Arduino - Motion Sensor - Relay

We are going to learn how to:

By connecting relay to light bulb, led strip, motor or actuator... We can use the motion 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×HC-SR501 Motion Sensor
1×Relay
1×Jumper Wires
1×(Optional) Solenoid Lock
1×(Optional) 12V Power Adapter
1×(Optional) DC Power Jack
1×(Recommended) Screw Terminal Block Shield for Arduino Uno
1×(Recommended) Breadboard Shield For Arduino Uno
1×(Recommended) Enclosure For Arduino Uno

Or you can buy the following sensor kits:

1×DIYables Sensor Kit (30 sensors/displays)
1×DIYables Sensor Kit (18 sensors/displays)
Please note: These are Amazon affiliate links. If you buy the components through these links, We will get a commission at no extra cost to you. We appreciate it.

About Relay and Motion Sensor

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

Wiring Diagram

Arduino Motion Sensor Relay Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Initial Setting

Time Delay AdjusterScrew it in anti-clockwise direction fully.
Detection Range AdjusterScrew it in clockwise direction fully.
Repeat Trigger SelectorPut jumper as shown on the image.
arduino motion sensor initial setting

Arduino Code

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-motion-sensor-relay */ const int MOTION_SENSOR_PIN = 7; // Arduino pin connected to the OUTPUT pin of motion sensor const int RELAY_PIN = A5; // Arduino pin connected to the IN pin of relay int motionStateCurrent = LOW; // current state of motion sensor's pin int motionStatePrevious = LOW; // previous state of motion sensor's pin void setup() { Serial.begin(9600); // initialize serial pinMode(MOTION_SENSOR_PIN, INPUT); // set arduino pin to input mode pinMode(RELAY_PIN, OUTPUT); // set arduino pin to output mode } void loop() { motionStatePrevious = motionStateCurrent; // store old state motionStateCurrent = digitalRead(MOTION_SENSOR_PIN); // read new state if (motionStatePrevious == LOW && motionStateCurrent == HIGH) { // pin state change: LOW -> HIGH Serial.println("Motion detected!"); digitalWrite(RELAY_PIN, HIGH); // turn on } else if (motionStatePrevious == HIGH && motionStateCurrent == LOW) { // pin state change: HIGH -> LOW Serial.println("Motion stopped!"); digitalWrite(RELAY_PIN, LOW); // turn off } }

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
  • Move your hand in front of 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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