Laser Tripwire Box with LCD Alert Using Arduino Uno

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Overview

This simple project involves creating a laser trip wire using an Arduino UNO. It integrates a laser module as its light source and an LDR module as its trigger, using an LCD module to provide real time sensor status and visual feedback. The text displayed on the LCD cycles between “INTRUDER ALERT", “TRIPWIRE ACTIVATED" and "MONITORING: BEAM INTACT” monitoring states.

Hardware Used

Software Use

Arduino IDE

Application Discussion

Arduino Uno R3

We're using an Arduino Uno as the main microcontroller for this project. It is a popular open-source microcontroller board based on the ATmega328P microcontroller.

Laser Module (KY – 008)

Pinout:

The KY‑008 is a compact, low-cost red laser transmitter module which integrates a 650 nm red laser diode, a current-limiting resistor, and three male header pins on a PCB. Designed for easy interfacing with Arduino, ESP32, Raspberry Pi, and similar, it's ideal for simple laser pointer functions, optical communication, or creating laser tripwire setups. Handle with care—never point the laser at eyes or reflective surfaces.

Specifications:

Feature	Specification
Laser Wavelength	650 nm (red beam)
Output Power	≤ 5 mW (Class IIIa/3A laser)
Operating Voltage	5 V (some sources suggest 3–5 V)
Operating Current	~30–40 mA
Temperature Range	−10 °C to +40 °C
Module Size	~18.5 × 15 mm (PCB); some list 15 × 24 mm
Heat & Regulation	Simple resistor-based current limiting; may heat under long operation

LDR Light Sensor Module

Pinout:

VCC – 5V

GND – GND

OUT – Signal output

The K853518 is a classic analog light sensor module based on a Light Dependent Resistor (LDR). It uses a simple voltage divider circuit and outputs a voltage proportional to ambient light levels. Ideal for Arduino, ESP32, Raspberry Pi Pico (with external ADC), etc.

Key Specifications

Operating Voltage: 3.0 – 5.5 V DC
Output Type: Analog voltage (direct output)
Layout & Dimensions: PCB with two mounting holes (~3 mm); board size ≈ 29 × 21 × 9.5 mm; weight ~2 g
Analog Range: Voltage varies linearly with light—higher in bright, lower in dark
LDR Characteristics (typical for similar modules): Dark ≈ 50 kΩ → Bright < 500 Ω
Signal Cable: 20 cm 3-wire cable included (VCC, GND, OUT)

Passive Buzzer Module 5V (FC – 07)

Pinout:

A compact PWM-driven sound module using a passive piezo buzzer. Requires a microcontroller to send square-wave signals (2–5 kHz typically) to produce sounds like tones or melodies. It doesn't buzz with steady DC voltage—only with oscillating signals.

Key Specifications

Feature	Details
Operating Voltage	3.3–5 V DC
Rated Current	< 30 mA typical
Drive Signal Frequency	PWM square‑wave, ~1.5–5 kHz (resonant freq ≈2.5 kHz)
Sound Level	≥ 85 dB @ 10 cm
PCB Size	~20 × 20 mm (some ~33 × 13 × 10 mm)
Weight	~3 g
Modules Includes	Often includes LED indicator, S8550 driver transistor, and a 3‑pin cable

LCD Module 16x02 with i2C

Pinout:

This module combines a standard 16×2 character LCD (HD44780-compatible) with an I2C “backpack” module, drastically simplifying wiring—just four wires: VCC, GND, SDA, and SCL. It’s ideal for microcontrollers like Arduino, ESP32, Raspberry Pi, and more.

Hardware Setup

Wiring Diagram:

Procedure: Step-by-Step Build Guide

Step 1: Gather Your Components

Arduino Uno
Laser Module (KY-008)
LDR Sensor (KY-018 or Keyes K853518)
10kΩ resistor
Passive Buzzer (FC-07)
Push Button
LCD 16x2 with I2C module
Breadboard
Jumper wires (male-to-male)
5V battery pack or USB power bank
USB cable (if using power bank)

Step 2: Power Setup

If using a USB power bank:

Plug the USB cable into the Arduino’s USB port.
This powers the Arduino and the 5V rail safely.

If using a 5V battery pack with open wires:

Connect Battery + (red) to Arduino 5V pin
Connect Battery – (black) to Arduino GND pin

On the breadboard, connect:

Arduino 5V → red power rail
Arduino GND → blue ground rail

Step 3: Wire the LCD (I2C 16x2)

LCD Pin	Connect To
VCC	Breadboard 5V
GND	Breadboard GND
SDA	Arduino A4
SCL	Arduino A5

Step 4: Wire the Laser Module (KY-008)

Laser Pin	Connect To
VCC	Breadboard 5V
GND	Breadboard GND
Signal	Arduino D9 (LASER_PIN)

Step 5: Wire the LDR + 10kΩ Resistor (Voltage Divider)

Place LDR across two breadboard rows.
Connect:

One LDR leg → Breadboard 5V rail
Other LDR leg → Arduino A0 (LDR_PIN) AND one end of a 10kΩ resistor.
Other end of the resistor → Breadboard GND rail

Step 6: Wire the Passive Buzzer (FC-07)

Buzzer Pin	Connect To
VCC	Breadboard 5V
GND	Breadboard GND
Signal	Arduino D8 (BUZZER_PIN)

Step 7: Wire the Push Button

Connect one leg of the push button → Arduino D6 (BUTTON_PIN)
Connect the other leg → Breadboard GND rail
(No need for an external resistor — INPUT_PULLUP is enabled in code.)

Step 8: Upload the Code

Open Arduino IDE.
Paste your provided sketch.
Make sure LiquidCrystal_I2C library is installed.
Connect Arduino to PC and upload the sketch.

Step 9: Test and Calibrate

Power up the system using your battery pack or USB power bank.
The LCD should display "System Ready".
Aim the laser beam directly at the LDR.
When the beam is blocked, the buzzer should sound, and LCD should say "INTRUDER ALERT".
Press the button to reset the system.

Step 10: Enclosure Building

· Drill holes and follow the initial plan for the enclosure use nonconductive adhesive to build the device with the enclosure provided.

Optional Tweaks

Adjust LDR_THRESHOLD if too sensitive or not triggering.

Software Setup

This is the Arduino sketch use for the project:

#include <Wire.h>

#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 16, 2);

// Pin definitions

#define LDR_PIN A0

#define LASER_PIN 9

#define BUZZER_PIN 8

#define BUTTON_PIN 7

#define LDR_THRESHOLD 600

#define DEBOUNCE_DELAY 50 // milliseconds

bool alertTriggered = false;

bool buttonPressed = false;

unsigned long lastDebounceTime = 0;

int lastButtonState = HIGH;

void setup() {

pinMode(LDR_PIN, INPUT);

pinMode(LASER_PIN, OUTPUT);

pinMode(BUZZER_PIN, OUTPUT);

pinMode(BUTTON_PIN, INPUT_PULLUP); // Internal pull-up

digitalWrite(LASER_PIN, HIGH); // Turn on laser

Serial.begin(9600);

lcd.init();

lcd.backlight();

lcd.setCursor(0, 0);

lcd.print("Laser Tripwire");

lcd.setCursor(0, 1);

lcd.print("System Ready");

delay(2000);

lcd.clear();

}

void loop() {

int ldrValue = analogRead(LDR_PIN);

int reading = digitalRead(BUTTON_PIN); // Current button state

Serial.print("LDR Value: ");

Serial.print(ldrValue);

Serial.print(" | Button: ");

Serial.println(reading == HIGH ? "PRESSED" : "NOT PRESSED");

// Debounce logic

if (reading != lastButtonState) {

lastDebounceTime = millis(); // reset debounce timer

}

//If button is press

if ((millis() - lastDebounceTime) > DEBOUNCE_DELAY) {

// if the button state has been stable for the debounce delay

if (reading == LOW && !buttonPressed) {

buttonPressed = true; // button press confirmed

if (alertTriggered) {

Serial.println("Button confirmed: RESET triggered!");

noTone(BUZZER_PIN);

alertTriggered = false;

lcd.clear();

lcd.setCursor(0, 0);

lcd.print("System Reset");

lcd.setCursor(0, 1);

lcd.print("Resuming...");

delay(2000);

lcd.clear();

}

if (reading == HIGH) {

buttonPressed = false; // ready for next press

}

lastButtonState = reading;

// Trigger alert if beam is broken

if (ldrValue < LDR_THRESHOLD && !alertTriggered) {

alertTriggered = true;

lcd.clear();

lcd.setCursor(0, 0);

lcd.print("!!! ALERT !!!");

lcd.setCursor(0, 1);

lcd.print("INTRUDER ALERT");

tone(BUZZER_PIN, 1000);

}

// Normal monitoring

if (!alertTriggered) {

lcd.setCursor(0, 0);

lcd.print("Monitoring... ");

lcd.setCursor(0, 1);

lcd.print("Beam Intact ");

}

delay(50); // Small delay for readability

}

Code Breakdown

Library Used:

#include <LiquidCrystal_I2C.h> - We used the LiquidCrystal I2C by Frank de Brabander

LDR (Light Dependent Resistor) Setup:

#define LDR_PIN A0
#define LDR_THRESHOLD 600

LDR_PIN A0: Reads the laser status through the LDR.
LDR_THRESHOLD 600: If the LDR value drops below this threshold, it means the laser beam is broken.

Laser Setup:

#define LASER_PIN 9

LASER_PIN 9: Activates the laser to form the tripwire.

Button Setup (for Reset):

#define BUTTON_PIN 7

BUTTON_PIN 7: Detects button press to reset the system after an alert.

Button Debounce Logic:

if ((millis() - lastDebounceTime) > DEBOUNCE_DELAY) {
if (reading == LOW && !buttonPressed) {
buttonPressed = true;
if (alertTriggered) {
noTone(BUZZER_PIN); // Stop buzzer
alertTriggered = false; // Reset alert

lcd.clear();
lcd.print("System Reset");
delay(2000); // Pause before resuming
lcd.clear();
}
}
}

Button Debounce: Ensures stable button press detection, and resets the alert when pressed.

Laser Beam Break (Intruder Detection):

if (ldrValue < LDR_THRESHOLD && !alertTriggered) {
alertTriggered = true;
tone(BUZZER_PIN, 1000); // Start buzzer
lcd.clear();
lcd.print("!!! ALERT !!!");
lcd.print("INTRUDER ALERT");
}

Intruder Detection: If the laser beam is broken, it triggers an alert by sounding the buzzer and showing the message on the LCD.

Normal Monitoring:

if (!alertTriggered) {
lcd.setCursor(0, 0);
lcd.print("Monitoring...");
lcd.print("Beam Intact");
}

Normal Monitoring: If no alert is triggered (beam intact), the system displays "Monitoring..." on the LCD.

Testing and Calibration

Test the device by triggering the laser module so that the LDR will trigger as well and the buzzer will turn on and pressed the button for resetting the device.
Adjust the code if necessary for compacting all the components in an enclosure box.

Final Adjustments

If the device is working properly, we can add the enclosure box for real-world deployment and for clean and tidy circuit and wire management.
Adjust LDR_THRESHOLD if too sensitive or not triggering

Optional Tweaks

Make a PCB out of it for permanent and neat wiring for stable device performance.

Video Demonstration

Conclusion

In conclusion, this Laser Tripwire Box project using the Arduino Uno, Laser Module, and OLED display offers a practical and interactive way to develop essential skills in microcontroller programming, sensor interfacing, and real-time alert systems. This project demonstrates how simple components like a laser and a light sensor can be combined with an OLED display to create an effective intrusion detection system. It provides valuable experience in building security-focused electronics, blending hardware and software to design a reliable and user-friendly solution. Through this project, you’ll enhance your problem-solving abilities, gain a deeper understanding of embedded systems, and explore practical applications in home security and monitoring—making it an ideal introduction to IoT and smart security solutions.

References

Arduino Uno Official Guide
Laser Module & Light Sensor Tutorials
OLED Display Integration with Arduino
Basic Security System Projects with Arduino

Authors (Capacitrio)

Mark A. Macahig
Knile Angelo B. Diez
Kent Lawrence M. Escobar

Tags: Arduino uno, Battery, Battery holder 14500 with knife/switch, Buzzer, I2c lcd, Intruder detection system, Laser module, Ldr, Push button, Relay

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Overview

Hardware Used

Software Use

Application Discussion

Pinout:

Pinout:

Pinout:

Pinout:

Hardware Setup

Software Setup

Code Breakdown

Library Used:

LDR (Light Dependent Resistor) Setup:

Laser Setup:

Button Setup (for Reset):

Button Debounce Logic:

Laser Beam Break (Intruder Detection):

Normal Monitoring:

Testing and Calibration

Final Adjustments

Optional Tweaks

Video Demonstration

Conclusion

References

Authors (Capacitrio)

Overview

Hardware Used

Software Use

Application Discussion

Pinout:

Pinout:

Pinout:

Pinout:

Hardware Setup

Software Setup

Code Breakdown

Library Used:

LDR (Light Dependent Resistor) Setup:

Laser Setup:

Button Setup (for Reset):

Button Debounce Logic:

Laser Beam Break (Intruder Detection):

Normal Monitoring:

Testing and Calibration

Final Adjustments

Optional Tweaks

Video Demonstration

Conclusion

References

Authors (Capacitrio)

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