使用I2S时如何确定ADC的实际采样频率？

编程问答 2022-06-01

问题描述

我在使用 I2S 测量来自 ADC 的信号时遇到问题。

    // Initialization of I2S buffer
    uint16_t* i2sReadBuffer = (uint16_t*)calloc(DMA_BUFFER_LEN,sizeof(uint16_t));
    size_t bytesRead;

    while (1) {

        // Read data in the buffer till its not full
        i2s_read(ADC_I2S_NUM,(void*)i2sReadBuffer,DMA_BUFFER_LEN * sizeof(uint16_t),&bytesRead,portMAX_DELAY);

        for (size_t i = 0; i < DMA_BUFFER_LEN; i++) {
            uint16_t value = i2sReadBuffer[i];
            printf("%d\n",value);
        }
    }

我已经成功得到一个信号并对其进行过滤，但设置了过滤器参数，因此采样频率在 1kHz 左右。 ECG signal before and after filtering

这意味着实际采样频率是 1kHz，但不是 10kHz，不是吗？ 如果不是，为什么过滤只适用于这些参数？

Matlab 处理代码：

xlsFile = 'ecg_data.xlsx';

[num,txt,raw] = xlsread(xlsFile);

input = cell2mat(raw);

a = fir1(100,[0.06 0.14],'stop');

in = input(:,2);

filtered = filter(a,1,in);

y = fft(filtered);

N = length(y);                   % Length of a vector

f = (0:N - 1 ) * 100 / N;        % Frequency vector

m = abs(y);                      % Magnitude
% y(m<1e-6) = 0;
p = unwrap(angle(y));            % Phase

X_vector = (1:3:N) / ((N - 1) * 1e-3);

title('Frequency spectrum')

subplot(2,2,1)
plot(f,m)
title('Magnitude')
ax = gca;
ax.XTick = X_vector;

subplot(2,2)
plot(f,P*180/pi)
title('Phase')
ax = gca;
ax.XTick = X_vector;

subplot(2,3)
plot(in)
title('Input singal')
xlabel('msec')
ax = gca;

subplot(2,4)
plot(filtered)
title('Filtered signal')
ax = gca;

I2S ADC 配置如下

#define SAMPLING_FREQ 10000
#define ADC_CHANNEL ADC1_CHANNEL_4
#define ADC_UNIT ADC_UNIT_1
#define DMA_BUFFER_LEN 1024
#define ADC_I2S_NUM I2S_NUM_0

static void init_i2s_adc(void) {
    i2s_config_t i2s_config = 
    {
        .mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_ADC_BUILT_IN),.sample_rate = SAMPLING_FREQ,.bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,.channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,.communication_format = I2S_COMM_FORMAT_STAND_MSB,.intr_alloc_flags = ESP_INTR_FLAG_LEVEL1,.dma_buf_count = 8,.dma_buf_len = DMA_BUFFER_LEN,.tx_desc_auto_clear = 1,.use_apll = 0,};
    adc1_config_channel_atten(ADC_CHANNEL,ADC_ATTEN_11db);
    adc1_config_width(ADC_WIDTH_12Bit);
    i2s_driver_install(ADC_I2S_NUM,&i2s_config,NULL);

    i2s_set_clk(ADC_I2S_NUM,SAMPLING_FREQ,I2S_BITS_PER_SAMPLE_16BIT,I2S_CHANNEL_MONO);
    i2s_set_adc_mode(ADC_UNIT,ADC_CHANNEL);
    i2s_adc_enable(ADC_I2S_NUM);
}

解决方法

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