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

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Ekostra Electronics

April 11, 2025

On April 5, 2025

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

}

Troubleshooting

No Response to Light

Adjust sensitivity potentiometer clockwise
Check wiring connections
Verify sufficient light source

Constant Trigger

Reduce sensitivity (turn CCW)
Check for ambient light interference
Increase detection threshold in code

Inconsistent Readings

Ensure stable power supply
Check for loose connections
Implement software smoothing

Hotline 24/7

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

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

Introduction

Key Features

💡 Light Sensing

📊 Dual Output

🎚️ Adjustable

🔌 Simple Interface

Technical Specifications

Pin Configuration

Wiring with Arduino

Basic Digital Detection

Analog Light Measurement

Advanced Applications

Auto-Calibration

Lux Calculation

Smart Lighting

Data Logging

Troubleshooting

No Response to Light

Constant Trigger

Inconsistent Readings

Project Ideas

Automatic Night Light

Weather Station

Smart Blinds

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Hotline 24/7

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

Introduction

Key Features

💡 Light Sensing

📊 Dual Output

🎚️ Adjustable

🔌 Simple Interface

Technical Specifications

Pin Configuration

Wiring with Arduino

Basic Digital Detection

Analog Light Measurement

Advanced Applications

Auto-Calibration

Lux Calculation

Smart Lighting

Data Logging

Troubleshooting

No Response to Light

Constant Trigger

Inconsistent Readings

Project Ideas

Automatic Night Light

Weather Station

Smart Blinds

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