RainDetectionSystem

Rain Detection System for Power Windows in AutomobilesGroup FourBrian Mitterer, Rob Herzog, Chintan PatelECE 445 Senior Design

RainDetectionSystem

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

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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

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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

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Rain Detection System

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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.

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Overall Block Diagram

Microcontroller

Motor / car controller for power windows

Override Switch/ Control

Sensors

Voltage RegulatorCar Battery

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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

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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

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Senor # 1 Diagram

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Sensor # 1 Performance Resistance

Sponge Thickness (in.) Avg. Resistance (Ohms)1/4 2.4 MΩ1/2 3.0 MΩ1/8 1.6 MΩ

Sensitivity needed to be soaked to detect

Dry Time ~ 4 - 6 hours

Reliability sponge will decay over time

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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.

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Sensor # 2 Diagram

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Sensor # 2 Performance

Clay failed to rise significantly and push the plate upwards in order to break the contact

Design idea was discontinued

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Sensor # 3 Overview

Uses rain droplets to complete circuit that sources current to microcontroller input

Consists of interweaving copper tracks on an ordinary PCB

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Sensor # 3 Diagram

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Sensor # 3 Performance

Resistance Varies by track spacing

Sensitivity Varies by track spacing

Dry Time ~1 hour

Repeatability Very repeatable and consistent

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Sensor # 3 Performance1/4 inch spacing1/8 inch spacing

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Sensor # 3 PerformanceSensor Resistance Vs. Number of Drops of Rain

Number of Drops

Res

ista

nce

(koh

ms)

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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

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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

10005 4.171000 200

iout in

i sensor

R kV V VR R k k

…after one drop

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Sensor Module Schematic

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Power Supply Module

Existing 12 V car battery used to power all components

Voltage regulator drops voltage to 5VSeveral components require 5V

PIC logical inputs PIC Vdd Relay

Capacitors added to reduce noise

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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

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Circuit Protection Module

Power Supply and Circuit Protection Schematic

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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

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PIC Schematic

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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

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Vehicle Interface Schematic

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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

1005 12100 2

outout in

out in

R kV V V VR R k R

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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

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Sensor Heating Element

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Software: PIC Flowchart

Sensors Fire? Is OverrideSwitch on?

Turn on motor for10 seconds and

then turn off

Is OverrideSwitch on?

Activity on thewindow switch?

Turn on Heat for 5minutes

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Power Considerations

Largest electrical system, car brights, typically consumes about 55 WattsBattery will drain after about 4 hours

Only significant power consumers are heating coils and window motors

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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

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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

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Sample Sensor Package

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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

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PCB with Components

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Future Developments (Cont.)

Implement into a vehicle Install relay at each window motorMake parallel connection to direct line to

battery Install PCB module near driver Install sensors at four corners on top of

vehicle

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Vehicle Installation Schematic

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Ethical Considerations

ProEliminates 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

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Credits

Special thanks to:Austin KirchhoffProfessor MakelaMark SmartTexas InstrumentsChief Enterprises

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Thank You

Questions?