Design scheme of FM audio spectrum analyzer based on MSP430

1 Introduction

In the actual broadcast television transmission work, the incoming test of the new transmitter, the daily indicator test of the transmitter, etc. all involve audio testing. The audio spectrum analyzer designed in this paper is to measure the spectrum of the audio signal from the perspective of the signal source, so as to determine the size of each frequency component, and provide reference for each audio index of the FM radio.

In this paper, the design scheme of the audio spectrum analyzer with MSP43 processor as the core is proposed. Guided by the relevant theoretical knowledge of digital signal processing, the advantages of the MSP430 processor are used to design and improve the audio spectrum, and finally the display on the TFT liquid crystal HD66772 is realized.

2. Spectrum analyzer design principle

Since the data processed in the digital system is obtained by sampling, the obtained data is necessarily discrete. For discrete data, a discrete Fourier transform is applied for processing.

Fast Fourier transform, which is a fast algorithm of discrete Fourier transform, can also be used to calculate the inverse transform of discrete Fourier transform, which has been widely adopted by digital spectrum analyzers. For a complex sequence of length N 0 1 1 , , , N ? Xx L x , the discrete Fourier transform formula is:

Discrete Fourier transform formula

Then a sequence of operations is decomposed into the form of the sum of the two operations, ( ) 1 X k and ( ) 2 X k can continue to be decomposed down, and finally decomposed into two points of FFT operations. If the output after the FFT operation is desired to be in natural order, the input sequence needs to be arranged in reverse order.

Figure 1 is an operation diagram of an 8-point FFT.

8-point FFT operation diagram

After the FFT operation, a time domain signal can be transformed into the frequency domain. Some signals are difficult to see in the time domain, but if you change to the frequency domain, it is easy to see the features, which is the general principle of the spectrum analyzer.

3. Design and implementation of spectrum analyzer

This paper introduces a design scheme of digital audio spectrum analyzer based on FFT. The audio signal is sampled and input by ADC. After ADC sampling is completed, the data is arranged in reverse order and FFT operation is performed. The result is displayed by TFT liquid crystal. The block diagram of the system is shown in Figure 2.

Spectrum Analyzer System Block Diagram

3.1 Audio Spectrum Analyzer Hardware Implementation

In order to achieve system functions, the 16-bit processor MSP430 is used to efficiently process the incoming data stream. The MSP430 comes with an ADC12 module. The sampled data of the ADC12 is calculated and passed through a 65K color liquid crystal display spectrum. The hardware system diagram of this system is shown in Figure 3.

Audio spectrum analyzer hardware implementation

The power module supplies power to the entire system. The system can also respond to user key events and process them accordingly. The serial port module is reserved for system expansion.

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