Difference between revisions of "Sensor-Dust"

#include <SoftwareSerial.h>
SoftwareSerial pmSerial(4, 5);  //PM2.5 sensor soft serail port 
#define INTERVAL_pm25             200
unsigned long pm25_time = millis();

void setup() {
  Serial.begin(9600); // See the connection status in Serial Monitor
  pmSerial.begin(2400);   //start the soft serial port at first 
}

void loop() {
  if (pm25_time > millis()) pm25_time = millis();
  if (millis() - pm25_time > INTERVAL_pm25) {
    Serial.println(PM25()) ;
    pm25_time = millis();    //更新计时器
  }
}

float PM25() {
  int data_s = 0;    //serial receives the data 
  int num = -1;      //serial receives the data and counts
  int sum = 0;       //checksum
  int cal[5];        //receive the data buffer
  float dustDensity = 0;  //PM2.5 intensity

  pmSerial.listen();
  while (1) {
    if (pmSerial.available() > 0) { //serail cache data
      data_s = pmSerial.read();   //read the serial cache data
      if (data_s == 0xAA) {        //attain the starting position of the data frame
        num = 0;                  //start to count 
      }
      else if (num >= 0) {
        cal[num++] = data_s; //read teh data and the number+1, and store the data into the buffer
        if (num == 6) {        //read to the last bit of the data frame 
          sum = cal[0] + cal[1] + cal[2] + cal[3];  //calculate the checksum 
          if (sum == cal[4] && cal[5] == 0xFF) {    //checksum match, the last bit of the data frame is 0xFF, representing the data frame received is normal
            dustDensity = (cal[0] * 256 + cal[1]) * (5.0 / 1024) * 550; //calculate the PM2.5 intensity, in ug/m3
          }
          else {     //the data received is abnormal
            dustDensity = 0;    //clear the intensity
          }
          break;
        }
      }
    }
  }
  pmSerial.stopListening();
  return dustDensity ;
}