project

 

 

 

 

 

 

 

                  CONCEPT OF PROJECT WORK

 

 

 

 

 

 

                                      

project work is nothing but doing some technical work under proper guidence. this is done usuallyby the      students and  every work to achieve its final objhectives or goals. This naturally relates to project work also.Before starting any project planning  must be done weather which projet should be selated.How it should performed etc  SO planning must be done either when beginning an enterpriseor to maintain any industry.So planning must be done very carefully as the effiency of our project depends on planning, improper planning will run the project

                   India is the second laregest countary regarding its population. The Govt is unable to provide empolyment forall the educated people,so it is putting more stress on techanical people to start their own industries under what will call "SELFEMPLOYMENT SCHEME " This helps in eradecating unempolyment and inproviding livelihood to educated unempolyment students.Govt is encouraging the enterperneurs by gaining laons to start enterprise. For this bank stared to provide new empolyment oppertunties by giving laons for small scale sectors called industrial develpoment bank of india It hs been enagaged in the folk of promotion from its financing of the small scale secoters from its inception .It sanctions to small scale secoters from its finencing of the small scale sectors have  incersed stedialy overthe year in 1970 to 1975.

If it is rs 1.30 crores at about 16% of total assistance distributed.in 1975 to 1980 its incresed to rs.990 croes to 26% and in 1980-1985. There after it further incerased to rs. 3700 croeses at any individual icannot start his industry without a proper knowledge about the project work as became a necessary "must" to techanical students. For this section reason project work has been inculed in the syallabus. the BTECH courese by the jntu hyderabad universites. this server as a gudencnce if not only individual starts an industry . This project work helpful for an individalfor his  livelihood but also indirectly helpful to the country.

                                  

                                             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.  collisions do not terminate with damage to one or two vehicles, rather, an ar ray 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  ultrasonic transceivers 

 

INTRODUCTION

STUDIES AND STATISTICS ON CAUSES OF ACCIDENTS AND ACCIDENT PREVENTION

GENERAL PRINCIPLES IN COLLISION AVOIDANCESYSTEMS

STOPPING DISTANCE AND ASSOCIATED FACTORS

VEHICLE BRAKING CAPABILITY

CALCULATING STOPPING DISTANCE

BLOCK DIAGRAM EXPLANATION

PSOC MIXED SIGNAL  CONTROLLER: CY8C27443

HALL EFFECT SENSOR ALLEGRO A1142

ULTRASONIC TRANSDUCER SQ40 T/R

PSOC RANGE MEASUREMENT

                                                  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

It is well known that driver errors are the main cause, orcontribute to increased severity, of most accidents. Forinstance, the Indiana Tri-level (Treat et al. 1979) founddriver errors to be a cause or severity-increasing factorin 93% of the accidents.

Furthermore,27% of allaccidents (USA 1997) were rear-end collisions. Thisshows the potential of forward collision avoidance (FCA)systems. The crucial part of the algorithm is the decisionmaking, and the conflicting considerations are:

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 2010 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.

   

           GENERAL PRINCIPLES IN COLLISION AVOIDANCESYSTEMS:

A collision avoidance system operates, generally,in the following manner: a sensor installed at thefront-end of a vehicle constantly scans the roadahead for vehicles or obstacles. When found, thesystem determines whether the vehicle is inimminent danger of crashing, and if so,automatic brakes should be applied .Usually one of these two criteria is used toactivate collision avoidance:

Worst-case criterion: The system assumes thatthe vehicle preceding the CAS-equipped vehiclecould brake at full braking power at any time. Inessence, it operates on a critical headwaydistance," that is, theminimum distancenecessary for the CASequipped vehicle to come to a stop in the event the leading car suddenlybrakes.

Time-to-collision criterion: The systemdetermines whether a collision is likely tohappen at prevailing speeds and distances withina certain time interval. In a  , time-to-collision is defined as the timeduration for the two vehicles to collide if theymaintain theirpresent speed and direction.Collision avoidance maneuvers include one ormore of the following actions:

Headway distance control: The system warns thedriver whenever his/her car isfollowing theleading car too closely. Some systems includeautomatic speed control, i.e., the CAS-equippedcar would automatically reduce its speed in orderto maintain a safe headway with the leadingvehicle

Hazard warning: The system warns the driver ofan object (moving or stationary) within itsprojected path so that the driver has sufficienttime to avoid a crash.

Automatic vehicle control: The system controlsthe vehicle's brakes and steering wheel, andapplies them automatically when it deems itnecessary. In actuality, there are currently nosystems that use automatic steering to preventcollisions, although the technology has beendeveloped and tested experimentally.

                 

                            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

The Automobile brakes are classified  according to the  different bases, as follows

1.    With respect to application :

(a)    Foot brake

(b)   Hand brake.

      2 .With respect to the numer  of wheels:

(a)   Two wheel brake 

(b)  Four wheel brake.

    3.With respect to the method of braking contact:

           (a) Internal expanding brakes.

           (b)external  contracting brakes

    4. With respect to the method of applying  the braking  force:

            (a) single acting  brakes

             (b) double acting  brakes.

     5 . With respect to the brake gear:

(a)   Mechanical  brakes.

(b)  Power brakes.

     6.  With respect to   the nature of power employed:  

(a)    Vacum brakes

(b)    Air  brakes

(c)      Hydraulic  brakes

(d)     Hydrostatic  brakes

(e)      Electric brakes. 

     

      7.   With respect to power transmission:

             (a) Direct acting brakes

             (b)  Geared brakes.

       8.    With respect to  power unit :

               (a) Cylinder brakes

               (b) diaphragm  brake,

                

              suspension system

The automobile frame and body are mounted on the front and rear axle not directy but some form of spring and shock absorbers.this done danp to raod

Shocks  transmitted  parts to the frame by the  wheels as they roll over the raod.  All these parts perform this function are collectively  called a suspenSion  system .Thus  the  suspension sytem includes springs , shockabsorbers and  their mounting s.The  suspension system of moter vechile is divided into

The rear-end  suspension and front  end suspensio

  Functions of  suspension sytem

1.    To prevent  the raod shocks from being  transmitted  to the  vechile frame

2.    To  preserve the stability of the vechile in pitching or rolling , while in motion

3.    To  safegured  the occupants from raod shocks

4.    To provide good raod  holding while driving ,corning and braking

5.    To maintain proper steering gemontery

      Tyre pressures

The tyre is  designed to be operated at certain pressure to the weiht and characteristics of the vehicle . Every manufarcturer recommends to maintain

The correct tyre pressure. In correct tyre pressure overheating , rapid tyre wear and unsafe steering If the tyre pressure is correct , tyre will have full tread contact with raod surface

    Trye tread and grip

 1.Front  tyre  shows an excessive  wear only on one side of the theard.  Check  camber.  If  it is correct, wear must be ascribed to the habbit of

Negotianing curves  at high speeds

 2. Tyres   shows a wear  particularly remarkable  on the both sides  of 

Tread rater  than  on the centre portion . Tyres   are inflated  at a pressure

Lower than specified . Under  such conditions ,the tread side surfaces are

Supporting most of the laod, while centre portion is deflected upwards

3.Tyres  shows wear on the  tread centre poration . tyres are inflated  at 

Pressure higer than specified. Under such conditions , tread cenral  portion is suppoting most of the  laod 

brake pad material

An automotive brake functions by converting thepedal, brake fluid is effectively pushed against the pistons vehicle’s kinetic energy into heat energy. During brakingof the brake caliper, which in turn forces the brake pads the heat energy is first borne by the two contact surfacesof the brake, namely the brake disc and the brake pad

brake alignment

vehicle weight

The co-efficient of friction of the road surface

wind speed

Wind is simply air in motion. It is produced by the uneven heating of the earth’s surface by energy from the sun.

slope of road

surface smoothness

The braking technique applied by the driver

Brake testing

 When the vechicle moving , it can be stopped by applying by applying  the brakes. It is to be noted here that brake peals cannot be passed instantaneously and the vehicle cannot be stopped instantaneously. First driver thinks, then lift the leg , presses the brake pedal and then the vehicle stop after moving some distance . So it is necessary to note how much time is required to stop the vehicle and how long it will travel after applying the brake . these two factors are directly dependent on the speed of  vehile.

1. stop test. For testing the brakes, this test is usually adopted by mechanic or driver after overhauling the brakes. He moves the vehicle at a speed and suddenly applies the brakes.  Then he checks how much time it has taken to stop and how long it has moved after applying  the brakes . Also he sees the impression of the four tyres on the raod, whether equl or not, and wheater the vehicle is pulling a side  or  not

2.stop watch test; to perform this test,the  vehicle is moved at about 70km/hr.

Then the brakes are applied . The time distance are noted

Let T=time taken to stop the vehicle after applying the brakes

D=distance moved by the vehicle after applying the brakes.

Then,brake efficiency is given by

n=(D-T²)*6.25

3.Brake testers are also used for testing the brakes. they work on the principle

Of decelerometer.  Taply  brake meter is a type of brake tester. This  brake meter is placed on the vehicle floor for testing the brakes. It consists of a round ring with numbers . There is pendulum inside the dial which remain dipped in oil. As soon as the vechile speed decreases which causes the pendulum ring to move. The  number on, the ring gives reading which can be Obtained by an inspection plate

         

                       

                 

                      

                             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 onthe 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:

             Work       = - umgd = - (mv₀²)/2       

                    _Friction

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

  What is Sensing ?

Collect information about the world

    Sensor - an electrical/mechanical/chemical device that maps an environmental attribute to a  quantitative measurement

Each sensor is based on a transduction principle - conversion of energy from one form to another

          `                   

                                  

                           BLOCK DIAGRAM EXPLANATION

As we can see, the major components required are:

PSoC Mixed-Signal Controller - CY8C27443

Ultrasonic Transducer – SQ40 T & SQ40 R

Hall Effect Sensor – 1142

      

  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 r eceiver SQ40R. The time from transmission to echo reception helps to calculate thedistance  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  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  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  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,

  V₀is the velocity at which it was travelling at the instant just before breaking

 u is the co-efficient of static friction

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 sur face  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 ar e 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:

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

2. The current velocity of the vehicle.

3. The climate selection at present, and

4.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 thestatus  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 speedor 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 f or 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

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

MORE ON THE MAJOR HARDWARE USED

     

         

               

       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 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

            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

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  advancedSBiCMOS 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. 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

  

                   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  thetransmitted 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 -40 ⁰ C to 85⁰ C

            

Limitations: The Ultrasonic transducer  has two  major limitaions -  narrow beam  angle  and weak received signal strength. The beamwidth is  close  to  55, which means that  only  if  the  obstacle  is almost  right  infront  of  the  transmitter  can the  waves  be  reflected  towards  the  recevier.  A  deviation  of  the  obstacle  will  hinder  the  process  of  range  detection  or  obstacle  detection practical models, multiple transducers will be required for efficient obstacle detection practical models, multiple transducers will be required for efficient obstacle detection 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.

                  

                      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.

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 lar ge 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 Times New Roman temperature value of 22°C:

                          

                                

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  tr ansmission  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 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).