MAIN PROJECT

DRAFT REPORT

HIGHWAY LINEAR COLLISION PREVENTION IN

AUTOMOBILES

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PROJECT ABSTRACT

We propose to design a device which could be used by automobiles in the highway for the purpose

of collision prevention. The main objective of this project is to avoid collisions between vehicles

which results in losses in massive proportions to life and economy. We will be specifically dealing

with accidents caused when a multitude of vehicles travelling in a linear manner collide. Such

collisions do not terminate with damage to one or two vehicles, rather, an array of cars go smashing

into one another.

So, we intend to design ultrasonic sensors (transceivers) both at the front and rear of a vehicle in

order to detect the range of another vehicle which is in its immediate vicinity. The data from the

transceivers along with the velocity of the vehicle and an emergency input from the driver of each

vehicle could be used to determine the status of the vehicle. This status, if found alarming will be

transmitted backwards to the vehicle immediately behind it. The vehicle which receives this “alert”

code, will take steps to slow down and also pass on the same code to the vehicle behind it, and so

on the code gets transmitted to all vehicles behind the troubled car which are in range of the

ultrasonic transceivers.

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INTRODUCTION

First of all it is very important that we understand the need for a collision prevention system in

automobiles. These are some of the statistics that compelled us to take up a small step towards the

prevention of road accidents, particularly Forward Collision.

There are 1.2 M fatalities yearly worldwide due to road accidents - 3242 people a day!

According to the World Health Organization, road accident fatalities worldwide are

expected to rise by 67% by the year 2020.

Over 20 million people are injured each year in road accidents

Financial damages of road accidents are ~2% of world GDP.

In the US, in 2003 there were 6 million accidents, costing $230 million; averaging $38,000

per accident – these statistics have been steady in recent years.

Studies and Statistics on Causes of Accidents and Accident Prevention:

93% of all accidents are due to human factor (Driver inattention cited as the primary cause

for accidents).

Nearly 80% of all crashes involve driver inattention within three seconds before the event.

Examples of types of inattention that increase crash risk:

Talking on a cell phone (increases risk by 30%)

Drowsiness (increases risk by 400% and responsible for ~23% of all crashes and

near-crashes)

Reaching for moving objects, like a falling cup (increases risk by 900%)

One in every five vehicle accidents is caused by drowsiness at the wheel, momentary

drowsiness or inattentiveness.

Run off road accidents account for nearly 20% of road accidents and are responsible for

60% of all road accident fatalities.

“In a study done at Volkswagen, an analysis of the pre-crash braking behavior shows that in

severe accidents about 85% of drivers either did not brake at all or not to the full possible

deceleration.”

Rear-end collision accidents account for about 28% of road accidents.

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STOPPING DISTANCE AND ASSOCIATED FACTORS

Many drivers drive in a false belief that if the car in front suddenly started braking, they would react

and brake and end up stopped the same distance apart.

The total stopping distance of a vehicle is made up of 4 components:

Human Perception Time: The human perception time; is how long the driver takes to see the

hazard, and the brain realize it is a hazard requiring an immediate reaction. This perception

time can be as long as ¼ to ½ a second.

Human Reaction Time: Once the brain realizes danger, the human reaction time is how long

the body takes to move the foot from accelerator to brake pedal. Again this reaction time

can vary from ¼ - ¾ of a second.

These first 2 components of stopping distance are human factors and as such can be

affected by tiredness, alcohol, fatigue and concentration levels. A perception and reaction

time of 2 or 3 seconds is possible. 2 seconds at 75 km/hr means the car travels 40 metres

before the brakes are applied.

Vehicle Reaction Time: Once the brake pedal is applied there is the vehicles reaction time

which depends on the brake pedal free-play, hydraulic properties of the brake fluid and

working order of the braking system.

Vehicle Braking Capability: The last factor than determines the total stopping distance is the

cars braking capability which depends on factors such as;

the type of braking system,

brake pad material,

brake alignment,

tyre pressures,

tyre tread and grip,

vehicle weight,

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suspension system,

the co-efficient of friction of the road surface,

wind speed,

slope of road,

surface smoothness

the braking technique applied by the driver

CALCULATING STOPPING DISTANCE

Assuming proper operation of the brakes on the vehicle, the minimum stopping distance for a

vehicle is determined by the effective coefficient of friction between the tires and the road, and the

driver's reaction time in a braking situation. The friction force of the road must do enough work on

the car to reduce its kinetic energy to zero. If the wheels of the car continue to turn while braking,

then static friction is operating, while if the wheels are locked and sliding over the road surface, the

braking force is a kinetic friction force only.

To reduce the kinetic energy to zero:

WorkFriction = - umgd = - (mv02)/2

so the stopping distance is:

d = (v02)/2ug

For calculating minimum stopping distance, we have provided two modes:

Dry Weather: The value of u is taken .8

Wet Weather: The value of u is taken .5

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BLOCK DIAGRAM

As we can see, the major components required are:

PSoC Mixed-Signal Controller - CY8C27443

Ultrasonic Transducer – SQ40 T & SQ40 R

Hall Effect Sensor – 1142

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BLOCK DIAGRAM EXPLANATION

1. ULTRASONIC TRANSDUCERS (SQ40 T/R)

The ultrasonic transducers are used with a dual purpose. The major and mostly common purpose is

that of detecting the range of an obstacle in front of the vehicle. This distance when coupled with

the velocity at which it is travelling gives us an idea about the safety of the vehicle.

The ranging works by transmitting a short pulse of sound at a frequency of 40Khz (ultrasonic sound

or ultrasound) through the transmitter SQ40T. Afterwards the microcontroller listens for an echo

through the receiver SQ40R. The time from transmission to echo reception helps to calculate the

distance from the object. The time from transmission of the pulse to reception of the echo is the

time taken for the sound energy to travel through the air to the object and back again.

Since the speed of sound is constant through air measuring the echo reflection time lets you

calculate the distance to the object using the DST equation:

Distance = (s * t)/2 (in metres)

2. HALL EFFECT SENSOR FOR VELOCITY

The Hall Effect sensor can sense changes in magnetic field and changes its output accordingly. If a

magnet is mounted on any rotating part of a moving vehicle (which is proportional to the velocity),

the change in output from the sensor will indicate the rpm of the rotating part. This rpm when

multiplied by a suitable circumference value will produce distance travelled in a minute. Thus we

can have the velocity of the vehicle.

3. USER DISCOMFORT SWITCH

If the user feels any discomfort during the journey, like a possible chest pain, this switch enables

him to communicate the data to the vehicles behind him. This will alert the other drivers of a

likelihood of breaking. This can help save critical reaction time on part of the drivers behind the

vehicle under scrutiny.

4. CLIMATE SELECT SWITCH

The stopping distance of a moving vehicle is given by the formula:

d = (v02)/2ug

Here, d is the distance required to bring the vehicle to a halt in metres,

v0 is the velocity at which it was travelling at the instant just before breaking,

u is the co-efficient of static friction

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and g is the acceleration due to gravity (9.8m/s2)

The co-efficient of static friction has a nominal value of 0.8 provided that the road surface is dry

and the tires are in good condition. The same value can degrade to 0.5 when the road surface

becomes wet or the tires are old or in bad condition. So based on the conditions, we have allowed

the user to select the appropriate mode in which the stopping distance is to be calculated.

5. LCD DISPLAYING ESSENTIAL DATA

The LCD display will provide the user with details such as:

i. Real-time distance from a vehicle/obstacle in front of it.

ii. The current velocity of the vehicle.

iii. The climate selection at present, and

iv. The status of the drive, whether it is under alert or not.

6. AUDIO AND VISUAL ALERTS

Audio visual alerts are useful for alerting the driver in case he is not looking at the LCD for the

status of his drive. The audio alerts includes a buzzer that switches on at the time of an alert

situation, and a bicolour LED which produces yellow colour during normal drive, and red colour at

times of alert.

7. PWM SPEED CONTROL

The PWM speed control is the method used for controlling the speed of the vehicle, (for

demonstration purposes we use DC motor driven miniature cars). We will be assigning 5 levels of

speed to these cars and according to the situation; they will be allowed to either increase the speed

or decrease by means of varying the duty cycle of the PWM.

8. PSoC MIXED SIGNAL CONTROLLER: CY8C27443

The PSoC Mixed Signal controller is more than just a microcontroller. It is a 28 pin IC with three

I/O ports. These ports can be used for analog or digitals functions. The advantage of PSoC is that it

integrates ASIC, FPGA and the usual code controlled functions of a microcontroller into a single

unit.

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The model can accommodate up to 8 digital blocks and 12 analog blocks within itself.

Digital blocks include – PWMs, Counters (8 to 32 bit), Timers (8 to 32 bit), UART 8 bit with

selectable parity (up to 2), SPI master and slave (up to 2), I2C slave and master (1 available as a

System Resource), Cyclical Redundancy Checker/Generator (8 to 32 bit), IrDA (up to 2) and

Pseudo Random Sequence Generators (8 to 32 bit).

The analog blocks include - Analog-to-digital converters (up to 4, with 6- to 14-bit resolution,

selectable as Incremental, Delta Sigma, and SAR), Filters (2, 4, 6, and 8 pole band-pass, low-pass,

and notch), Amplifiers (up to 4, with selectable gain to 48x), Instrumentation amplifiers (up to 2,

with selectable gain to 93x), Comparators (up to 4, with 16 selectable thresholds), DACs (up to 4,

with 6- to 9-bit resolution), Multiplying DACs (up to 4, with 6- to 9-bit resolution), High current

output drivers (four with 30 mA drive as a Core Resource), 1.3V reference (as a System Resource),

DTMF dialer, Modulators, Correlators, Peak detectors and a few more.

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MORE ON THE MAJOR HARDWARE USED

1. PSoC Mixed-Signal Controller - CY8C27443

PSoC® (Programmable System-on-Chip) is a family of mixed-signal arrays made by Cypress

Semiconductor, featuring a microcontroller and configurable integrated analog and digital

peripherals. PSoC is software configured, mixed-signal array with built-in MCU core. The core is a

Cypress proprietary, very-small Harvard architecture machine called the M8C. The M8C is an 8-bit

machine with a rich 256 instructions. PSoC has three separate memory spaces: RAM, Flash and IO

Registers (which control and access the configurable blocks and fixed functions). The device is

created using SONOS technology.

PSoC resembles an ASIC in its flexibility and integration: blocks can be assigned a wide range of

functions and interconnected on-chip. Unlike an ASIC, there is no special manufacturing process

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required to create the custom configuration - only startup code which is created by Cypress' PSoC

Designer IDE.

PSoC resembles an FPGA in that at power up it must be configured, but this configuration occurs

by loading instructions from the built-in Flash memory. Unlike an FPGA, the current generation of

PSoC cannot have its digital functions reprogrammed by VHDL or verilog; it can only be

configured with register settings.

PSoC most closely resembles a microcontroller in usage, since the programs written by a user

execute code to interact with the user-specified peripheral functions (called "User Modules"),

utilizing automatically generated APIs and interrupt routines. PSoC Designer IDE generates the

startup configuration code and peripheral APIs automatically based upon the users selections in a

visual-studio-like GUI.

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2. Hall Effect Sensor – Allegro A1142

INTRODUCTION

The Hall Effect was discovered by Dr. Edwin Hall in 1879 while he was a doctoral candidate at

Johns Hopkins University in Baltimore. Dr. Hall found when a magnet was placed so that its field

was perpendicular to one face of a thin rectangle of gold through which current was flowing, a

difference in potential appeared at the opposite edges. He found that this voltage was proportional

to the current flowing through the conductor, and the flux density or magnetic induction

perpendicular to the conductor.

Hall Effect devices when appropriately packaged are immune to dust, dirt, mud, and water. These

characteristics make Hall Effect devices better for position sensing than alternative means such as

optical and electromechanical sensing. Hall Effect devices used in motion sensing and motion limit

switches can offer enhanced reliability in extreme environments. As there are no moving parts

involved within the sensor or magnet, typical life expectancy is improved compared to traditional

electromechanical switches. The sensing of wheel rotation is especially useful in anti-lock brake

systems. The principles of such systems have been extended and refined to offer more than anti-

skid functions, now providing extended vehicle "handling" enhancements.

APPLICATION

A Hall Effect sensor is a transducer that varies its output voltage in response to changes in magnetic

field density. Hall sensors are used for proximity switching, positioning, speed detection, and

current sensing applications.

Hall sensors are commonly used to time the speed of

wheels and shafts, such as for internal combustion engine

ignition timing or tachometers. In the pictured wheel

carrying two equally spaced magnets, the voltage from

the sensor will peak twice for each revolution. This

arrangement is commonly used to regulate the speed of

diskette drives.

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ALLEGRO A1142 DESCRIPTION

The A1142 device is sensitive, two-wire, unipolar, Hall Effect switches that are factory -

programmed at end-of-line to optimize magnetic switchpoint accuracy. These devices use a

patented high frequency chopper stabilization technique, produced using the Allegro advanced

BiCMOS wafer fabrication process, to achieve magnetic stability and to eliminate offset inherent in

single-element devices exposed to harsh application environments.

Commonly found in a number of automotive applications, these switches are utilized to sense seat

track position, seat belt buckle presence, hood/trunk latching, and shift selector position. The

A1142has the following output: the currents switch LOW in the presence of a south-polarity

magnetic field of sufficient strength, and switch HIGH otherwise.

This shows the output characteristic of the sensor.

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3. ULTRASONIC TRANSDUCER SQ40 T/R

The word Ultrasonic means „above sound‟, which means above the human hearing range which is

approx 300Hz to 14 KHz. Therefore any frequency that is above the human hearing wavelength and

below the low frequency RF wavelength may be considered as ultrasonic or „ultrasound‟.

Ultrasonic ranging is performed by transmitting a pulse of high frequency sound, then counting

how long it takes for its echo to be detected. Because sound through a given medium (liquid or air)

is a known quantity, it can be considered a constant, the length of time taken between the

transmitted pulse and the received echo can be converted into distance. This is called Time of Flight

(TOF).

The SQ40 as the name suggests, operates at 40Khz. This is the frequency at which the sensitivity of

the ultrasonic receiver is greatest. The transmitter is the one marked SQ40 „T‟ and the receiver is

the other, which is marked as SQ40 „R‟. Its operating range is -400 C to 85

0 C.

Limitations: The Ultrasonic transducer has two major limitaions - narrow beam angle and weak

received signal strenth. The beamwidth is close to 550, which means that only if the obstacle is

almost right infront of the transmitter can the waves be reflected towards the recevier. A slight

deviation of the obstacle will hinder the process of range detection or obstacle detection. In

practical models, multiple transducers will be required for efficient obstacle detection.

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The received signal strength is another hindrance towards the comfortable working of the device as

the received signal at the receiever is only at about a few millivolts. This has to be greatly

amplified and filtered before it can be verified as being a legitimate signal from noise signals.

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PSoC RANGE MEASUREMENT

There are several ways to measure distance without contact. Some products have infrared light

emitters and receivers that determine an object‟s distance by implementing the optical triangulation

method. Other devices have laser-based systems that increase accuracy and precision. For

electrically conductive metal objects, the eddy current method is an option, and capacitive sensors

that are independent of the metal used in the measured objects can be used.

The PSoC range finder measures the amount of time it takes for a pulse of sound to travel to a

particular surface and return. Then, the device calculates the distance based on the estimated speed

of sound. The only required components are a PSoC microcontroller, two 40-kHz ultrasonic

transducers, two resistors, and two capacitors. Similar circuits are typically complicated and

expensive, consisting of a large number of integrated circuit and passive components.

The block diagram of range measurement module is divisible into two parts: the transmitting

section and receiving section. Each section contains several PSoC blocks. Using the PSoC chip

family, all of the digital and analog devices are on-board with the microcontroller.

Several PSoC microcontroller resources were used in this module. The following PSoC digital

resources were used: five 8-bit counters, an 8-bit serial transmitter, two 8-bit PWMs, and a digital

inverter. The following analog resources: one programmable gain amplifier (PGA), two two-pole

pass band filters, a programmable threshold comparator, and a reference multiplexer. In addition,

the LCD toolbox software module is also.

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This is a screen shot of the PSoC Designer with the Device Editor showing the placement of the

PSoC‟s digital and analog resources. As you can see, a large number of resources are required. All

of the digital blocks and several analog blocks are employed. For this application, all of the digital

blocks are required.

The software modules include the LCD toolbox user module and a complete set of library routines

that allows you to write numbers and strings to a two-line LCD using standard Hitachi HD44780

commands.

PRINCIPLES

The transmission section is based on four digital blocks allocated in the DBA00, DBA01, DBA02,

and DBA03 blocks. An 8-bit counter (called "Time Base") provides a 17,240-Hz time base

frequency. Sound velocity depends on ambient air temperature, which is calculated for an air

temperature value of 22°C:

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where T is equal to the air temperature (°C). So, for a middle value of 22°C:

For a round-trip ping, we have:

And with a 24-MHz MCU clock and period of 12:

An 8-bit counter (F40kHz) drives the ultrasonic transmitter and a digital inverter (F40kHz_inv).

The phase of the voltage applied to the positive and negative terminals of the sensor has been

shifted 180°, so two times the supply voltage is applied to the sensor.

The 40-kHz transmission enables an 8-bit counter (called "Meter") that increments one step per

centimeter. The Meter clock input is Time Base (17,240 Hz).

The ultrasonic receiver‟s positive terminal is connected to an amplification chain based on a

programmable gain amplifier (PGA_1) and two two-pole pass band filters (BPF2_1 and BPF2_2).

The first pass band filter is designed for a 40-kHz center frequency and a correspondent gain of 33

dB. The second filter is also designed for a 40-kHz center frequency, but it has a 10-dB passband

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gain. Because of the discrete value of the capacitors integrated in the switched-capacitor analog

blocks, the real frequency response is different from the nominal one.

The range detection module has a 40-kHz operating frequency, a range of 25 to 200 cm, and 1-cm

resolution. In addition, it requires only a single 5-VDC power supply and draws just 25 mA (23 mA

without the LCD).