In Order of Presentation:
Ishaan Sandhu
DannY Kang
Arslan Qaiser
Eric Otte
Anuar Tazabekov

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

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

Background
• Transmits/Receives IR Beams
• Expensive
• Inaccurate (False Readings)
• Uneven Sensing Area

Background
• Higher Accuracy – Less False
Positives
• Smaller Size – Sleek Design
• Cheaper
• Fewer Components – Less
Complex

Background
• Three Main Types:
• Displacement
• Accelerometer
• Pressure
• Capacitance
• Fringe Fields
• Dielectric differences

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

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

DC Power
Source
• Overall Design uses 3 layers
• Flex Layer – Capacitive Sensor Capacitive
Sensor Traces on PCB
• C-D Converter (
AD7746
)
• Buck Converter Circuit
• Microcontroller (
PIC18F4520
)
• Wiper Switch
YES
Capacitive-to-
Digital
Converter
Circuit
Microcontroller
Output Voltage
Comparison
Is voltage between
X ≤ Voltage ≤ Y ?
NO
Turn the wiper on.
Water detected on the windshield.
Keep wipers off.

Part Name
Analog Devices AD7151
Cap-to-Dig Converter
Analog Devices AD7745
Cap-to-Dig Converter
Analog Devices AD7746
Cap-to-Dig Converter
Analog Devices AD7747
Cap-to-Dig Converter
Analog Devices AD7746
Evaluation Board
468-MP Adhesive
Microcontroller
Coaxial Cable Assembly
Fabricate with Flexible
PCB
Total
Quantity
4
4
4
4
1
8
1
3
2
29
Cost
$12.68
$38.00
$34.32
$38.00
$136.62
$42.40
$0
$57.08
$180.00
$539.10

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