Arduino Sensor–Actuator Integration

LDR Sensor with LED and Buzzer Outputs

This project implements a real-time sensor–actuator system using an LDR (Light Dependent Resistor) as the analog input sensor and two actuators: an LED and a buzzer. The system reads light intensity values through the LDR and activates the actuators based on predefined threshold levels.
This work demonstrates analog sensing, threshold-based decision making, and hardware interfacing on the Arduino platform.

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🔧 Components Used

• Arduino UNO
• LDR (Light Dependent Resistor)
• 10kΩ resistor (for voltage divider)
• LED + 220Ω resistor
• Active Buzzer
• Jumper wires
• Breadboard

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📡 Working Principle

The LDR forms a voltage divider whose output voltage varies with the surrounding light intensity.
The Arduino reads this analog value from pin A0 and performs the following logic:

• If LDR < 350 → LED turns ON
• If LDR < 450 → Buzzer turns ON
• Otherwise, both actuators remain OFF

Two separate thresholds are used to demonstrate multi-actuator control based on sensor intensity levels.

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Hardware Setup

🛠 Circuit Connections

LDR Sensor:

• LDR → 5V
• LDR → A0
• 10k resistor → A0 to GND

LED Actuator:

• Long leg → Digital Pin 8
• Short leg → GND via 220Ω resistor

Buzzer Actuator:

• Positive (+) → Digital Pin 9
• Negative (–) → GND

A Tinkercad schematic and real circuit image are included in the /images folder.

## Demo Video

Watch the project demo here

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💻 Arduino Code

int ldrPin = A0;
int ledPin = 8;
int buzzerPin = 9;

// PERFECT thresholds for your LDR values:
int thresholdOn  = 380;  // touching
int thresholdOff = 550;  // hand away

bool state = false;

void setup() {
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
}

void loop() {
  // Smooth values
  int v1 = analogRead(ldrPin);
  delay(3);
  int v2 = analogRead(ldrPin);
  delay(3);
  int v3 = analogRead(ldrPin);
  int value = (v1 + v2 + v3) / 3;

  Serial.println(value);

  // Hysteresis logic
  if (!state && value < thresholdOn) {
    state = true;   
  }
  else if (state && value > thresholdOff) {
    state = false;  
  }

  // LED
  digitalWrite(ledPin, state ? HIGH : LOW);

  // Buzzer
  if (state) tone(buzzerPin, 1000);
  else noTone(buzzerPin);

  delay(100);
}