Arduino ESP8266 + GSM800L + 4 Switch Relay To Light On Off

#include <ESP8266WiFi.h>
#include <SoftwareSerial.h>

// WiFi credentials
const char* ssid = "WIFI_NAMW;
const char* password = "WIFI_PASSWORD";

// Trusted phone number
String trustedNumber = "+91XXXXXXXXXX"; // Replace with your SIM number

// GPIO definitions for NodeMCU
#define RELAY1 5    // D1
#define RELAY2 4    // D2
#define RELAY3 14   // D5
#define RELAY4 12   // D6
#define GSM_RX 13   // D7 (NodeMCU receives from GSM TX)
#define GSM_TX 15   // D8 (NodeMCU sends to GSM RX, use level shifter!)

// Relay pins array
const int relayPins[4] = {RELAY1, RELAY2, RELAY3, RELAY4};

// GSM Serial
SoftwareSerial gsm(GSM_RX, GSM_TX);

// Web server
WiFiServer server(80);

void setup() {
  Serial.begin(9600);
  gsm.begin(9600);

  // Initialize GSM for SMS text mode
  delay(1000);
  gsm.println("AT");
  delay(500);
  gsm.println("AT+CMGF=1");        // Set SMS text mode
  delay(500);
  gsm.println("AT+CNMI=2,2,0,0,0"); // Show new SMS on serial
  delay(500);

  // Relay pin setup
  for (int i = 0; i < 4; i++) {
    pinMode(relayPins[i], OUTPUT);
    digitalWrite(relayPins[i], HIGH); // Active LOW = OFF
  }

  // Connect to WiFi
  WiFi.begin(ssid, password);
  Serial.print("Connecting to WiFi");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  server.begin();
  Serial.println("\n✅ WiFi connected");
  Serial.print("📡 IP Address: ");
  Serial.println(WiFi.localIP());
}

void loop() {
  handleSMS();         // Handle SMS commands
  handleWebRequest();  // Handle web browser control
}

// Handle incoming SMS from trusted number
void handleSMS() {
  static String buffer = "";

  while (gsm.available()) {
    char c = gsm.read();
    Serial.write(c); // Debug output
    buffer += c;

    // Check if there's a new SMS notification
    if (buffer.indexOf("+CMT:") != -1) {
      int senderStart = buffer.indexOf("\"") + 1;
      int senderEnd = buffer.indexOf("\"", senderStart);
      String senderNumber = buffer.substring(senderStart, senderEnd);
      senderNumber.trim();

      Serial.println("📞 Sender: " + senderNumber);

      int msgStart = buffer.indexOf("\n", senderEnd) + 1;
      String messageBody = buffer.substring(msgStart);
      messageBody.trim();
      messageBody.toUpperCase();

      Serial.println("📩 Message: " + messageBody);

      if (senderNumber == trustedNumber) {
        // Relay control via SMS commands
        if (messageBody.indexOf("ON1") >= 0) {
          digitalWrite(relayPins[0], LOW);
          Serial.println("Relay 1 ON");
        }
        if (messageBody.indexOf("OFF1") >= 0) {
          digitalWrite(relayPins[0], HIGH);
          Serial.println("Relay 1 OFF");
        }
        if (messageBody.indexOf("ON2") >= 0) {
          digitalWrite(relayPins[1], LOW);
          Serial.println("Relay 2 ON");
        }
        if (messageBody.indexOf("OFF2") >= 0) {
          digitalWrite(relayPins[1], HIGH);
          Serial.println("Relay 2 OFF");
        }
        if (messageBody.indexOf("ON3") >= 0) {
          digitalWrite(relayPins[2], LOW);
          Serial.println("Relay 3 ON");
        }
        if (messageBody.indexOf("OFF3") >= 0) {
          digitalWrite(relayPins[2], HIGH);
          Serial.println("Relay 3 OFF");
        }
        if (messageBody.indexOf("ON4") >= 0) {
          digitalWrite(relayPins[3], LOW);
          Serial.println("Relay 4 ON");
        }
        if (messageBody.indexOf("OFF4") >= 0) {
          digitalWrite(relayPins[3], HIGH);
          Serial.println("Relay 4 OFF");
        }
        if (messageBody.indexOf("ONALL") >= 0) {
          for (int i = 0; i < 4; i++) {
            digitalWrite(relayPins[i], LOW);
          }
          Serial.println("All Relays ON");
        }
        if (messageBody.indexOf("OFFALL") >= 0) {
          for (int i = 0; i < 4; i++) {
            digitalWrite(relayPins[i], HIGH);
          }
          Serial.println("All Relays OFF");
        }
      } else {
        Serial.println("⚠️ Unauthorized sender: " + senderNumber);
      }

      buffer = ""; // Clear buffer for next message
    }
  }
}

// Handle HTTP requests to control relays
void handleWebRequest() {
  WiFiClient client = server.available();
  if (!client) return;

  while (!client.available()) delay(1);

  String request = client.readStringUntil('\r');
  client.readStringUntil('\n');

  // Relay control via web
  if (request.indexOf("/on1") != -1) digitalWrite(relayPins[0], LOW);
  if (request.indexOf("/off1") != -1) digitalWrite(relayPins[0], HIGH);
  if (request.indexOf("/on2") != -1) digitalWrite(relayPins[1], LOW);
  if (request.indexOf("/off2") != -1) digitalWrite(relayPins[1], HIGH);
  if (request.indexOf("/on3") != -1) digitalWrite(relayPins[2], LOW);
  if (request.indexOf("/off3") != -1) digitalWrite(relayPins[2], HIGH);
  if (request.indexOf("/on4") != -1) digitalWrite(relayPins[3], LOW);
  if (request.indexOf("/off4") != -1) digitalWrite(relayPins[3], HIGH);

  // Simple HTML page for control
  client.println("HTTP/1.1 200 OK");
  client.println("Content-Type: text/html");
  client.println();
  client.println("<h1>Relay Control Panel</h1>");
  for (int i = 0; i < 4; i++) {
    client.print("Relay ");
    client.print(i + 1);
    client.print(": <a href='/on");
    client.print(i + 1);
    client.print("'>ON</a> | <a href='/off");
    client.print(i + 1);
    client.println("'>OFF</a><br>");
  }

  delay(10);
  client.stop();
}