Lab1b-2C2007

Lab1b-2C2007 - ECE 2C Laboratory Manual 1b Microphone...

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1 © Bob York ECE 2C Laboratory Manual 1b Microphone Circuit Overview In this second part of the lab#1 you will construct a microphone circuit using a compact electret condenser microphone cartridge. The audio amplifier and microphone are important building blocks of many audio communications systems, and will be used in our ultrasonic transceiver system. Table of Contents Pre-lab Preparation 2 Before Coming to the Lab 2 Parts List 2 Schedule for Lab #1 2 Full Schematics for Lab #1b 3 Background information 4 Microphones 4 In-Lab Procedure 6 1.1 Some comments on our choice of ICs 6 Why the LM353? 6 1.2 Microphone Pre-amplifier 6 1.3 Simple One-Way Audio Link System 8 1.4 Possible Improvements 10
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2 Microphone Circuit © Bob York 2 Pre-lab Preparation Before Coming to the Lab Read through the lab experiment to familiarize yourself with the components and assembly sequence. Before coming to the lab, each group should obtain a parts kit from the ECE Shop. With reference to the full schematic in Figure 1-1, calculate the lower cutoff frequency imposed by capacitors C1 and C2 and the resistances in the circuit: low f =______________Hz high f =______________Hz Parts List The ECE2 lab is stocked with resistors so do not be alarmed if you kits does not include the resistors listed below. Some of these parts may also have been provided in an earlier kit. 1 Electret Condenser Microphone Cartridge MIC 1 LF353N Dual Wide-band JFET Op-amp U1 1 8-pin low-profile IC socket 2 2.2kOhm 1/4W R3,R5 2 10kOhm 1/4W R1,R2 1 33kOhm 1/4W R4 11 0 k t r i m p o t R 6 1 1uF 25V electrolytic (PC lead) C1 1 10uF 25V electrolytic (PC lead) C3 2 100uF 25V electrolytic (PC lead) C6,C7 1 0.001uF capacitor (CKO5 low-volt. Ceramic) C2 2 0.1uF capacitor (CKO5 low-volt. Ceramic) C4,C5 1 4.5" x 2.5" vectorboard Microphone Preamp Schedule for Lab #1 To stay on schedule, you must do the following: Week #1: Audio amplifier
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Pre-lab Preparation 3 © Bob York 3 Full Schematics for Lab #1b Figure 1-1 – Schematic for the microphone preamplifier.
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4 Microphone Circuit © Bob York 4 Background information Microphones A speaker can be used in reverse to create a microphone. In the case the incoming sound wave leads to a mechanical deflection of the cone and voice-coil. According to Faraday’s law, a time-varying current will be induced because the coil is moving in through a magnetic field (produced by the permanent magnet). Although any speaker could be used for a microphone, most speakers are unnecessarily large for this purpose, except in simple intercom applications where it is common to use the same component to perform both the speaker and microphone functions. +V
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This note was uploaded on 12/28/2011 for the course ECE 2C taught by Professor Yue during the Fall '08 term at UCSB.

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Lab1b-2C2007 - ECE 2C Laboratory Manual 1b Microphone...

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