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THE DIRECT READING OF ULTRASOUND DISTANCE METER

SIT1 AFIZAH MOHD ALI HANAFlAH

This Project Report Is Submitted In Partial Fulfillment of Requirements for

the Degree of Bachelor in Electrical Engineering (Industry Power)

Faculty of Electrical Engineering

Kolej Universiti Teknikai Kebangsaan Malaysia

May 2006

ABSTRACT

Ultrasound is sound with a frequency approximately above 40kHz, greater than the

upper limit of human hearing. The ultrasound waves follow the rules of propagation

and reflection; it can be reflected and absorbed by a medium. The ultrasound can be

produced by sending a high frequency alternating for example using ultrasonic

transmitter. Hence this project is done to implement the direct reading of ultrasound

distance meter. This approach is used in order to measure the Qstance (in

centimeter) using ultrasound signal to a target. Air is used as the medium for the

ultrasound to transmit while the distance is horizontally located The SRF04 consists

of transmitter and receiver, requiring a short trigger pulse and providing an echo

pulse. The echo line is therefore a pulse whose width is proportional to the distance

to the object. Theoretically, ultrasound signal is send to a target then time is taken by

counter (clock) and finally the distance will appear at 7- segment display panel.

ABSTRAK

ClZtrasound adalah bunyi yang menghasilkan frekuensi sekitar 40 KHz yang

melebihi had pendengaran bag^ seseorang manusiaGelombang ultrmwtd

mematuhi hukum pembiasan dan pantulan dimana ia dapat dipantulkan dan diserap

oleh medium. Wtrasound boleh dihasilkan dengan menghantarkan fkkuensi yang

tinggi contohnya menggunakan pemancar ultrasonik. Justeru itu projek ini

di hasil kan untuk mengukur j arak dengan memancarkan ul~ra~ozmd. Dengan

kaedah ini sesuatu jarak dalam unit sentimeter dapat diketahui apabila ultrasound

dipancarkan ke arah sesuatu objek Medium penghantaraan adalah udara manakala

objek diletakkan secara melintang dari pemancar sernasa ujian dijalankan

Pemancar dan penerima jenis SRF04 digunakan dalam projek ini dimana ia

memerlukan signal pendek untuk dihidupkan dan akan mengbasilkan gelombang

pantulan dimana ia berkadar langsung dengan jarak dari objek tersebut. Secara

teorinya, signal ul~rmound akan dihantm ke target kemudia litar pengira akan

menentukan masa yang diambil untuk signal dipantul dan diserap semula oleh

penerima. Sebagainya outputnye, jarak akan dipaparkan pada p e l 7-bahagian

1 3 Scope

The ultrasound distance meter consists of several circuits that are very

important that need to be study of the operation and find the best design. Each

component that been needed in this project had to been specific and fulfill the

target of this project After doing research and study, below are the main

components and set as the scope of this project. It consists of three difference

circuit:

1. Triggering circuit

2. SRF04 ultrasonic circuit

3. Counter and Display circuit

1.4 Problem Statement

Before the ultrasound distance meter been develop, the users fkce some

difficulties to measure distance such as:

1. The equipments used are not high-tech created.

2. The reading is not precisely and accurate measured.

3. The devices carmot display the reading in digital d u e .

4. It required long time to complete the measure process.

These are few probIems users face using conventional equipment:

1. Geologies face difficulties to measure distance from one surface to

another surface.

2. Scientists especially surgeons have to know the exact l o d o n for

detecting cancer cell.

3. Military should able to measure opponents coordinate precisely.

Below is few application of ultrasound distance meter that been applied in industry

and commercials used:

1. To locate a school of fish

2. Medical purpose; physical therapy, cancer treatment, scanning fetus

3. Detect crack in metal widely used by geologies

4. Use as ultrasonic cleaners for jewellery, lenses

1.5 Layout of Thesis

This report consists of six chapters. Chapter 1 gives the overview of the

entire project with a summary of the project background and the objectives of the

project.

Chapter 2 consists of literahue review that been used in order to understand

and have a better view for this project. Therefore literature review on several of

topic related had been done throughout this period throughout journals, books and

related internet sites.

Chapter 3 discuss about methodology that consist of all the component that

been used for this circuit. It also included the function and the operation of each

component.

Chapter 4 consists of discussion on the result. It will show the final result for this

project

Chapter 5 will gives the recommendations for this report and highli&ts the

suggestions for the future development.

Chapter 6 will conclude the project that been develop.

CHAPTER 2

LITERATURE REVIEW

Reviews of available literature of this project have been performed to ensure

more understanding to construct ultrasonic distance meter. The areas that were

focused are on behavior of ultrasound through journals, books, and internet.

2.1 Progressive wave fields

The ultrasonic field produced by a transducer obeys all the physical laws of

wave phenomena. It can be thought of as being produced by many small point

sources making up the transducer face and thus producing a characteristic

interference pattern at any point in the field. As ultrasound is propagated fi-om the

transducer, there is a zone where the overall beam size remains relatively constant

(the near field), though there are many variations of intensity within the zone itself,

both across and along the beam axis. This zone is followed by a zone where the

beam diverges and becomes more uniform the far field. For a circular piston source

of diameter D radiating sound of wavelength lambda, the Fresne zone extends from

the transducer to a distance equal to D2/4 lambda (when D is much greater than

lambda); beyond this distance is the Fraunhofer zone of the transducer [I]. For a

given radius of the transducer, the near field becomes more complex (exhibiting

more maxima and minima) as the wavelength of the ultrasound becomes shorter.

The acoustic field of a pulsed transducer can be thought of as being

composed of contributions from all the frequencies within the bandwidth of a short

pulse. It has been shown in Figure 2.1 that the near field is less structured than that

of transducer, and that the length of the near field corresponds to that of transducer

oscillating at the centre frequency of the pulsed field.

X sin 0 = 1.22j=j

E~'4'4+r; I -4 Fnr field ' I rx

I (Fraunh~fw I Near field I zone} (Fresnel zone}

Distance from transducer ( ~ a v e l e q t h s )

W+HO 823.4

Figure 2.1 : Prediction of ultrasonic waveforms in highly attenuating plastic

materials [I].

2.2 Speed of Sound

The speed, c at which ultrasonic vibrations are transmitted through a medium

is inversely proportional to the square root of the product of the density, o and the

adiabatic compressibility, B of the material, such that in equation 2.1. The speeds

together with the frequency, f of the ultrasound determine the wavelength lambda,A

of the waves that are propagated as in equation 2.2.

2.3 Measurement of ultraslow dynamic

Ultrasonic sensors are commonly used for a wide variety of noncontact

presence, proximity, or distance measuring applications. These devices typically

transmit a short burst of ultrasonic sound toward a target, which reflects the sound

back to the sensor. The system then measures the time for the echo to return to the

sensor and computes the distance to the target using the speed of sound in the

medium .The wide variety of sensors currently on the market differ from one

another in their mounting configurations, environmental sealing, and electronic

features. Acoustically3 they operate at different frequencies and have different

radiation pattern.

i. Variation in the speed of sound

ii. Variation in the wavelength of sound .*-

111. Variation in the attenuation of sound

iv. Variation of the amplitude

2.4 Speed of Sound in Air as a Function of Temperature

In an echo ranging system, the elapsed time between the emission of the

ultrasonic pulse and its return to the receiver is measured. The range distance to the

target is then computed using the speed of sound in the transmission medium, which

is usually air. The accuracy of the target distance measurement is directly

proportional to the accuracy of the speed of sound used in the calculation. The actual

speed of sound is a function of both the composition and temperature of the medium

through which the sound travels.

speed

Temperature ( degree C)

Figure 2.2: The speed of sound is plotted as a function of the temperature. At room temperature, sound travels at -13,500 ips [2].

2.5 Wavelength of Sound As a Function of Sound Speed and Frequen.cy

The wavelength of sound changes as a function of both the speed of sound and the frequency, as shown by the expression:

Figure 2.3 is a plot of the wavelength of sound as a function of frequency at mom

temperature in air.

Wavelength

Frequency (kHz)

Figure 2.3: The wavelength of sound in air at room temperahrre is plotted as a

function of frequency

2.6 Relative Echo Levels from a Flat Surface for different Ultrasonic

Frequencies

If the sound pulse is reflected from a large flat surface, then the entire beam

is reflected. This total beam reflection is equivalent to a virtual source at twice the

distance. Therefore, the spreading loss for the sound reflected from a large flat

surface is equal to 20 log (2R), and the absomon loss is equal to 2QR. For this to

hold, it is important that the reflecting surface be both larger than the entire sound

beam to ensure total reflection, and perpendicular to the sound beam [3].

Reflecting plate

Figure 2.4: A sound beam reflected from a flat surface is equivalent to the sound as

generated from virtual transducer at an equal range behind the reflecting

plate.

tal Ultrasonic Properties

and is a vibration at a frequency above the range of human

0 kHz. The microphones and loudspeakers used to receive and

nd are called transducers. Most ultrasonic sensors use a

both transmit the sound pulse and receive the reflected echo,

,t frequencies between 40 kHz and 250 kHz. A variety of

iransducers are used in these systems. The foliowing sections

how the sound pulse is affected by some of the fundamental

of the medium in which the sound travels.

~~truc t ion and Refraction of Sound,

somd is critical in determining the acoustics of a room or concert

absorption of sound waves which produce reverbemtion

ities. More expensive ultrasound transducers have wider

and can actually be used to test concert hall acoustics on a

of the concert hall design. The speed, v is related to f aml

e time it takes for one wavelength of the sound to go by is the

Note that as f increases, h goes down, but the speed v

(2.4)

CHAPTER 3

METHODOLOGY

3.1 The Hardware Development

The flow charts of hardware development in Figure 3.1 shows the step of

progress which will be followed to achieve the project objective. The first step is

searching information, the activities in this step is to find out the resources and

references about the ultrasound distance meter. Next step is to find out the scope,

objective, problem and expectations of this project.

Step 3 is to identifl suitable circuits and components, by doing this step the

concept and the circuit operation can be understand because there are many kinds

of circuits that can operate as ultrasound distance meter.

Next step is simulation using Multisim This step is uses to simulate the

input triggering circuit. The Multisim can approve the circuit and ensure the

components that been used can give the short input for the SRF04 to activate. If the

result satisfied the condition, the input triggering circuit is been constructed. The

same method is applied for counter and display circuit before been constructed

Next step is interfkcing all the circuit that been constructed and test the

functionality. This step is to test the circuit whether it operates according to

achieve the expected result.

Finally, project realization. If the output of the circuit is within the expected

resulf which means the objective of this project is achieved

I Searching Information (

Find out scope, objectives, problem I statements and axpeutation result

I Identii suitable cimuits and components k

\..,-, triggering ~ircu~.,-*~ -.._

T

1 Consauct input triggering circuit with

Consbud crounter and display circuit

Interfacing all the circuit been constructed

Project realization

Figure 3.1 : Flow Chart of Hardware Development

.....................................

Triggering circuit

Target (wall)

.....................................

Reset - Counter and Clock 7 Segment Display * i

Figure 3.2: Block diagram of hardware design

3.1.1 General Operation of Ultrasound Distance Meter

Figure 3.2 shows that the block diagrams of hardware design. First,

transmitter will be activated to generate ultrasonic pulse after receiving pulse from

triggering circuit. Triggering circuit will generate a square pulse for a certain

length of time depending on time constant of the circuit. It is combination of two

unit of 555 timer (monostable circuit) to produce a short trigger pulse for activate

SRF04. When SRF 04 is activated, it will produce output pulse with high

frequency approximately 40 kHz (ultrasonic pulse). So the ultrasonic pulse will hit

the target (wall) that located horizontally. Then the echo pulse will hit the receiver.

The width of the pulse is actually present the flight time of sonic burst. The output

from receiver will then multiply with the frequency of square wave. The frequency

of square wave will be generated by 555 timer in counter and clock circuit. The

counter circuit is to obtain the total time for the ultrasound to travel back and

forward. It will start counting when the signal is transmitted and stop counting

upon receiving the reflected signal. The calculation for the distance is actually

done using counter circuit using 7490 counter and 7447 counter.

In this chapter, all the components that been used is discuss and explain in

details. Basically, there are three main circuits that going to be discussed. It

included:

1. Input trigger circuit

2. Transmitter & receiver (SRF04)

3. Counter and display circuit

Each component is related to each other starting from trigger circuit until 7-

segment display. Each circuit that been design is simulated using Multisim in order

to know the output of each circuit. After all circuit is design, these circuit will be

interfacing to another circuit to make it complete and produce output in terms of

distance by display the value at 7-segment display panel. Below are the descriphons

of all the related circuit that has been develop in this project

3.2 INPUT TRIGGER CIRCUIT

In this project trigger circuit is constructed to generate trigger jmlse for

activate SRFO4. Triggering circuit will generate a short triggering pulse that will be

used to activate SRFO4 with minimum value approximately lops. This circuit

consists of 555 timer, AND gate, resistors, variable resistor, capacitors with 12volt

as the input supply. Figure 3.3 shows the input triggen'ng circuit. Both 555 Timer

works as monostable multivibrator in this circuit. The second 555 Timer is used

variable resistor to generate shorter pulse compared to the pulse that generated by

first 555 Timer. Then the output fiom both timer will be multiplied at NAND gate to

get final output that has short pulse. This is because only short pulse needed as input

triggering pulse to activate SRF04.

16

555 TIMER (monostable),

-.

# I

7400 7400

555 TIMER

7400 #2

Figure 3.3: Input triggering circuit

3.2.1 555 TIMER

The 8-pin 555 timer must be one of the most useful chips ever made and it is

used in many projects. A popular version is the NE555 and this is suitable in most

cases where a '555 timer' is specified So, for this project two units of 555 timer will

be used in triggering circuit. Three of the most common circuits that using 555 IC

are:

The Astable Circuit produces a continuous train of pulses at any frequency

you require. The name "astable" means "never stable" - the output of the

circuit never stays stable in any of the two states.

The Monostable Circuit produces one pulse of a set length in response to a

trigger input such as a push button. The output of the circuit stays in the low

state until there is a trigger input, hence the name "monostable" meaning

"one stable state".

The Bistable Circnit toggles between the states. Triggering one input sets

the output to the low state, while triggering another input sets the output to

the high state. The name "bistablen means "two stable states".

$ THR 21

Figure 3.4: 555 timer

Table 3.1 : Pin function of 555 timer

iNo. Name Purpose

'1 GND Ground 1

12 TR A short pulse on the trigger starts the timer

'During a timing interval, the output stays at +V,

A timing interval can be interrupted by applying a reset pulse I

F'CV Control voltage allows access to the internal voltage divider (Zn Vcc) I

16 THR The threshold at which the interval ends I

Connected to a capacitor whose discharge time will influence the, 17 DIS I

I timing intend 1

v+, '8 The positive supply voltage which must be between 5 and 15 V

:Vcr

3.2.1.1 Operation of 555 Timer

All IC timers rely upon an external capacitor to determine the off-on time

intervals of the output pulses. It takes a finite period of time for a capacitor (C) to

charge or discharge through a resistor (R). Those times are clearly defined and can

be calculated given the values of resistance and capacitance.

The basic RC charging circuit is shown in Figure 3.5. Assume that the

capacitor is initially discharged. When the switch is closed, the capacitor begins to

charge through the resistor. The voltage across the capacitor rises fiom zen, up to

the value of the applied DC voltage. The time that it takes for the capacitor to charge

to 63.7% of the applied voltage is known as the time constant (t). That time can be

calculated by simple expression:

Trigger . . . . . . . . . . . . : Extended pulse does - . - - . - . . - - . .

Capacitor fl 213 Vcc Voltage .----

: o v - . . . . . - . . . . . - . . . . - . . . . . . . . . - . . . +Vcc

Output I-- .- o v -c t i -

+ vcc Reset

o v A reset pulse applied during timing interval terminates the output pulse

Figure 3.5: Input and Output pulse for 555 Timer

3.2.1.1.1 555 Timer as A Monostable Circuit

Figure 3.6: Monostable Circuit

Figure 3.6 shows that when 555 IC is used to produce an monostable circuit-

it only will pulse once. Monostable circuits can be used to turn lights/LED on or off

just once. The easiest way of recognizing that a 555 IC has been set up as

monostable when Pin 6 and Pin 7 are connected together and go to the positive

terminal.

Monostable multivibrator often called a one shot multivibrator is a pulse

generating circuit in which the duration of this pulse is determined by the RC

network connected externally to the 555 timer. In a stable or standby state, the

output of the circuit is approximately zero or a logic-low level. The time for which

output remains high is determined by the external RC network connected to the

timer. At the end of the timing interval, the output automatically reverts back to its

logic-low stable state. The output stays low until trigger pulse is again applied Then

the cycle repeats.

The monostable circuit has only one stable state (output low) hence the name

monostable.The waveforms in figure 3.7 illustrate the operation of a monostable. A

monostable circuit produces one pulse of a set length (time period T) in response to

a trigger input such as a push button. The output of the circuit stays in the low state

until there is a trigger input, hence the name "monostable" meaning "one stable

state".

This type of circuit is ideal for use in a "push to operate" system. Testing can

be done by pushing a button to start a model's mechanism moving, and the

mechanism will automatically switch off after a set time. Another use for the circuit

is to 'de-bounce' a push button input to a digital.

TRIGGER INPUT

-C( MONOSTABLE TRIGGERED

GUTPUT m*mE m -

TIME PERIOD T

Figure 3.7: Monostable input and output waveform

A monostable circuit produces a single output pulse when triggered It is

called a monostable because it is stable in just one state: 'output low'. The 'output

high' state is temporary. The circuit diagram of the 555 monostable circuit is given

in figure 3.6 Notice that the resistor value R and the capacitor d u e C are

unspecified. The values of these components determine the length of time that the

monostable output is in the high state, and they may be calculated using the equation

below.

The duration of the pulse is called the time period (T) and this is determined

by resistor R 1 and capacitor C 1 :

timeperiod, T = 1.1 x Rl x C1 (3.2)

3.2.2 The 74LS00 IC

The output is high when either of inputs A or B is high, or if neither is high.

In other words, it is normally high, going low only if both A and B is high.

GND 4 Figure 3.8: The 74LS00 IC

Table 3.2: Truth table for AND Gate

I INPUT / OUTPUT /

3.2.3 Troubleshooting the input triggering circuit

Troubleshooting for this circuit is done to make sure the output is supposed

to be. Figure shows the complete circuit for input triggering circuit. So by putting

LED at each timer and at 7400 IC it will show the sequence of the lighting as in

simulation using the Multisim. Once the push button is push, LED 1 and LED 3 at

both timer will light on but LED 3 at the second timer light off first Shortly after

that, the LED 5 at 7400 IC will light on in a short time as the final output that going

to be the input triggering circuit for SRFO4. Another method is used to troubleshoot

this circuit is by using oscilloscope. When the push button is push, a short pulse can

be detected occur showing that a small pulse is been generated by this circuit.

This high performance ultrasonic range finder is compact and measures an

amazingly wide range from 3cm to 3m. The sensor transmits a burst of pulses; if there

is a sonically reflective obstacle, then that burst will be reflected back to the receiver

component of the sensor. The sensor works by ultrasounds and contains all the

electronics in charge to make the measurement. Its use is as simple as to send the

starting pulse and to measure the width of the return pulse. Of very small size,

SRF04 emphasizes by his under consumption, high accuracy and low price. The

figure to the right shows the simple case. Our job is to determine the range d given

that we can measure the time taken to get the echo. The first important thing to know

is the speed (velocity) of sound in air, Vs, at sea level, at room temperature, which is

approximately:

Vs = 343 meters per second

So, if we know the amount of time between the transmission and the

reception (t, in seconds) then all we need to do is half t (because t represents a return

trip) and multiply by the speed of sound.

That is:

t dzstance,r = Vsx -

2

where r is in meters