Arduino - Light Sensor Triggers Relay

We are going to learn how to:

By connecting relay to light bulb, led strip, motor or actuator... We can use the light sensor to control light bulb, led strip, motor or actuator...

About Relay and Light Sensor

If you do not know about relay and light sensor (pinout, how it works, how to program ...), learn about them in the following tutorials:

Wiring Diagram

Arduino Light Sensor Relay Light Bulb Wiring Diagram

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Arduino Code

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-light-sensor-triggers-relay */ // constants won't change const int LIGHT_SENSOR_PIN = A0; // Arduino pin connected to light sensor's pin const int RELAY_PIN = 3; // Arduino pin connected to Relay's pin const int ANALOG_THRESHOLD = 500; // variables will change: int analogValue; void setup() { pinMode(RELAY_PIN, OUTPUT); // set arduino pin to output mode } void loop() { analogValue = analogRead(LIGHT_SENSOR_PIN); // read the input on analog pin if(analogValue < ANALOG_THRESHOLD) digitalWrite(RELAY_PIN, HIGH); // turn on Relay else digitalWrite(RELAY_PIN, LOW); // turn off Relay }

Quick Steps

  • Connect Arduino to PC via USB cable
  • Open Arduino IDE, select the right board and port
  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to Arduino
Arduino IDE Upload Code
  • Radiates light to sensor
  • See the change of relay's state

Code Explanation

Read the line-by-line explanation in comment lines of source code!

Video Tutorial

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