Arduino Nano - Light Sensor Relay

This tutorial instructs you how to use Arduino Nano and light sensor to trigger relay. In detail:

Arduino Nano activates the relay if the analog value of the light sensor is less than a certain threshold.
Arduino Nano deactivates the relay if the analog value of the light sensor is greater than a certain threshold.

By connecting a relay to a light bulb, LED strip, motor or actuator, we can use the Arduino Nano and light sensor to manage the operation of the light bulb, LED strip, motor or actuator.

The light sensor is also known as photoresistor, light-dependent resistor, photocell, LDR. The Arduino Nano utilizes a light sensor to measure the ambient light level, and it activates the relay when it's dark, and deactivates it when it's bright.

Hardware Preparation

1	×	Arduino Nano
1	×	USB A to Mini-B USB cable
1	×	Light Sensor
1	×	10 kΩ resistor
1	×	Relay
1	×	Warning Light Bright Waterproof
1	×	12V Power Adapter
1	×	DC Power Jack
1	×	Breadboard
1	×	Jumper Wires
1	×	(Recommended) Screw Terminal Expansion Board for Arduino Nano
1	×	(Recommended) Breakout Expansion Board for Arduino Nano
1	×	(Recommended) Power Splitter For Arduino Nano

Or you can buy the following sensor kits:

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

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Additionally, some of these links are for products from our own brand, DIYables.

Overview of Relay and Light Sensor

If you are unfamiliar with relay and light sensor (including pinout, how it works, and programming), the following tutorials can help:

Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Arduino Nano Code

/* * 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-light-sensor-relay */ const int LIGHT_SENSOR_PIN = A0; // The Arduino Nano pin connected to light sensor's pin const int RELAY_PIN = 2; // The Arduino Nano pin connected to Relay's pin const int ANALOG_THRESHOLD = 500; int analog_value; void setup() { pinMode(RELAY_PIN, OUTPUT); // set arduino pin to output mode } void loop() { analog_value = analogRead(LIGHT_SENSOR_PIN); // read the input on analog pin if(analog_value < ANALOG_THRESHOLD) digitalWrite(RELAY_PIN, HIGH); // turn on Relay else digitalWrite(RELAY_PIN, LOW); // turn off Relay }

Detailed Instructions

Plug the USB cable into both the Arduino Nano and the PC.
Launch the Arduino IDE, choose the correct board and port.
Copy the code and open it in the Arduino IDE.
Click the Upload button in the Arduino IDE to compile and upload the code to the Arduino Nano.

Emit light source towards the sensor
Check out the alteration in the relay's status

Code Explanation

Check out the line-by-line explanation contained in the comments of the source code!

Video Tutorial

Learn More

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