Published February 20, 2026 © MIT

ESP32 4G LTE Based Home Automation System

A WiFi-free IoT automation system using ESP32 and 4G LTE that enables real-time cloud relay control anywhere with SIM network coverage. 🚀

BeginnerFull instructions provided8 hours21

ESP32 4G LTE Based Home Automation System

Things used in this project

Software apps and online services

Arduino IDE

Story

📌 1. Project Overview

This project demonstrates a SIM based 4G LTE Home Automation System that works without WiFi.

Instead of using router-based IoT, this system uses:

ESP32

ESP32

4G LTE Module (SIM7600 / A7670C)

4G LTE Module (SIM7600 / A7670C)

HTTP Cloud Communication

HTTP Cloud Communication

Web Dashboard

Web Dashboard

Relay Control

Relay Control

It is designed for:

Farms

Farms

Remote water pumps

Remote water pumps

Industrial control

Industrial control

Street light automation

Street light automation

Villages without broadband

Villages without broadband

🧰 2. Complete Hardware Required

✅ Main Components

Component

Specification

ESP32 Dev Board

38 Pin or 30 Pin

4G LTE Module

SIM7600 / A7670C

Active SIM Card

4G Data Enabled

Relay Module

4 Channel 5V

Power Supply

5V 2A (ESP32)

Power Supply (LTE)

5V 2A or 12V (module specific)

⚠️ Important Power Note

LTE modules draw high current (up to 2A peak).

Do NOT power LTE module from ESP32 5V pin.

Do NOT power LTE module from ESP32 5V pin.

Use dedicated stable power supply.

Use dedicated stable power supply.

🔌 3. Hardware Wiring

📡 ESP32 ↔ LTE Module (UART)

ESP32

LTE Module

TX2 (GPIO17)

RX2 (GPIO16)

GND

Use Serial2 for communication.

🔁 ESP32 ↔ Relay Module

ESP32 GPIO

Relay

GPIO 4

IN1

GPIO 5

IN2

GPIO 18

IN3

GPIO 19

IN4

GND

Relay VCC → 5V external supply.

🌐 4. Software Architecture

User → Web Dashboard → Server API → LTE Network → ESP32 → Relay

Communication protocol: HTTP GET & POST

💻 5. Server Side Setup (Important)

You need:

Hosting (Shared hosting / VPS)

Hosting (Shared hosting / VPS)

MySQL database

MySQL database

PHP API files

PHP API files

📁 Database Table Example

Create table:

CREATE TABLE relay_control (id INT PRIMARY KEY AUTO_INCREMENT,r1 INT DEFAULT 0,r2 INT DEFAULT 0,r3 INT DEFAULT 0,r4 INT DEFAULT 0);

CREATE TABLE relay_control (
id INT PRIMARY KEY AUTO_INCREMENT,
r1 INT DEFAULT 0,
r2 INT DEFAULT 0,
r3 INT DEFAULT 0,
r4 INT DEFAULT 0
);

Insert initial row:

INSERT INTO relay_control (r1, r2, r3, r4) VALUES (0, 0, 0, 0);

INSERT INTO relay_control (r1,r2,r3,r4) VALUES (0,0,0,0);

📜 getRelayState.php

<?php$conn = new mysqli("localhost", "user", "pass", "database");$result = $conn->query("SELECT * FROM relay_control WHERE id=1");$row = $result->fetch_assoc();echo "R1=".$row['r1'].", R2=".$row['r2'].", R3=".$row['r3'].", R4=".$row['r4'];?>

<?php
$conn = new mysqli("localhost","user","pass","database");
$result = $conn->query("SELECT * FROM relay_control WHERE id=1");
$row = $result->fetch_assoc();

echo "R1=".$row['r1'].",R2=".$row['r2'].",R3=".$row['r3'].",R4=".$row['r4'];
?>

📜 updateRelay.php

<?php$conn = new mysqli("localhost", "user", "pass", "database");$r1 = $_GET['r1'];$r2 = $_GET['r2'];$r3 = $_GET['r3'];$r4 = $_GET['r4'];$conn->query("UPDATE relay_control SET r1=$r1, r2=$r2, r3=$r3, r4=$r4 WHERE id=1");echo "Updated";?>

<?php
$conn = new mysqli("localhost","user","pass","database");

$r1 = $_GET['r1'];
$r2 = $_GET['r2'];
$r3 = $_GET['r3'];
$r4 = $_GET['r4'];

$conn->query("UPDATE relay_control SET r1=$r1,r2=$r2,r3=$r3,r4=$r4 WHERE id=1");

echo "Updated";
?>

📡 6. LTE Module AT Command Flow

Step 1 – Check Communication

AT

Expected Response:

OK

Step 2 – Check SIM

AT+CPIN?

AT+CPIN?

Response:

READY

READY

Step 3 – Network Registration

AT+CREG?

AT+CREG?

Response:

0, 1 (Registered)

0,1  (Registered)

Step 4 – Set APN

Example Airtel:

AT+CGDCONT=1, "IP", "airtelgprs.com"

AT+CGDCONT=1,"IP","airtelgprs.com"

Step 5 – Activate PDP

AT+CGATT=1AT+CGACT=1, 1

AT+CGATT=1
AT+CGACT=1,1

After this module gets IP and internet is active.

🧠 7. ESP32 Firmware Logic

🔄 Main Loop Logic

Initialize LTE

Initialize LTE

Connect to network

Connect to network

Send HTTP GET request

Send HTTP GET request

Parse response

Parse response

Update relays

Update relays

Delay 3–5 seconds

Delay 3–5 seconds

Repeat

Repeat

🧑‍💻 Basic ESP32 Code Structure

#include <HardwareSerial.h>HardwareSerial sim(2);void setup() { Serial.begin(115200); sim.begin(115200, SERIAL_8N1, 16, 17);}void loop() { sim.println("AT"); delay(1000); while(sim.available()){ Serial.write(sim.read()); } delay(5000);}

#include <HardwareSerial.h>

HardwareSerial sim(2);

void setup() {
  Serial.begin(115200);
  sim.begin(115200, SERIAL_8N1, 16, 17);
}

void loop() {

  sim.println("AT");
  delay(1000);

  while(sim.available()){
    Serial.write(sim.read());
  }

  delay(5000);
}

You will expand this for:

HTTP initialization

HTTP initialization

URL call

URL call

Reading HTTP response

Reading HTTP response

Parsing relay data

Parsing relay data

📊 8. HTTP Request Example (Module Side)

For SIM7600:

AT+HTTPINITAT+HTTPPARA="URL", "http://yourdomain.com/getRelayState.php"AT+HTTPACTION=0AT+HTTPREAD

AT+HTTPINIT
AT+HTTPPARA="URL","http://yourdomain.com/getRelayState.php"
AT+HTTPACTION=0
AT+HTTPREAD

Parse the returned string.

🔁 9. Relay Update Logic Example

If response:

R1=1, R2=0, R3=1, R4=0

R1=1,R2=0,R3=1,R4=0

Then:

digitalWrite(4, HIGH);digitalWrite(5, LOW);digitalWrite(18, HIGH);digitalWrite(19, LOW);

digitalWrite(4, HIGH);
digitalWrite(5, LOW);
digitalWrite(18, HIGH);
digitalWrite(19, LOW);

🛡 10. Stability Features To Add

If HTTP fails → retry

If HTTP fails → retry

If network lost → reinitialize PDP

If network lost → reinitialize PDP

If SIM not detected → halt relay

If SIM not detected → halt relay

Default relay OFF on boot

Default relay OFF on boot

Serial debug logging enabled

Serial debug logging enabled

💡 11. Real World Applications

Borewell motor ON/OFF

Borewell motor ON/OFF

Street light timer system

Street light timer system

Solar inverter remote control

Solar inverter remote control

Factory machine control

Factory machine control

Smart irrigation system

Smart irrigation system

🔮 13. Possible Improvements

HTTPS secure requests

HTTPS secure requests

MQTT instead of HTTP

MQTT instead of HTTP

OTA firmware update

OTA firmware update

Mobile app dashboard

Mobile app dashboard

Energy monitoring integration

Energy monitoring integration

👨‍💻 Author

Mr. Abhishek MauryaFounder – Yarana IoT GuruOfficial Contact: +91-7052722734

Website: https://yaranaiotguru.in

❤️ Final Conclusion

This project demonstrates a complete end-to-end 4G LTE IoT automation system that works without WiFi.

From hardware wiring to server API to AT command handling — everything is fully controlled via cellular network.

It is ideal for remote and industrial IoT deployments.

✅ Complete Code

#include <HardwareSerial.h>

HardwareSerial sim(2);

// 🔁 Relay Pins
#define R1 4
#define R2 5
#define R3 18
#define R4 19

String serverURL = "http://yourdomain.com/getRelayState.php";
String apn = "airtelgprs.com";

void sendAT(String cmd, int waitTime = 2000) {
  sim.println(cmd);
  delay(waitTime);
  while (sim.available()) {
    Serial.write(sim.read());
  }
}

void setup() {
  Serial.begin(115200);
  sim.begin(115200, SERIAL_8N1, 16, 17);

  pinMode(R1, OUTPUT);
  pinMode(R2, OUTPUT);
  pinMode(R3, OUTPUT);
  pinMode(R4, OUTPUT);

  digitalWrite(R1, LOW);
  digitalWrite(R2, LOW);
  digitalWrite(R3, LOW);
  digitalWrite(R4, LOW);

  Serial.println("Initializing LTE Module...");

  sendAT("AT");
  sendAT("ATE0"); // Echo off
  sendAT("AT+CPIN?");
  sendAT("AT+CREG?");
  sendAT("AT+CGATT=1");

  // 📡 Set APN
  sendAT("AT+CGDCONT=1,\"IP\",\"" + apn + "\"");
  sendAT("AT+CGACT=1,1");

  Serial.println("LTE Initialization Complete");
}

void fetchRelayState() {

  Serial.println("Fetching Relay State...");

  sendAT("AT+HTTPTERM",1000);
  sendAT("AT+HTTPINIT");
  sendAT("AT+HTTPPARA=\"CID\",1");
  sendAT("AT+HTTPPARA=\"URL\",\"" + serverURL + "\"");
  sendAT("AT+HTTPACTION=0",5000);
  sendAT("AT+HTTPREAD",3000);

  String response = "";

  while (sim.available()) {
    response += (char)sim.read();
  }

  Serial.println("Response:");
  Serial.println(response);

  // 🔍 Parse Response Example: R1=1,R2=0,R3=1,R4=0
  if (response.indexOf("R1=1") != -1) digitalWrite(R1, HIGH);
  else digitalWrite(R1, LOW);

  if (response.indexOf("R2=1") != -1) digitalWrite(R2, HIGH);
  else digitalWrite(R2, LOW);

  if (response.indexOf("R3=1") != -1) digitalWrite(R3, HIGH);
  else digitalWrite(R3, LOW);

  if (response.indexOf("R4=1") != -1) digitalWrite(R4, HIGH);
  else digitalWrite(R4, LOW);

  sendAT("AT+HTTPTERM");
}

void loop() {

  fetchRelayState();

  delay(5000); // 5 sec polling interval
}