How to Build an IoT Indoor Weather Station Using CircuitDigest Cloud

// Copyright (c) 2026 Circuit Digest
// SPDX-License-Identifier: MIT
//
// DHT11 -> CircuitDigestCloud gauge display + SMS alert at 40°C
// Board target: ESP32
// DHT11 data pin: GPIO 23
//
// Library: CircuitDigestCloud v2.x (manages WiFi + TLS internally —
// no WiFi.begin() or WiFiClientSecure needed in this sketch).
//
// - Publishes "temperature" to the dashboard's temperature-1 slot,
//   "humidity" to humidity-1 (gauge widget), "light intensity" to
//   analog-input-1, and "pressure" to level-1 (value widget) every 5s.
// - SMS alert message reports both live temperature and humidity.
// - Sends one SMS alert when temperature >= 40°C.
// - Won't send another SMS until temperature drops back below 38°C
//   (hysteresis, so you don't get spammed while it hovers around 40).
// - 0.96" I2C SSD1306 OLED shows live temperature + whether the SMS
//   alert has been sent. Wiring: SDA -> GPIO21, SCL -> GPIO22 (ESP32
//   default I2C pins), VCC -> 3.3V, GND -> GND.
// - BH1750 ambient light sensor (I2C, shares SDA/SCL with the OLED)
//   publishes lux to the "Light intensity" widget (analog-input-1),
//   shows the reading on the OLED, and auto-adjusts OLED brightness
//   (dim in the dark, bright in daylight).
// - BMP280 pressure sensor (I2C, same shared bus) tracks barometric
//   pressure trend over ~3 hours and shows a simple weather forecast
//   ("Rising", "Falling", "Steady") on the OLED.
// - Buzzer (GPIO4) sounds continuously while temperature >= 40°C OR
//   the forecast reads "Falling" (rain likely). Turns off once both
//   conditions clear.
//
// Requires libraries: "Adafruit SSD1306", "Adafruit GFX Library",
// "BH1750" by Christopher Laws, and "Adafruit BMP280 Library"
// (install all via Arduino Library Manager).
#include <WiFi.h>          // only used here for the plain SMS HTTP request
#include <DHT.h>
#include <DHT_U.h>
#include <CircuitDigestCloud.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <BH1750.h>
#include <Adafruit_BMP280.h>
// ---------------- Sensor ----------------------------------------------------
#define Temp_SensorPin 23
DHT_Unified dht(Temp_SensorPin, DHT11);
float temperature = 0.0;
float humidity = 0.0; // DHT11 measures both temp and humidity, no extra hardware needed
// ---------------- Buzzer ------------------------------------------------------
#define BUZZER_PIN 4   // active buzzer module signal pin
// Some active buzzer modules turn ON when the signal pin is HIGH, others turn
// ON when it's LOW. If your buzzer sounds immediately on boot (or never turns
// off), flip this constant to the other value.
#define BUZZER_ON_LEVEL  LOW   // <-- try LOW first (common for many modules); change to HIGH if wrong
#define BUZZER_OFF_LEVEL (BUZZER_ON_LEVEL == HIGH ? LOW : HIGH)
bool buzzerOn = false;
// ---------------- OLED (0.96" SSD1306, I2C) ----------------------------------
#define SCREEN_WIDTH   128
#define SCREEN_HEIGHT  64
#define OLED_RESET     -1     // no dedicated reset pin
#define OLED_ADDRESS   0x3C   // most 0.96" SSD1306 modules use 0x3C (some use 0x3D)
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);
String smsStatusText = "Monitoring...";
// ---------------- BH1750 (ambient light) --------------------------------------
BH1750 lightMeter;                 // default I2C address 0x23 (ADDR pin low/unconnected)
float luxLevel = 0.0;
const char *LUX_SLOT = "analog-input-1"; // slot key from dashboard ("Light intensity" widget)
// OLED brightness auto-adjust range (contrast 0-255)
// Lower lux -> higher contrast (brighter screen); higher lux -> lower contrast.
const float   LUX_MIN_FOR_SCALE = 0.0;    // lux at/below this -> screen at max brightness
const float   LUX_MAX_FOR_SCALE = 1000.0; // lux at/above this -> screen at min brightness
const uint8_t OLED_CONTRAST_MIN = 10;     // dimmest screen setting
const uint8_t OLED_CONTRAST_MAX = 255;    // brightest screen setting
// ---------------- BMP280 (barometric pressure -> weather forecast) -----------
Adafruit_BMP280 bmp; // I2C
float pressureHpa = 0.0;
String forecastText = "Collecting";
// Rolling pressure history for trend detection.
// PRESSURE_HISTORY_LEN samples spaced PRESSURE_SAMPLE_INTERVAL apart cover
// a ~3 hour window, which is the standard window for barometric forecasting.
const int PRESSURE_HISTORY_LEN = 6;
const unsigned long PRESSURE_SAMPLE_INTERVAL = 30UL * 60UL * 1000UL; // 30 min
float pressureHistory[PRESSURE_HISTORY_LEN];
int   pressureHistoryCount = 0;   // how many slots are filled so far
int   pressureHistoryIndex = 0;   // next slot to write (circular buffer)
unsigned long lastPressureSample = 0;
// ---------------- WiFi -------------------------------------------------------
const char *ssid     = "XXXXXXXXXX";       // <-- your WiFi SSID
const char *password = "XXXXXXXXXX";      // <-- your WiFi password
// ---------------- CircuitDigestCloud (for the gauge) -------------------------
const char *DEVICE_ID        = "XXXXXX-XXXXXX-XXXXXX"; // your Physical Device ID from CircuitDigest Cloud
const char *CONNECTION_KEY   = "XXXXXX-XXXXXX";     // your device Connection Key from CircuitDigest Cloud
const char *TEMPERATURE_SLOT = "temperature-1";                        // slot key from dashboard
const char *HUMIDITY_SLOT    = "humidity-1";                           // slot key from dashboard (gauge widget)
const char *PRESSURE_SLOT    = "level-1";                              // slot key from dashboard (value widget)
CircuitDigestCloud cd; // no constructor args — library owns its own TLS client
// ---------------- SMS (Circuit Digest Cloud SMS API) --------------------------
const char* apiKey       = "cd_moh_240626_11WynF";   // Your API key from Circuit Digest Cloud website
const char* templateID   = "102";            // Your SMS template ID
const char* mobileNumber = "917539912128";   // Recipient number with country code
char        var1[8]      = "0";              // Template variable: temperature at trigger time
char        var2[8]      = "0";              // Template variable: humidity at trigger time
// ---------------- Alert thresholds -------------------------------------------
const float SMS_TRIGGER_TEMP = 40.0;  // send SMS at/above this
const float SMS_RESET_TEMP   = 38.0;  // must drop below this before next SMS can fire
bool alertActive = false;             // true = SMS sent, waiting for reset
// ---------------- Timers ------------------------------------------------------
unsigned long lastSensorRead = 0;
const unsigned long SENSOR_INTERVAL = 2000;   // read DHT11 every 2s
unsigned long lastPublish = 0;
const unsigned long PUBLISH_INTERVAL = 5000;  // push to gauge every 5s
// ---------------------------------------------------------------------------
void read_temperature() {
 sensors_event_t event;
 dht.temperature().getEvent(&event);
 if (!isnan(event.temperature)) {
   temperature = event.temperature;
   Serial.print("Temperature: ");
   Serial.println(temperature);
 } else {
   Serial.println("DHT11 read failed!");
 }
 sensors_event_t humidityEvent;
 dht.humidity().getEvent(&humidityEvent);
 if (!isnan(humidityEvent.relative_humidity)) {
   humidity = humidityEvent.relative_humidity;
   Serial.print("Humidity: ");
   Serial.print(humidity);
   Serial.println(" %");
 } else {
   Serial.println("DHT11 humidity read failed!");
 }
 updateDisplay();
}
// ---------------------------------------------------------------------------
void read_lux() {
 float reading = lightMeter.readLightLevel();
 if (reading >= 0) { // BH1750 returns a negative value on read error
   luxLevel = reading;
   Serial.print("Light: ");
   Serial.print(luxLevel);
   Serial.println(" lx");
 } else {
   Serial.println("BH1750 read failed! Re-initializing sensor...");
   if (lightMeter.begin(BH1750::CONTINUOUS_HIGH_RES_MODE, 0x23, &Wire)) {
     Serial.println("BH1750 re-init OK.");
   } else {
     Serial.println("BH1750 re-init failed, will retry next cycle.");
   }
 }
 setOledBrightness();
 updateDisplay();
}
// ---------------------------------------------------------------------------
void setOledBrightness() {
 // Map lux -> OLED contrast, INVERTED: dimmer room = brighter screen,
 // brighter room = dimmer screen.
 float clamped = constrain(luxLevel, LUX_MIN_FOR_SCALE, LUX_MAX_FOR_SCALE);
 uint8_t contrast = map((long)clamped, (long)LUX_MIN_FOR_SCALE, (long)LUX_MAX_FOR_SCALE,
                         OLED_CONTRAST_MAX, OLED_CONTRAST_MIN); // note: swapped from before
 display.ssd1306_command(SSD1306_SETCONTRAST);
 display.ssd1306_command(contrast);
}
// ---------------------------------------------------------------------------
void read_pressure() {
 float reading = bmp.readPressure(); // returns Pa
 if (!isnan(reading) && reading > 0) {
   pressureHpa = reading / 100.0; // Pa -> hPa
   Serial.print("Pressure: ");
   Serial.print(pressureHpa);
   Serial.println(" hPa");
 } else {
   Serial.println("BMP280 read failed!");
   return;
 }
 // Sample into the trend-history buffer every 30 min
 unsigned long now = millis();
 if (now - lastPressureSample >= PRESSURE_SAMPLE_INTERVAL || lastPressureSample == 0) {
   lastPressureSample = now;
   pressureHistory[pressureHistoryIndex] = pressureHpa;
   pressureHistoryIndex = (pressureHistoryIndex + 1) % PRESSURE_HISTORY_LEN;
   if (pressureHistoryCount < PRESSURE_HISTORY_LEN) pressureHistoryCount++;
   updateForecast();
 }
}
// ---------------------------------------------------------------------------
void updateForecast() {
 if (pressureHistoryCount < 2) {
   forecastText = "Collecting";
   return;
 }
 // Oldest sample currently in the buffer
 int oldestIndex = (pressureHistoryIndex + PRESSURE_HISTORY_LEN - pressureHistoryCount) % PRESSURE_HISTORY_LEN;
 float oldest = pressureHistory[oldestIndex];
 float trend = pressureHpa - oldest; // hPa change over the buffered window
 String direction;
 if (trend >= 1.5) {
   direction = "Rising";
 } else if (trend <= -1.5) {
   direction = "Falling";
 } else {
   direction = "Steady";
 }
 forecastText = direction;
}
// ---------------------------------------------------------------------------
void updateBuzzer() {
 // Sound the buzzer if either condition is true:
 //  - alertActive is true (same 40°C trigger / 38°C reset hysteresis as the SMS), OR
 //  - the pressure trend shows "Falling" (rain likely)
 bool shouldSound = alertActive || (forecastText == "Falling");
 if (shouldSound && !buzzerOn) {
   digitalWrite(BUZZER_PIN, BUZZER_ON_LEVEL);
   buzzerOn = true;
   Serial.println("Buzzer ON");
 } else if (!shouldSound && buzzerOn) {
   digitalWrite(BUZZER_PIN, BUZZER_OFF_LEVEL);
   buzzerOn = false;
   Serial.println("Buzzer OFF");
 }
}
// ---------------------------------------------------------------------------
void updateDisplay() {
 display.clearDisplay();
 // Title
 display.setTextSize(1);
 display.setTextColor(SSD1306_WHITE);
 display.setCursor(0, 0);
 display.println("ESP32 Weather Station");
 display.drawLine(0, 10, SCREEN_WIDTH - 1, 10, SSD1306_WHITE);
 // Temperature
 display.setCursor(0, 14);
 display.print("Temp: ");
 display.print(temperature, 1);
 display.print(" C");
 // Pressure
 display.setCursor(0, 24);
 display.print("Pressure: ");
 display.print(pressureHpa, 0);
 display.print(" hPa");
 // Forecast
 display.setCursor(0, 34);
 display.print("Forecast: ");
 display.print(forecastText);
 // Lux reading
 display.setCursor(0, 44);
 display.print("Lux: ");
 display.print(luxLevel, 0);
 // SMS alert status line at the bottom
 display.setCursor(0, 54);
 display.print("SMS: ");
 display.print(smsStatusText);
 display.display();
}
// ---------------------------------------------------------------------------
void sendSMS() {
 if (WiFi.status() != WL_CONNECTED) {
   Serial.println("WiFi not connected, can't send SMS!");
   smsStatusText = "Failed (No WiFi)";
   updateDisplay();
   return;
 }
 WiFiClient client; // plain HTTP client, separate from CircuitDigestCloud's own MQTT/TLS connection
 String apiUrl = "/api/v1/send_sms?ID=" + String(templateID);
 Serial.print("Connecting to SMS server...");
 if (!client.connect("www.circuitdigest.cloud", 80)) {
   Serial.println("Connection to SMS server failed!");
   smsStatusText = "Failed (No Conn)";
   updateDisplay();
   return;
 }
 Serial.println("connected!");
 dtostrf(temperature, 4, 1, var1); // var1 -> current temperature, e.g. "40.2"
 dtostrf(humidity, 4, 1, var2);    // var2 -> current humidity, e.g. "43.2"
 String payload = "{\"mobiles\":\"" + String(mobileNumber) +
                   "\",\"var1\":\"" + String(var1) +
                   "\",\"var2\":\"" + String(var2) + "\"}";
 client.println("POST " + apiUrl + " HTTP/1.1");
 client.println("Host: www.circuitdigest.cloud");
 client.println("Authorization: " + String(apiKey));
 client.println("Content-Type: application/json");
 client.println("Content-Length: " + String(payload.length()));
 client.println();
 client.println(payload);
 int responseCode = -1;
 while (client.connected() || client.available()) {
   if (client.available()) {
     String line = client.readStringUntil('\n');
     Serial.println(line);
     if (line.startsWith("HTTP/")) {
       responseCode = line.substring(9, 12).toInt();
     }
     if (line == "\r") break;
   }
 }
 if (responseCode == 200) {
   Serial.println("SMS sent successfully!");
   smsStatusText = "SENT!";
 } else {
   Serial.print("Failed to send SMS. Error code: ");
   Serial.println(responseCode);
   smsStatusText = "Failed (" + String(responseCode) + ")";
 }
 updateDisplay();
 client.stop();
}
// ---------------------------------------------------------------------------
void setup() {
 Serial.begin(115200);
 delay(200);
 dht.begin();
 // ---- Buzzer init ----
 pinMode(BUZZER_PIN, OUTPUT);
 digitalWrite(BUZZER_PIN, BUZZER_OFF_LEVEL); // start silent
 // ---- OLED init ----
 Wire.begin(21, 22); // SDA, SCL (ESP32 default I2C pins) — shared by OLED and BH1750
 if (!display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDRESS)) {
   Serial.println("SSD1306 OLED not found! Check wiring/address.");
 } else {
   display.clearDisplay();
   display.setTextSize(1);
   display.setTextColor(SSD1306_WHITE);
   display.setCursor(0, 20);
   display.println("Starting up...");
   display.display();
 }
 // ---- BH1750 init (retry a few times — it occasionally fails on the
 //      first attempt right after power-up or while WiFi is starting) ----
 Wire.setClock(100000); // 100kHz — more reliable than 400kHz on a shared bus with long wires
 bool bh1750Ok = false;
 for (int attempt = 1; attempt <= 5 && !bh1750Ok; attempt++) {
   bh1750Ok = lightMeter.begin(BH1750::CONTINUOUS_HIGH_RES_MODE, 0x23, &Wire);
   if (!bh1750Ok) {
     Serial.print("BH1750 init attempt ");
     Serial.print(attempt);
     Serial.println(" failed, retrying...");
     delay(300);
   }
 }
 if (!bh1750Ok) {
   Serial.println("BH1750 not found after 5 attempts! Check wiring/address.");
 }
 // ---- BMP280 init (try 0x76 then 0x77, retry a few times) ----
 bool bmpOk = false;
 for (int attempt = 1; attempt <= 5 && !bmpOk; attempt++) {
   bmpOk = bmp.begin(0x76) || bmp.begin(0x77);
   if (!bmpOk) {
     Serial.print("BMP280 init attempt ");
     Serial.print(attempt);
     Serial.println(" failed, retrying...");
     delay(300);
   }
 }
 if (bmpOk) {
   bmp.setSampling(Adafruit_BMP280::MODE_NORMAL,
                    Adafruit_BMP280::SAMPLING_X2,   // temperature oversampling
                    Adafruit_BMP280::SAMPLING_X16,  // pressure oversampling
                    Adafruit_BMP280::FILTER_X16,
                    Adafruit_BMP280::STANDBY_MS_500);
 } else {
   Serial.println("BMP280 not found after 5 attempts! Check wiring/address.");
 }
 // ---- CircuitDigestCloud setup (drives the gauge) ----
 // begin() connects WiFi itself and starts the MQTT session — no manual
 // WiFi.begin() loop needed. It blocks until WiFi connects (default), then
 // brings up MQTT in the background.
 cd.setDebug(&Serial); // prints [CD] status lines to Serial; call before begin()
 cd.begin(ssid, password, DEVICE_ID, CONNECTION_KEY);
}
// ---------------------------------------------------------------------------
void loop() {
 cd.loop(); // keep the cloud connection alive (non-blocking)
 unsigned long now = millis();
 // --- Read DHT11 + BH1750 periodically ---
 if (now - lastSensorRead >= SENSOR_INTERVAL) {
   lastSensorRead = now;
   read_temperature();
   read_lux();
   read_pressure();
   // --- SMS alert logic with hysteresis ---
   if (!alertActive && temperature >= SMS_TRIGGER_TEMP) {
     sendSMS();
     alertActive = true; // don't fire again until it cools down
   } else if (alertActive && temperature < SMS_RESET_TEMP) {
     alertActive = false; // re-armed for next time it crosses 40°C
     smsStatusText = "Monitoring...";
     updateDisplay();
   }
   updateBuzzer(); // check after alertActive is current for this cycle
 }
 // --- Push to CircuitDigestCloud widgets periodically ---
 // Requires CircuitDigestCloud library v2.1.0+ for the batched
 // publish() overload (sends all readings in a single MQTT message).
 if (now - lastPublish >= PUBLISH_INTERVAL) {
   lastPublish = now;
   cd.publish({{TEMPERATURE_SLOT, temperature},
               {LUX_SLOT,         luxLevel},
               {HUMIDITY_SLOT,    humidity},
               {PRESSURE_SLOT,    pressureHpa}});
 }
}