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Guide for the 4-Pin LDR (Light Dependent Resistor) Module

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Ekostra Electronics

On April 5, 2025

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4-Pin Light-Dependent Photosensitive Sensor (LDR) Module

Ambient Light Detection for Arduino and DIY Electronics

Introduction

The 4-Pin LDR Module is a light-sensitive sensor that detects ambient light intensity using a photoresistor. This module provides both digital and analog outputs, making it ideal for automatic lighting systems, weather stations, and smart home applications.

Key Features

💡 Light Sensing

Detects visible light spectrum (400-700nm)

📊 Dual Output

Digital (TTL) and Analog signals

🎚️ Adjustable

Sensitivity potentiometer

🔌 Simple Interface

4-pin connection (VCC, GND, DO, AO)

Technical Specifications

Operating Voltage	3.3V – 5V DC
Resistance Range	200Ω (light) – 20MΩ (dark)
Response Time	≈20ms (rise), ≈30ms (fall)
Spectral Peak	540nm (green light)
Output Signals	Digital (TTL) + Analog
Dimensions	32mm × 14mm

Pin Configuration

Pin	Label	Description	Arduino Connection
1	VCC	Power (3.3V-5V)	5V
2	GND	Ground	GND
3	DO	Digital Output	Digital Pin
4	AO	Analog Output	Analog Pin

Note: The module includes a sensitivity adjustment potentiometer (clockwise increases sensitivity)

Wiring with Arduino

// Basic Connections:
// VCC → 5V
// GND → GND
// DO  → D2 (Digital Input)
// AO  → A0 (Analog Input)
 
// For best results, position sensor away from direct light sources

// Basic Connections:

// VCC → 5V

// GND → GND

// DO → D2 (Digital Input)

// AO → A0 (Analog Input)

// For best results, position sensor away from direct light sources

Important: Avoid exposing the LDR to strong light sources (>100,000 lux) for extended periods

Basic Digital Detection

// Digital Output Example
const int ldrDigital = 2;

void setup() {
  pinMode(ldrDigital, INPUT);
  Serial.begin(9600);
}

void loop() {
  if (digitalRead(ldrDigital) == LOW) {
    Serial.println("Bright light detected!");
    // Add your response code here
  }
  delay(100);
}

// Digital Output Example

const int ldrDigital = 2;

void setup() {

pinMode(ldrDigital, INPUT);

Serial.begin(9600);

}

void loop() {

if (digitalRead(ldrDigital) == LOW) {

Serial.println("Bright light detected!");

// Add your response code here

}

delay(100);

}

Analog Light Measurement

// Analog Output Example
const int ldrAnalog = A0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  int lightValue = analogRead(ldrAnalog);
  Serial.print("Light level: ");
  Serial.println(lightValue);
  
  if (lightValue < 300) {  // Adjust threshold as needed
    Serial.println("Dark environment detected");
  }
  delay(200);
}

// Analog Output Example

const int ldrAnalog = A0;

void setup() {

Serial.begin(9600);

}

void loop() {

int lightValue = analogRead(ldrAnalog);

Serial.print("Light level: ");

Serial.println(lightValue);

if (lightValue < 300) { // Adjust threshold as needed

Serial.println("Dark environment detected");

}

delay(200);

}

Advanced Applications

Auto-Calibration

// Automatic baseline calibration
int baseline = 0;

void calibrate() {
  for(int i=0; i<10; i++) {
    baseline += analogRead(A0);
    delay(100);
  }
  baseline /= 10;
  Serial.print("Calibrated baseline: ");
  Serial.println(baseline);
}

// Automatic baseline calibration

int baseline = 0;

void calibrate() {

for(int i=0; i<10; i++) {

baseline += analogRead(A0);

delay(100);

}

baseline /= 10;

Serial.print("Calibrated baseline: ");

Serial.println(baseline);

}

Lux Calculation

// Approximate lux calculation
float calculateLux(int rawValue) {
  // Calibration values needed for accuracy
  float voltage = rawValue * (5.0 / 1023.0);
  return pow(10, (voltage - 1.0) / 0.5); // Example conversion
}

// Approximate lux calculation

float calculateLux(int rawValue) {

// Calibration values needed for accuracy

float voltage = rawValue * (5.0 / 1023.0);

return pow(10, (voltage - 1.0) / 0.5); // Example conversion

}

Smart Lighting

// Automatic light control
void controlLED(int lightLevel) {
  if(lightLevel < 300) {
    digitalWrite(LED_PIN, HIGH);
  } else {
    digitalWrite(LED_PIN, LOW);
  }
}

// Automatic light control

void controlLED(int lightLevel) {

if(lightLevel < 300) {

digitalWrite(LED_PIN, HIGH);

} else {

digitalWrite(LED_PIN, LOW);

}

Data Logging

// Light level monitoring
void logLightLevel() {
  int light = analogRead(A0);
  Serial.print(millis()/1000);
  Serial.print(",");
  Serial.println(light);
  delay(60000); // Log every minute
}

// Light level monitoring

void logLightLevel() {

int light = analogRead(A0);

Serial.print(millis()/1000);

Serial.print(",");

Serial.println(light);

delay(60000); // Log every minute

}