1. Rain Detection System for Power Windows in Automobiles
Group Four
Brian Mitterer, Rob Herzog, Chintan Patel
ECE 445 Senior Design

2. Introduction
We designed a sensor system that detects rain and rolls up the windows in an automobile
The object is to grant the driver the convenience of having his or her car windows automatically close in the event of rain
Add picture of a car?

3. Benefits
Protects the inside of a vehicle from water damage caused by rain
Provides safety to the driver and passengers by eliminating distraction
Provides convenience to drivers by allowing them to keep windows open while they are away and not having to rush out to close them if it begins to rain

4. Product Features Reliable and low cost
Compatible with any car with power windows
Automatic drying with complete rooftop coverage
Compact and easy to install
User-override switch

5. Rain Detection System

6. System Overview Hardware components: Software components:
Rain sensors, override switch, microcontroller, motor relays, voltage regulator and car battery
Software components:
Microcontroller (PIC) logic to implement the various functionalities.

7. Overall Block Diagram Microcontroller
Motor / car controller for power windows
Override Switch/ Control
Sensors
Voltage Regulator
Car Battery

8. Sensors Three proposals for the sensor to be used in the system
Plan was to test all three designs and make an engineering decision based on resistance, sensitivity, reliability and dry time

9. Sensor # 1 Overview
First rain sensor design had three copper conducting plates with sponge material between them
With this sensor placed on-end on top of the vehicle, rain water would saturate the sponges
This would complete the circuit and allow current to flow from one conducting plate to another through the water in the sponge

10. Senor # 1 Diagram

11. Sensor # 1 Performance Resistance Sensitivity Dry Time Reliability
Sponge Thickness (in.) Avg. Resistance (Ohms) 1/ MΩ 1/ MΩ 1/ MΩ
Sensitivity
needed to be soaked to detect
Dry Time
~ hours
Reliability
sponge will decay over time

12. Sensor # 2 Overview
Second rain sensor design consisted of two copper conducting plates covered with insulation on five sides
Plates in contact during dry conditions, allowing current to flow
Super-absorbent clay placed underneath one of the plates would expand, pushing up on the plate above it and breaking the circuit.
Clay would dry and shrink back to its normal size, bringing the plate back into place.

13. Sensor # 2 Diagram

14. Sensor # 2 Performance
Clay failed to rise significantly and push the plate upwards in order to break the contact
Design idea was discontinued

15. Sensor # 3 Overview
Uses rain droplets to complete circuit that sources current to microcontroller input
Consists of interweaving copper tracks on an ordinary PCB

16. Sensor # 3 Diagram

17. Sensor # 3 Performance Resistance Sensitivity Dry Time Repeatability
Varies by track spacing
Sensitivity
Dry Time
~1 hour
Repeatability
Very repeatable and consistent

18. Sensor # 3 Performance
1/8 inch spacing
1/4 inch spacing

19. Sensor # 3 Performance Sensor Resistance Vs. Number of Drops of Rain
Resistance (kohms)
Number of Drops

20. Sensor # 3 Performance
Quarter inch spaced copper tracks with rounded edges chosen
Nearly as sensitive to drops as 1/8” version
Much less susceptible to false positives

21. Sensor Module
Consists of 4 identical sensors for full coverage of car rooftop
Each sensor receives 5V DC from Power Supply Module
Outputs to PIC microcontroller, ~0 or ~5 V
Drop-down resistor (Ri)
Ri determines PIC input voltage
Ri changed to 1MΩ from 5.8MΩ to reduce sensitivity
…after one drop

22. Sensor Module Schematic

23. Power Supply Module
Existing 12 V car battery used to power all components
Voltage regulator drops voltage to 5V
Several components require 5V
PIC logical inputs
PIC Vdd
Relay
Capacitors added to reduce noise

24. Circuit Protection Module
1 A fuse protects voltage regulator and PIC microcontroller from high current
Diode provides polarity protection
100 μF capacitor protects voltage regulator and PIC microcontroller from voltage spikes during ignition

25. Power Supply and Circuit Protection Schematic
Circuit Protection Module
Rain
Detection
System

26. PIC Overview
The PIC microcontroller was used to implement the logic needed for the system
Some of the functions include reading the sensors, timing the window motor to be driven, and sensing activity on the window switch of the car

27. PIC Schematic
Rain
Detection
System

28. Vehicle Interface
30 A, normally closed Bosch mini relays used to implement rain detection system with existing window user interface
Existing window system electrically isolated from rain detection system
PIC controls switching between current system and rain system

29. Vehicle Interface Schematic

30. Window Switch Detection
Want to reset the rain detection system after the driver has pressed the car window switch
Requires a parallel connection to the current 12 V line to the car window motor
Use VDR to drop 12 V to 5 V for PIC input
Use 100 K ohms for drop down resistor
R2 = 140 k ohms

31. Improvements: Drying Time
Mounted sensor on an angle to allow for water to run off of it
Implemented heating element underneath sensor
Nichrome wire rated at 0.12 ohm / inch
Wrapped wire underneath sensor by means of screws drilled into sides of sensor
Powered by 12 V line, switched on by PIC by means of a MOSFET

32. Sensor Heating Element

33. Software: PIC Flowchart

34. Power Considerations
Largest electrical system, car brights, typically consumes about 55 Watts
Battery will drain after about 4 hours
Only significant power consumers are heating coils and window motors

35. Power Considerations (Cont.)
Heating Coils
Powered directly from battery
3 ohm resistance
40 watts consumption
2 of 4 sensors contain heating coils
Heating coils on for 5 minutes
Window Motors
Each motor consumes about 15 watts of power
Window motors on for 10 seconds

36. Sensor Packaging 4 sensors to be located on top of the vehicle
Need protection against foreign objects
Allow for rain to enter through top
Allow for rain to drain out the bottom

37. Sample Sensor Package

38. Future Developments
Mount circuit protection, voltage regulator, PIC, resistors, and transistors onto PCB
Package PCB into a module to be mounted inside the car
Package to include a user override switch and LED to show power on

39. PCB with Components

40. Future Developments (Cont.)
Implement into a vehicle
Install relay at each window motor
Make parallel connection to direct line to battery
Install PCB module near driver
Install sensors at four corners on top of vehicle

41. Vehicle Installation Schematic

42. Ethical Considerations
Pro
Eliminates driver distraction of having to close windows when it begins to rain
Con
Potential safety hazard when windows close without detecting whether someone or something is in the path of the window

43. Credits Special thanks to: Austin Kirchhoff Professor Makela
Mark Smart
Texas Instruments
Chief Enterprises

44. Thank You
Questions?