Rain Detection System for Power Windows in Automobiles

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

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

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

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 Sponge Thickness (in.) Avg. Resistance (Ohms)1/42.4 MΩ 1/2 3.0 MΩ 1/8 1.6 MΩ • Sensitivity • needed to be soaked to detect • Dry Time • ~ 4 - 6 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 • Varies by track spacing • Sensitivity • Varies by track spacing • 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. Rain Detection System Circuit Protection Module Power Supply and Circuit Protection Schematic

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. Rain Detection System PIC Schematic

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. 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 Window Switch Detection

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. 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 Power Considerations (Cont.)

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?