Arduino Easy Smart Home Series: Timer-Based Relay Switch with RTC: Automate Your Devices!

Arduino Timer-Based Relay Switch with RTC: Automate Your Devices

Take control of your home appliances with this exciting Arduino Timer-Based Relay Project! ⚡ Schedule multiple ON/OFF times offline using an RTC module, perfect for lights, fans, or motors. Ideal for beginners, hobbyists, and makers who want a simple yet effective offline smart home automation solution. This project is fully customizable, expandable, and teaches important concepts in electronics, time management automation, and Arduino programming. 🕒💡

Table of Contents

• Introduction
• Required Hardware
• Arduino IDE Setup
• Wiring the Components
• Arduino Code
• How It Works
• Testing Your Project
• Advanced Modifications
• Common Issues and Troubleshooting
• Learning Insights
• Conclusion

1. Introduction

This project allows you to automate appliances to turn ON and OFF at different times using an Arduino UNO and an RTC (Real-Time Clock) module. It’s completely offline, meaning you don’t need Wi-Fi or any external server. You can define multiple time slots for your devices, making it suitable for:

• Turning lamps on/off at specific times
• Fan automation during hot/cold hours
• Garden watering or small motorized tasks
• Simple offline smart home setups

By doing this project, you’ll also learn how to interface RTC modules, handle timed events in Arduino, and expand automation with multiple devices. It’s beginner-friendly but also serves as a foundation for more advanced smart home systems. 🚀

2. Required Hardware

• Arduino UNO , ~500Rs
• 5V Relay Module , ~100Rs (choose one rated for your appliance)
• RTC Module DS3231 or DS1307 , ~300Rs
• Jumper wires & breadboard , ~250Rs
• Optional: 16×2 LCD Display with I2C module , ~300Rs
• Low voltage appliance or LED for testing
• Arduino IDE installed on your PC

3. Arduino IDE Setup

1. Download and install the Arduino IDE from the official Arduino website.
2. Connect your Arduino UNO to your PC using a USB cable. The green power LED on the board should light up.
3. Open Arduino IDE and install the RTClib library:
   • Go to Sketch → Include Library → Manage Libraries
   • Search for RTClib by Adafruit
   • Click “Install”
4. Select the correct board and COM port:
   • Tools → Board → Arduino UNO
   • Tools → Port → COMX (where your Arduino is connected)
5. Verify the IDE setup by uploading a simple Blink sketch to ensure the board is working properly.

4. Wiring the Components

Wiring is simple and straightforward. Follow these instructions carefully:

• Relay Module:
  • IN pin → Arduino D2
  • VCC → 5V
  • GND → GND
• RTC Module DS3231/DS1307:
  • SDA → A4 (Arduino UNO)
  • SCL → A5 (Arduino UNO)
  • VCC → 5V
  • GND → GND
• Optional LCD Display (I2C):
  • SDA → A4
  • SCL → A5
  • VCC → 5V
  • GND → GND
• Test appliance or LED:
  • Connect the positive lead to NO (Normally Open) of relay
  • Connect negative lead to common ground/power supply

Double-check all wiring before powering the Arduino to prevent damage to components.

5. Arduino Code

Upload this code to your Arduino. It supports multiple scheduled ON/OFF slots:

#include <Wire.h>
#include <RTClib.h>

RTC_DS3231 rtc;
int relayPin = 2;

struct TimeSlot {
  int onHour;
  int onMinute;
  int offHour;
  int offMinute;
};

TimeSlot slots[] = {
  {8, 0, 8, 5},
  {12, 30, 12, 35},
  {18, 0, 18, 10}
  // Add more time slots if wanted
};

int numSlots = sizeof(slots)/sizeof(slots[0]);

void setup() {
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, LOW);
  Serial.begin(9600);
  if(!rtc.begin()){
    Serial.println("RTC not found!");
    while(1);
  }
}

void loop() {
  DateTime now = rtc.now();

  for(int i=0; i<numSlots; i++){
    if(now.hour() == slots[i].onHour && now.minute() == slots[i].onMinute){
      digitalWrite(relayPin, HIGH);
      Serial.println("Relay ON");
    }
    if(now.hour() == slots[i].offHour && now.minute() == slots[i].offMinute){
      digitalWrite(relayPin, LOW);
      Serial.println("Relay OFF");
    }
  }
  delay(1000);
}

6. How It Works

The RTC module keeps accurate real-time data even when the Arduino is powered off. The Arduino continuously reads the current hour and minute and compares it with the predefined time slots. When the current time matches the ON time, the relay switches ON; when it matches the OFF time, the relay switches OFF. This allows fully automated appliances on your schedule. You can add unlimited slots for multiple devices or times.

7. Testing Your Project

1. Upload the code to your Arduino.
2. Connect your test appliance or LED to the relay.
3. Open Serial Monitor at 9600 baud to view real-time status.
4. Wait for the scheduled time to see relay ON/OFF events.
5. Check appliance response for correct timing.

8. Advanced Modifications

• Add more time slots in the slots[] array for additional scheduled events.
• Use a 16×2 LCD to display current time and next scheduled relay event.
• Integrate multiple relays to control multiple devices independently.
• Add buttons to manually override relay events without modifying code.

9. Common Issues and Troubleshooting

• RTC not detected: Verify SDA/SCL connections and VCC/GND. Try another RTC module if needed.
• Relay not switching: Check relay power supply, Arduino pin, and connected load rating.
• Incorrect time slots: Ensure RTC is set to correct time using an initial setup sketch.

Comment below to get a reply if you face any issues! Our community and I will help you debug your project.

10. Learning Insights

• Learn to interface RTC modules with Arduino effectively.
• Understand offline timed automation logic for relays.
• Gain skills in smart home offline projects without Wi-Fi.
• Practice expanding projects with multiple devices and scheduled events.

11. Conclusion

This Arduino Timer-Based Relay with RTC project is a simple yet powerful offline automation solution. You can schedule multiple appliances, expand the system with more relays, integrate LCD displays, and build a small offline smart home. Perfect for beginners and makers looking to learn electronics, coding, and practical automation. Stay tuned for more projects in the ArduNova Maker Series! 🚀

By Kaushal Haladi