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.