ECE 480

1
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

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Outline

• Introduction
• Design Requirements
• Proposed Design Solution
• Testing Results
• Budget
• Demonstration
• Conclusions

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Introduction

• Automotive Safety and Convenience
• Automatic Headlights
• Hands-Free Calling
• Automatic Braking
• Automatic Windshield Wipers
• Currently Optical (Expensive, Inaccurate)
• DT6 Proposes Using a Capacitive Based Sensor

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Capacitive Sensor Basics
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Design Requirements

• Functionality
• Detect rain through 6 mm of glass
• Output control signals to wipers
• Accuracy
• Differentiate multiple levels of rain
• Ignore false stimuli on windshield, i.e.
  hands and dirt

• Compatibility
• Fit in existing housing area (1250 mm2)
• Mount via adhesive to windshield
• Cost
• Production cost lt 16 per unit

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System Block Diagram
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Design Flowchart
Control Unit
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Sensor Traces

• COMSOL
• 3D Modeling Software
• Visual User Interface
• Calculates the base capacitance
• Can model dielectrics
• Top layer
• Bottom Layer
• Simulates electric field lines
• Sensitivity

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Capacitance-to-Digital Converter
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• Analog Devices AD7745
• Industry-leading accuracy down to 4 fF change in
  capacitance
• Interfaces with sensor traces to monitor
  capacitance (/- 4 pF)
• Converts changing capacitance to 24-bit digital
  output signal
• Output routed to PIC using the I2C communication
  system

10
Microcontroller
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• Microchip PIC16F1826
• 8-bit microcontroller, programmable in C code
• Initializes and configures AD7745 for operation
• Streams data from AD7745 and compares to known
  data ranges
• Data falling in range will activate appropriate
  wiper control signals

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Budget
COMPONENT COST
PIC16F1826 Microcontroller 0.90
AD7745 CDC 4.50
ADP3301-5 Voltage Regulator 1.40
Surface-mount Passive Components 0.10
Two-layer PCB Production and Assembly 4.00 (est)
Plastic Enclosure 0.50 (est)
Total 11.40 (est)
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Capacitive vs. Optical
Design Team 6 Supplier (TRW) Change
Technology Capacitive Optical
Cost per Unit 11.40 16.41 31 ?
Physical Size 1,750 mm2 3,850 mm2 46 ?
Detection Area 960 mm2 560 mm2 72 ?
Clear line of site No need Required
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Software
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Demonstration
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Conclusions

• Successful completion of the project
• Exceeds all design requirements
• Higher accuracy
• Larger sensing area
• Smaller enclosure
• Significant savings

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Q A
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Thank You