A DIY automatic gain control of an audio amplifier

Abstract

This report describes the project of designing an automatic gain control of an amplifier system to provide fixed amplitude of audio output, despite variations of its input signal. Automatic Gain Control (AGC) is used to adjust volume level of the audio output to compensate for loud or soft spoken speakers. The most common application is when people speak into a microphone, the inconsistency effect of soft and loud tone in addition to varying distances between the speaker and microphone can result in amplitude variation. The aim of the AGC amplifier is to move the signal level close to the desired volume level. In EE2073 project [3], an Automatic Gain Control of audio amplifier system was constructed by using NI ELVIS and runs a LabVIEW program on a PC. The aim of this project is to replace the PC and ELVIS with a cost effective, compact and portable embedded controller called NI myRIO-1900. It is a reconfigurable I/O FPGA board with a high-performance dual core processor and FPGAs. It is programmed as a feedback controller to perform automatic gain adjustment to the audio amplifier circuit. Basically, the implementation of the project is through optimizing and integrating the software and hardware parts together. Software task includes the design and development of LabVIEW program on a FPGA chip myRIO. Additionally, PCB board of audio amplifier circuit has been designed and fabricated to improve and upgrade the overall hardware design to be more compact and user-friendly. Technically, the objective of this project has been achieved by implementing LabVIEW program downloaded inside myRIO controller to operate the whole project as an embedded system removing PC and ELVIS.