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#include <M5StickC.h> 

#define pin 26

unsigned long duration;
unsigned long starttime;
unsigned long sampletime_ms = 30000;
unsigned long lowpulseoccupancy = 0;
float ratio = 0;
float concentration = 0;

void setup(){
  M5.begin();
  M5.Lcd.setRotation(1);
  M5.Lcd.setTextSize(2);
  
  pinMode(pin,INPUT);
  
  starttime = millis();//get the current time;
  Serial.print("start");

}

// the loop routine runs over and over again forever
void loop() {
 duration = pulseIn(pin, LOW);
 lowpulseoccupancy = lowpulseoccupancy+duration;
 if ((millis()-starttime) > sampletime_ms)//if the sampel time == 30s
 {
   ratio = lowpulseoccupancy/(sampletime_ms*10.0); // Integer percentage 0=>100
   concentration = 1.1*pow(ratio,3)-3.8*pow(ratio,2)+520*ratio+0.62; // using spec sheet curve
   M5.Lcd.fillScreen(TFT_BLACK);
   M5.Lcd.setCursor(25, 20);
   M5.Lcd.printf("%4.2f pcs",concentration);
   M5.Lcd.setCursor(25, 40);
   M5.Lcd.printf("/0.01cf",concentration);
    
   lowpulseoccupancy = 0;
   starttime = millis();
 }
}