Capacitive Rain Sensor for
Automatic Wiper Control
ECE 480 – Team 6
In Order of Presentation:
Ishaan Sandhu
Danny Kang
Arslan Qaiser
Eric Otte
Anuar Tazabekov
Outline
• Introduction
• Design Requirements
• Proposed Design Solution
• Testing Results
• Budget
• Demonstration
• Conclusions
Introduction
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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
Capacitive Sensor Basics
Sensor Traces
Form Base
Capacitance
E-field Generated
by Applying AC
Voltage
Objects Interfere
with E-field
Capacitance of
Sensor Changes
Design Requirements
Functionality
Compatibility
• Detect rain through 6 mm of glass
• Fit in existing housing area (1250 mm2)
• Output control signals to wipers
• Mount via adhesive to windshield
Accuracy
Cost
• Differentiate multiple levels of rain
• Production cost < $16 per unit
• Ignore false stimuli on windshield, i.e.
hands and dirt
System Block Diagram
Capacitive
Sensor
Control Unit
Wiper
System
Design Flowchart
Capacitive
Sensor Traces
on PCB
Voltage
Regulator
(5 V DC)
YES
Capacitive-toDigital
Converter
Circuit
Is Capacitance
Between
X ≤ Farads ≤ Y ?
Microcontroller
NO
Control Unit
Activate
Wipers
Keep Wipers
Off
Sensor Traces
COMSOL
• 3D Modeling Software
• Visual User Interface
• Calculates the base
capacitance
• Can model dielectrics
– Top layer
– Bottom Layer
• Simulates electric field
lines
– Sensitivity
Capacitance-to-Digital Converter
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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
Microcontroller
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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
Budget
COMPONENT
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)
Capacitive vs. Optical
Design Team 6 Supplier (TRW)
Technology
Change
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
Software
Visual Basic Application
Microcontroller
Start
Start
Login
Wait for
Interrupt
Main
Initialize
Wait for UI
Start
Reset
Clear all
Fields
Get Data
Graph and
Interpret
Get Data
Demonstration
Conclusions
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Successful completion of the project
Exceeds all design requirements
Higher accuracy
Larger sensing area
Smaller enclosure
Significant savings
Q&A
Thank You