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Design Distance Measurer Based On Fpga Information Technology Essay

Paper Type: Free Essay Subject: Information Technology
Wordcount: 5345 words Published: 1st Jan 2015

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There are variety applications in range finder devices. Their main use is in areas where traditional measuring devices such as rulers, tape measures and other measuring devices are impropriate. Nowadays, the traditional measuring device can be replace by modern measuring device such as distance measurer based on laser. It has been implemented in short range distance even long range distance. The idea for using laser for range finding came when we can see that contractor had many problems in measuring the distance of the building especially from the floor to the ceiling. When it came to very high ceiling, such as in hall, stadium even close sport-court, the use of rulers or tape measures really a waste of time even need very hard work. This can be classified as uses in low tech world but in the high tech world, this distance measurer based on laser can be use with binocular in military use, especially for sniper. The observer can get the real distance of the enemy where the sniper can snipe from very far distance. This project is designed to be a laser distance measurer of detecting the distance of the object (wall) up to 10 meter away. The design based on simple physics, the distance travelled between two locations can be easily calculated if the speeds of travel are known. This device calculates the time is takes for a laser travel to, rebound off and return from a stationary object

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1.2 Problem Statement

Before this, we measure the distance using ruler or measuring tape, so this project design is to help human being by saving time and effort so we can measure the distance faster than before. With the help of Field Programmable Gate Arrays (FPGA) and the laser sensor, the design is more advance with the one click system and we can get the distance measurement by no time. In military use, the project will help by saving the life of the sniper as well.

1.3 Objective of the Project

The objective of this project is to design distance measurer based on laser using FPGA as the microcontroller of the design.

1.4 Project Scope

This project paper will involve in the analysis and design distance measurer based on laser, and FPGA as the microcontroller. These concepts are:

The user will press the button as input.

The laser will activate and laser beam will go direct to the object or surface.

Laser beam will hit the object or surface and reflected it back.

The sensor will picks up the signal.

The flight time from the start and end will be measured.

The corresponding distance of the reflecting object or surface is displayed in digital which is in 7 segment display.

A few things that need to be considered for this design are:

Types of laser sensors.

How the instrumentation operates.

Output characteristic.

Many more issues need to be taken for consideration and this issue will be approached further in the coming chapters.

1.5 Project Plan

Generally, this project is divided into five main chapters; namely Introduction, Literature Review, Methodology, Results and Discussion and Conclusion.

CHAPTER 1 discusses on project overview, problem statement, the objective of the project, the scope in order to achieve the objective of the project and the thesis outline.

CHAPTER 2 will focus on the literature review of the theory of laser based distance measurer and its development. There are also detailed introduction of the project and the background of various types of FPGA controller, i.e. VHDL, Verilog-HDL, Altera Quartus..

CHAPTER 3 describes about the methodology that will be used in order to complete this project which include the design of laser distance measurer using FPGA as the controller. This will include the selection of the technique use to measure the distance using the laser and the program to be compile with the FPGA board. Furthermore, it also discuss about how the program work on the hardware so that the project with give the result that I want.

CHAPTER 4 discusses on the simulation results obtained. The detailed discussion is made to verify the performance and characteristics of the project. It will also discuss the problems and findings throughout the design and simulation of the system.

CHAPTER 5 reviews the project outcomes upon the completion. Some suggestions are also made for better improvement in the future so that if anyone want to continue this project for better performance, they will know the basic of how this project start..

CHAPTER II

LITERATURE REVIEW

2.1 Distance measurement

Distance is a numerical description of how the objects are apart. In physics or everyday discussion, distance may refer to a physical length, or an estimate based on other criteria. In mathematics, a distance function or metric is a generalization of the concept of physical distance (Distance, 2010). In science, measurement is the process of estimating or determining the magnitude of a quantity like length or mass, compared with a measurement unit, like a meter or a kilogram (Measurement, 2010). The measure term can also be used to refer to a specific result obtained by the method of measurement Distance measurement is a process where we need distance measuring instrument which can measure the distance if the distance is short or long. The SI unit for each measurement is the meter (m) but there are many units of length such as feet, yard, inches etc, but they are not classified as SI unit of length.

Remote sensing using the light sensor is widely used for implementing mobile robot. The main attraction of the distance light detecting means is its user friendliness of how to use it without need knowledge about it. The measurement precision is somewhat limited and care must be taken to ensure that the environment is not subject to temperature changes and the sensor should not be confused by stray reflections from material adjacent to the target. Even with these limitations, laser range finder has a wide application especially when the target is far away and the action required is low. But sometimes the laser must be reflected after the laser strike any target, which means that if the laser hit a transparent material, the calculation cannot be done.

But the light system based on distance measurement are inherently more accurate than ultrasound techniques because of the narrow beam angles commonly used and the restrictions of freedom inevitably fundamentally mechanical acoustic signal generation and detection. These are wide ranges of techniques that can be used to measure distance using light. These vary greatly in cost and function of the laser distance measuring system is very expensive in cost compared to the system for measuring distance using ultrasonic.

2.2 Optical Distance Measurement

2.2.1 Introduction

Wide variety of industrial, commercial and research use optical sensor for distance measurement. Most sensors use visible or infrared laser beam to project a light spot on a target, the surface on which distance should be measured, the distance from the place back in the light detecting portion of the probe is measuring several ways

There are several factors to consider when specifying a laser distance sensor. They include maximum range, sensitivity, target reflectance and specularity, accuracy and resolution and sampling frequency.

2.2.2 Definition

Some of the terms that related to optical sensing (e.g. laser or ultrasonic) and distance measurement that must be take notes as some knowledge before the measurement can be done. Some of the knowledge that must be take notes is defined and described briefly here (Glossary of Laser Sensor Terminology, 2010).

Target: When a laser pointed at some surface, the light is reflected into the detector in an optical sensor. This can refer to a surface or material designed to reflect light, in which the sensor is pointed. To determine the maximum range of a sensor, reflectance target is the most important factor

Cooperative Target: A target or any material designed by the manufacture to reflect the light to a sensor detector. It also provides the return signal to the receiver input higher after the laser beam and more. Cooperative target include glass cube, reflectors corner, retro reflective tape and other material made by several manufacturers. In some applications, the mirror can also be used as targets of cooperation.

Figure 2.1: Cooperative Target (Module 6)

Uncooperative Target: The material is not specifically designed to reflect light onto the sensor while taking the measurement. Can be generally referred to an object that scattering light. The term is used because the target in return cannot be reflected beam, this includes metal or painted surfaces, liquids and solids or loose granular

Figure 2.2: Uncooperative Target (Module 6)

Retro reflection: The reflection of light off a target object or surface back in the direction from which it came, for a wide range of angle of incident, either it came in 180° reflection or any degree as long it reflect to it sources. It can be said that the retro reflection will produce minimum scattering light. Retro reflection is achieved through multiple reflections within a retro reflector. Retro reflectors include corner cubes and retro reflective tape. A high quality corner cube retro reflector will return virtually all the light entering it to its source. Corner cubes may be used to extend range hundreds or thousands of times over ordinary surfaces. A corner cube array was left on the moon to allow accurate measurement of its distance from the earth. Some of the example item that commonly being used in many applications is retro reflective tape. It typically consists of microspheres or cubes of glass or plastic which act like many tiny retro reflectors.

Figure 2.3: Retro reflection Surface (Retroreflector, 2010)

Diffuse Reflection: This terms is being use when a light strikes the target and scattered over a wide angle which mean the incident ray reflected in many angles.. Plain white paper of flat (not glossy) wall paint is good diffuse materials. It can be classified as the best uncooperative targets, and may be measured to over a wide range of incident angles (up to 80 degrees for some materials).

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Figure 2.4: Diffuse Reflection Surface (Diffuse Reflection, 2010)

Specular Reflection: It occurs when the light strikes a shiny or mirror-like surface and is reflected away in one angle which is same to the angle it reflects. Glass, liquid surfaces and polished metal are specula and generally it needs a sensor configured specifically for specula surfaces. This behaviour is described in the law of reflection where it totally follows the law itself.

Figure 2.5: Specular Reflection Surface (Specular Reflection, 2010)

Reflectance: The amount of light reflected from the target, expressed as a percentage of incidents light. Diffuse reflectance refers to the amount of light scattered in all directions by a diffuse target. Specular reflectance refers to the amount of reflected light is reflected for example a mirror. Reflectance depends on the target color and composition and the frequency of light is reflected. Diffuse surfaces often vary from 3% to 95% reflectance. Many surfaces such as pain and glossy coated paper are diffuse and specular components of reflection

Maximum Range: The maximum distance of sensors that picks up the reflected light and to obtain an accurate measurement of the distance. The maximum range may be limited by laser power, the amount of light reflected from the target and the sensitivity of the detector. It may also be limited by the measurement method used and the distance that the sensor is accurately calibrated

Laser Power: It is the optical power level emitted by the laser sensor. The power can be specified as average power or peak power and average, if the sensor output pulses of intermittent light. If all other factors being equal, the maximum range increases in proportion to the square root of laser power, if power is multiplied by four, it will double the maximum range it can achieved. Laser power is expressed in Watts Mill (mW) or watts (W).

Sample Rate: The frequency of a sensor updates its output range. The sampling frequency capability of remote sensors varies widely, depending on the measurement method that being used and the design of the devices. The sampling frequency can be as low as one sample every few seconds and run a million samples per second..

Response Time: It is the delay between the time changes in target position and the time changes of the sensor output. This may be more than one sample interval, if the sensor is processing or calibration of the intermediate samples during transmission of the previous sample and then taking the next measurement.

Sensitivity: A measure of the ability to obtain a reading on a dark target or with low laser power. Sensitivity decreases at long ranges.

Depth of Field: The span of distance over which a measurement sensor can measure distances accurately. This may be limited by the approach of light focus collection and the maximum distance that reflect enough light to the sensor. These two factors will determine how changes in the sensitivity of the sensor with distance.

2.2.3 Performance Of Optical Sensor On Specula And Diffuse Targets

All sensors require a bit of laser light to the back surface of the target to operate. The amount of light needed is a measure of the sensitivity of the device. In general, the most sensitive devices are more expensive and accurate measurement of high sampling frequency requires more thought than for lower sampling frequencies.

For diffuse targets, the higher the reflectance of the target, the best performance of a sensor will be. Lightweight materials such as wood, paper or white paint is non-cooperative targets that work well at all distances. The 50 darkest carbonaceous materials feet from a rangefinder can return only one ten-millionth of the light that reaches them at a rangefinder. The maximum range and depth of field can be limited to as little as 1.5 of what is possible with ordinary, light-colours surfaces.

In addition to the amount of light a surface reflects the way light is reflected can affect the performance of an optical sensor. Many surfaces are partly specula and partially diffuse. These can be difficult to measure the amount of light reflected to a sensor may vary considerably with the angle of the target surface.

2.2.4 Accuracy, Repeatability and Resolution

The accuracy of a sensor is a measure of the difference can be provided between the reading of a sensor and the actual distance measured. The resolution is the smallest change in measured distance. The resolution is the smallest change in the distance a sensor can detect and is usually a value smaller than the precision error. Accuracy can be affected by reflection from the target temperature, ambient light, which will generally not affect the resolution.

Repeatability is the measure of the stability of the sensor over time. Generally, the sample repeatability sample will be lower for very fast sampling rates, because less time is used for measuring average. As the sampling frequency is lowered, the repeatability will improve, but this cannot continue indefinitely. Beyond some deceleration rate of the sample, the repeatability will start to get worse as the long-term drift in the components and changes in temperature cause changes in output of the sensor.

2.2.5 Spot Size and Divergence

Other specifications which may be important are the laser spot size and divergence of the beam. Some applications require a small spot for high-resolution, measurement while others require a larger diameter spot of averaging rough surfaces or for eye safety concerns.

2.2.6 Visible and Infrared Lasers

Both visible and infrared (IR) laser are used in distance measurement. For some applications, the advantage of being able to see the spot is an advantage, while others do not want the place to be seen. For some sensors, they have two versions of visible and infrared. IR versions are slightly more sensitive and more accurate than the version visible and IR models have a wider range of laser powers.

2.2.7 Class of Lasers

2.2.7,1 Class I

It has no possibility damaging the eye. That is because of a low power of the output (in which eye damage case is impossible, even after the hours of exposure), or because of an enclosure preventing the access of the users to the laser beam during normal operation, any individual, independently of the conditions of exposure to the eyes or the skin, No one can expect to be wounded by a laser of class I. No requirements of safety are necessary to use with the devices of laser class. The lasers of class I are apparatuses with low power which are regarded as sure of all the potential dangers. Some examples of the use of the laser of class I are as follows: the printers laser, CD-ROM devices, the geological equipment of survey and the laboratory equipment of analysis (Laser Safety, 2010).

Figure 2.6: Example of Class I Application – Laser Printer

(Application of Laser Product, 2008)

2,2,7,2 Class II

Class II laser can damage the eyes of the person if deliberately looks in the beam for one prolonged period (i.e > 15 minutes). Power of output can be up to 1 mW. This category includes the lasers that emitting a visible light. Certain pointers lasers are in this category. The lasers of class II are of low power which is less than 1mW, lasers of the visible light which could cause damage with the eyes of a person. Some examples of laser use of class II are: demonstrations in class, the pointers laser, devices of aiming and the distance measuring equipment. Avoid looking in a laser beam of class II or pointing a laser beam of class II in the eyes of another person. Avoid looking at class II of the beams laser with telescopic devices. To carry out that the light of a laser beam of class II in the eyes causes a normal reaction to divert the glance or to close the eyes (Laser Safety Policy, 2010).

Figure 2.7: Example of Class II Application – Barcode Scanner

(Application of Laser Product, 2008)

2.2.7.3 Class IIa

Laser class where it is in the low-power output of Class II ans the laser requires in excess of 1000 seconds of continuous viewing to produce a burn to the retina. Commercial laser scanners are in this subclass (Laser Safety, 2010).

Figure 2.8: Example of Class IIa Application – Laser Disco Light

(Starfield Projector, 2007)

2.2.7.4 Class IIIa

The lasers of class IIIa are from continuous wave. The lasers in this class are most of the time dangerous in combination with the optical instruments which change the density of diameter or power of beam. The power of the output is not exceeding 5 MW. The density of power of beam cannot exceed 2.5 mW/square centimetres. Many sights of laser for weapons with fire and indicators of laser are in this category of devices with intermediate output power (1-5 mW). Some examples of the uses of laser of class IIIa are identical to that laser of class II with the most popular uses being indicators of laser and modules of laser scanner. The direct viewing of the laser beam of IIIa of class could be dangerous with the eyes. Directly do not look at the laser beam of IIIa of class (Laser Safety, 2010)

.

Figure 2.9: Example of Class IIIa Application – Military Equipment

(Marushin M16A1)

2.2.7.5 Class IIIb

The lasers in this class can damage if the beam enters the eye directly. This generally applies to the lasers actuated starting from 5-500 mW. The lasers in this category can damage permanent eye with exposures of 1/100th one second or less according to the force of the laser and the lasers at the end of high power of this class can also present a fire hazard and can slightly burn the skin. A diffuse reflection is generally not dangerous but the specular reflections can be like dangerous that is direct exposures. All times that occupying a control field of laser, carry the suitable protection of eye. Protective Eyewear is recommended when the direct viewing of beam of the lasers of IIIb of class can occur. Some examples of the uses of laser of IIIb of class are spectrometry, stereo lithography, and the light of entertainment shows (Laser Safety Policy, 2010).

Figure 2.10: Example of Class IIIb Application – Military Equipment

(Azari, 1998-2009)

2.2.7.6 Class IV

The lasers of class which is the majority of entertainment, industrialists, scientists, military and medical are in this category. Some examples of use of laser of class IV are surgery, research, drilling, cutting, welding, and the lasers micromachining in this class produced powers moreover than >500mW or pulsed of >10 J/cm2 in the beam and can damage considerably and permanent the eye or the skin without being magnify by optical system of eye or instrumentation. It can be dangerous to peel or observe diffuse reflexions of the laser beam in the nominal zone of risk. The lasers of class IV are devices of high power. The direct beam and the diffuse reflections of the lasers of class IV are dangerous with the eyes and the skin. The devices of laser of class IV can also be a fire hazard according to the reaction of the target once struck. Orders much larger are required to ensure the sure exploitation of this class of the devices of laser. All times that occupying a control field of laser, carry the suitable protection of eye. The majority of the damage of eye of laser occur reflected beams of the light of laser of class IV, thus maintain all materials reflective left the beam. Do not place your hand or any other part of body in the laser beam of class IV (Laser Safety, 2010).

Figure 2.11: Example of Class IV Application – Laboratory Equipment

(Oxford, 2009)

2.2.8 Method of Measuring Distance Based On Laser

Lasers can be used in various ways to measure distances or travel without physical contact. Laser length measurements allow the most sensitive and accurate records for extremely rapid and larger measurement ranges, even if these qualities are usually not combined with a single technique. According to specific requests, very different technical approaches may be appropriate. Some laser applications such as in architecture, inspection of manufacturing facilities, crime scene investigation (CSI), and the army (Paschotta D. R., 2010).

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2.2.8.1 Triangular Measurement Method

It exploits the ability of a laser beam to propagate in a well-collimated form (ie with small divergence) over long distances. In a typical case, the laser beam illuminates a point and the laser is essentially used as a pointer. Diffuse or specular reflections of this item are followed by a detector that is mounted in a distance from the laser beam, so that the laser source, object and detector form a triangle. The principal is same like the ship trying to find the distance from the shore (Encyclopedia of Laser Physics and Technology, 2010).

Figure 2.12: Triangulation Method

(B., C., & D., 2010)

The high detection rate, it is possible to control the position of a moving or vibrating example: part of some machines. The precision obtained is very accurate compared with other devices. For diffuse reflections, the distance may be limited by the obligation to receive a sufficient amount of reflected optical power, with specular reflection, a greater distance can be measured, but a sort of angular alignment is required (Paschotta D. R., 2010).

2.2.8.2 Time-Of-Flight Measurement Method

Time of flight measurements are often used to measure a distance, used for example in an airplane, possibly in the form of laser scanning radar. Here, a device sends an optical pulse and measure short time until a reflected portion of the pulse is controlled. The distance is then calculated using the speed of light.

This method usually used for measuring distance, like hundreds of meters or several miles. By using advanced techniques (involving high-quality telescopes, very sensitive photo detector, etc..) With the precision of a few centimeters, it is possible to measure e.g. the distance between Earths and to obtain an accurate profile of a dam.

Over time, measures are preferably used in flight for long distances, the beam quality of laser source is crucial. For large distances, high pulse energies are required. This may raise issues of laser safety, especially if the laser wavelength is not in the eye safe region. For nanojoule to microjoule pulse energies (as required for medium distances), it is possible to use a chip laser passive Q-switched Er: Yb glass, which can generate pulses rather short (the duration of the order of 1 ns) with pulse energies of Yb: about 10 μJ in the spectral region to eye safety (Paschotta D. R., 2010).

2.2.8.3 Phase Shift Measurement Method

The method of phase shift usually use in laser rangefinders, a technique for measuring distances in the following manner. A laser beam with sinusoidally modulated optical power is sent to a target. Some reflected light (diffuse sources or specular reflections) is monitored, and phase modulation power is compared to the light sent. The phase shift obtained is 2Ï€ times the time of flight time frequency modulation. This shows that higher modulation frequencies can result in better spatial resolution. Although the phase shift is directly proportional to the duration of the flight, the length of time of flight method should be reserved for cases where one really measures a delay time more directly.

Figure 2.13: Phase Shift Method

(Dixon & Henlich, 1997)

With regard to an interferometer, the phase shift method has an ambiguity in the distance, because with the distance from the phase varies periodically. However, the frequency is much greater than in an interferometer, since the frequency modulation is much smaller than the optical frequency. In addition, ambiguity can be easily removed, for example, by measuring with two different modulation frequencies.

2.3 FPGA

Field-programmable gate arrays (FPGA) are ICs that contain an array of identical logic blocks with programmable interconnections. It also can be classified as one of the programmable logic device (PLD). There are also some other type of PLD which is Simple Programmable Logic Device (SPLD) and Complex Programmable Logic Device (CPLD). The user can program the function realized by each logic block and the connections between the blocks. FPGAs have revolutionized the way prototyping and designing are done. The flexibility offered by reprogrammable FPGAs has enhanced the design process. There are a variety of FPGA products available in market now. Xilinx, Altera, Lattice Semiconductor, Actel, Cypress, Quick Logic and Atmel are examples of companies that design and sell FPGAs.

2.3.1 DE2 Board

Figure 2.14: DE2 Board Model EP2C35F672C6

(DE2 Development and Education User Manual)

The following hardware is provided on the DE2 board:

Altera Cyclone® II 2C35 FPGA device

Altera Serial Configuration device – EPCS16

USB Blaster (on board) for programming and user API control; both JTAG and Active Serial (AS) programming modes are supported

512-Kbyte SRAM

8-Mbyte SDRAM

4-Mbyte Flash memory (1 MByte on some boards)

SD Card socket

4 pushbutton switches

8 toggle switches

18 red user LEDs

9 green user LEDs

50-MHz oscillator and 27-MHz oscillator for clock sources

24-bit CD-quality audio CODEC with line-in, line-out, and microphone-in jacks

VGA DAC (10-bit high-speed triple DACs) with VGA-out connector

TV Decoder (NTSC/PAL) and TV-in connector

10/100 Ethernet Controller with a connector

USB Host/Slave Controller with USB type A and type B connectors

RS-232 transceiver and 9-pin connector

PS/2 mouse/keyboard connector

IrDA transceiver

Two 40-pin Expansion Headers with diode protection

2.3.2 Block Diagram of the DE2 Board

Figure 2.15: Block Diagram of DE2 Board Model EP2C35F672C6

(DE2 Development and Education User Manual)

2.3.3 Cyclone II

Altera Cyclone II FPGA density range has 68,416 logic elements (GE) and provide up to 622 usable I / O pins and up to 1.1 Mbits of embedded memory. Cyclone II FPGAs are manufactured on 300mm wafers. The low cost and optimized feature set of Cyclone II FPGAs make ideal solutions for a wide range of automotive, consumer, communications, video processing, test and measurement, and other end-market solutions. Devices that support the Fast-On feature are designated with an “A” in the code of the controller. The EP2C5A is only available in the class of vehicle speed. The EP2C8A and EP2C20A are only available in the category of industrial speed. The EP2C15A is only available with the Fast-On feature and is available in both commercial and industrial categories.

Figure 2.16: DE2 Board Model EP2C35F672C6

(DE2 Development and Education User Manual)

2.3.4 Evolution of Programmable Logic

An FPGAs has grown in the past twenty years since the introduction. In the early 1970s, Programmable Logic Devices (PLDs) had been on the market. These devices used two-level logic structures which are AND plane as the first level of logic which generally fixed while the second level known as OR plane which is programmable.

Figure 2.17: Some Example Of PLD Basic Circuit

(David, 2006)

2.3.5 FPGA Types

Configuration Technology

Technology Overview And Features

SRAM Based

An external device program the device on power up. It allows fast reconfiguration. Configuration is volatile. Device can be reconfigured in circuit.

Anti-Fuse Based

Configuration is set by burning internal fuses to implements the desired functionality. Configuration is non volatile and cannot be changed.

EPROM based

Configuration is similar to EPROM devices. Configuration is non-volatile. Device must be configured out of the circuit.

EEPROM based

Configuration is similar to EEPROM devices. Configuration is non-volatile. Device must be configured out of the circuit.

2.3.6 Advantages of FPGAs

However they have compensating advantages, largely due to the fact that they are standard parts.

FPGA has larger capacity, more architecture and more register than other PLD. It is because the FPGA is the evolution of the PLD before it.

There is no wait from completing the design to obtaining a working chip. The design can be programmed into the FPGA and tested immediately.

FPGAs are excellent prototyping vehicles. When the FPGA is used in the final design, the jump from prototype to product is much smaller and easier to negotiate.

The same FPGA can be used in several different designs, reducing inventory costs.

2.3.7 Disadvantages of FPGAs

FPGAs are not custom parts, so they aren’t good at any particular function as dedicated chip designed for that application. FPGAs are generally slower and burn more power than custom logic. FPGAs are also relatively expensive.

2.3.8Types of FPGA

Reprogrammable (SRAM-based)

Xilinx, Altera

 

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