05-03-2013, 02:22 PM
DESIGN OF A COMPUTER-BASED SYSTEM TO PROCESS AN ANALOG SIGNAL
DESIGN OF A COMPUTER.pdf (Size: 1.69 MB / Downloads: 58)
ABSTRACT
This project has the aim of designing a system that can make decision electronically thereby speeding up the operations made and improving electronic system by using digital system. The work to be done was concentrated on acquiring analog signal and processing of this acquired signal using a personal computer. Digital filters were designed using Matlab programming to process the acquired signals. This was achieved through the use of electronic equipments such as signal generator, oscilloscope, computer and interfacing circuit. In fact, the main task to be carried out in this project is to design a computer-based system to acquire and process an analog signal generated by front end devices such as function generator. There were two ways to realize the practice of this project. The first one consisted the use of zelscope software as oscilloscope which analyzes signal originates from mobile phone. The mobile phone was used to play music (audio signal) in order to be analyzed by zelscope on PC screen. On other hand, this audio signal from mobile phone were acquired and analyzed with matlab programming Language.
General introduction
An oscilloscope is one of the equipments needed to perform this research. Therefore, an understanding of its working principle is required. To better understand the oscilloscope controls, one need to know a little more about how oscilloscopes display a signal .Although there are two types of oscilloscopes: analog and digital, in this work only the analog will be used. Analog oscilloscopes work somewhat differently than digital oscilloscopes. However, several of the internal systems are similar. Analog oscilloscopes are somewhat simpler in concept and are described first, followed by a description of digital oscilloscopes. The working principle of these two types of oscilloscope and the difference between them will be shown clearly in the following chapters. Computers are used at the heat of almost every electronic system due to the fact that their ability to quickly process and store large amount of data makes system more versatile and perform many functions. The filters used here are digital because computers understand only digital data. The design of these digital filters was done using Matlab software.
Structure of project report
This project report contains five chapters. The first chapter is introduction which discusses about overview and motivation of this work .The second chapter is literature review which provides details about what others have done concerning this research and set a benchmark for the current as well as justifying the specific solution techniques. The third chapter deals with the system design. The fourth chapter discusses the obtained result. Finally, the fifth chapter is all about the conclusion and recommendations giving summary of the main findings statement of the encountered problem as well as limitations.
Statement of the problem
It has been observed that all over the world today’s electronics equipments are all almost of digital in nature. Before the development of the digital equipments, the use of early devices in some applications did not give the accurate output especially in Telecommunication due to many factors including easy attraction of random disturbances or variations introduced in system leading to the delay and losses for the signal. This problem will be recovered by the use of digital equipments associated by some software. But nowadays; the arrival of digital equipments makes the system very suitable and fast. Even due to the flexibility, digital system will lead the low cost equipments. Due to these advantages of digital system, today and future’s life will become digitalized.
Definitions A signal is any kind of physical quantity that conveys
information. Audible speech is certainly a kind of signal, as it conveys the thoughts (information) of one person to another through the physical medium of sound. Hand gestures are signals, too, conveying information by means of light.
Types of signal There are two kind of signal: analog and digital signal. The difference between these signals is described below. An analog signal is a kind of signal that is continuously variable whereas a digital signal is one having discrete set of values [9]. A well-known example of analog versus digital is that of clocks: analog being the type with pointers that slowly rotate around a circular scale, and digital being the type with decimal number displays or a "second-hand" that jerks rather than smoothly rotates. The analog clock has no physical limit to how finely it can display the time, as its "hands" move in a smooth, pauseless fashion. The digital clock, on the other hand, cannot convey any unit of time smaller than what its display will allow for [9].
Basic analog signal measurements
To measure analog signal, it is better to know the instrumentation and instrument. Instrumentation is a field of study and work centering on and control of physical processes. These physical processes include pressure, temperature, flow rate, and chemical consistency. An instrument is a device that measures and/or acts to control any kind of physical process. Due to the fact that electrical quantities of voltage and current are easy to measure, manipulate, and transmit over long distances, they are widely used to represent such physical variables and transmit the information to remote locations [4][9].The most widely used instrument to measure such electrical quantity is oscilloscope as it being described its working principle below in fig.2.1.
Digital Oscilloscopes
Based on [9], some of the systems that make up digital oscilloscopes are the same as those in analog oscilloscopes; however, digital oscilloscopes contain additional data processing systems.
With the added systems, the digital oscilloscope collects data for the entire waveform and then displays it. When you attach a digital oscilloscope probe to a circuit, the vertical system adjusts the amplitude of the signal, just as in the analog oscilloscope. Next, the analog-to-digital converter (ADC) in the acquisition system samples the signal at discrete points in time and converts the signal's voltage at these points to digital values called sample points. The horizontal system's sample clock determines how often the ADC takes a sample. The rate at which the clock "ticks" is called the sample rate and is measured in samples per second.
The sample points from the ADC are stored in memory as waveform points. More than one sample point may make up one waveform point. Together, the waveform points make up one waveform record. The number of waveform points used to make a waveform record is called the record length. The trigger system determines the start and stop points of the record. The display receives these record points after being stored in memory.
Conclusion
To achieve and verify the hypothesis of design a computer based system to process an analog signal, interfacing circuit between PC sound card and signal generator, different circuit sections have been designed and their operating conditions have set out. This is illustrated by the designed circuit with different sections. Zelscope software used as oscilloscope to display signal from mobile phone. A signal generator plays role of setting a fixed frequency, voltage (amplitude) required for the whole sound card by using interface circuit and oscilloscope for displaying a signal. In this implementation 0.5v was used as input to the sound card jack. According to the generated signal using signal generator, it has been found that the output frequency and amplitude of generated signal increase or decrease by adjusting manually a variable resistance in order to control the sound card input voltage (amplitude) .The 16KΩ input resistor, 50KΩ variable resistor and 1N914 diodes also have been designed for protection issues of the PC sound card to allow a small amplitude from signal generator to be used on PC sound card Matlab software have played important role for data acquisition and filtering . For filtering effect, the design of Digital filter have done using fdatool but noise in the signal did not completely eliminated due to the unfixed frequency of original signal from harmonics of songs.