IoT Air Quality Monitor

#include <Arduino.h>
#include <Wire.h>
#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>
#include <ESP8266HTTPClient.h>
#include <WiFiClientSecureBearSSL.h>
#include <SoftwareSerial.h>
#include <Adafruit_BME280.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <time.h>
#include <math.h>
#include "config.h"

// PMS5003 TX -> NodeMCU D5 (GPIO14). This sensor transmits by itself.
constexpr uint8_t PMS_RX_PIN = D5;
constexpr uint8_t ALERT_LED_PIN = D6;
Adafruit_SSD1306 oled(128, 64, &Wire, -1);
bool oledOk = false;
SoftwareSerial pms;
Adafruit_BME280 bme;
ESP8266WebServer server(80);
const char caCert[] PROGMEM = R"EOF_CERT(
-----BEGIN CERTIFICATE-----
MIIDrzCCApegAwIBAgIQCDvgVpBCRrGhdWrJWZHHSjANBgkqhkiG9w0BAQUFADBh
MQswCQYDVQQGEwJVUzEVMBMGA1UEChMMRGlnaUNlcnQgSW5jMRkwFwYDVQQLExB3
d3cuZGlnaWNlcnQuY29tMSAwHgYDVQQDExdEaWdpQ2VydCBHbG9iYWwgUm9vdCBD
QTAeFw0wNjExMTAwMDAwMDBaFw0zMTExMTAwMDAwMDBaMGExCzAJBgNVBAYTAlVT
MRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5j
b20xIDAeBgNVBAMTF0RpZ2lDZXJ0IEdsb2JhbCBSb290IENBMIIBIjANBgkqhkiG
9w0BAQEFAAOCAQ8AMIIBCgKCAQEA4jvhEXLeqKTTo1eqUKKPC3eQyaKl7hLOllsB
CSDMAZOnTjC3U/dDxGkAV53ijSLdhwZAAIEJzs4bg7/fzTtxRuLWZscFs3YnFo97
nh6Vfe63SKMI2tavegw5BmV/Sl0fvBf4q77uKNd0f3p4mVmFaG5cIzJLv07A6Fpt
43C/dxC//AH2hdmoRBBYMql1GNXRor5H4idq9Joz+EkIYIvUX7Q6hL+hqkpMfT7P
T19sdl6gSzeRntwi5m3OFBqOasv+zbMUZBfHWymeMr/y7vrTC0LUq7dBMtoM1O/4
gdW7jVg/tRvoSSiicNoxBN33shbyTApOB6jtSj1etX+jkMOvJwIDAQABo2MwYTAO
BgNVHQ8BAf8EBAMCAYYwDwYDVR0TAQH/BAUwAwEB/zAdBgNVHQ4EFgQUA95QNVbR
TLtm8KPiGxvDl7I90VUwHwYDVR0jBBgwFoAUA95QNVbRTLtm8KPiGxvDl7I90VUw
DQYJKoZIhvcNAQEFBQADggEBAMucN6pIExIK+t1EnE9SsPTfrgT1eXkIoyQY/Esr
hMAtudXH/vTBH1jLuG2cenTnmCmrEbXjcKChzUyImZOMkXDiqw8cvpOp/2PV5Adg
06O/nVsJ8dWO41P0jmP6P6fbtGbfYmbW0W5BjfIttep3Sp+dWOIrWcBAI+0tKIJF
PnlUkiaY4IBIqDfv8NZ5YBberOgOzW6sRBc4L0na4UU+Krk2U886UAb3LujEV0ls
YSEY1QSteDwsOoBrp+uvFRTp2InBuThs4pFsiv9kuXclVzDAGySj4dzp30d8tbQk
CAUw7C29C79Fv1C5qfPrmAESrciIxpg0X40KPMbp1ZWVbd4=
-----END CERTIFICATE-----
)EOF_CERT";
BearSSL::X509List trustAnchor(caCert);

uint16_t pm1 = 0, pm25 = 0, pm10 = 0;
uint32_t pmAt = 0, lastEnv = 0, lastUpload = 0;
bool pmSeen = false, bmeOk = false, envValid = false;
float temperature = NAN, humidity = NAN, pressure = NAN;
String uploadStatus = "Not sent yet";
uint8_t frame[32];
size_t framePos = 0;

bool freshPM() { return pmSeen && millis() >= 30000 && (uint32_t)(millis() - pmAt) < 15000; }
uint16_t wordAt(int i) { return (uint16_t(frame[i]) << 8) | frame[i + 1]; }
void readParticles() {
  while (pms.available()) {
    uint8_t c = pms.read();
    if (framePos == 0 && c != 0x42) continue;
    if (framePos == 1 && c != 0x4d) { framePos = (c == 0x42) ? 1 : 0; continue; }
    frame[framePos++] = c;
    if (framePos == sizeof(frame)) {
      uint16_t sum = 0;
      for (int i = 0; i < 30; ++i) sum += frame[i];
      if (wordAt(2) == 28 && sum == wordAt(30)) {
        // Atmospheric environment readings, in micrograms per cubic metre.
        pm1 = wordAt(10); pm25 = wordAt(12); pm10 = wordAt(14);
        pmAt = millis(); pmSeen = true;
      }
      framePos = 0;
    }
  }
}
void readEnvironment() {
  if (!bmeOk) bmeOk = bme.begin(0x77, &Wire);
  if (!bmeOk) { envValid = false; return; }
  temperature = bme.readTemperature();
  humidity = bme.readHumidity();
  pressure = bme.readPressure() / 100.0f;
  envValid = isfinite(temperature) && isfinite(humidity) && isfinite(pressure);
}
// An instantaneous screening trigger, not a health-based safe limit.
bool pollutionAlert() { return freshPM() && pm25 >= PM25_ALERT_UG_M3; }
void updateLocalDisplay() {
  digitalWrite(ALERT_LED_PIN, pollutionAlert() ? HIGH : LOW);
  if (!oledOk) return;
  String text;
  if (freshPM()) {
    text = "PM1: " + String(pm1) + " ug/m3\nPM2.5: " + String(pm25) + " ug/m3\nPM10: " + String(pm10) + " ug/m3\n";
  } else text = "PM: unavailable\n\n\n";
  if (envValid) {
    text += "T:" + String(temperature, 1) + "C H:" + String(humidity, 0) + "%\n";
    text += "P:" + String(pressure, 0) + " hPa\n";
  } else text += "Env unavailable\n\n";
  text += !freshPM() ? "PM SENSOR NOT READY\n" : pollutionAlert() ? "HIGH PM2.5!\n" : "PM2.5 below alert\n";
  text += WiFi.status() == WL_CONNECTED ? "WiFi connected" : "WiFi disconnected";
  static String previous;
  if (text == previous) return;
  previous = text;
  oled.clearDisplay();
  oled.setCursor(0, 0);
  oled.print(text);
  oled.display();
}
void servePage() {
  String page = F("<!doctype html><html><head><meta name='viewport' content='width=device-width,initial-scale=1'><meta http-equiv='refresh' content='5'><title>Air monitor</title></head><body><h1>Air quality monitor</h1>");
  if (freshPM()) {
    page += "<p>PM1.0: " + String(pm1) + " &micro;g/m&sup3;<br>PM2.5: " + String(pm25) + " &micro;g/m&sup3;<br>PM10: " + String(pm10) + " &micro;g/m&sup3;</p>";
  } else page += F("<p>Particle readings warming up or unavailable.</p>");
  if (envValid) page += "<p>Temperature: " + String(temperature, 1) + " &deg;C<br>Humidity: " + String(humidity, 1) + "%<br>Pressure: " + String(pressure, 1) + " hPa</p>";
  else page += F("<p>Environmental sensor unavailable.</p>");
  if (!freshPM()) page += F("<p>Alert: particle sensor unavailable.</p>");
  else page += pollutionAlert() ? F("<p>Alert: high PM2.5.</p>") : F("<p>PM2.5 below alert threshold.</p>");
  page += "<p>Cloud: " + uploadStatus + "</p>";
  page += F("<p>Indicative readings only; not a certified pollution measurement.</p></body></html>");
  server.send(200, "text/html", page);
}
void sendCloud() {
  if (!strlen(THINGSPEAK_WRITE_KEY)) { uploadStatus = "Add a ThingSpeak write key in config.h"; return; }
  if (WiFi.status() != WL_CONNECTED) { uploadStatus = "Wi-Fi disconnected"; return; }
  if (time(nullptr) < 1704067200) { uploadStatus = "Waiting for internet time"; return; }
  if (!freshPM() && !envValid) { uploadStatus = "No valid sensor data"; return; }
  String url = "https://api.thingspeak.com/update?api_key=" + String(THINGSPEAK_WRITE_KEY);
  if (freshPM()) url += "&field1=" + String(pm1) + "&field2=" + String(pm25) + "&field3=" + String(pm10);
  if (envValid) url += "&field4=" + String(temperature, 1) + "&field5=" + String(humidity, 1) + "&field6=" + String(pressure, 1);
  BearSSL::WiFiClientSecure client;
  client.setTrustAnchors(&trustAnchor);
  client.setTimeout(6000);
  HTTPClient http;
  http.setTimeout(6000);
  if (!http.begin(client, url)) { uploadStatus = "Cloud connection setup failed"; return; }
  int code = http.GET();
  String body = code == HTTP_CODE_OK ? http.getString() : "";
  if (code == HTTP_CODE_OK && body.toInt() > 0) uploadStatus = "Last update accepted";
  else uploadStatus = "Update failed (HTTP " + String(code) + ")";
  http.end();
  Serial.println(uploadStatus);
}
void setup() {
  Serial.begin(115200);
  pinMode(ALERT_LED_PIN, OUTPUT);
  digitalWrite(ALERT_LED_PIN, LOW);
  Wire.begin(D2, D1);
  oledOk = oled.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  if (oledOk) { oled.setTextSize(1); oled.setTextColor(SSD1306_WHITE); }
  else Serial.println("OLED unavailable at 0x3C");
  pms.begin(9600, SWSERIAL_8N1, PMS_RX_PIN, -1, false, 256);
  readEnvironment();
  server.on("/", servePage);
  server.begin();
  WiFi.mode(WIFI_STA);
  if (strlen(WIFI_NAME)) WiFi.begin(WIFI_NAME, WIFI_PASSWORD);
  configTime(0, 0, "pool.ntp.org", "time.nist.gov");
  Serial.println("Air monitor starting. Set Wi-Fi and ThingSpeak in include/config.h.");
}
void loop() {
  readParticles();
  server.handleClient();
  uint32_t now = millis();
  static bool announced = false;
  if (WiFi.status() == WL_CONNECTED && !announced) {
    Serial.print("Dashboard: http://"); Serial.println(WiFi.localIP()); announced = true;
  } else if (WiFi.status() != WL_CONNECTED) announced = false;
  if ((uint32_t)(now - lastEnv) >= 5000) { lastEnv = now; readEnvironment(); }
  updateLocalDisplay();
  if ((uint32_t)(now - lastUpload) >= 60000) { lastUpload = now; sendCloud(); }
  yield();
}