[HC32F448 Review] +ADC Sampling + FFT Analysis
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Chapter 9: ADC Sampling + FFT Analysis
Continuing from the configuration in the previous article, the DSP library has been configured in the previous article. Next, we will test the use of ADC to collect analog data for Fourier analysis.
First, refer to the example to configure the ADC. The parameters of the ADC are relatively simple. What needs to be noted is its clock. It has two clocks, including the conversion clock PCLK2 and the digital interface clock PCLK4. The conversion clock PCLK2 has three clock sources, including the system clock, PLLHQ, and PLLHR. If the system clock is used, the highest main frequency is 50MHz. If PLLHQ and PLLHR are used, the frequency can be multiplied to 60MHz through PLL. PCLK4 has three clock sources like PCLK2. For convenience, the system clock is used here, PCLK2=50MHz, PCLK4=100MHz.
ADC has several scanning modes, single scan, continuous scan, buffered scan, etc. Here we choose the continuous scan mode: stcAdcInit.u16ScanMode=ADC_MD_SEQA_CONT;
At the same time, the trigger source selects software trigger:
ADC_Start(CM_ADC1);
Then run the following program in a loop: query the status bit, then clear it to zero and read the data.
while(ADC_GetStatus(ADC_UNIT, ADC_EOC_FLAG) != SET);
ADC_ClearStatus(ADC_UNIT, ADC_EOC_FLAG);
ADC_DATA[ADCnum]=ADC_UNIT->DR10;
Because real-time analysis is not possible at present, FFT analysis can only be performed when the data is full of 1024. Input a 1KHz square wave, and the figure below is the waveform measured by ADC
Then perform FFT analysis on the data and take the first 64 data for plotting. It can be found that there are signals with multiple frequencies. In addition to the 1KHz fundamental wave, there are also 3KHz 3rd harmonic, 5KHz 5th harmonic, etc. This is in line with the characteristics of a square wave: it is composed of the superposition of sinusoidal waves of multiple frequencies.
The figure below shows the waveform measured by a virtual oscilloscope and the results of FFT analysis, which are basically consistent.
The above is the effect I can achieve at present. Since the following problems have not been solved, there is no way to achieve a more practical FFT effect:
1. There is no problem of transferring ADC data through DMA, because the related problems have not been solved, and I am not familiar with using DMA, so I cannot transfer 1024 ADC data at one time.
2. After turning on the ADC conversion completion interrupt (ADC_INT_EOCA), it is found that it gets stuck, which makes the buttons on the development board unusable. The main reason may be interrupt conflict. The interrupt of HC32 is very powerful, but it is still difficult for me to understand it. I will study it later if I have the opportunity.
3. I found that the system would freeze if the timer output PWM wave and FFT were turned on at the same time. I don’t know why. Another thing is that the FFT seems to be unstable and there will be problems when it is turned on with multiple peripherals. I will study it when I have the chance.
4. Because the waveforms are output through the serial port and then drawn in Excel, if you want it to be more intuitive, you need to display it on the LCD or transmit it to the host computer in real time. The host computer draws the line in real time. This has higher requirements because it is similar to an oscilloscope and takes more time.
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