es3_lab5 - Tufts University School of Engineering...

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Tufts University School of Engineering Department of Electrical and Computer Engineering ES3 - Introduction to Electrical Circuits Fall 2007 Lab Section: Friday 2:30-4:30pm Experiment 5 Interfacing Circuits to Computers Name: Teddy Portney Edward . [email protected] tufts . edu Submitted to: Bertan Hallacoglu Experiment Performed: November 30, 2007 Experiment Due: December 7, 2007
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I. PURPOSE The purpose of this lab was to provide an introduction to the popular computer- programming environment called Matlab. This lab also provided an opportunity to apply topics covered in lecture, such as analog-to-digital conversion and vice versa. The idea of frequency response introduced in the previous lab was expanded and deepened using Matlab. Specifically, using another idea introduced in this lab, digital filters, the idea of frequency response was expanded and modified to produce a more appealing sound. Another prominent concept in this laboratory is the idea of audio sampling and how it affects, or even causes, aliasing. II. INTRODUCTION Computers are an integral part of every field of engineering. It is virtually impossible to be an engineer without a strong background with computers. More specific to electrical engineering, which, in addition to digital signals used by computers, consists of many analog signals used in common circuits. Combining these two common parts of electrical engineering is a common challenge, as it requires converting digital signals to analog, or vice versa. Specifically, in this lab, a digital audio signal, created with code in the Matlab programming environment, was outputted by the computer’s sound card, which is itself a digital-to-analog converter. It takes this digital signal and changes it to a series of time- changing voltages, which then get applied to whatever component is attached to the audio out jack on the computer. This component is most commonly a speaker, or series of speakers, although it is also somewhat common to find an amplifier in this situation. This is what was used in these lab experiments, as the sound card voltages, when applied to a small, non-self amplified speaker such as the ones used in the lab, produce sound waves too weak to be heard by human ears. As a speaker is an output device, a microphone is the coordinating input device. A microphone works in a fashion very similar to a speaker, only in reverse. In fact, in a previous lab, a speaker was used as a microphone. Instead of using an electrical current to produce sound waves, a microphone uses sound waves to produce an electrical current. This current is then transmitted by wire back to the computer’s sound card, which, in the reverse process of the one described above, converts the analog signal input from the microphone into a digital signal which can be read, plotted, or even analyzed in Matlab.
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es3_lab5 - Tufts University School of Engineering...

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