GSM-Based Decorative lights control

Abstract

This project allows users to switch ON/OFF Christmas lights other electrical devices using a phone call or SMS, making it highly reliable even in areas with poor or no internet availability.

During festive occasions like Christmas, decorative lights, outdoor illumination, and electrical appliances are used extensively to create a joyful atmosphere. However, manually switching these loads ON and OFF can be inconvenient, especially when users are away from home, working late hours, or managing installations in remote locations. This Smart GSM-Based Light Control System addresses this problem by enabling remote control of electrical loads using simple SIM800L GSM module, without relying on Wi-Fi or continuous internet connectivity.

This project allows users to switch ON/OFF Christmas lights or other electrical devices using a phone call or SMS, making it highly reliable even in areas with poor or no internet availability. Unlike Wi-Fi-based systems, GSM works over basic mobile networks, ensuring wider coverage, better reliability, and uninterrupted control during festivals when network congestion is common.

Following are the components used:

1. GSM Module (SIM800L): Receives phone calls or SMS. Communicates using AT commands.

2. Node MCU (ESP 8266): Microcontroller, processes GSM signals coming via TX/RX and controls relay operation.

3. Relay Module: Electrically isolates low-voltage control circuit from AC lights. Switches Christmas lights safely.

4. Buck Converter (LM2596): Steps down DC to 4.4v required for SIM800L to work properly.

5. Electrolytic Capacitor (1000µF, 25v): To handle current peak during transmission by SIM800L module.

6. 2 18650 Li Ion Batteries

7. Breadboard and Jumper wires

Circuit Connections:

SIM800L TX → NodeMCU D7 (GPIO13)
SIM800L RX → NodeMCU D8 (GPIO15)

GND → Common Ground

VCC → Buck Converter output(set to 4 to 4.4v)

Relay IN → D1

Relay VCC → 5V

Relay GND → GND

GSM modules draw sudden current bursts, which can reset or malfunction the system. So we will add a 1000µF near Vcc and Gnd of GSM module.

Working:

User makes a phone call or sends an SMS( depending on our programming)
GSM module detects the incoming command
GSM sends response data to the microcontroller via UART
Microcontroller reads and processes the command
Relay is switched ON or OFF
Christmas lights turn ON or OFF accordingly

Here is the basic code I tried with in the Arduino IDE, we can place any decorative light in the relay load side:

#define RELAY_PIN D1

bool relayState = false;
String buffer = "";
unsigned long lastRingTime = 0;
int ringCount = 0;

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(RELAY_PIN, OUTPUT);

  digitalWrite(LED_BUILTIN, HIGH); // OFF
  digitalWrite(RELAY_PIN, LOW);    // OFF (adjust if active LOW)

  Serial.begin(115200);
  Serial.swap();   // GSM on D7/D8

  delay(12000);    // SIM800L boot

  Serial.println("AT");
  delay(300);
  Serial.println("ATE0");
  delay(300);
}

void loop() {
  yield();

  while (Serial.available()) {
    char c = Serial.read();
    buffer += c;

    // Detect RING
    if (buffer.indexOf("RING") != -1) {
      unsigned long now = millis();

      if (now - lastRingTime > 1500) {  // debounce
        ringCount++;
        lastRingTime = now;
      }

      buffer = "";
    }

    // If 2 rings detected → toggle
    if (ringCount >= 2) {
      relayState = !relayState;

      digitalWrite(RELAY_PIN, relayState ? HIGH : LOW);
      digitalWrite(LED_BUILTIN, relayState ? LOW : HIGH);

      Serial.println("ATH"); // hang up

      ringCount = 0;
    }

    if (buffer.length() > 300) buffer = "";
  }
}

Following are the advantages I see to this project:

No Wi-Fi or Internet required
Long-range control
Safe electrical isolation using relay
Cost-effective and scalable
Suitable for rural and urban areas

I had this in my mind because not everyone is able to fully attend or enjoy holidays due to work commitments and responsibilities. In such situations, celebrations often become limited or delayed. This project was designed to ensure that even when people are physically away, they can still experience the warmth and joy of occasions like Christmas by remotely lighting up their homes. In a small but meaningful way, it helps preserve the festive spirit, reminding us that celebration is not only about presence, but also about connection and thoughtful use of technology.

Attachments

References

SIMCom Wireless Solutions, SIM800L GSM/GPRS Module Hardware Design, SIMCom Ltd.
Arduino IDE Documentation. https://www.arduino.cc/
Espressif Systems, ESP8266EX Datasheet, Espressif Systems Inc. https://nodemcu.readthedocs.io/en/release/
MP1584 / LM2596 Buck Converter Module Datasheet, Monolithic Power Systems / Texas Instruments
AT Command Set for GSM Modules, SIMCom AT Command Manual
https://app.cirkitdesigner.com/

Category : Project

GSM-Based Decorative lights control

Table of contents

Abstract

Project

Attachments

References