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ECE 480 – Team 6In Order of Presentation:

Ishaan SandhuDanny Kang

Arslan QaiserEric Otte

Anuar Tazabekov

Capacitive Rain Sensor for Automatic Wiper Control

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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

Sensor Traces Form Base

Capacitance

E-field Generated by Applying AC

Voltage

Objects Interfere with E-field

Capacitance of Sensor Changes

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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 < $16 per unit

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System Block Diagram

Capacitive Sensor Control Unit Wiper

System

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Design Flowchart

Voltage Regulator (5 V DC)

Keep Wipers Off

Capacitive Sensor Traces

on PCB

Activate Wipers

Capacitive-to-Digital

Converter Circuit

Microcontroller

YES

NO

I s Capacitance Between

X Farads Y ≤ ≤ ?

Control Unit

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Sensor TracesCOMSOL • 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

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

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Microcontroller

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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BudgetCOMPONENT 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

Start

Login

Main

Wait for UI

Start Reset

Clear all Fields

Get Data

Graph and Interpret

Start

Wait for Interrupt

Initialize

Get Data

Visual Basic Application Microcontroller

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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