Introduction

A reed switch is an electrical switch that when exposed to a magnetic field, closes a circuit and allows the flow of current. 

In this guide, you will learn how to use a reed switch with an Arduino to turn an LED on and off. 

After mastering this basic concept, you will be able to use reed switches in more advanced Arduino projects!
    • Insert your Reed Switch into Breadboard so that the header pins are facing your Arduin

    • This module is quite delicate - so be careful when handling it!

    • Connect Arduino Digital 11 to Reed Switch.

    • Connect Arduino GND to the 'S' of the Reed Switch.

    • The Reed Switch is not polarised so you could switch around the '–' and 'S' jumper wires.

  1. const int reed_pin = 11; // Pin connected to reed switch
    const int led_pin = 13; // LED pin - active-high
    
    void setup()
    {
      Serial.begin(9600);
      pinMode(reed_pin, INPUT_PULLUP);
      pinMode(led_pin, OUTPUT);
    }
    
    void loop()
    {
      int proximity = digitalRead(reed_pin); // Read the state of the switch
      if (proximity == LOW) // If the pin reads low, the switch is closed.
      {
        Serial.println("Switch closed");
        digitalWrite(led_pin, HIGH); // Turn the LED on as magnet passes
      }
      else
      {
        digitalWrite(led_pin, LOW); // Turn the LED off
      }
    }
    • Copy this code to your Arduino IDE.

    • Upload it to your Arduino.

    • Open the Serial Monitor.

    • As you pass a magnet by the glass tube - the circuit will close and the LED on your Arduino should turn on.

    • The normal state of a Reed switch is closed.