Transcript Proposal-Presentation

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
Agenda
• Introduction
• Background
• Design Specifications
• Conceptual Design
• Proposed Design Solution
• Hardware Specifications
• Reflection
Introduction
GPS
Ipod/MP3
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 mm2)
• 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 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
DC Power
Source
• Overall Design uses 3 layers
• Flex Layer – Capacitive Sensor
Capacitive-toDigital
Converter
Circuit
Capacitive
Sensor Traces
on PCB
• C-D Converter (AD7746)
• Buck Converter Circuit
Microcontroller
• Microcontroller (PIC18F4520)
• Wiper Switch
Output Voltage
Comparison
Is voltage between
X ≤ Voltage ≤ Y ?
YES
Turn the wiper on.
Water detected on
the windshield.
NO
Keep wipers off.
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?