ECE 480 Team 6

bendembarrassΗλεκτρονική - Συσκευές

2 Νοε 2013 (πριν από 3 χρόνια και 5 μήνες)

83 εμφανίσεις

ECE 480


Team 6

In Order of Presentation:

Ishaan Sandhu

DannY Kang

Arslan Qaiser

Eric Otte

Anuar Tazabekov

Capacitive Rain Sensor for Automatic Wiper Control

Agenda



Introduction



Background



Design Specifications



Conceptual Design



Proposed Design Solution



Hardware Specifications



Reflection


Introduction

Ipod/MP3

GPS

In
-
Dash

DVD Player

Safety

Satellite Radio

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



Sense water through windshield



Communicate with microcontroller



Control Wiper System



ACCURACY



Differentiate between various
objects



Differentiate varying rain levels




COMPATIBILITY



Fit in existing housing (1250 mm
2
)



Mount via adhesive




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 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
Cap
-
to
-
Dig Converter

4

$12.68

Analog Devices AD7745
Cap
-
to
-
Dig Converter

4

$38.00

Analog Devices AD7746
Cap
-
to
-
Dig Converter

4

$34.32

Analog Devices AD7747
Cap
-
to
-
Dig Converter

4

$38.00

Analog Devices AD7746
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?