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...

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×Light Sensor
1×10 kΩ resistor
1×Relay
1×Warning Light Bright Waterproof
1×12V Power Adapter
1×Breadboard
n×Jumper Wires
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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

Image is developed using Fritzing. Click to enlarge image

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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Light Sensor and Relay on Commercial Products

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