SENSORS/ACTUATORS

Arduino Nano - LDR Module

The LDR light sensor module can sense and measure the light in its surroundings. It has two outputs: one is a digital output that can be either low or high, and the other is an analog output.

This tutorial instructs you how to use an Arduino Nano and an LDR light sensor module to detect and measure the amount of light. We will cover the following:

Connecting the LDR light sensor module to an Arduino Nano.
Programming the Arduino Nano to detect light by reading the digital signal from the LDR light sensor module.
Programming the Arduino Nano to measure the light level by reading the analog signal from the LDR light sensor module.

image source: diyables.io

Later on, you can change the code so that when the light is detected, it can turn on an LED or a light bulb by using a relay.

If you prefer a light sensor in its raw form, I suggest exploring the tutorial on the Arduino Nano - Light Sensor.

Hardware Preparation

1	×	Arduino Nano
1	×	USB A to Mini-B USB cable
1	×	LDR Light Sensor Module
1	×	Jumper Wires
1	×	(Optional) 9V Power Adapter for Arduino Nano
1	×	(Recommended) Screw Terminal Adapter for Arduino Nano

Or you can buy the following sensor kit:

DIYables Sensor Kit 30 types, 69 units

Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you. We appreciate your support.

Overview of LDR Light Sensor Module

The LDR light sensor module can be used to find out if there is light or measure how much light is present in the surrounding area. It offers two choices through a digital output pin and an analog output pin.

Pinout

The LDR light sensor module has four pins with specific functions:

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

image source: diyables.io

Additionally, the LDR light sensor module includes two LED indicators:

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

How It Works

Regarding the DO pin:

The module comes with a built-in potentiometer that allows you to adjust the sensitivity or light threshold.
When the light intensity in the surroundings is higher than the threshold value (considered as light), the sensor's output pin becomes LOW, and the DO-LED turns on.
When the light intensity in the surroundings is lower than the threshold value (considered as dark), the sensor's output pin becomes HIGH, and the DO-LED turns off.

Regarding the AO pin:

The value read from the AO pin decreases as the light intensity in the surroundings increases (more light).
The value read from the AO pin increases as the light intensity in the surroundings decreases (less light).

Note that adjusting the potentiometer does not affect the value read from the AO pin.

Wiring Diagram

Since the light sensor module has two outputs, you can choose to use one or both of them, depending on what you need.

The wiring diagram between Arduino Nano and the LDR light sensor module when using DO only.

The wiring diagram between Arduino Nano and LDR Light Sensor Module

This image is created using Fritzing. Click to enlarge image

The wiring diagram between Arduino Nano and the LDR light sensor module when using AO only.

The wiring diagram between Arduino Nano and LDR Module

This image is created using Fritzing. Click to enlarge image

The wiring diagram between Arduino Nano and the LDR light sensor module when using both AO an DO.

The wiring diagram between Arduino Nano and Light Sensor Module

This image is created using Fritzing. Click to enlarge image

Arduino Nano Code - Read value from DO pin

/* * This Arduino Nano code was developed by newbiely.com * * This Arduino Nano code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-nano/arduino-nano-ldr-module */ #define DO_PIN 2 // Arduino Nano's pin connected to DO pin of the ldr module void setup() { // Initialize the Serial to communicate with the Serial Monitor. Serial.begin(9600); // initialize the Arduino Nano's pin as an input pinMode(DO_PIN, INPUT); } void loop() { int light_state = digitalRead(DO_PIN); if (light_state == HIGH) Serial.println("The light is NOT present"); else Serial.println("The light is present"); }

Detailed Instructions

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

COM6

Send

The light is present The light is present The light is NOT present The light is NOT present The light is NOT present The light is present The light is present The light is present

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, it is possible to customize the code to activate an LED or a light when light is detected. Alternatively, you can make a servo motor rotate. For detailed instructions and additional information, please refer to the tutorials provided at the end of this guide.

Arduino Nano Code - Read value from AO pin

/* * This Arduino Nano code was developed by newbiely.com * * This Arduino Nano code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-nano/arduino-nano-ldr-module */ #define AO_PIN A0 // Arduino Nano's pin connected to AO pin of the ldr module void setup() { // Initialize the Serial to communicate with the Serial Monitor. Serial.begin(9600); } void loop() { int light_value = analogRead(AO_PIN); Serial.print("AO value: "); Serial.println(light_value); }

Detailed Instructions

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

COM6

Send

AO value: 145 AO value: 146 AO value: 146 AO value: 572 AO value: 678 AO value: 945 AO value: 956 AO value: 1001 AO value: 1002 AO value: 1012 AO value: 1013 AO value: 645 AO value: 546 AO value: 346 AO value: 172

Autoscroll Show timestamp

Clear output

9600 baud

Newline

Video Tutorial

Function References

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