Rain Detection System
for Power Windows in
Automobiles
Group Four
Brian Mitterer, Rob Herzog, Chintan Patel
ECE 445 Senior Design
Rain
Detection
System
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
Rain
Detection
System
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

Rain
Detection
System
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
Rain Detection System
Rain
Detection
System
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.
Rain
Detection
System
Overall Block Diagram
Sensors
Override Switch/ Control
Microcontroller
Car Battery
Motor / car controller for
power windows
Voltage Regulator
Rain
Detection
System
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

Rain
Detection
System
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
Rain
Detection
System
Senor # 1 Diagram
Rain
Detection
System
Sensor # 1 Performance

Resistance
Sponge Thickness (in.)
1/4
1/2
1/8

needed to be soaked to detect
Dry Time


2.4 MΩ
3.0 MΩ
1.6 MΩ
Sensitivity


Avg. Resistance (Ohms)
~ 4 - 6 hours
Reliability

sponge will decay over time
Rain
Detection
System
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.
Rain
Detection
System
Sensor # 2 Diagram
Rain
Detection
System
Sensor # 2 Performance
Clay failed to rise significantly and push
the plate upwards in order to break the
contact
 Design idea was discontinued

Rain
Detection
System
Sensor # 3 Overview
Uses rain droplets to complete circuit that
sources current to microcontroller input
 Consists of interweaving copper tracks on
an ordinary PCB

Rain
Detection
System
Sensor # 3 Diagram
Rain
Detection
System
Sensor # 3 Performance

Resistance
 Varies

Sensitivity
 Varies

by track spacing
Dry Time
 ~1

by track spacing
hour
Repeatability
 Very
repeatable and consistent
Rain
Detection
System
Sensor # 3 Performance
1/8 inch spacing
1/4 inch spacing
Rain
Detection
System
Sensor # 3 Performance
Resistance (kohms)
Sensor Resistance Vs. Number of Drops of Rain
Number of Drops
Rain
Detection
System
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
Rain
Detection
System
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

Ri
Vout  Vin 
 Ri  Rsensor

1000k



5


  4.17V
 1000k  200k 

…after one drop
Rain
Detection
System
Sensor Module Schematic
Rain
Detection
System
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
Rain
Detection
System
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

Rain
Detection
System
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

Rain
Detection
System
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

Rain
Detection
System
Vehicle Interface Schematic
Rain
Detection
System
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

 Rout 
 100k 
Vout  Vin 
  5V  12V 

 100k  R2 
 Rout  Rin 

R2 = 140 k ohms
Use 100 K ohms for drop
down resistor
Rain
Detection
System
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
Rain
Detection
System
Sensor Heating Element
Rain
Detection
System
Software: PIC Flowchart
Sensors Fire?
Is Override
Switch on?
Is Override
Switch on?
Activity on the
window switch?
Turn on motor for
10 seconds and
then turn off
Turn on Heat for 5
minutes
Rain
Detection
System
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
Rain
Detection
System
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
Rain
Detection
System
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

Rain
Detection
System
Sample Sensor Package
Rain
Detection
System
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

Rain
Detection
System
PCB with Components
Rain
Detection
System
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
Rain
Detection
System
Vehicle Installation Schematic
Rain
Detection
System
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
Rain
Detection
System
Credits

Special thanks to:
 Austin
Kirchhoff
 Professor Makela
 Mark Smart
 Texas Instruments
 Chief Enterprises
Rain
Detection
System
Thank You
Questions?
Rain
Detection
System