ECE 480 Team 6 Capacitive Rain Sensor for

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

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

Introduction GPS Ipod/MP 3 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 mm 2) • Communicate with microcontroller • Mount via adhesive • Control Wiper System • ACCURACY • Differentiate between various objects • Differentiate varying rain levels • COST • Cheaper than optical sensor • Overall cost < $12

Conceptual Design Sensor Traces • Not Your Typical Capacitor! • Sensing Area – Copper Traces • Designed for Base Capacitance ≈ 5 p. F • 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 AD 7746 • Measures 24 -bit capacitance • Accurate to the femto-Farad • Built in temp and humidity sensor for auto-compensation • AD 7151 and AD 7747 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 PIC 18 F 4520 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 (9 V Batteries) • Production Design will use car battery • PIC needs steady 5 V • AD 7746 (C-D) needs steady 5. 6 V • Buck Converter Circuit

Proposed Design Solution PCB Layout Final design has two parts: • Flex PCB: • Sensor Traces • Mounts via 3 M Adhesive • Standard 2 -layer FR 4 PCB: • C-D Converter • Microcontroller

Hardware Specifications • Overall Design uses 3 layers • Flex Layer – Capacitive Sensor • C-D Converter (AD 7746) • Buck Converter Circuit • Microcontroller (PIC 18 F 4520) • Wiper Switch

Budget Part Name Quantity Cost Analog Devices AD 7151 Cap-to-Dig Converter 4 $12. 68 Analog Devices AD 7745 Cap-to-Dig Converter 4 $38. 00 Analog Devices AD 7746 Cap-to-Dig Converter 4 $34. 32 Analog Devices AD 7747 Cap-to-Dig Converter 4 $38. 00 Analog Devices AD 7746 Evaluation Board 1 $136. 62 468 -MP Adhesive 8 $42. 40 Microcontroller 1 $0 Coaxial Cable Assembly 3 $57. 08 Fabricate with Flexible PCB 2 $180. 00 Total 29 $539. 10

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