitance ≈ 5 pF
• Creates E-field When AC Voltage Applied
• Objects Interfere with E-field – Change Cin
• Design Parameters: Size, Spacing, Pattern
• Dielectric Insulators are Vital!
                           Conceptual Design

   Capacitance Monitoring Circuitry
• Need Circuitry to Monitor the Capacitance Value of the Sensor Traces
• Possible Design: RC Multi-vibrator - Change in C = Change in Time Constant
• Better Alternative: Dedicated IC’s – Capacitance to Digital Conversion
• Interface to Microcontroller for Software Processing
                          Conceptual Design

        Microcontroller / Processor

• Inputs Capacitance Data from C-D IC
• Sensor Response to Rain Can Be Characterized
• Software Algorithms To Discriminate Rain from
Others
• Varying Wiper Speed In Response to Amount of
Rain
• Prototype – Microcontroller
• Production – Body Control Module
                   Proposed Design Solution

  Capacitance-to-Digital Converter
• Use Analog Devices AD7746
• Measures 24-bit capacitance
• Accurate to the femto-Farad
• Built in temp and humidity
sensor for auto-compensation
• AD7151 and AD7747 models
can also be used
                    Proposed Design Solution

   Differential Sensor Trace Design
• Three Separate Traces
• Source Excitation Voltage
Applied To Center Trace
• Two Differentially Connected
Traces
• Test Results to Determine
Best Design (spacing, patterns,
etc)
                   Proposed Design Solution

      PIC18F4520 Microcontroller
• Why we chose the PIC:
   • Variety of I/O Ports
   • Easy to use interface
   • C++ programming
   • Free!
• Can compare voltages
               Proposed Design Solution

Power Supply and Requirements

  • Prototype will use batteries (9V Batteries)
  • Production Design will use car battery
  • PIC needs steady 5V
  • AD7746 (C-D) needs steady 5.6V
  • Buck Converter Circuit
                        Proposed Design Solution

                          PCB Layout
Final design has two parts:
   • Flex PCB:
      • Sensor Traces
      • Mounts via 3M Adhesive

   • Standard 2-layer FR4 PCB:
      • C-D Converter
      • Microcontroller
       Hardware Specifications

• Overall Design uses 3 layers
• Flex Layer – Capacitive Sensor
• C-D Converter (AD7746)
• Buck Converter Circuit
• Microcontroller (PIC18F4520)
• Wiper Switch
                          Budget
     Part Name             Quantity    Cost
Analog Devices AD7151
                              4       $12.68
 Cap-to-Dig Converter
Analog Devices AD7745
                              4       $38.00
 Cap-to-Dig Converter
Analog Devices AD7746
                              4       $34.32
 Cap-to-Dig Converter
Analog Devices AD7747
                              4       $38.00
 Cap-to-Dig Converter
Analog Devices AD7746
                              1       $136.62
   Evaluation Board
  468-MP Adhesive             8       $42.40
   Microcontroller            1         $0
Coaxial Cable Assembly        3       $57.08
Fabricate with Flexible
                              2       $180.00
         PCB
        Total                29       $539.10
                 Reflection
• Background
• Design Specifications
• Conceptual Design
• Proposed Design Solution
• Hardware Specifications
• Questions?

								
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