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

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?

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

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

Rain Detection System

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.

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

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

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

Senor # 1 Diagram

Sensor # 1 Performance Resistance Sensitivity Dry Time Reliability Sponge Thickness (in.) Avg. Resistance (Ohms) 1/4 2.4 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

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.

Sensor # 2 Diagram

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

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

Sensor # 3 Diagram

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

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

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

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

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

Sensor Module Schematic

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

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

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

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

PIC Schematic Rain Detection System

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

Vehicle Interface Schematic

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

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

Sensor Heating Element

Software: PIC Flowchart

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

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

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

Sample Sensor Package

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

PCB with Components

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

Vehicle Installation Schematic

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

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

Thank You Questions?