Design of a spectral sound-level meter for automatic meteorological stations

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Supervisor:
Kiss Domokos
Department of Automation and Applied Informatics

The thesis topic is to design spectral sound-level meter for automatic meteorological

stations. The new instrument can measure the noise level around 60 dB range and the range of

20Hz-10kHz. The design was important to make a cheap and modern instrument.

The noise is converted by simple electret microphone into an electrical signal by a

variable amplifier, int this case, by a dynamic compressor. This amplifies the microphone

signal, that it comes out roughly at the same level, thus allowing it to measure the full range

with the similar accuracy. The output signal of dinamic compressor is inserted into an analog

input of the microcontroller (Microchip dsPIC33FJ64GP802). The dsPIC 10-bit A / D

converter is sampling at 20 kHz. The microcontroller uses a 512 point discrete Fourier

transformation is carried out, and thus arises the spectrum from 20Hz to 10kHz, 20-Hz

increments. Then there is a possibility that we use "A" weighting and other weighting to get

the desired spectrum. "A" weighting is applied to the measurement of environmental and

industrial noise. Most of the household appliances' noise are given in dB (A). The sound level

meter sends the spectrum and the sound pressure level via RS-485 to the data logger. The

protocol used for - which providedby the Boreas Ltd. - can be found in the appendix.

In the first chapter, the topic of the thesis introduced, then the theoretical foundations

reviewed. The next chapter the avaible solutions on the market will be looked through. In the

third chapter of the sensor block diagram is presented. The fourth chapter in the gained

experience of the design is reviewed. The fifth chapter the implementation is described, while

the last chapter the experience and development opportunities are summarized .

The experience of the design concluded that the sensor can measure the ambient noise,

and can be applied at the automatic meteorological stations of Boreas Ltd. Thus it became

possible to continuously monitor noise levels.

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