dsm501a_oled128x32_arduino_nano.ino

#include <string.h>
#include <U8g2lib.h>

#define PM10PIN 3
#define PM25PIN 6
#define ALARMSOUNDER 8

int i;
unsigned long duration10;
unsigned long duration25;
unsigned long starttime;
unsigned long endtime;
unsigned long sampletime_ms = 30000;
unsigned long lowpulseoccupancy10 = 0;
unsigned long lowpulseoccupancy25 = 0;
float ratio10 = 0;
float ratio25 = 0;
float concentration10 = 0;
float concentration25 = 0;

U8G2_SSD1306_128X32_UNIVISION_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE, /* clock=*/ SCL, /* data=*/ SDA);

void playAlarm() {
  for(i = 0; i < 255; i = i + 2) {
    tone(ALARMSOUNDER, i*50);
    delay(5);
  }
  for(i = 255; i > 1; i = i - 2) {
    tone(ALARMSOUNDER, i*50);
    delay(5);
  }
  noTone(ALARMSOUNDER);
}

void setup() {
  Serial.begin(115200);
  u8g2.begin();
  u8g2.setFontMode(1);
  u8g2.setFont(u8g2_font_profont15_mf);
  pinMode(PM10PIN,INPUT);
  pinMode(PM25PIN,INPUT);
  pinMode(ALARMSOUNDER, OUTPUT);
  starttime = millis(); 
}

void loop() {
  duration10 = pulseIn(PM10PIN, LOW);
  duration25 = pulseIn(PM25PIN, LOW);
  if (10 < duration10 < 90) lowpulseoccupancy10 += duration10;
  if (10 < duration25 < 90) lowpulseoccupancy25 += duration25;
  endtime = millis();
  if ((endtime-starttime) > sampletime_ms) {
    ratio10 = (lowpulseoccupancy10-endtime+starttime + sampletime_ms)/(sampletime_ms*10.0);  // Integer percentage 0=>100
    ratio25 = (lowpulseoccupancy25-endtime+starttime + sampletime_ms)/(sampletime_ms*10.0);  // Integer percentage 0=>100
    concentration10 = 1.1*pow(ratio10,3)-3.8*pow(ratio10,2)+520*ratio10+0.62; // using spec sheet curve
    concentration25 = 1.1*pow(ratio25,3)-3.8*pow(ratio25,2)+520*ratio25+0.62; // using spec sheet curve
    u8g2.setCursor(0,15);
    u8g2.print("PM1.0: ");
    if (lowpulseoccupancy10 != 0) {
      u8g2.print(String(concentration10) + "ppm");
    } else {
      u8g2.print(String(0));
    }
    u8g2.setCursor(0,32);
    u8g2.print("PM2.5: ");
    if (lowpulseoccupancy25 != 0) {
      u8g2.print(String(concentration25) + "ppm");
    } else {
      u8g2.print(String(0));
    }
    u8g2.sendBuffer();
    u8g2.clearBuffer();
    if ((lowpulseoccupancy10 != 0 && lowpulseoccupancy25 !=0) && (concentration10 > 5000 || concentration25 > 5000)) playAlarm();
    lowpulseoccupancy10 = 0;
    lowpulseoccupancy25 = 0;
    starttime = millis();
  } 
}