PM2_5.ino

// based on https://github.com/Hypfer/esp8266-vindriktning-particle-sensor

#include <ESP8266WiFi.h>
#include <SoftwareSerial.h>
#define PIN_UART_RX 4 //D2 on Wemos D1 Mini
#define PIN_UART_TX 13 // UNUSED


struct particleSensorState_t { 
  unsigned long avgPM25;
  unsigned long measurements[5] = {0, 0, 0, 0, 0};
  int measurementIdx = 0;
};

particleSensorState_t state;
byte serialRxBuf[255];

SoftwareSerial particleSensorSerial(PIN_UART_RX, PIN_UART_TX);

unsigned long statusPublishPreviousMillis = millis();
const long statusPublishInterval = 5000; //5sec

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  particleSensorSerial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  handleUart(); 

    if (statusPublishInterval <= (millis() - statusPublishPreviousMillis)) {
    statusPublishPreviousMillis = millis();

    if (state.avgPM25 > 0) {
      //publishState();
    }

  }
}



boolean parseState() {
  unsigned long pm25 = serialRxBuf[3] * 256 ^ 3 + serialRxBuf[4] * 256 ^ 2 + serialRxBuf[5] * 256 ^ 1 + serialRxBuf[6];

  Serial.print("Received PM 2.5 reading: ");
  Serial.println(pm25);

  if (pm25 > 0) {
    state.measurements[state.measurementIdx] = pm25;

    state.measurementIdx = (state.measurementIdx + 1) % 5;

    if (state.measurementIdx == 0) {
      unsigned long avgPM25 = 0;
      boolean invalid = false;

      for (int i = 0; i < 5; i++) {
        if (state.measurements[i] == 0) {
          invalid = true;
        } else {
          avgPM25 += state.measurements[i];
        }
      }

      if (invalid == false) {
        state.avgPM25 = avgPM25 / 5;

        Serial.print("New Avg PM25: "); Serial.println(state.avgPM25);
      }
    }
  }

  clearRxBuf();
}

int rxBufIdx = 0;

void clearRxBuf() {
  //Clear everything for the next message
  memset(serialRxBuf, 0, sizeof(serialRxBuf));
  rxBufIdx = 0;
}



void handleUart() {

  if (particleSensorSerial.available()) {
    Serial.print("Receiving:");
  }

  int prevIdx = rxBufIdx;

  while (particleSensorSerial.available()) {
    serialRxBuf[rxBufIdx++] = particleSensorSerial.read();
    Serial.print(".");

    //Without this delay, receiving data breaks for reasons that are beyond me
    delay(15);

    if (rxBufIdx >= 64) {
      clearRxBuf();
    }
  }

  if (prevIdx != rxBufIdx) {
    Serial.println("Done.");
  }



  if (serialRxBuf[0] == 0x16 && serialRxBuf[1] == 0x11 && serialRxBuf[2] == 0x0b) {
    parseState();

    Serial.print("Current measurements: ");
    Serial.print(state.measurements[0]); Serial.print(", ");
    Serial.print(state.measurements[1]); Serial.print(", ");
    Serial.print(state.measurements[2]); Serial.print(", ");
    Serial.print(state.measurements[3]); Serial.print(", ");
    Serial.print(state.measurements[4]); Serial.print("\n");
  } else {
    clearRxBuf();
  }
}