Laser Light Alarm Circuit using Arduino

This article is for simple Laser Light Alarm Circuit using Arduino.

A laser light shines on an LDR.

When someone blocks the laser beam, the LDR changes its value.

Arduino reads this change and turns ON the buzzer to make alarm sound.

A reset button stops the alarm.

The system is low cost and easy to build.

Good for home, school labs and small projects.

Arduino Coding:

/* Laser Security System with Laser Control */

int ldrPin = A0;
int buzzerPin = 8;
int resetPin = 7;
int laserPin = 9; // new laser control pin

int threshold = 500;
int alarmState = 0;

void setup() {
pinMode(buzzerPin, OUTPUT);
pinMode(resetPin, INPUT_PULLUP);
pinMode(laserPin, OUTPUT); // set laser pin as output

digitalWrite(laserPin, HIGH); // turn laser ON
}

void loop() {
int sensorValue = analogRead(ldrPin);

if(sensorValue > threshold) {
alarmState = 1;
}

if(digitalRead(resetPin) == LOW) {
alarmState = 0;
}

if(alarmState == 1) {
digitalWrite(buzzerPin, HIGH);
} else {
digitalWrite(buzzerPin, LOW);
}

delay(50);
}

Coding Explanation:

• ldrPin reads LDR voltage.
• buzzerPin controls buzzer.
• resetPin reads button.
• threshold sets when alarm should start.
• When LDR value goes above threshold the alarmState becomes 1.
• Button pull up means pressing button gives LOW.
• When pressed alarmState becomes 0.
• If alarmState is 1 then buzzer turns ON.
• If not then buzzer turns OFF.
• Delay makes reading stable.

Circuit Working:

Parts List:

Laser module gives one straight beam to the LDR.

When light hits LDR, its resistance becomes low.

When beam breaks then LDR resistance becomes very high.

LDR and 10k resistor make simple voltage divider.

Arduino reads this voltage on analog pin.

If voltage goes high above set value then it means laser is blocked.

Then Arduino turns ON buzzer pin and alarm starts.

Reset button goes to one digital pin of Arduino.

When button is pressed then Arduino stops buzzer and clears alarm state.

Formula:

Below is the Voltage divider formula:

Vout = Vin * (R2 / (R1 + R2))

where,

• Vout means output voltage.
• Vin means input voltage.
• R1 means LDR.
• R2 means 10k fixed resistor.

How to Build:

To build a Laser Light Alarm Circuit using Arduino follow the below steps for connection:

• Collect all parts same like in circuit picture.
• Put LDR R1 in series with 10k resistor R2.
• One side of LDR goes to 5V.
• Other side of LDR goes to A0 pin.
• This same point also connects to one side of 10k resistor.
• Other side of 10k resistor goes to GND.
• Laser module VCC goes to 5V.
• Laser module GND goes to GND.
• Buzzer positive goes to pin 8 of Arduino.
• Buzzer negative goes to GND.
• Reset button one side goes to pin 7.
• Other side of button goes to GND.
• Arduino 5V and GND go to breadboard power rails.
• All parts must share same ground.

Conclusion:

This project for Laser Light Alarm Circuit using Arduino is simple for beginners.

It uses few cheap parts.

Laser and LDR make effective tripwire.

Arduino controls alarm easily.

This circuit is good for learning sensors, inputs and outputs.

Can be improved with more sensors or wireless alert.

References:

Laser Security Alarm System Problem