Arduino - Door Sensor Toggle Relay

In a previous tutorial , We have learned how to turn on the relay if the door is open, and turn off relay if the door is closed. In this tutorial, We are going to learn how to toggle relay each time door is closed.

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

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×Door Sensor
1×Relay
1×Warning Light Bright Waterproof
1×12V Power Adapter
n×Jumper Wires
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About Relay and Door Sensor

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

Wiring Diagram

Arduino Door Sensor Relay Wiring Diagram

Image is developed using Fritzing. Click to enlarge image

Arduino Code - Door Sensor Toggles Relay

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-door-sensor-toggle-relay */ // constants won't change const int DOOR_SENSOR_PIN = 13; // Arduino pin connected to door sensor's pin const int RELAY_PIN = 3; // Arduino pin connected to relay's pin // variables will change: int relayState = LOW; // the current state of relay int lastDoorState; // the previous state of door sensor int currentDoorState; // the current state of door sensor void setup() { Serial.begin(9600); // initialize serial pinMode(DOOR_SENSOR_PIN, INPUT_PULLUP); // set arduino pin to input pull-up mode pinMode(RELAY_PIN, OUTPUT); // set arduino pin to output mode currentDoorState = digitalRead(DOOR_SENSOR_PIN); } void loop() { lastDoorState = currentDoorState; // save the last state currentDoorState = digitalRead(DOOR_SENSOR_PIN); // read new state if (lastDoorState == HIGH && currentDoorState == LOW) { // state change: HIGH -> LOW Serial.println("The door-closing event is detected"); // toggle state of relay relayState = !relayState; // control relay arccoding to the toggled state digitalWrite(RELAY_PIN, relayState); } }

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
  • Move the magnet close to the reed switch and them move it far from the reed switch. Repeat this several times
  • See the change of relay's state

Code Explanation

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

In the code, relayState = !relayState is equivalent to the following code:

if(relayState == LOW) relayState = HIGH; else relayState = LOW;

Video Tutorial

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Door Sensor and Relay on Commercial Products

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