Building a Simple Alarm System with Arduino

Difficulty Level: Intermediate

In this tutorial, we’ll create a simple alarm system using Arduino, a PIR motion sensor, a buzzer, and an LED. When motion is detected, the alarm system will activate the buzzer and LED as a visual and audible alert.

Components Required

• 1 x Arduino (e.g., Uno)
• 1 x PIR motion sensor
• 1 x Buzzer
• 1 x LED
• 1 x Resistor (220 ohms for the LED)
• Breadboard and jumper wires

Wiring the Circuit

Follow the wiring instructions below:

• Connect the PIR sensor VCC pin to 5V and GND to GND. The signal pin connects to digital pin D2 on the Arduino.
• Connect the buzzer positive lead to digital pin D8 and the negative lead to GND.
• Connect the LED anode (long leg) to digital pin D7 and the cathode (short leg) through a 220 ohm resistor to GND.

Arduino Code

The following code detects motion and triggers the alarm system:

#define PIR_PIN 2     // PIR sensor input pin
#define BUZZER_PIN 8  // Buzzer output pin
#define LED_PIN 7     // LED output pin

void setup() {
  pinMode(PIR_PIN, INPUT);       // Set PIR sensor as input
  pinMode(BUZZER_PIN, OUTPUT);   // Set buzzer as output
  pinMode(LED_PIN, OUTPUT);      // Set LED as output
  Serial.begin(9600);            // Initialize serial monitor
}

void loop() {
  int pirState = digitalRead(PIR_PIN);  // Read PIR sensor

  if (pirState == HIGH) {               // If motion is detected
    digitalWrite(BUZZER_PIN, HIGH);     // Activate the buzzer
    digitalWrite(LED_PIN, HIGH);        // Turn on the LED
    Serial.println("Motion detected!");
  } else {
    digitalWrite(BUZZER_PIN, LOW);      // Turn off the buzzer
    digitalWrite(LED_PIN, LOW);         // Turn off the LED
  }

  delay(500);  // Delay between readings
}
        

Code Explanation

• PIR_PIN: The digital pin connected to the signal pin of the PIR sensor.
• BUZZER_PIN: The digital pin controlling the buzzer.
• LED_PIN: The digital pin controlling the LED.
• digitalRead(PIR_PIN): This function reads the state of the PIR sensor (HIGH when motion is detected, LOW when no motion).
• digitalWrite(): Turns the buzzer and LED on or off depending on whether motion is detected.
• Serial.println(): Prints messages to the Serial Monitor, useful for debugging.

Testing the System

1. Upload the code to the Arduino.
2. Ensure all components are wired correctly.
3. Place the PIR sensor in an area where it can detect motion.
4. When motion is detected, the LED should light up, and the buzzer will sound.

Conclusion

You've successfully created a simple alarm system using a PIR sensor, buzzer, and LED. This project can be expanded by adding a keypad to deactivate the alarm, a display to show information, or even connecting it to a Wi-Fi module for remote monitoring.