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	×	Jumper Wires
1	×	(Optional) Solenoid Lock
1	×	(Optional) 12V Power Adapter
1	×	(Optional) DC Power Jack
1	×	(Optional) 9V Power Adapter for Arduino
1	×	(Recommended) Screw Terminal Block Shield for Arduino Uno
1	×	(Optional) Transparent Acrylic 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 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

This image is created 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

We are considering to make the video tutorials. If you think the video tutorials are essential, please subscribe to our YouTube channel to give us motivation for making the videos.

Door Sensor and Relay on Commercial Products

The Best Arduino Starter Kit

See the best Arduino kit for beginner