Arduino - Door Sensor Toggle LED

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

Hardware Required

1	×	Arduino Uno
1	×	USB 2.0 cable type A/B
1	×	Door Sensor
1	×	LED
1	×	220 ohm resistor
1	×	Breadboard
1	×	Jumper Wires
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 LED and Door Sensor

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

Wiring Diagram

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Arduino Code - Door Sensor Toggles LED

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-door-sensor-toggle-led */ // constants won't change const int DOOR_SENSOR_PIN = 9; // Arduino pin connected to door sensor's pin const int LED_PIN = 3; // Arduino pin connected to LED's pin // variables will change: int ledState = LOW; // the current state of LED 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(LED_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 LED ledState = !ledState; // control LED arccoding to the toggled state digitalWrite(LED_PIN, ledState); } }

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 LED's state

Code Explanation

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

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

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

Video Tutorial

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