Desk Air Quality Monitor

#include <Arduino.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <WiFi.h>
#include <WebServer.h>
#include <WiFiClientSecure.h>
#include <time.h>
#include <SensirionI2cScd4x.h>
#include <Adafruit_PM25AQI.h>
#include <Adafruit_GFX.h>
#include <Adafruit_ST7789.h>

// Enter these only if you want the station to join your home Wi-Fi and use internet time/Telegram.
const char* WIFI_SSID = "";
const char* WIFI_PASSWORD = "";
const char* TELEGRAM_BOT_TOKEN = "";
const char* TELEGRAM_CHAT_ID = "";
const char* AP_NAME = "Study-Air-Station";
const char* AP_PASSWORD = "studyair2026";

const int SCD_SDA_PIN = 21;
const int SCD_SCL_PIN = 22;
const int PMS_RX_PIN = 16;
const int PMS_TX_PIN = 17;
const int TFT_CS_PIN = 5;
const int TFT_DC_PIN = 26;
const int SD_CS_PIN = 13;
const int SPI_SCK_PIN = 18;
const int SPI_MISO_PIN = 19;
const int SPI_MOSI_PIN = 23;
const int FAN_PIN = 27;
const int BUZZER_PIN = 33;
const int LED_R_PIN = 25;
const int LED_G_PIN = 32;
const int LED_B_PIN = 14;
const int SILENCE_PIN = 4;
const int PAGE_PIN = 0; // Onboard BOOT button, held low when pressed.
const uint8_t BUZZER_CHANNEL = 0;
const uint8_t RED_CHANNEL = 1;
const uint8_t GREEN_CHANNEL = 2;
const uint8_t BLUE_CHANNEL = 3;

const uint16_t CO2_WARN = 1000;
const uint16_t CO2_BAD = 1200;
const uint16_t PM25_WARN = 15;
const uint16_t PM25_BAD = 35;
const uint32_t SAMPLE_INTERVAL_MS = 5000;
const uint32_t LOG_INTERVAL_MS = 60000;
const uint32_t GRAPH_INTERVAL_MS = 300000;

SensirionI2cScd4x scd4x;
Adafruit_PM25AQI pms;
Adafruit_ST7789 tft(TFT_CS_PIN, TFT_DC_PIN, -1);
WebServer server(80);

struct Reading {
  uint16_t co2 = 0;
  float temperature = NAN;
  float humidity = NAN;
  uint16_t pm25 = 0;
  uint16_t pm10 = 0;
  bool scdOk = false;
  bool pmsOk = false;
};
Reading reading;
uint16_t co2Trend[288];
uint16_t pmTrend[288];
uint16_t trendCount = 0;
uint16_t trendHead = 0;
uint8_t airLevel = 0; // 0 green, 1 yellow, 2 red
uint8_t page = 0;
bool sdReady = false;
bool alertSilenced = false;
bool lastSilenceState = HIGH;
bool lastPageState = HIGH;
uint32_t lastSample = 0;
uint32_t lastLog = 0;
uint32_t lastGraph = 0;
uint32_t lastTelegram = 0;

String timestampText() {
  time_t now = time(nullptr);
  if (now < 1700000000) return String("uptime_") + String(millis() / 1000);
  struct tm timeInfo;
  localtime_r(&now, &timeInfo);
  char buffer[24];
  strftime(buffer, sizeof(buffer), "%Y-%m-%d %H:%M:%S", &timeInfo);
  return String(buffer);
}

String jsonReading() {
  String out = "{\"time\":\"" + timestampText() + "\",\"co2\":" + String(reading.co2);
  out += ",\"temperature\":" + String(reading.temperature, 1);
  out += ",\"humidity\":" + String(reading.humidity, 1);
  out += ",\"pm25\":" + String(reading.pm25) + ",\"pm10\":" + String(reading.pm10);
  out += ",\"level\":" + String(airLevel) + ",\"sd\":" + String(sdReady ? "true" : "false") + "}";
  return out;
}

void setRgb(uint8_t r, uint8_t g, uint8_t b) {
  ledcWrite(LED_R_PIN, r); ledcWrite(LED_G_PIN, g); ledcWrite(LED_B_PIN, b);
}

void updateOutputs() {
  bool bad = airLevel == 2;
  digitalWrite(FAN_PIN, bad ? HIGH : LOW);
  if (airLevel == 0) setRgb(0, 180, 0);
  else if (airLevel == 1) setRgb(180, 100, 0);
  else setRgb(200, 0, 0);
}

void beepAlert() {
  if (!alertSilenced) {
    ledcWriteTone(BUZZER_PIN, airLevel == 2 ? 2400 : 1600);
    delay(120);
    ledcWriteTone(BUZZER_PIN, 0);
  }
}

void drawScreen();

void readSensors() {
  bool changed = false;
  bool dataReady = false;
  uint16_t co2 = 0;
  float temperature = NAN, humidity = NAN;
  if (scd4x.getDataReadyStatus(dataReady) == 0 && dataReady &&
      scd4x.readMeasurement(co2, temperature, humidity) == 0 && co2 > 0) {
    changed |= reading.co2 != co2;
    reading.co2 = co2;
    reading.temperature = temperature;
    reading.humidity = humidity;
    reading.scdOk = true;
  }
  PM25_AQI_Data pmData;
  if (pms.read(&pmData)) {
    changed |= reading.pm25 != pmData.pm25_env || reading.pm10 != pmData.pm100_env;
    reading.pm25 = pmData.pm25_env;
    reading.pm10 = pmData.pm100_env;
    reading.pmsOk = true;
  }
  uint8_t prior = airLevel;
  if ((reading.scdOk && reading.co2 >= CO2_BAD) || (reading.pmsOk && reading.pm25 >= PM25_BAD)) airLevel = 2;
  else if ((reading.scdOk && reading.co2 >= CO2_WARN) || (reading.pmsOk && reading.pm25 >= PM25_WARN)) airLevel = 1;
  else airLevel = 0;
  updateOutputs();
  if (airLevel > prior) beepAlert();
  if (changed || airLevel != prior) drawScreen();
}

void addTrendPoint() {
  co2Trend[trendHead] = reading.co2;
  pmTrend[trendHead] = reading.pm25;
  trendHead = (trendHead + 1) % 288;
  if (trendCount < 288) trendCount++;
}

uint16_t trendAt(uint16_t index) {
  uint16_t first = (trendHead + 288 - trendCount) % 288;
  return co2Trend[(first + index) % 288];
}

void drawHeader(uint16_t color, const char* label) {
  tft.fillRect(0, 0, 320, 26, color);
  tft.setTextColor(ST77XX_WHITE, color);
  tft.setTextSize(2);
  tft.setCursor(6, 5);
  tft.print(label);
}

void drawScreen() {
  uint16_t color = airLevel == 0 ? ST77XX_GREEN : (airLevel == 1 ? ST77XX_YELLOW : ST77XX_RED);
  tft.fillScreen(ST77XX_BLACK);
  drawHeader(color, airLevel == 0 ? "AIR: GOOD" : (airLevel == 1 ? "AIR: FAIR" : "OPEN WINDOW"));
  tft.setTextSize(2);
  tft.setTextColor(ST77XX_WHITE, ST77XX_BLACK);
  if (page == 0) {
    tft.setCursor(10, 42); tft.printf("CO2  %u ppm", reading.co2);
    tft.setCursor(10, 72); tft.printf("PM2.5  %u ug/m3", reading.pm25);
    tft.setCursor(10, 102); tft.printf("PM10   %u ug/m3", reading.pm10);
    tft.setCursor(10, 142); tft.printf("Temp  %.1f C", reading.temperature);
    tft.setCursor(10, 172); tft.printf("Humidity %.0f%%", reading.humidity);
    tft.setTextSize(1); tft.setCursor(10, 215);
    tft.print(sdReady ? "Logging to microSD" : "microSD unavailable");
  } else {
    tft.setTextSize(1); tft.setCursor(8, 35); tft.print("CO2 24-hour trend (5 min points)");
    tft.drawRect(8, 50, 304, 150, ST77XX_WHITE);
    uint16_t maxValue = 1200;
    for (uint16_t i = 0; i < trendCount; i++) if (trendAt(i) > maxValue) maxValue = trendAt(i);
    if (maxValue < 600) maxValue = 600;
    for (uint16_t i = 1; i < trendCount; i++) {
      int x0 = 9 + (i - 1) * 302 / 287;
      int x1 = 9 + i * 302 / 287;
      int y0 = 198 - (int)((uint32_t)trendAt(i - 1) * 146 / maxValue);
      int y1 = 198 - (int)((uint32_t)trendAt(i) * 146 / maxValue);
      if (y0 < 51) y0 = 51; if (y1 < 51) y1 = 51;
      tft.drawLine(x0, y0, x1, y1, ST77XX_CYAN);
    }
    tft.setCursor(10, 210); tft.printf("now %u ppm, scale %u", reading.co2, maxValue);
    tft.setCursor(10, 225); tft.print("Press BOOT to return");
  }
}

void appendLog() {
  if (!sdReady) return;
  File file = SD.open("/air.csv", FILE_APPEND);
  if (!file) { sdReady = false; return; }
  file.printf("%s,%u,%.1f,%.1f,%u,%u,%u\n", timestampText().c_str(), reading.co2,
              reading.temperature, reading.humidity, reading.pm25, reading.pm10, airLevel);
  file.close();
}

String urlEncode(const String& value) {
  String out;
  const char* hex = "0123456789ABCDEF";
  for (size_t i = 0; i < value.length(); i++) {
    char c = value[i];
    if (isalnum(c)) out += c;
    else if (c == ' ') out += '+';
    else { out += '%'; out += hex[(c >> 4) & 15]; out += hex[c & 15]; }
  }
  return out;
}

void sendTelegramAlert() {
  if (WiFi.status() != WL_CONNECTED || strlen(TELEGRAM_BOT_TOKEN) == 0 || strlen(TELEGRAM_CHAT_ID) == 0) return;
  if (millis() - lastTelegram < 900000) return;
  lastTelegram = millis();
  String message = airLevel == 2 ? "Study Air Station: CO2 " + String(reading.co2) + " ppm, PM2.5 " + String(reading.pm25) + " ug/m3. Open a window."
                                 : "Study Air Station: air quality is elevated. CO2 " + String(reading.co2) + " ppm.";
  WiFiClientSecure client;
  client.setInsecure();
  if (client.connect("api.telegram.org", 443)) {
    String path = "/bot" + String(TELEGRAM_BOT_TOKEN) + "/sendMessage?chat_id=" + String(TELEGRAM_CHAT_ID) + "&text=" + urlEncode(message);
    client.print("GET " + path + " HTTP/1.1\r\nHost: api.telegram.org\r\nConnection: close\r\n\r\n");
    client.stop();
  }
}

void setupWeb() {
  server.on("/", []() {
    String html = "<!doctype html><html><meta name=viewport content='width=device-width'><style>body{font-family:sans-serif;background:#101820;color:#fff;margin:24px}.card{padding:18px;background:#1f2d36;border-radius:12px;max-width:420px}b{color:#66e0ff}</style><body><div class=card><h1>Study Air Station</h1><p>Refreshes every 10 seconds.</p><div id=d>Loading...</div></div><script>async function u(){let r=await fetch('/api');let x=await r.json();d.innerHTML='<p><b>'+x.time+'</b></p><p>CO2: '+x.co2+' ppm</p><p>PM2.5: '+x.pm25+' ug/m3 &nbsp; PM10: '+x.pm10+' ug/m3</p><p>Temperature: '+x.temperature+' C &nbsp; Humidity: '+x.humidity+'%</p><p>Air level: '+['good','fair','bad'][x.level]+'</p><p>microSD: '+(x.sd?'ready':'not ready')+'</p>'}u();setInterval(u,10000)</script></body></html>";
    server.send(200, "text/html", html);
  });
  server.on("/api", []() { server.send(200, "application/json", jsonReading()); });
  server.begin();
}

void setupNetwork() {
  if (strlen(WIFI_SSID) > 0) {
    WiFi.mode(WIFI_STA);
    WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
    uint32_t started = millis();
    while (WiFi.status() != WL_CONNECTED && millis() - started < 15000) delay(250);
  }
  if (WiFi.status() == WL_CONNECTED) configTime(0, 0, "pool.ntp.org", "time.nist.gov");
  else { WiFi.mode(WIFI_AP); WiFi.softAP(AP_NAME, AP_PASSWORD); }
}

void setup() {
  Serial.begin(115200);
  pinMode(FAN_PIN, OUTPUT); digitalWrite(FAN_PIN, LOW);
  pinMode(SILENCE_PIN, INPUT); // External 10 kOhm resistor holds this high.
  pinMode(PAGE_PIN, INPUT_PULLUP);
  ledcAttach(BUZZER_PIN, 2000, 8);
  ledcAttach(LED_R_PIN, 5000, 8);
  ledcAttach(LED_G_PIN, 5000, 8);
  ledcAttach(LED_B_PIN, 5000, 8);
  setRgb(0, 0, 0);
  Wire.begin(SCD_SDA_PIN, SCD_SCL_PIN);
  scd4x.begin(Wire, 0x62);
  scd4x.stopPeriodicMeasurement(); delay(500);
  scd4x.startPeriodicMeasurement();
  Serial2.begin(9600, SERIAL_8N1, PMS_RX_PIN, PMS_TX_PIN);
  pms.begin_UART(&Serial2);
  SPI.begin(SPI_SCK_PIN, SPI_MISO_PIN, SPI_MOSI_PIN, SD_CS_PIN);
  tft.init(240, 320); tft.setRotation(1); tft.fillScreen(ST77XX_BLACK);
  sdReady = SD.begin(SD_CS_PIN);
  if (sdReady && !SD.exists("/air.csv")) {
    File file = SD.open("/air.csv", FILE_WRITE);
    if (file) { file.println("timestamp,co2_ppm,temperature_c,humidity_pct,pm25_ugm3,pm10_ugm3,level"); file.close(); }
  }
  setupNetwork();
  setupWeb();
  drawScreen();
}

void loop() {
  server.handleClient();
  bool silenceNow = digitalRead(SILENCE_PIN);
  bool pageNow = digitalRead(PAGE_PIN);
  if (lastSilenceState == HIGH && silenceNow == LOW) { alertSilenced = true; drawScreen(); }
  if (lastPageState == HIGH && pageNow == LOW) { page = 1 - page; drawScreen(); }
  lastSilenceState = silenceNow;
  lastPageState = pageNow;
  uint32_t now = millis();
  if (now - lastSample >= SAMPLE_INTERVAL_MS) { lastSample = now; readSensors(); if (airLevel > 0) sendTelegramAlert(); }
  if (now - lastLog >= LOG_INTERVAL_MS) { lastLog = now; appendLog(); }
  if (now - lastGraph >= GRAPH_INTERVAL_MS) { lastGraph = now; addTrendPoint(); if (page == 1) drawScreen(); }
  delay(10);
}