Ultrasonic Range Meter
Senior Project Submitted to the Department of Computer and Communication
EngineeringAmerican University College of Science and Technology
In Partial Fulfillment of the Requirements for the Degree of Bachelor of Science
InComputer and Communication Engineering
Maroun Daher Rami Freih
Gaby Al Jawabira
August 2006
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Abstract
The Ultrasonic Range Meter is an efficient way to measure the distance of unreachable
obstacles. It is based on sending sound waves through a specific medium and observing
the returning echoes to measure the distance from the device to the obstacle.
The device is divided into three parts, transmitter, receiver and the microcontroller. The
transmitter consists of an electronics circuitry which generates electrical signal .In
addition, an electromechanical transducer to convert electrical signal to physical form to
drive through the medium, which is air. The receiver also consists of an electronics
circuitry which detects the echoes bounced back from the obstacles. The microcontroller
is programmed for selectivity sequence and to calculate the time of flight of the signal to
find the distance and display it.
The system architecture of the Ultrasonic Range Meter was built to be cheaper, requires
less power and delivers better performance. It can be reconfigured to adapt to a variety of
pulsed Ultrasonic systems.
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Table of Contents
Chapter 1 Introduction 1
1.1 History of ultrasonic waves....................................................1
1.2 History of ultrasonic applications...........................................3
1.3 Future development of this technology...................................6
Chapter 2 Problem statement 7
2.1 Introduction.............................................................................7
2.2 Motivation...............................................................................7
2.3 Characteristics.........................................................................7
2.4 Conclusion..............................................................................8
Chapter 3 Constraints 9
3.1 Introduction.............................................................................9
3.2 Minimum target size and ultrasonic medium..........................9
3.3 Target range............................................................................9
3.4 Range measurement accuracy.................................................9
3.5 The battery............................................................................10
3.6 Weight and size.....................................................................10
3.7 Budget...................................................................................10
3.8 Time......................................................................................10
3.9 Number of engineers.............................................................10
3.10 Conclusion..........................................................................10
Chapter 4 Solutions 11
4.1 Introduction...........................................................................11
4.2 Hand-held laser range meter device......................................11
3
4.2.1 Description.........................................................................11
4.2.1.1 Time of flight measurement……………………............11
4.2.1.2 Triangulation…………………………………………...12
4.2.2 The advantages…………………………………………...13
4.2.3 The disadvantages ……………………………………….13
4.3 Hand-held ultrasonic range meter device.............................13
4.3.1 Description……………………………………………….13
4.3.2 The advantages…………………………………………...14
4.3.3 The disadvantages………………………………………..14
4.4 Comparison...........................................................................14
4.5 Conclusion............................................................................15
Chapter 5 System Design 16
5.1 Introduction...........................................................................16
5.2 The overall system…………………………………………16
5.2.1 Calculation of the distance to an object……….................17
5.3 Ultrasonic system..................................................................18
5.3.1 Ultrasonic transmitter……………….……………………19
5.3.1.1 The 555 timer datasheet………………………………..20
5.3.2 Ultrasonic receiver……………………………………….21
5.3.2.1 Basis of the operational amplifier. …………………….21
5.3.2.2 The difference gain amplification……………………...22
5.3.2.3 Signal amplification circuit…………………………….23
5.3.2.4 Datasheet of the TL082 operational amplifier…………24
5.3.3 Detection circuit………………………………………….26
5.3.4 The microcontroller...........................................................27
5.3.4.1 The CCP capture mode..................................................28
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5.4 The program……………………………………………….29
5.4.1The flowchart......................................................................29
5.4.2 Include file “bit.h”.............................................................30
5.4.3 The main program..............................................................31
5.5 Power supply and battery…………………………………..38
5.6 Ultrasonic sensors.................................................................38
5.6.1 Electrostatic ultrasonic sensors…………………………..40
5.6.2 Piezoelectric ultrasonic sensors………………………….40
5.7 The schematic of the ultrasonic range meter design……….42
Chapter 6 System Implementation 46
6.1 Factors affecting the performance of ultrasonic sensors.......46
6.1.1Radiation pattern…………………………….……………46
6.1.2 Frequency, wavelength and attenuation………………….48
6.2 Environmental factors………………………….. …………48
6.2.1Temperature…………………………………….. ……….49
6.2.2 Pressure and humidity……………………………………50
6.2.3 Medium…………………………………………………..50
6.2.4 Acoustic interference…………………………………….51
6.2.5 Radio frequency interference…………………………….52
6.3 Target consideration………………………………………..52
6.3.1 Composition………………………………………. …….52
6.3.2 Size and shape………………………………....................52
6.3.3 Position and orientation………………………………….53
6.4 Power of the detected signal.................................................55
6.5 Noise.....................................................................................55
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6.6 Errors.....................................................................................55
6.6.1 Truncation errors…………………………………………56
6.6.2 Cosine error………………………………........................57
6.6.3 Reflection error…………………………………………..57
Chapter 7 System Testing 58
7.1 System Testing......................................................................58
7.2 Testing the Transmitter…………………………………….59
7.3 Testing the Receiver……………………………………….60
7.4 Testing the Detection Circuit………………………………61
7.5 Conclusion…………………………………………………61
Chapter 8 Time line, Cost and conclusion 62
8.1 Time line..............................................................................62
8.2 Cost of the ultrasonic range meter design…………………63
8.3 Conclusion………………………………………………...64
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List of Figures
Figure 2.1: The hand-held ultrasonic range meter device……………………....7
Figure 2.2: Description of each part of the device……………………………...8
Figure 4.1: Hand-held laser range meter device……………………………….12
Figure 4.2: Hand-held ultrasonic range meter device………………………….13
Figure 4.3: Beam width comparison of ultrasonic waves and laser beams…....15
Figure 5.1: General block diagram…………………………………………….17
Figure 5.2: Theoretical graph of the pulses and its echo-reflection pulse……..18
Figure 5.3: The overall design of the ultrasonic system……………………….18
Figure 5.4: The transmitter circuit design………………………………..…….19
Figure 5.5: The 555 block diagram…………………………………………….20
Figure 5.6: The receiver circuit design………………………………………..21
Figure 5.7: The difference gain amplification…………………………………22
Figure 5.8: The circuit of the signal amplification…………………………….23
Figure 5.9: Pin connections top view of the TL082 operational amplifier……24
Figure 5.10: The detection circuit……………………………………………...26
Figure 5.11: The microcontroller top view…………………………………….27
Figure 5.12: The flowchart of the program…………………………………….30
Figure 5.13: The power supply circuit…………………………………………38
Figure 5.14: The SQ-40T/R ultrasonic transducer……………………………..41
Figure 5.15: The sensitivity of the SQ-40T/R with respect to the frequency….41
Figure 5.16: The overall schematic of the Ultrasonic range meter…………….43
Figure 5.17: The printed circuit board diagram of the microcontroller………..44
Figure 5.18: The printed circuit board of the transmitter and receiver………...44
Figure 5.19: The packaging of the device……………………………………...45
Figure 6.1: Geometric approximation of the ultrasonic beam width…………..47
Figure 6.2: Beam pattern with respect to amplitude…………………………...48
Figure 6.3: Graph of speed with respect to temperature……………………….50
Figure 6.4: Undetected large object due to reflection………………………….53
Figure 6.5: Object offset due to ultrasonic beam width………………………..54
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Figure 6.6: Range error due to angle between object and sonar……………….54
Figure 6.7: Error (increasing accuracy VS increasing precision)……………...56
Figure 7.1: Graph of error with respect to the measured distance……………..59
Figure 7.2: The transmitter oscilloscope graph………………………………...59
Figure 7.3: The receiver oscilloscope graph…………………………………...60
Figure 7.4: The transmitter and the receiver oscilloscope graph………………60
Figure 7.5: The detection oscilloscope graph………………………………….61
Figure 8.1: Timeline graph…………………………………………………….62
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List of Tables
Table 4.1: Solutions comparison with respect to its accuracy and precision….15
Table 5.1: The delay times of boundary range………………………………...16
Table 5.2: The datasheet of the 555 timer……………………………………...20
Table 5.3: The datasheet of the TL082 operational amplifier…………………25
Table 5.4: The microcontroller specifications………………………………....28
Table 5.5: The Ultrasonic sensor specifications……………………………….38
Table 6.1: The speed of sound at each temperature……………………………49
Table 6.2: The ultrasonic wave speed through different mediums…………….51
Table 7.1: Distance measurement with its error……………………………….58
Table 8.1: Distribution of work………………………………………………..62
Table 8.2(a, b): Components and prices……………………………………….63
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List of Terms, Symbols and Abbreviations
A Average Error
CCD Charge Couple Device
cm centi-meter
cMUTs Capacitive micro-machined Ultrasonic Transducer
D Spot Diameter
KHz Kilo-Hertz
MHz Mega-Hertz
MUT micro-machined Ultrasonic Transducer
NDT Non Destructive Testing
POD Probability of detection
PSD Position Sensitive Detector
PZT Lead-Zirconate Titanate
QNDT Quantitative Non Destructive Testing
Rx Receiver
S Distance
SNR Signal to Noise Ratio
T Truncation Error
t time of flight
Tx Transmitter
UT Ultrasonic Testing
Vi input Voltage
Vo output Voltage
λ Wavelength of sound
µs micro second
Є The target response to the ultrasonic wave
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CHAPTER 1
Introduction
1.1 History of ultrasonic waves
Prior to World War II, sonar, the technique of sending sound waves through water and
observing the returning echoes to characterize submerged objects, inspired early
ultrasound investigators to explore ways to apply the concept to medical diagnosis. In
1929 and 1935, Sokolov studied the use of ultrasonic waves in detecting metal objects.
Mulhauser, in 1931, obtained a patent for using ultrasonic waves, using two transducers
to detect flaws in solids. Firestone (1940) and Simons (1945) developed pulsed ultrasonic
testing using a pulse-echo technique.
Shortly after the close of World War II, researchers in Japan began to explore the medical
diagnostic capabilities of ultrasound. The first ultrasonic instruments used an A-mode
presentation with blips on an oscilloscope screen. That was followed by a B-mode
presentation with a two dimensional, gray scale image. Japan's work in ultrasound was
relatively unknown in the United States and Europe until the 1950s. Researchers then
presented their findings on the use of ultrasound to detect gallstones, breast masses, and
tumors to the international medical community. Japan was also the first country to apply
Doppler ultrasound, an application of ultrasound that detects internal moving objects such
as blood coursing through the heart for cardiovascular investigation. Ultrasound pioneers
working in the United States contributed many innovations and important discoveries to
the field during the following decades. Researchers learned to use ultrasound to detect
potential cancer and to visualize tumors in living subjects and in excised tissue. Real-time
imaging, another significant diagnostic tool for physicians, presented ultrasound images
directly on the system's CRT screen at the time of scanning. The introduction of spectral
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Doppler and later color Doppler depicted blood flow in various colors to indicate the
speed and direction of the flow. The United States also produced the earliest hand held
"contact" scanner for clinical use, the second generation of B-mode equipment, and the
prototype for the first articulated-arm hand held scanner, with 2-D images. The Non-
Destructive Testing NDT has been practiced for many decades, with initial rapid
developments in instrumentation spurred by the technological advances that occurred
during World War II and the subsequent defense effort. During the earlier days, the
primary purpose was the detection of defects. As a part of "safe life" design, it was
intended that a structure should not develop macroscopic defects during its life, with the
detection of such defects being a cause for removal of the component from service. In
response to this need, increasingly sophisticated techniques using ultrasonic, eddy
currents, x-rays, dye penetrants, magnetic particles, and other forms of interrogating
energy emerged. In the early 1970's, two events occurred which caused a major change in
the NDT field. First, improvements in the technology led to the ability to detect small
flaws, which caused more parts to be rejected even though the probability of component
failure had not changed. However, the discipline of fracture mechanics emerged, which
enabled one to predict whether a crack of a given size will fail under a particular load
when a material's fracture toughness properties are known. Other laws were developed to
predict the growth rate of cracks under cyclic loading (fatigue). With the advent of these
tools, it became possible to accept structures containing defects if the sizes of those
defects were known. This formed the basis for the new philosophy of “damage tolerant”
design. Components having known defects could continue in service as long as it could
be established that those defects would not grow to a critical, failure producing size.
A new challenge was thus presented to the nondestructive testing community. Detection
was not enough. One needed to also obtain quantitative information about flaw size to
serve as an input to fracture mechanics based predictions of remaining life. The need for
quantitative information was particularly strongly in the defense and nuclear power
industries and led to the emergence of quantitative nondestructive evaluation (QNDE) as
a new engineering/research discipline. A number of research programs around the world
were started, such as the Center for Nondestructive Evaluation at Iowa State University
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(growing out of a major research effort at the Rockwell International Science Center); the
Electric Power Research Institute in Charlotte, North Carolina; the Fraunhofer Institute
for Nondestructive Testing in Saarbrucken, Germany; and the Nondestructive Testing
Centre in Harwell, England.[2]
1.2 History of ultrasonic applications
Ultrasonic sensing techniques have earned a pre-eminent position in a variety of fields
including medicine, nondestructive testing and process monitoring, geophysics, and sonar
surveillance. Ultrasonic flow sensors have been employed for a number of years for
performing intraoperative or extracorporeal blood flow measurements. Intraoperative
flow measurements are typically conducted to monitor blood flow in various vessels
during vascular, cardiac, transplant, plastic and reconstructive surgery. Transit-time
ultrasonic flow sensors detect the acoustic propagation time difference between the
upstream and downstream ultrasonic transmissions in a moving fluid and process this
information to derive a fluid flow rate. Ultrasonic array transducers rely on wave
interference for their beam forming effects, and typically include a plurality of individual
transducer elements organized as either a one-dimensional (linear) array or a two-
dimensional array. Ultrasound is used as a non-invasive technique for obtaining image
information about the structure of an object which is hidden from view, and is widely
known as a medical diagnostic tool as well as a tool for non-destructive testing and
analysis in the technical arts. Ultrasound diagnostic imaging systems are in widespread
use for performing ultrasonic imaging and measurements. Ultrasonic imaging sensors act
as both transmitters and receivers of ultrasonic energy. The sensor first acts as a
transmitter; emitting ultrasonic energy in a train of high frequency pulses, typically in the
range of 2 to 10 Mhz. Then the transmitter is turned off and the sensor acts as a receiver,
which listens for returned echoes at the transmitted frequency. Ultrasonic sensors are
used to make remote distance measurements. One particular use of ultrasonic sensors is
within a vehicle occupant protection system within a vehicle. Ultrasonic range finders
typically use ultrasonic frequencies which are inaudible to the human ear. These high
frequencies have inherently shorter wavelengths, which lead to greater positional
accuracy than audible frequencies. Parking aid systems of today usually consist of an
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electronic control unit and several ultrasonic sensors. Each ultrasonic sensor possesses a
separate data line, since, in order to improve evaluation, echo information from several
ultrasonic sensors is required at a certain instant. Thus, the evaluation of several ULS on
the basis of one transmitted sound wave permits more precise conclusions to be made
about the position of and the range of the obstacle. Ultrasonic sensors are equipped in
robots and used for detecting objects positioned along a robot travel path. Such ultrasonic
sensors are adapted to convert a pulse signal into an ultrasonic wave energy which is, in
turn, radiated at a search area.
Ultrasonic testing UT has been practiced for many decades. Initial rapid developments in
instrumentation spurred by the technological advances from the 1950's continue today.
Through the 1980's and continuing through the present, computers have provided
technicians with smaller and more rugged instruments with greater capabilities.
Thickness gauging is an example application where instruments have been refined make
data collection easier and better. Built-in data logging capabilities allow thousands of
measurements to be recorded and eliminate the need for a "scribe." Some instruments
have the capability to capture waveforms as well as thickness readings. The waveform
option allows an operator to view or review the A-scan signal of thickness measurement
long after the completion of an inspection. Also, some instruments are capable of
modifying the measurement based on the surface conditions of the material. For
example, the signal from a pitted or eroded inner surface of a pipe would be treated
differently than a smooth surface. This has led to more accurate and repeatable field
measurements.
Many ultrasonic flaw detectors have a trigonometric function that allows for fast and
accurate location determination of flaws when performing shear wave inspections.
Cathode ray tubes, for the most part, have been replaced with LED or LCD screens.
These screens, in most cases, are extremely easy to view in a wide range of ambient
lighting. Bright or low light working conditions encountered by technicians have little
effect on the technician's ability to view the screen. Screens can be adjusted for
brightness, contrast, and on some instruments even the color of the screen and signal can
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be selected. Transducers can be programmed with predetermined instrument settings. The
operator only has to connect the transducer and the instrument will set variables such as
frequency and probe drive. Along with computers, motion control and robotics have
contributed to the advancement of ultrasonic inspections. Early on, the advantage of a
stationary platform was recognized and used in industry. Computers can be programmed
to inspect large, complex shaped components, with one or multiple transducers collecting
information. Automated systems typically consisted of an immersion tank, scanning
system, and recording system for a printout of the scan. The immersion tank can be
replaced with squirter systems, which allows the sound to be transmitted through a water
column. The resultant C-scan provides a plan or top view of the component. Scanning of
components is considerably faster than contact hand scanning; the coupling is much more
consistent. The scan information is collected by a computer for evaluation, transmission
to a customer, and archiving.
Today, quantitative theories have been developed to describe the interaction of the
interrogating fields with flaws. Models incorporating the results have been integrated
with solid model descriptions of real-part geometries to simulate practical inspections.
Related tools allow the Nondestructive Evaluation NDE to be considered during the
design process on an equal footing with other failure-related engineering disciplines.
Quantitative descriptions of NDE performance, such as the probability of detection
(POD), have become an integral part of statistical risk assessment. Measurement
procedures initially developed for metals have been extended to engineered materials
such as composites, where anisotropy and inhomogeneity have become important issues.
The rapid advances in digitization and computing capabilities have totally changed the
faces of many instruments and the type of algorithms that are used in processing the
resulting data. High-resolution imaging systems and multiple measurement modalities for
characterizing a flaw have emerged. Interest is increasing not only in detecting,
characterizing, and sizing defects, but also in characterizing the materials. Goals range
from the determination of fundamental microstructural characteristics such as grain size,
porosity, and texture (preferred grain orientation), to material properties related to such
failure mechanisms as fatigue, creep, and fracture toughness. As technology continues to
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advance, applications of ultrasound also advance. The high-resolution imaging systems in
the laboratory today will be tools of the technician tomorrow.
1.3 Future development of this technology
Looking to the future, those in the field of NDE see an exciting new set of opportunities.
The defense and nuclear power industries have played a major role in the emergence of
NDE. Increasing global competition has led to dramatic changes in product development
and business cycles. At the same time, aging infrastructure, from roads to buildings and
aircraft, present a new set of measurement and monitoring challenges for engineers as
well as technicians. Among the new applications of NDE spawned by these changes is
the increased emphasis on the use of NDE to improve the productivity of manufacturing
processes. Quantitative nondestructive evaluation (QNDE) both increases the amount of
information about failure modes and the speed with which information can be obtained
and facilitates the development of in-line measurements for process control. The phrase,
"you cannot inspect in quality, you must build it in," exemplifies the industry's focus on
avoiding the formation of flaws. Nevertheless, manufacturing flaws will never be
completely eliminated and material damage will continue to occurring in-service so
continual development of flaw detection and characterization techniques are necessary.
Advanced simulation tools that are designed for inspectability and their integration into
quantitative strategies for life management will contribute to increase the number and
types of engineering applications of NDE. With growth in engineering applications for
NDE, there will be a need to expand the knowledge base of technicians performing the
evaluations. Advanced simulation tools used in the design for inspectability may be used
to provide technical students with a greater understanding of sound behavior in materials.
As globalization continues, companies will seek to develop, with ever increasing
frequency, uniform international practices. In the area of NDE, this trend will drive the
emphasis on standards, enhanced educational offerings, and simulations that can be
communicated electronically. The coming years will be exciting as NDE will continue to
emerge as a full-fledged engineering discipline.
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CHAPTER 2
Problem statement
2.1 Introduction
The main purpose of this project is to measure the distance to unreachable objects,
obstacles or places using a portable device.
Figure 2.1: The hand-held ultrasonic range meter device.
2.2 Motivation
The motivation of using this device is when construction engineers at any sites need to
measure distances to unreachable places in a quick and easy way using this device with
high efficiency and accuracy.
2.3 Characteristics
This device detects the distance to an object and shows the result in centimeters. This
device is activated by a trigger mechanism, pressing the trigger for one time will give us
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the distance to an object if there was no error like poor aiming. The distance to an object
is displayed using a digital display with a high intensity in order to be seen in any lighting
conditions.
It is a simple and portable device similar to a gun as shown in Figure 2.2 that uses a laser
pointer to aim at a specific area to get the reflection at the receiver side.
Figure 2.2: Description of each part of the device.
2.4 Conclusion
In order to design and build a portable device, the weight of the device is a primary
problem. The technology of using ultrasonic to measure distances is in continuous
progress, features have been added to this technology to make it easy to use and more
accurate by assigning more challenging constraints. The constraints of our device are
discussed in the next chapter.
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CHAPTER 3
Constraints
3.1 Introduction
Defining the constraints of our device will help to design and then build the hand-held
ultrasonic range meter device. By defining these constraints, the problems will be clearer,
the suitable solutions will become easier to find and those constraints will help to get the
design needed from the engineer.
3.2 Minimum target size and ultrasonic medium
The minimum target size is 40cm*40cm in order to get detection at the receiver side.
The ultrasonic medium is air.
3.3 Target range
The target range is the distance range between the person who is using the hand-held
ultrasonic range meter device and the targeted object. The target range consists of two
boundaries, one is the minimum distance limit and the other is the maximum distance
limit. If the operator of the hand-held ultrasonic range meter device exceeds these two
boundaries, the hand-held ultrasonic range meter device may not detect the distance or
may display a false detection.
The target range is between 10 centimeters and 300 centimeters.
3.4 Range measurement accuracy
Each specific distance has an error percentage; the more samples sent the less the error is.
The range measurement accuracy is the accuracy of the distances measured between the
operator of the hand-held ultrasonic range meter device and the targeted object; it allows
knowing how much each distance is close to the real value of the distance. The range
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measurement accuracy is +/- 3 cm. The less this value is, the more accurate distances
would be calculated by the hand-held ultrasonic range meter device.
3.5 The battery
A 9 V battery could be used to activate this device.
3.6 Weight and size
Our device would not exceed the weight 0.5 kilogram. This weight is acceptable for the
operator to carry the hand-held ultrasonic range meter device and to fix his arm while
aiming at the targeted object.
The area of the cover is 15cm x 7 cm, and the height is 8 cm.
3.7 Budget
This hand-held ultrasonic range meter device is between 50 U.S dollars and 75 U.S
dollars.
3.8 Time
The time estimated to accomplish the hand-held ultrasonic range meter device is one
month due to the changes in the constraints.
3.9 Number of engineers
The number of engineers working on the hand-held ultrasonic range meter device is three
engineers.
3.10 Conclusion
After discussing and choosing the constraints, the solutions for these sets of challenging
problems are to be discussed and solved physically and mathematically in the next
chapter.
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CHAPTER 4
Solutions
4.1 Introduction
To solve the problem of detecting the distance to an object, many solutions are presented.
In this chapter the solutions are discussed, all the advantages and disadvantages are shown.
The comparison between these solutions will help to determine which solution has more
advantages and satisfies the constraints at the same time.
4.2 Hand-held laser range meter device
4.2.1 Description
This device is characterized by its accuracy and portability; it uses a laser beam. The two
techniques might be used to measure the distance. There are two techniques that have
been used in order to measure distances, the time of flight technique and the triangulation
technique.
4.2.1.1 Time of flight measurement
Even the fastest photon requires a certain period of time to cover the distance from the
sensor to the target and back. This time is directly proportional to the distance traveled,
taking into account the velocity of light in the medium involved, which may be easily
derived from the velocity of light in a vacuum. The cost and complexity of this method
depends upon the precision and resolution required.
Data acquisition and analysis electronics must cope with ns and sub-ns time scales:
decimeter ranges may be easily resolved by nanosecond pulses but precision in the
millimeter and sub-millimeter range requires pulse lengths of a few tens of picoseconds
and the associated electronics. Clearly, a poorly resolved pulse will lead to uncertainty in
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the accuracy of the measurement; the standard deviation in measured distance is
proportional to the optical pulse rise time and is inversely proportional to the signal-to-
noise ratio. At ranges of a few kilometers and above, a different problem arises; at such
distances the amount of reflected photons which reach the detector is very small. Signal
intensity can be improved by optimum beam focusing at the source, or by the use of a
retro reflector mounted in the target.
4.2.1.2 Triangulation
Triangulation is the most commonly used method for distances of 10 meters or less. A
laser or LED is used to produce a collimated beam which then impinges on the surface of
the target. The target reflects light in many directions, some of the reflected light reaching
the detector. The position of the reflected light focused onto the detector depends on the
distance between the sensor and target. Detectors such as position sensitive detectors
(PSD), diode arrays or CCD arrays enable the reflected light to be detected with high
spatial resolution and at high sampling frequencies. The sensor-object distance is
calculated trigonometrically and accuracies of better than 0.5% are the norm.
Measurement times of less than 10 ms are common, allowing real-time study of moving
or vibrating objects. The light source should be compact and should produce an intense,
small spot of light with minimal divergence. Amplitude modulation is used in order to
eliminate the effects of stray (background) light.
Figure 4.1: Hand-held laser range meter device.
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4.2.2 The advantages
As shown in Figure 4.1, the hand-held laser range meter device is a portable device.
It is characterized with its high accuracy and high precision. The laser beam consists of a
small beam width which reaches a long target range.
4.2.3 The disadvantages
The poor aiming on the targeted object causes a bad reflection of the laser and that would
display a false detection of the object’s distance that has been targeted.
The atmospheric conditions may affect the ranging capabilities of the hand-held laser
range meter device. The rain and snow reflect the laser beam and that may display a false
detection of the object’s distance.
4.3 Hand-held ultrasonic range meter device
4.3.1 Description:
This device works on the same concept of the laser gun device but the difference is that it
uses a large beam width of ultrasonic waves as shown in Figure 4.2. The time of flight
and triangulation techniques might be used to measure the distance using ultrasonic
waves.
Figure 4.2: Hand-held ultrasonic range meter device.
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4.3.2 The advantages
The hand-held ultrasonic range meter device is a portable device as shown in Figure 4.2.
The hand-held ultrasonic range meter device is characterized with its precision and high
accuracy. Atmospheric conditions will not affect the capabilities of the device.
4.3.3 The disadvantages
The beam of the hand-held ultrasonic range meter device consists of a large beam width
as shown in Figure 4.2 and that may cause a false detection of the object’s distance at the
receiver side because the beam may hit a group of objects placed near each others and the
reflection of the ultrasonic wave is caused by several objects. The object must be flat and
not an absorber and it should be normal to the direction of the ultrasonic wave. This
device could be jammed and is affected by interference.
4.4 Comparison
After looking at the advantages and the disadvantages, the best solution is to use the gun
device using laser beams. The beam width of the hand-held laser range meter device is
smaller than the beam width of the hand-held ultrasonic range meter device as shown in
Figure 4.5; this enables the operator of the hand-held laser range meter device to hit a
specific object and get less reading errors unlike other devices.
The comparison has shown that the hand-held ultrasonic range meter devices could be
better in some cases because it will not be affected by the atmospheric conditions. As
shown in Table 4.1, using a descending order from the best accuracy and precision of the
devices to the worst, the most accurate and precise is the hand-held laser range meter
device. The second is the hand-held ultrasonic range meter device. Depending on our
constraints, our choice was to design an ultrasonic range meter because of the budget and
availability of the components.
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Table 4.1: Solutions comparison with respect to its accuracy and precision.
Figure 4.3: Beam width comparison of ultrasonic waves and laser beams.
4.5 Conclusion
Each solution has its advantages and disadvantages depending on the situation where the
device is used; the hand-held laser range meter device is a fast growing technology
because of its efficiency and its accuracy as well as the hand-held ultrasonic range meter
device as shown in Table 4.1. In the next chapter the design of the hand-held ultrasonic
range meter device will be implemented.
CHAPTER 5
Devices Hand-held laser
range meter
Hand-held ultrasonic
range meter
Accuracy High accuracy High accuracy
Precision High precision Precise
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System Design
5.1 Introduction
All designs are based on specific constraints. The design of the hand-held ultrasonic
range meter device is based on measuring the distance using the time of flight technique.
The process of this design is more explained in details in the next section.
5.2 The overall system
The calculations are done by the following way. First of all, the device calculates the time
that the ultrasonic wave took to reach the targeted object and come back to the receiver.
Thus, if we need to calculate the time needed for the ultrasonic wave to reach the object
from the device, we divide the previous time we had by two. Second, the device
multiplies the time by the speed of sound (340 m/s) to get the distance between the device
and 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 this equation:
Distance = (s * t)/2 (in meters) (5.1)
Where: s [m/s] is the speed of sound in air and t [s] is the round trip echo time.
Table 5.1: The delay times of boundary range
Round trip echo
time
Distance
t = 588 us10 cm
26
t = 17.6 ms3 m
.
Figure 5.1: General block diagram.
5.2.1 Calculation of the distance to an object
The hand-held Ultrasonic Range meter device offers precise ranging information from
roughly 10cm to 3 meters. The ranger works by transmitting a pulse of sound outside the
range of human hearing. This pulse travels at the speed of sound away from the ranger in
a cone shape and the sound reflects back to the ranger from any object/target in the path
of this sonic wave. The ranger pauses for a brief interval after the sound is transmitted
and then awaits the reflected sound in the form of an echo. The controller driving the
ranger then requests a ping; the ranger creates the sound pulse, and waits for the return
echo. If received, the ranger reports this echo to the controller and the controller can then
compute the distance to the object based on the elapsed time.
The Pulse Trigger Input line should be held low and then brought high for a minimum of
100μsec to initiate the sonic pulse. The pulse is generated on the falling edge of this input
trigger. The ranger’s receiver circuitry is held in a short blanking interval of 600 μsec to
avoid noise from the initial ping and then it is enabled to listen for the echo. The echo
line is low until the receive circuitry is enabled. Once the receive circuitry is enabled, the
falling edge of the echo line signals an echo detection or nothing if there is no reflection.
The long-range measurement is difficult a little. To measure the correct distance, the
following conditions are necessary.
The object must be perpendicular to the range meter.
The surface of the object must be flat.
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There is not object which reflects the ultrasonic around.
Figure 5.2: Theoretical graph of the pulses and its echo-reflection pulse.
5.3 Ultrasonic system
It consists of a transmitter and receiver pair on the device and a microcontroller with a
digital display. There are two different transducers for transmitter and receiver. The
transmitter transmits and the receiver waits for the reflected signals. The Figure 5.3
illustrates this system.
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Figure 5.3: The overall design of the ultrasonic system.
5.3.1 Ultrasonic Transmitter
The transmitter consists of an electronics circuitry and an electromechanical transducer.
The electronic circuitry generates the required frequency electrical signal and the
electromechanical transducer converts that electrical signal into the physical form and
activates the open medium surface. This oscillating physical surface creates the ultrasonic
Waves. The oscillating surface creates a pressure variation and ultimately a pressure
wave with a frequency equal to that of the surface oscillation. The Figure 5.4 shows the
generation of ultrasonic waves.
Figure 5.4: The transmitter circuit design.
The transmitter was designed to oscillate at a resonant frequency of about 40 KHz. The
555 timer generates a 40 KHz sinusoidal ultrasonic wave. The frequency is calculated by
using the following formula:
F = 1.44 / 2 * R1 * C = 1.44 / 2 * 15.6 KΩ * 1nF = 46 kHz. (5.1)
This design of the transmitter was done in way to get the closest value to 40 KHz by
adjusting the resistor and the capacitor to the values shown in the Figure 5.4.
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5.3.1.1 The 555 timer datasheet
The 555 monolithic timing circuits is highly stable controller capable of producing
accurate time delays, or oscillation .In the delay time of operation, the time is precisely
controlled by one external resistor and capacitor .For a stable operation as an oscillator,
the free running frequency and the duty cycle are both accurately controlled with two
external resistors and one capacitor. As shown in Figure 5.5:
Figure 5.5: The 555 block diagram.
The Table 5.2 shows the datasheet of the 555 timer, the parameter rating and the units
characterized by each component.
Table 5.2: The datasheet of the 555 timer
Symbol Parameter Rating Unit
VCC Supply Voltage +16 V
Pd Maximum allowable
power dissipation 600 mW
TAOperating ambient
temperature range0 to 70 ºC
VTH (Vcc = 5v) Threshold voltage 3.33 V
VTRIG(Vcc = 5v) Trigger Voltage 1.67 V
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VRESET Reset Voltage 0.3 to 1.0 V
.5.3.2 Ultrasonic Receiver
The receiver also has the same configuration except that it has a receiver electronic
circuitry and a transducer, which converts the ultrasonic sound waves into an electrical
signal. The sound waves travel into the medium and are reflected by an object in the path
of the waves. This reflected wave is then sensed by the receiver, which actually calculates
the time of flight of the signal to find the distance. The Figure 5.6 illustrates the receiver
circuit.
Figure 5.6: The receiver circuit design.
5.3.2.1 Basis of the operational amplifier
The operational amplifier is the amplifier with the very big voltage gain.
In case of TL082 to be using this time, at the specification, the voltage gain becomes
150V/mV. It is the 15 V output in 0.1 mV of the input. To say becomes 150,000 times of
gain. In case of the operational amplifier, the value of the voltage gain doesn't have the
relation too much. Anyway, the fact that the voltage gain is big is important.
31
5.3.2.2 The Difference Gain amplification
There are positive input and negative input in the operational amplifier.
The voltage gain can be calculated by the following formula.
G = Vo/Vi = -(Rf/Ri) (5.2)
Figure 5.7: The difference gain amplification.
Using the voltage divider formula:
Vb = V1 * R2/(R1 + R2) (5.3)
The current passing through Ri is the same current passing through Rf because the
current entering the negative input is negligible in μA (in the ideal operational amplifier,
it is considered zero) and this gives the following equation:
(Vi – Va) / Ri = (Va – Vo) / Rf (5.4)
Vo = (V1 * R2 * (Rf + Ri) / (R1 + R2) * Ri)– Vi * Rf / Ri (5.5)
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5.3.2.3 Signal amplification circuit
The signal amplification circuit is illustrated below in the Figure 5.8.
Figure 5.8: The circuit of the signal amplification.
The ultrasonic signal which was received with the reception sensor is amplified by 2500
times (68dB) of voltage with the operational amplifier with two stages.
The voltage gain G is 100 times at the first stage (40dB) and 25 times (28dB) at the next
stage. Generally, the positive and the negative power supply are used for the operational
amplifier. The circuit this time works with the single power supply of +5 V. Therefore,
for the positive input of the operational amplifiers, the half of the power supply voltage is
applied as the bias voltage and it is made 2.5 V in the central voltage of the amplified
alternating current signal.
When using the operational amplifier with the negative feedback, the voltage of the
positive input terminal and the voltage of the negative input terminal become equal
approximately. So, by this bias voltage, the side of the positive and the side of the
negative of the alternating current signal can be equally amplified. When not using this
bias voltage, the distortion causes the alternating current signal. When the alternating
current signal is amplified, this way is used when working the operational amplifier for
the two power supply with the single power supply.
Using the formula in 5.1:
Vi is the input voltage at the ultrasonic transducer.
Vo1 is the output voltage of the first amplification stage.
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Vo2 is the output voltage of the second amplification stage.
At minimum distance, d = 10 cm,
Vi max = 2.50004 V.
Vo1 = (5 * 47K * (100k + 1k) / (47k + 47k) * 1K) - 2.50004 * 100k / 1k = 2.496 V.
Vo2 = (5 * 47K * (100k + 3.9k) / (47k + 47k) * 3.9K) - 2.496 * 100k / 3.9k = 2.6 V.
At maximum distance, d = 3 m,
Vi max = 2.4999 V.
Vo1 = (5 * 47K * (100k + 1k) / (47k + 47k) * 1K) - 2.4999 * 100k / 1k = 2.46 V.
Vo2 = (5 * 47K * (100k + 3.9k) / (47k + 47k) * 3.9K) - 2.46 * 100k / 3.9k = 2.50156 V.
ΔVi = 2.50004 – 2.4999 = 0.04 mV.
A slight change in Vi formed a bigger change in Vo2.
Δ Vo2 = ΔVi * Gain = 0.04 * 2500 = 100 mV.
5.3.2.4 Data of the TL082 operational amplifier
As for TL082, the two operational amplifiers are enclosed with the one package.
Figure 5.9: Pin connections top view.
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Table 5.3: The datasheet of the TL082 operational amplifier.
Symbol Symbol Value Unit
Supply VoltageVCC
VEE
+18
-18V
Differential Input Voltage VID ±30 V
Input Voltage Range VIDR ±15 V
Output Short Circuit
DurationtSC Continuous
Power Dissipation
(Plastic Package)
PD
1/8JA
680
10
mW
mW/°C
Operating Ambient
Temperature RageTA 0 - +70 °C
Storage Temperature Range Tstg -65 - +150 °C
Slew rate SR 16 V/μs
Gain bandwidth product GBW 4 MHz
The magnitude of the input voltage must not exceed the magnitude of the supply voltage
or 15V, whichever is less. The output may be shorted to ground or either supply.
Temperature and/or supply voltages must be limited to ensure that power dissipation
ratings are not exceeded.
For the 741 operational amplifier, GBW = 1 MHz, SR = 0.5 V/μs.
For the TL082 operational amplifier, GBW = 4 MHz, SR = 16 V/μs.
Vi(t) = 0.04 cos ( 40000 * 2 * Π * t) mV.
Vo(t) = 100 cos ( 40000 * 2 * Π * t) mV.
(Vo(t))′ = 2 * Π * 40000 * 0.1 = 0.025 V/μs.
0.025 V/μs < 0.5 V/μs the 741 operational amplifier could be used.
0.025 V/μs < 16 V/μs the TL082 operational amplifier could be used.
The TL082 operational amplifier has a better slew rate.
For a 10% error in the frequency, F = 40000 * 0.9 = 36000 Hz.
The required gain bandwidth product for a gain = 2500 is,
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GBW = 36000 * 2500 = 90 MHz > 4 MHz.
The signal amplification is split into two stages because of this gain bandwidth product.
The maximum gain G max = 4 MHz / 36000 Hz = 111.11.
The maximum gain is greater than the gain for the first stage 100 and the second stage 25.
5.3.3 Detection circuit
The detection is done to detect the received ultrasonic signal. It is the half-wave
rectification circuit which used the 1N4148 diodes.
Figure 5.10: The detection circuit.
The DC voltage according to the level of the detection signal is gotten by the capacitor
behind the diode. The 1N4148 diode is used because it is a fast switching diode.
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5.3.4 The microcontroller
Figure 5.11: The microcontroller top view.
The microcontroller used in this project is the 40 pin PIC16f877A. This microcontroller
was chosen because it consists of two timers, two capture modes CCP, five ports, a good
size of memory and its low price compared to other microcontroller with less
functionality. By manipulating the program of this project, this microcontroller with its
big number of ports could be added to a robot or other applications and also it could
control other applications due to the measured distance needed to react for.
The clock used for this project is 4 MHz. The port B is an output port used for the digital
display of the distance measured. The bit RC4 of the port C is used to enable the
transmitter in order to send pulses. The bit RC2/CCP1 of the port C is used for its capture
mode by capturing the echo reflected, it is connected to the receiver.
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Table 5.4: The microcontroller specifications.
Device PIC16f877a
Program
memory
Bytes 14.3 K
# single word
instruction
8192
Data SRAM (Bytes) 368
EEPROM (Bytes) 256
I/O 33
Ports A, B, C, D, E
10 bit A/D (ch) 8
CCP (PWM) 2
MSSP
SPI yes
Master I²C yes
USART yes
Timers 8/16 bit 2/1
Comparators 2
5.3.4.1 The CCP capture mode
This project makes use of the CCP module (in its capture mode) to accurately measure
the signal reception time at the CCP port pin. When a signal triggers the CCP module the
value of timer 1 is stored in a CCP register (or captured).
If you store the value of timer 1 and then enable the CCP after transmitting an ultrasound
pulse the CCP will trigger when the comparator activates i.e. as soon as an ultrasonic
echo is received.
Subtracting the stored value from the CCP register value gives the time delay in machine
cycles. Since the project uses a 4MHz main clock then the time delay will be measured in
micro-seconds.
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5.4 The program
This program is written in C code. It is compiled using the program MicroC in order to
generate the Hex file. It consists of an include header “bit.h”, the main program with
eight functions.
5.4.1 The flowchart
It enters a continuous loop calling “ulta_gen” the routine that generates the ultrasound at
40 kHz. The “ultra_gen” routine is set up using the simulator to set the timing of the
output signal for a period of 25 μs (40 kHz). This is then repeated every 40 ms.
The required refresh rate of the seven segment display is 20 ms so the display update
routine “seg_display_int” is called twice over the 40 ms period. The display update
routine takes 20 ms and calling this twice creates the total 4 0ms delay. The display relies
on persistence of vision to make it appear that the display is not flickering; a refresh rate
of 50Hz or more does the job (1 / 50 Hz = 20 ms).
In theory the maximum distance that you could measure is (20 ms * 340 m) / 2 = 3.4 m,
but in practice this is limited by the signal conditioning circuits. If they were changed,
more range could be got. If a capture occurs indicated by “gCapInt”, then the distance
calculation is performed and the value of variable “val” is updated. “val” is the value
displayed by the seven segment display routine “seg_display_int”, so “val” is
continuously refreshed to the seven segment display.
The interrupt routine is only enabled when required and when the capture occurs, only
the first capture is stored. So that later reflections are ignored by resetting “gCapOn”.
The first reflection should be the strongest and therefore the closest object. When
captured, the variables “t_capL”, “t_capH” and “t_capO” are set to the value of the
capture register which will be the value of timer 1 when the capture module triggered.
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Figure 5.12: The flowchart of the program.
5.4.2 Include file “bit.h”
This macro preserves the current value of the 'PORT' or register. WRITEPORT is the
same as writing to a port but preserves the keepmask bits.
The macro WRITEPORT(port,newval,keepMask) is used to write only to specific bits of
a port. The PORT is read, keepMask bits are preserved when the data value is output to
the port.
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#define WRITEPORT(port,newval,keepMask) \
(port) = ((newval) & (~keepMask)) | ((port) & (keepMask));
#define setBit(var, bitnum) (var)|=(1<<(bitnum))
#define resBit(var, bitnum) (var)&=~(1<<(bitnum))
#define clearBit(var, bitnum) (var)&=~(1<<(bitnum))
#define testBit(var, bitnum) (var)&(1<<(bitnum))
This code is saved as an include header file “bit.h”.
5.4.3 The main program
#include "bit.h" // macro
// globals for interrupt.
unsigned int T1_O = 0; // timer1 overflow updated in interrupt routine.
unsigned short gCapInt = 0; // captured something in interrupt routine.
unsigned short gfCapOn = 1; // control capture only capture 1st value.
unsigned int t_capL = 0; // timer 1 low.
unsigned int t_capH = 0; // timer 1 high.
unsigned int t_capO = 0; // timer 1 overflow.
unsigned int gCapVal = 0; // captured this.
void init(void) {
// set CCP to capture mode every rising edge.
CCP1CON = 0x05;
ADRESH = 0;
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// Timer 1 on
T1CON = (1<<TMR1ON); }
void init_ports(void) {
PORTA = 0;
TRISA = 0;
PORTB = 0;
TRISB = 0; // 0=o/p - sets analogue pins to digital output.
PORTC = 0;
TRISC = 0x04; // 0=o/p Receive on RC2.
}
void enable_interrupts(void) {
// Timer 1
PIR1 &= ~(1<<TMR1IF); // Zero T1 overflow register value.
// Capture
PIR1 &= ~(1<<CCP1IF); // Zero Capture flag
// Interrupt enable
PIE1 = (1<<CCP1IE);
// Global interrupt enable.
INTCON = (1<<GIE) | (1<<PEIE); // enable global & peripheral
}
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void disable_interrupts(void) {
INTCON &= ~(1<<GIE); // disable global & peripheral
}
int2seg(unsigned short digit) {
unsigned short r;
unsigned short ret[10] = { 0x3F, 0x06, 0x5B, 0x4F, 0x66,
0x6D, 0x7D, 0x07, 0x7F, 0x6F };
if (digit<0 || digit>9) {
r = 0x7f; }
else { r =( ret[digit] & 0x1f ) | \
( (ret[digit] & 0x60)<< 1); }
return r;
}
void seg_display_int(unsigned int val) {
char op[7];
IntToStr(val,op);
// Display the lower 4 digits.
PORTB=int2seg(op[2]-'0');
setBit(PORTA,0);
delay_ms(4);
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resBit(PORTA,0);
PORTB=int2seg(op[3]-'0');
setBit(PORTA,1);
delay_ms(4);
resBit(PORTA,1);
PORTB=int2seg(op[4]-'0');
setBit(PORTA,2);
delay_ms(4);
resBit(PORTA,2);
PORTB=int2seg(op[5]-'0');
setBit(PORTA,3);
delay_ms(4);
resBit(PORTA,3);
PORTA &= ~0xe4; // turn off all resBit should do this
PORTA=0;
PORTB=0x00;
}
// generate 4 pulses of ultrasonic at 32kHz (8 periods of 32kHz).
void gen_ultra(void) {
setBit(PORTC,4);
delay_us(12);
44
resBit(PORTC,4);
delay_us(11);
setBit(PORTC,4);
delay_us(12);
resBit(PORTC,4);
delay_us(11);
setBit(PORTC,4);
delay_us(12);
resBit(PORTC,4);
delay_us(11);
setBit(PORTC,4);
delay_us(12);
resBit(PORTC,4);
delay_us(11); }
void main() {
unsigned int i,val,s1,s2,tH,tL,tO;
char op[12];
unsigned long calc=0;
init_ports();
init();
gCapInt=0; // Reset capture indicator.
while(1) { gfCapOn = 1; // allow one capture value
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tO = T1_O; // Get the current timer value.
tH = TMR1H;
tL = TMR1L;
t_capL = 0; t_capH = 0; t_capO = 0; // initialise capture
gen_ultra();
enable_interrupts();
seg_display_int(val);
disable_interrupts(); // had 20 ish ms of time so stop
if (! gCapInt) { // no echo from soft output ? try loud
enable_interrupts();
seg_display_int(val);
seg_display_int(val);
disable_interrupts(); // had 20 ish ms of time so stop
}
// Did we get any echo from soft or loud?
if (gCapInt) { // captured anything ?
gCapInt=0; // reset for next time
// 4MHz clock so timer 1 returns us
// gCapVal * 1,000,000 = seconds.
// speed of sound in air at 20degC = 340m/s
// (gCapVal*1000000*340)/(2*100) = distance in cm
s1=(t_capH-tH);
s2=(t_capL-tL);
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calc = ((s1)<<8)+s2;
calc *= 34;
calc /= 2000; // output in cm
val = (int)calc; } } // while(1)
}
void interrupt(void) {
// Free run Timer 1 get the overflow to extend counter here.
if (PIR1 & (1<<TMR1IF) ) { // T1 overflowed ?
PIR1 &= ~(1<<TMR1IF); // clear timer1 overflow bit.
T1_O++; }
// Capture
if (PIR1 & (1<<CCP1IF)) {
PIR1 &= ~(1<<CCP1IF); // Zero Capture flag.
if (gfCapOn) { // allow only 1 capture
gfCapOn = 0;
t_capL = CCPR1L;
t_capH = CCPR1H;
t_capO = T1_O;
gCapInt = 1; // signal that a capture occured.
} } // Interrupts are only enabled at a specific point from program.
// They are not re-enabled here
// Note GIE set by RETFIE instruction
}
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5.5 Power supply and battery
The Ultrasonic transmitter and receiver require four connections to operate. First there
are the power and ground lines. The Ultrasonic transmitter and receiver require a 5V
power supply capable of handling roughly 50mA of continuous output. The remaining
two wires are the signal wires, one to enable or disable the transmitter and the other to get
the returned echo. The microcontroller needs also a 5V to operate. This 5V power supply
is got using a regulator. The user can use a 12V DC power supply or a 9V battery to
operate this device illustrated in Figure 5.13.
Figure 5.13: The power supply circuit.
5.6 Ultrasonic sensors
A market survey has been done to select the best available ultrasonic proximity sensor
available at that time. The following are some of the sensors that have been considered
for the development of this system.
Table 5.5: The Ultrasonic sensor specifications.
Transducer Range Beam
angle
Measurement speed Frequency Sensitivity
SQ-40T/R 10 cm - 3 m 30º 20 ms 40 Khz high
SensComp
600
15 cm –10.7 m 15º 200 ms 50 Khz good
The ultrasonic transducers are optimized for 25 kHz, 32 kHz, 40 kHz or wide bandwidth
transducers. This project uses a 40 kHz transducer but it will still work with the others if
48
the appropriate changes to the software are being made. The receiver and generator
circuits will work as they are. The 40 kHz signal is easily generated by the
microcontroller but detection requires a sensitive amplifier and a peak detector.
Transducers are devices that convert electrical energy to mechanical energy, or vice
versa. The transducer converts received echoes into analog electrical signals that are
output from the transducer. Ultrasonic transducers operate to radiate ultrasonic waves
through a medium such as air. Transducers generally create ultrasonic vibrations through
the use of piezoelectric materials such as certain forms of crystals or ceramic polymers.
The overall capacitance of a transducer is dependent upon the area and the thickness of
the piezo material.
Ultrasonic transducers are available in various technical forms. Ultrasonic transducers are
typically formed of either piezoelectric elements or of micro-machined ultrasonic
transducer (MUT) elements. For industrial use, solid-state transducers are usually used,
because of their robustness. They basically include a piezoceramic device as an element
for converting between electric signals and acoustic signals and a resonant adapter layer,
with which the transfer of sound to the air is optimized. The piezoelectric elements
typically are made of a piezoelectric ceramic such as lead-zirconate-titanate (PZT), with a
plurality of elements being arranged to form a transducer. Piezoceramic ultrasonic
transducers are the transducers of choice for rugged, industrial applications because they
are efficient and environmentally robust. These sensors have been used in industry for
numerous applications; however have not been capable of short range object detection
until recently. A micro-machined ultrasonic transducer (MUT) is formed using known
semiconductor manufacturing techniques resulting in a capacitive ultrasonic transducer
cell that comprises a flexible membrane supported around its edges over a silicon
substrate. The membrane is supported by the substrate and forms a cavity. The MUT may
be electrically energized to produce an appropriate ultrasonic wave. Similarly, when
electrically biased, the membrane of the MUT may be used to receive ultrasonic signals
by capturing reflected ultrasonic energy and transforming that energy into movement of
the electrically biased membrane, which then generates a receive signal. Capacitive
micro-machined ultrasonic transducers (cMUTs) are tiny diaphragm-like devices with
49
electrodes that convert the sound vibration of a received ultrasound signal into a
modulated capacitance. For transmission the capacitive charge is modulated to vibrate the
diaphragm of the device and thereby transmit a sound wave. In general, ultrasonic
transducers are constructed by incorporating one or more piezoelectric vibrators which
are electrically connected to pulsing-receiving system. [3]
5.6.1 Electrostatic Ultrasonic Sensors
Electrostatic ultrasonic sensors operate similar to an electrical capacitor. These sensors
usually are composed of a fixed conductive plate and a free metallic surface coated with a
layer of insulation that separates the two plates.
When an electric potential is placed across the fixed conductive plate, the free metallic
surface is pulled against the fixed plate. When an oscillating electrical potential is applied
to the fixed plate, the free plate oscillates at a similar frequency thereby creating acoustic
pressure waves. When receiving an ultrasonic signal, the Electrostatic ultrasonic sensors
produce a varying capacitance created by the pressure waves hitting the free metallic
surface.
5.6.2 Piezoelectric Ultrasonic Sensors
Piezoelectric ultrasonic Sensors are composed of a Piezo material and an acoustic
surface. The Piezo material can either be a crystal or ceramic. The Piezo material is
attached to the acoustic surface such that any physical changes in the geometry of the
material will affect the acoustic surface.
When an electrical potential is placed across the Piezo material, the geometry changes
thereby disturbing the acoustic surface.
When an oscillating electrical potential is placed across the Piezo material, the acoustic
surface generates an acoustic signal. When receiving an ultrasonic signal, the ultrasonic
waves strike the acoustic surface thereby compressing the Piezo material.
The Piezo material emits electrons when compressed thereby creating an electrical signal.
50
Piezoelectric materials vibrate in response to alternating voltages of certain frequencies
applied across the material. Piezoelectric elements are similar to common analog
capacitors in that piezo elements generally include two electrodes separated by a
piezoelectric material that functions as a dielectric, shown in Figure 5.14 and the
sensitivity with respect to frequency is described in Figure5.15.[3]
Figure 5.14: The SQ-40T/R ultrasonic transducer.
Figure 5.15: The sensitivity of the SQ-40T/R with respect to the frequency.
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5.7 The schematic of the ultrasonic range meter design:
The functionality of this system can be divided into three main parts as shown in Figure
5.27; the transmitter, the receiver, the microcontroller and the digital display.
The transmitter, enabled via the microcontroller, is designed to activate a 555 oscillator
with a frequency of 40 KHz. The width of the pulse is 0.1 ms, every 40 ms a pulse is
transmitted.
One of the most important and sophisticated part of the device is the receiver.
The receiver consists of a signal amplification stage and peak detection stage.
The signal is amplified by a gain of 2500 in order to reduce the noise effect.
In order to reduce the cost of the power supply of the device, the +/- Vcc was avoided
and 0-5 V power supply was used in the design of the signal amplification stage.
The peak detection is used to transform the signal into a pulse.
The microcontroller controls all the parts in the device and performs all the arithmetic
calculations of the distance and displays it on the 7-segment digital display. This process
of distance calculation is continuously repeated as long as the device is turned on.
The laser pointer on the device is used to pinpoint the target in order to get less error
caused by the malfunction use of the device.
The program used in the PCB design is ExpressPCB which is a professional program.
The design of the PCB is splitted into two PCB circuits as shown in Figures 5.28, 5.29;
one for the transmitter and receiver and the other for the microcontroller with transistors
used to enable the 7-segment display.
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Figure 5.16: The overall schematic of the Ultrasonic range meter.
53
Figure 5.17: The printed circuit board diagram of the microcontroller.
Figure 5.18: The printed circuit board diagram of the transmitter and receiver.
54
Figure 5.19: The packaging of the device.
55
Chapter 6
System Implementation
6.1 Factors affecting the performance of Ultrasonic sensors
Position/distance measurement using ultrasonic sensors is based on the principle of
measuring the time of flight of the ultrasonic waves in a particular medium. There are
number of factors which affect the accuracy of measurement and therefore should be
taken into consideration while designing the ultrasonic sensing system. The following are
some of the factors.
6.1.1 Radiation pattern:
All ultrasonic sensors have their specific radiation pattern associated with it.
This acoustic radiation pattern is a function of spatial angle called beam angle. Beam
angle, Ω is defined as the total angle between the points at which the sound power
reduces to half its peak value, commonly known as 3 dB points.
The spot diameter of the beam can be formulated as.
D = 2R tan (0.5 Ω) (5.6)
Where, D = spot diameter in centimeters.
R = target range in centimeters.
Ω = beam angle in degrees.
At minimum range, R = 10 cm and Ω = 30º.
D = 2 * 10 * tan (15º) = 5.358 cm.
At maximum range, R = 300 cm and Ω = 30º.
D = 2 * 300 * tan (15º) = 160.769 cm.
56
Radiation pattern consists of a main lobe and side lobes. Radiation power is dominant
mainly in the front region of the sensor, so as to say that the main lobe is directly in front
of the sensor, followed by side lobes sidewise with null region in between these lobes.
Radiation pattern is mainly determined by factors such as the frequency of operation and
the size, shape and acoustic phase characteristics of the vibrating surface. The beam
pattern of the transducer is independent of its nature as a transmitter or receiver.
In most of the application, side lobes are suppressed and narrow beams are used. This
suppression is achieved by the processing system and so, the radiation pattern of the
transducer may not be same as the radiation pattern of the whole ultrasonic sensing
system. The narrowness of the beam pattern is a function of the diameter of the radiating
surface to the wavelength of the sound at the operating frequency. As the D/λ ratio
increases, beam narrows out whereas as D/λ ratio decreases, beam broadens. For most of
the application narrow beam is desired and therefore D/λ ratio should be more. The
following Figures 6.1, 6.2 show the radiation pattern, its main lobe and side lobes with
the relative attenuation.
Figure 6.1: Geometric approximation of the ultrasonic beam width.
57
Figure 6.2: Beam pattern with respect to amplitude.
6.1.2 Frequency, wavelength and attenuation:
The frequency of the ultrasonic sensing system is determined by the resonant frequency
of the ultrasonic transducer. The selection of this transducer is made considering number
of factors such as transducer size, measurement resolution, measurement range,
background noise and attenuation. The wavelength of the ultrasonic wave can be found
out with the following formula,
λ = C/f (6.1)
Where λ is the wavelength, C is the velocity of sound equal to 340 m/s at 20º C and f is
the frequency equal to 40 KHz.
C, velocity of sound varies with variation in temperature, pressure, medium type,
humidity, air turbulence, conventional currents. So before calculating the wavelength, the
speed of sound is required to be calculated.
λ = 340/40 = 8.5 mm.
6.2 Environmental factors:
The attenuation of sound power depends on the speed of sound, which depends on many
environmental factors like temperature, medium, pressure, humidity, acoustic
interference, radio frequency interference.
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6.2.1 Temperature
The velocity of sound in a medium varies with temperature. So, the time taken by the
sound to echo back to the receiver will vary and since this time of flight is proportional to
the measured distance. The measured distance will vary with the variation in temperature.
Thus the variation in temperature introduces errors in the measurement.
The sound wave propagation speed in the air depends on the temperature. So, to measure
the distance more correctly, it is necessary to revise according to the temperature. The
sound wave propagation speed can be calculated using one of the two formulas.
V = 331.5 + 0.6 * T [ m/sec ] (6.2)
T : The temperature (°C)
Table 6.1: The speed of sound at each temperature.
Temperature (°C) in air Speed of sound (m/sec)
-10 325.5
0 331.5
10 337.5
20 343.5
30 349.5
40 355.5
50 361.5
59
300
310
320
330
340
350
360
370
-10 0 10 20 30 40 50
Temperature ºC
Sp
eed
of
so
un
d m
/s
Figure 6.3: Graph of speed with respect to temperature
In this project, the speed of sound used in this program is 340 m/s because this speed is
relative to the temperature 20 ºC which is an average value. A temperature sensor could
be added to this project with a small manipulation to the program, in order to use the right
speed value. In this way, this device would be used in all atmospheric conditions. [4]
6.2.2 Pressure and humidity
As the pressure reduces, the density of particle in the medium decreases thus providing
less and less resistance to the traveling wave. Although slightly pressure effects the
velocity of sound wave, humidity which is defined as the moisture content in the medium
basically has a very little effect on the velocity of sound but it actually effect the radiating
surface. The acoustic pressure p must satisfy the three-dimensional wave equation.
(6.3)
6.2.3 Medium
Velocity of sound depends on the kind of medium the sound travels. Sound speed varies
with different medium. The Table 6.2 summarizes some of the medium with the sound
velocity in it.
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Table 6.2: The ultrasonic wave speed through different mediums
Medium Speed, m/s at 10°C
Air 331.5
Ammonia 414.8
Argon 301.9
Carbon Dioxide 257.8 (low frequency)
Carbon Disulfide 184.7
Carbon Monoxide 337.1
Chlorine 205.4
Ethylene 313.9
Helium 969.8
Hydrogen 1269.4
Illuminating Gas 490.4
Methane 431.9
Neon 434.9
Nitric Oxide 324.9
Nitrogen 334.06
Nitrous Oxide 261.8
Oxygen 317.2
.
6.2.4 Acoustic Interference
If the environment contains number of objects that generates background noise and if this
background noise falls in the sensitive frequency of the receiver of the ultrasonic sensing
system, it will result in erroneous measurement.
This error is more pronounced when the amplitude/power of the background noise is
more then the echo itself resulting in very low SNR (signal to noise ratio), which is
undesirable. Typically, the background noise is less at higher frequency and so narrow
beam angles works best in an area where background noise is high.
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6.2.5 Radio Frequency Interference
Radio frequency signal present in the environment also affects the ultrasonic sensing
system.
6.3 Target Consideration
The principle of ultrasonic sensing is based on transmission of sound wave followed by
the reflection of the echo. These echoes are summed up at the receiver. The return echo is
a function of target distance, geometry, surface, size, composition, orientation of
object/sensor etc.
6.3.1 Composition
Some of the objects are good reflector and some are good absorber. So the amount of
echo returned back depends on the kind of material the object is composed of. This
finally effects the measurement as it varies from object to object for the same fix distance
of the target from the sensor. The object must not be composed of soft surfaces that
absorb most of the sound energy.
6.3.2 Size and shape
Size and shape affects the amount of echo reflected back to the receiver. For example, for
large planner object (object size >> beam size) almost all the ultrasonic wave will be
reflected back to the receiver. Whereas in case where the object is very small as
compared to the beam size, then part of the ultrasonic sound wave will be reflected to the
receiver and the rest will be lost. The shape determines the angle at which the ultrasonic
wave will be reflected. Common to all ultrasonic ranging systems is the problem of
ultrasonic reflection. With light waves, our eye can see objects because the incident light
energy is scattered by most objects, which means that some energy will reach our eye,
despite the angle of the object to us or to the light source. This scattering occurs because
the roughness of an object's surface is large compared to the wavelength of light 550 nm.
Only with very smooth surfaces such as a mirror does the reflectivity become highly
directional for light rays. Ultrasonic energy has wavelengths much larger 6.35 mm in
comparison. Therefore, ultrasonic waves find almost all large flat surfaces reflective in
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nature. The amount of energy returned is strongly dependent on the incident angle of the
sound energy.
Figure 6.4 shows a case where a large object is not detected because the energy is
reflected away from the receiver.
Figure 6.4: Undetected large object due to reflection.
6.3.3 Position and Orientation
If the size of object is small as compared to the beam size, then the measurement depends
on the position of the object in the beam region. When object is on the main lobe axis, the
reflected echo reaching to the receiver will be very strong and if it is out of axis, the
reflected echo will be weak.
Although the basic range formula is accurate, there are several factors when considering
the accuracy of the result. Since the speed of sound relies on the temperature, a 10N
temperature difference may cause the range to be in error by 1%.
Geometry also affects range in two major ways. The range equation assumes that the
sonar beam width is negligible. An object may be off center, but normal to the
transmitted beam. The range computed will be correct, but the X-component may be in
error. Using the formula: X = R * sin f (6.4)
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At a range of 9 meters and a beam width of 30N, the X component would be 2.33 meters
off center. Figure 6.5 illustrates this.
Figure 6.5: Object offset due to ultrasonic beam width.
Another geometric effect is shown in Figure 6.6. When the object is at an angle to the
receiver, the range computed will be to the closest point on the object, not the range from
the center line of the beam. This is called cosine error.
Figure 6.6: Range error due to angle between object and sonar.
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6.4 Power of the detected signal
We need to calculate the power of the detected laser beam in order to detect the reflection
at the receiver in a maximum distance range. Power of the detected signal is calculated by
the following way:
Pdet = Pult * є * δ * S / (4 * π * R²) (6.5)
Pult is the power of the emitted ultrasonic wave.
S is the object target area that reflected the echo.
R is the distance between the device and the target.
є is the target response to the ultrasonic wave.
δ is the geometric form-factor for propagation of the ultrasonic wave and the response
signal through the ambient media (air, water …).
6.5 Noise
The output of the sensor involves noise, which is primarily introduced because of the
uncertainty of the echo which might comes back from the false object/target. Also the
attenuation of the sonic burst depends on the position of the object/target in the lobe
region.
6.6 Errors
In general it is desired to develop the worst case analysis to permit the design of the
hand-held ultrasonic range meter device capable of operation under all conditions with a
minimum error (maximum acceptable error is +/- 3 cm). The errors associated with both
calculations and measurements can be characterized with regard to their accuracy and
precision as shown in Figure 6.7. Accuracy refers to how closely a computed or
measured value agrees with the true value. Precision refers to how closely individual
computed or measured values agree with each other.
65
Figure 6.7: (a) The samples are inaccurate and imprecise. (b) The samples
are accurate and imprecise. (c) The samples are inaccurate and
precise. (d) The samples should be accurate and precise in order
to get the acceptable error.
6.6.1 Truncation errors
The truncation errors are those that result from using an approximation in place of an
exact mathematical procedure.
For a distance that is being measured, the hand-held ultrasonic range meter device
showed a distance R but the real distance was R +/- 3 cm. This means that the error is at
its maximum.
At a minimum distance range, with the distance equal to 10 cm.
T1 is the real time of the real distance for the echo to propagate, get reflected by the
targeted object then get back to the receiver.
T1 = (0.1 m * 2) / 340 m/s = 588 μs.
T2 is the time captured by the microcontroller for the echo to propagate, get reflected by
the targeted object then get back to the receiver.
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T2 = (0.12 m * 2)/ 340 m/s = 705 μs.
Truncation error = ((T2 – T1)/T2) * 100 = 16.6 %. (6.6)
At a maximum distance range, with the distance equal to 300 cm.
T1 is the real time of the real distance for the echo to propagate, get reflected by the
targeted object then get back to the receiver.
T1 = (3 m * 2) / 340 m/s = 17.6 ms.
T2 is the time captured by the microcontroller for the echo to propagate, get reflected by
the targeted object then get back to the receiver.
T2 = (3.07 m * 2)/ 340 m/s = 18.05 ms.
Truncation error = ((T2 – T1)/T2) * 100 = 2.54 %. (6.7)
6.6.2 Cosine error
The effect attributable to cosine error occurs with ultrasonic when the position of this
ultrasonic range meter device is not in true alignment with the target. Since the distance
to be determined is relative to the position of the object with respect to the position of the
device, any deviation from true alignment results in an increase in the distance displayed.
6.6.3 Reflection error
Reflection can also give rise to erroneous reading, often due to the size and shape of the
targeted object or due to the presence of many objects near to the targeted object.
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Chapter 7
Testing and results
7.1 System testing
This experiment was done at a 17 ºC and that increased the error. It consisted of
measuring the distance from the device to a flat wall. Eleven measurements were done in
this experiment.
The average error A = (2 + 2 + 2 + 3 + 3 + 3 + 3 + 3 + 4 + 5 + 7) / 11 = 3.36 cm.
Table 7.1: Distance measurement with its error.
Real measurements
in cm
Device measurements
in cm
Error
in cm
10 12 +2
20 21 +2
30 32 +2
40 43 +3
50 53 +3
75 77 +3
100 103 +3
150 153 +3
200 204 +4
250 255 +5
300 307 +7
The Figure 7.1 shows the variation of error with respect to distance. The error increases
as long as the distance increases.
68
0
1
2
3
4
5
6
7
8
12 21 32 43 53 77 103 153 204 255 307
Device measurements cm
erro
r cm
Figure 7.1: Graph of error with respect to the measured distance
7.2 Testing the Transmitter
The transmitter was enabled and tested on the oscilloscope shown in Figure 7.2 to get the
desired frequency. The voltage/division used on this oscilloscope is 2 V/div and the
time/division used is 20 μs/div.
The period is about 1.1. To get the value, 1.1 * 20 μs = 22 μs.
F = 1 / 22 μs = 45.4 KHz.
Figure 7.2: The transmitter oscilloscope graph.
69
7.3 Testing the Receiver
The Figure 7.3 shows the receiver oscilloscope graph where the transmitted and received
echoes are present on the second stage of the signal amplification. The voltage/division
used on this oscilloscope is 2 V/div and the time/division used is 5 ms/div.
Figure 7.3: The receiver oscilloscope graph.
The Figure 7.4 shows the transmitter and receiver oscilloscope graph where the
transmitted and received echoes are present on the second stage of the signal
amplification. The voltage/division used on this oscilloscope is 2 V/div for the signal
amplification stage of the receiver, 1 V/div for the transmitter and the time/division used
is 2 ms/div.
Figure 7.4: The transmitter and the receiver oscilloscope graph.
70
7.4 Testing the Detection circuit
The detection oscilloscope graph is done showing a detection of the reflected echo for a
72 cm distance. The first part is for the signal amplification of the receiver and the second
part is for the detection part of the receiver.
Figure 7.5: The detection oscilloscope graph.
The voltage/division used on this oscilloscope is 2 V/div for the signal amplification
stage of the receiver, 5 V/div for the peak detection and the time/division used is 1
ms/div. The period measured on the oscilloscope is about 4.2.
To get the value of it, 4.2 * 1 ms = 4.2 ms, this is 72 cm of distance. Looking at the
detection oscilloscope graph from left to right, the first peak is the transmitted pulse but
the second is the received pulse as shown in Figure 7.5.
7.5 Conclusion
The solutions of the problems and the design of our device according to our constraints.
These solutions are the preliminary solutions of the most important problems and they
can be improved at anytime.
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Chapter 8
Timeline, Cost and conclusion
8.1 Timeline
Time needed to complete each part of this project.
Ultrasonic transmitter and receiver (three weeks)
Microcontroller with the program (two weeks)
Building the circuits (one week)
Figure 8.1: Timeline graph.
The time needed to complete the hand-held ultrasonic range meter device is one month
and two weeks as shown in Figure 8.1 and Table 8.1 shows how the work was
distributed.
Table 8.1: Distribution of work.
Euclid Team Ultrasonic
Transmitter
Ultrasonic
Receiver
Program Circuits
Maroun Daher X X X X
Rami Freih X X X
Gaby Al Jawabira X X X
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8.2 Cost of the ultrasonic range meter design
The components of this project was selected carefully to get the most efficient ,less
error ,cheaper and which can be modified to adapt to a variety of pulsed ultrasonic
systems. The Table 8.2, show the cost of the components.
Table 8.2(a): Components and prices
Quantity Resistors Capacitors Price
6 1 kΩ - 1200 L.L.
2 5.6 kΩ 15 pF 900 L.L.
2 47 kΩ 3.3 nF 900 L.L.
2 100 kΩ 470 μF 900 L.L.
1 56 Ω 1 nF 450 L.L.
1 3.9 kΩ 1.2 nF 450 L.L.
1 10 kΩ 10 nF 450 L.L.
1 - 120 nF 250 L.L.
1 - 220 nF 250 L.L.
1 - 10 μF 250 L.L.
1 - 22 μF 250 L.L.
Quantity Transistors ICs Diodes Others Price
1 C32725 TL082 1N4007 SQ40-T 9500 L.L.
1 - NE555 - SQ40-R 5500 L.L.
1 - 7805 - 4 MHz clock 1500 L.L.
1 - 16F877A - - 7500 L.L.
2 - - 1N4148 - 1000 L.L.
5 BC548 - - - 2750 L.L.
4 - - - 7 segment display 2000 L.L.
Table 8.2(b): Components and prices
73
Adding the cost of the electrical components used in the Tables 8.2(a), (b), it cost 34000
L.L. By adding the cost of the packaging, the PCB and the laser pointer, the overall
handheld ultrasonic range meter device cost was 55000 L.L.
8.3 Conclusion
During the process of designing and implementing the hand-held ultrasonic range meter
device, the personal and professional benefits were extremely important.
Teamwork was the most interesting part, dividing the project into several parts related to
each other, helped in reducing the time of completing the project. Each individual worked
on a specific part and in the end all the work was combined into a whole working device.
The importance of the device is based on calculating accurate distances. The device can
be used in many different fields and categories like distance calculation in construction
field, robots, car sensor to avoid obstacles and many other applications.
The building process of the device was based on using as much as possible from the
courses taken in the university, like Programming I, II, Circuits I, II, Analog Integrated
Circuits, Electronics and Field Theory.
The cost of the device was minimized as much as possible in order to benefit more
financially and decrease its price in the market.
74
References
[1] Ultrasonic instruments and devices by Emmanuel P. Papadakis, ElSevier academic press
[2]http://www.ndted.org/EducationResources/CommunityCollege/Ultrasonics/Introduction/history.htm
[3] http://www.electronics-manufacturers.com/info/sensors-and-detectors/ultrasonic-sensor.html
[4] http://www.hobby-elec.org/e_srm1_4.htm
Software:
Microsoft Word.
Microsoft Excel.
Microsoft Visio.
Microsoft Paint.
Express PCB.
Circuit Maker.
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