SENSORS/ACTUATORS

INTERNET OF THING (IoT)

ESP32 - LDR Module

The LDR light sensor module can sense and measure light around it. It has two outputs: a digital output that can be either LOW or HIGH, and an analog output.

In this tutorial, we will learn how to use an ESP32 and an LDR light sensor module together to detect and measure the amount of light. Here's what we'll cover:

How to connect the LDR light sensor module to an ESP32.
How to program the ESP32 to detect light by reading the digital signal from the LDR light sensor module.
How to program the ESP32 to measure the light level by reading the analog signal from the LDR light sensor module.

image source: diyables.io

Afterward, you can change the code to make an LED or a light bulb turn on (using a relay) when it senses light.

If you're interested in a light sensor in its raw form, I suggest exploring the tutorial for the ESP32 - Light Sensor.

Hardware Used In This Tutorial

1	×	ESP-WROOM-32 Dev Module
1	×	USB Cable Type-C
1	×	LDR Light Sensor Module
1	×	Breadboard
1	×	Jumper Wires
1	×	(Recommended) Screw Terminal Expansion Board for ESP32

Or you can buy the following sensor kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

Disclosure: some of these links are affiliate links. We may earn a commission on your purchase at no extra cost to you. We appreciate it.

Introduction to LDR Light Sensor Module

The LDR light sensor module can be used to find out if there is light or how much light there is in the area around it. It has a digital output pin and an analog output pin for different options.

Pinout

The LDR light sensor module has four pins:

VCC pin: Connect this pin to the power source (between 3.3V to 5V).
GND pin: Connect this pin to the ground (0V).
DO pin: This is a digital output pin. It gives a HIGH signal when it's dark and LOW when it's light. You can adjust the threshold between dark and light using a built-in potentiometer.
AO pin: This is an analog output pin. The value decreases as the light gets brighter and increases as the light gets darker.

image source: diyables.io

Additionally, the LDR light sensor module is equipped with two LED indicators:

The PWR-LED indicator shows the power status.
The DO-LED indicator reflects the state of light on the DO pin: it illuminates when there is light and remains off when it is dark.

How It Works

Regarding the DO pin:

The LDR light sensor module has a potentiometer that allows you to adjust the sensitivity or threshold for detecting light.
When the light intensity in the surrounding environment is above the set threshold (considered as light), the output of the sensor on the DO pin becomes LOW, and the DO-LED turns on.
When the light intensity in the surrounding environment is below the set threshold (considered as dark), the output of the sensor on the DO pin becomes HIGH, and the DO-LED turns off.

Regarding the AO pin:

The value read from the AO pin is inversely proportional to the light intensity in the surrounding environment. In other words, as the light intensity increases (brighter), the value on the AO pin decreases.
Similarly, as the light intensity decreases (darker), the value on the AO pin increases.

It's important to note that adjusting the potentiometer does not affect the value on the AO pin.

Wiring Diagram

The light sensor module offers two outputs, DO and AO, which can be used individually or together.

How to connect ESP32 and ldr module using breadboard

ESP32 LDR Light Sensor Module wiring diagram

This image is created using Fritzing. Click to enlarge image

How to connect ESP32 and ldr module using screw terminal block breakout board

If you're unfamiliar with how to supply power to the ESP32 and other components, you can find guidance in the following tutorial: How to Power ESP32.

ESP32 Code - Read value from DO pin

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-ldr-module */ #define DO_PIN 13 // ESP32's pin GPIO13 connected to DO pin of the ldr module void setup() { // initialize serial communication Serial.begin(9600); // initialize the ESP32's pin as an input pinMode(DO_PIN, INPUT); } void loop() { int lightState = digitalRead(DO_PIN); if (lightState == HIGH) Serial.println("It is dark"); else Serial.println("It is light"); }

Quick Instructions

If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
Do the wiring as above image.
Connect the ESP32 board to your PC via a micro USB cable
Open Arduino IDE on your PC.
Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
Copy the above code and open with Arduino IDE
Click Upload button on Arduino IDE to upload code to ESP32
Cover and uncover the LDR light sensor module by your hand or something
See the result on Serial Monitor.

COM6

Send

It is light It is light It is dark It is dark It is dark It is light It is light It is light

Autoscroll Show timestamp

Clear output

9600 baud

Newline

If you observe that the LED status remains constantly on or off, regardless of the presence of light, you have the option to adjust the potentiometer. This adjustment allows you to finely tune the light sensitivity of the sensor.

Furthermore, the code can be modified according to your requirements. For instance, you can program the LED to activate or the light to turn on when light is detected. Additionally, you have the flexibility to make a servo motor rotate. Detailed instructions and tutorials on these customization options can be found at the end of this guide.

ESP32 Code - Read value from AO pin

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-ldr-module */ #define AO_PIN 36 // ESP32's pin GPIO36 connected to AO pin of the ldr module void setup() { // initialize serial communication Serial.begin(9600); // set the ADC attenuation to 11 dB (up to ~3.3V input) analogSetAttenuation(ADC_11db); } void loop() { int lightValue = analogRead(AO_PIN); Serial.print("The AO value: "); Serial.println(lightValue); }

Quick Instructions

Copy the above code and open with Arduino IDE
Click Upload button on Arduino IDE to upload code to ESP32
Cover and uncover the LDR light sensor module by your hand or something
See the result on Serial Monitor.

COM6

Send

The AO value: 145 The AO value: 146 The AO value: 146 The AO value: 572 The AO value: 1678 The AO value: 1945 The AO value: 2956 The AO value: 3001 The AO value: 3098 The AO value: 4005 The AO value: 4005 The AO value: 1645 The AO value: 1546 The AO value: 346 The AO value: 172

Autoscroll Show timestamp

Clear output

9600 baud

Newline

※ NOTE THAT:

This tutorial uses the analogRead() function to read values from an ADC (Analog-to-Digital Converter) connected to a LDR module. The ESP32 ADC is good for projects that do NOT need high accuracy. However, for projects that need precise measurements, please note:

The ESP32 ADC is not perfectly accurate and might need calibration for correct results. Each ESP32 board can be a bit different, so you need to calibrate the ADC for each individual board.
Calibration can be difficult, especially for beginners, and might not always give the exact results you want.

For projects that need high precision, consider using an external ADC (e.g ADS1115) with the ESP32 or using an Arduino, which has a more reliable ADC. If you still want to calibrate the ESP32 ADC, refer to ESP32 ADC Calibration Driver

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Function References

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