Design and Construction of a Microcontroller-Based Human Audio Noise Monitoring and Control System
Mwoha, Paul Irungu
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Audio noise monitoring and control has been a subject of research for several decades. Researchers have developed audio noise monitoring systems which rely on computers, internet and mobile telephone services which are costly and bulky and whose output is not easy to associate with any medical or psychological effects of noise. Active noise control has been explored using digital signal processors and field programmable gate arrays which are more costly than microcontrollers. Complex algorithm has been used to develop most of the existing active noise control systems. This research involved design and construction of a prototype audio-visual noise monitor and controller based on AT91SAM3X8E microcontroller. The target noise was in the human audio frequency range and the environment was selected using a keypad. Four micro-electro-mechanical system microphones were used as the primary transducers to convert the sound waves to analogue electric signals. The signals were multiplexed, fed to an A-weighting filter and demultiplexed. They were then transferred to the input of the microcontroller, which was programmed to compare the average noise levels to certain set points based on known national and international health standards. Once sound pressure level surpassed the thresholds, the microcontroller triggered the fetching of a pre-recorded audio file which was then fed to an audio amplifier and to a loudspeaker to give audio feedback to the audience about the noise level. Numerical value of the noise level, the environment, the set points and the warning message were displayed using a liquid crystal display unit. At the same time, automatic audio noise control was initiated. A hybrid active/passive noise cancellation headset was designed and implemented involving analog audio noise cancelling circuitry with digital monitoring. Timely, World Health Oganisation based audio and visual feedback messages about the noise levels were achieved. A 17.10% average sound pressure level reduction index was attained from the noise control headset. The AT91SAM3X8E microcontroller was found to be a good candidate for human audio noise monitoring and control. This work recommends further exploration into possible use of better electronic components and test equipments towards improvement of results obtained from the procedures used.