LDR (Light Sensor) with ESP32 DOIT DevKit v1 – Step-by-Step Tutorial

Introduction

An LDR (Light Dependent Resistor) is a sensor that changes its resistance based on light intensity:

• In bright light, its resistance is low (more current flows).
• In darkness, its resistance is high (less current flows).

By connecting the LDR to an analog input pin of ESP32, we can measure the light intensity and use it in IoT projects. In this tutorial, we’ll connect the LDR to GPIO 35 of ESP32 DOIT DevKit v1 and display the sensor values in the Serial Monitor.

Components Required

• ESP32 DOIT DevKit v1
• LDR sensor
• 10kΩ resistor (for voltage divider)
• Breadboard and jumper wires
• USB cable

Circuit Diagram

• One end of LDR → 3.3V
• Other end of LDR → GPIO 35
• Also connect 10kΩ resistor between GPIO 35 and GND

⚠️ This forms a voltage divider circuit, allowing ESP32 to read varying light levels as an analog value.

Arduino Coe

// LDR with ESP32 DOIT DevKit v1
// LDR connected to GPIO 35

int ldrPin = 35;   // LDR connected to ADC pin
int ldrValue = 0;  // Variable to store LDR reading

void setup() {
  Serial.begin(115200);  // Start Serial Monitor
}

void loop() {
  ldrValue = analogRead(ldrPin); // Read LDR value (0-4095)
  Serial.print("LDR Value: ");
  Serial.println(ldrValue);
  delay(500); // Small delay for stability
}

Step-by-Step Code Explanation

Define Variables

int ldrPin = 35;
int ldrValue = 0;

• Assign GPIO 35 for LDR input.
• Create variable ldrValue to store sensor readings.

Setup Serial Monitor

Serial.begin(115200);

Starts serial communication to display sensor values.

Loop Function

ldrValue = analogRead(ldrPin);
Serial.print("LDR Value: ");
Serial.println(ldrValue);

• Reads LDR analog value (range: 0–4095 on ESP32).
• Prints it to the Serial Monitor.
• Higher value = more light, lower value = less light.

Output

• Open the Serial Monitor (115200 baud rate).
• Cover the LDR → Values decrease (darkness).
• Shine a light → Values increase (brightness).

Real-Life Applications

• Automatic Street Lights – turn ON in darkness, OFF in daylight.
• Smart Home Systems – adjust lighting based on room brightness.
• Solar Tracking Systems – detect sunlight intensity for solar panels.
• Energy Saving Devices – dim/brighten lights automatically.

Troubleshooting

Problem	Cause	Solution
Constant value (no change)	Wrong wiring	Check LDR + resistor connections
Values always HIGH	No voltage divider	Ensure 10kΩ resistor connected to GND
Flickering values	Noise in sensor	Add small capacitor (0.1µF) across LDR & resistor
Serial Monitor not showing	Wrong baud rate	Use 115200 baud in Arduino IDE