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ECE 480 – Team 6

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

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ECE 480 – Team 6

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  1. Capacitive Rain Sensor for Automatic Wiper Control ECE 480 – Team 6 In Order of Presentation: Ishaan Sandhu DannY Kang Arslan Qaiser Eric Otte Anuar Tazabekov

  2. Agenda • Introduction • Background • Design Specifications • Conceptual Design • Proposed Design Solution • Hardware Specifications • Reflection

  3. Introduction GPS Ipod/MP3 In-Dash DVD Player Safety Satellite Radio

  4. BackgroundOptical Rain Sensors • Transmits/Receives IR Beams • Expensive • Inaccurate (False Readings) • Uneven Sensing Area

  5. BackgroundWhy Capacitive? • Higher Accuracy – Less False Positives • Smaller Size – Sleek Design • Cheaper • Fewer Components – Less Complex

  6. BackgroundBasics of Capacitive Sensors • Three Main Types: • Displacement • Accelerometer • Pressure • Capacitance • Fringe Fields • Dielectric differences

  7. Design Specifications • COMPATIBILITY • Fit in existing housing (1250 mm2) • Mount via adhesive • COST • Cheaper than optical sensor • Overall cost < $12 • FUNCTIONALITY • Sense water through windshield • Communicate with microcontroller • Control Wiper System • ACCURACY • Differentiate between various objects • Differentiate varying rain levels

  8. Conceptual DesignSensor 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!

  9. Conceptual DesignCapacitance 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

  10. Conceptual DesignMicrocontroller / 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

  11. Proposed Design SolutionCapacitance-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

  12. Proposed Design SolutionDifferential 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)

  13. Proposed Design SolutionPIC18F4520 Microcontroller • Why we chose the PIC: • Variety of I/O Ports • Easy to use interface • C++ programming • Free! • Can compare voltages

  14. Proposed Design SolutionPower 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

  15. Proposed Design SolutionPCB Layout • Final design has two parts: • Flex PCB: • Sensor Traces • Mounts via 3M Adhesive • Standard 2-layer FR4 PCB: • C-D Converter • Microcontroller

  16. Hardware Specifications • Overall Design uses 3 layers • Flex Layer – Capacitive Sensor • C-D Converter (AD7746) • Buck Converter Circuit • Microcontroller (PIC18F4520) • Wiper Switch

  17. Budget

  18. Reflection • Background • Design Specifications • Conceptual Design • Proposed Design Solution • Hardware Specifications • Questions?

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