[M5Stack] mic input test (speaker noise suppressed) refer to https://gist.github.com/ksasao/485ffbccbf3c47ea9cb814d3484e85e0

analog_mic_draw.ino

#include <driver/adc.h>
#include <M5Stack.h>

const int _bufSize = 128;
int _buf[_bufSize];      // adc buffer for suppress speaker noise

int _pos = 0;
int _old = 0;
int _count = 0;
int _offset = 0;

void setup() {
  Serial.begin(115200);
  M5.begin();
  M5.Lcd.setBrightness(200);

  adc1_config_width(ADC_WIDTH_12Bit);
  adc1_config_channel_atten(ADC1_CHANNEL_0,ADC_ATTEN_0db);
}

void loop() {
  int v = adc1_get_raw(ADC1_CHANNEL_0);
  dacWrite(25, 0);  // for reduce hum noise

  int p = _count % _bufSize;
  _buf[p] = v;

  // bulk draw to reduce speaker noise
  if(p == _bufSize - 1){
    // calc offset
    int buf = 0;
    for(int i=0; i< _bufSize; i++){
      buf += _buf[i];
    }
    int offset = buf / _bufSize;

    // draw
    for(int i=0; i< _bufSize; i++){
      int current = (_buf[i] - offset)/3 + 120;
      M5.Lcd.drawLine(_pos, 0, _pos,240, BLACK);
      M5.Lcd.drawLine(_pos - 1, _old, _pos, current, WHITE);
      _old = current;
      _pos = (_pos+1) % 320;
    }
  }
  _count++;
  M5.update();
}