Feliz Navidad learners! Christmas is just around the corner. What better way to welcome our guests than a fine Christmas song? In this beginner friendly tutorial, I’ll teach you how I made an automated door greeting device using a magnetic reed switch, a digital speaker module, and an Arduino UNO.

What you’ll need:

Arduino UNO
Magnetic reed switch
Digital Speaker Module
2 LEDs
2 x 220? resistors
1 x 10k? resistor

Magnetic Reed Switches

For us to understand how magnetic reed switches work, we will follow this guide from randomnerdtutorials. First, using a breadboard, build the schematic diagram below.

Basically, what this circuit will do is it will light up the yellow LED when the reed switch is together and light up the red LED when it is separated. Upload the code below to see for yourself!

/*
  
 Created by Rui Santos
 
 All the resources for this project:
 Home

 
*/

int ledOpen=8;
int ledClose=10;
int switchReed=6;

void setup(){
  pinMode(ledOpen, OUTPUT);
  pinMode(ledClose, OUTPUT);
  pinMode(switchReed, INPUT);
  Serial.begin(9600);
}

void loop(){
  
  if (digitalRead(switchReed)==HIGH){
    digitalWrite(ledOpen, LOW);
    digitalWrite(ledClose, HIGH);
    Serial.println("Your Door is Closed");
  }
  else {
    digitalWrite(ledOpen, HIGH);
    digitalWrite(ledClose, LOW);
    Serial.println("Your Door is Open");
  }
  delay(1);
}

You can put your LED and reed switch pins on any GPIO pins on the Arduino. Just be sure to define them correctly in your own program.

Yellow LED lights up when reed switch is together.

Red LED lights up when reed switch is separated.

Now let’s add the digital speaker module into our switch mechanism. Just like the LEDs, you can insert the speaker into any GPIO pins you want, just indicate where you’ve put it in the program.

To test the speaker, copy the code below and upload it into your Arduino.

const int buzzer = 9;
void setup()
{
  pinMode(buzzer, OUTPUT); 
}
void loop()
{ 
  tone(buzzer, 1000); // Send 1KHz sound signal...
}

You should hear a constant 1kHz sound from the speaker. To test further, let’s send 1kHz signal pulses by adding a delay.

const int buzzer = 9; 
void setup()
{
  pinMode(buzzer, OUTPUT); 
}
void loop(){
  tone(buzzer, 1000); 
  delay(250);       
  noTone(buzzer);     
  delay(250);          
}

You’ll hear a sound akin to an alarm. Doesn’t this give you an idea on where we can use this? Congratulations! Yes, you’ve just made the simplest door alarm security system in history! Try attaching the whole system on your door.

Power Supply

Of course, to make this work you’ll need a small power bank or power supply of some sort. In my case, I made a rechargeable and current-adjustable power supply using a 18650 battery, a used TP4056 charging board and a MT3608 step up converter. I don’t advise doing this but if you, by chance, have this boards lying on a box somewhere, you’re most welcome to do this as well.

Making the Speakers Sing

To make the digital speaker play a tune, we’ll assign all the frequencies of all notes possible using this code:

#define NOTE_B0  31
#define NOTE_C1  33
#define NOTE_CS1 35
#define NOTE_D1  37
#define NOTE_DS1 39
#define NOTE_E1  41
#define NOTE_F1  44
#define NOTE_FS1 46
#define NOTE_G1  49
#define NOTE_GS1 52
#define NOTE_A1  55
#define NOTE_AS1 58
#define NOTE_B1  62
#define NOTE_C2  65
#define NOTE_CS2 69
#define NOTE_D2  73
#define NOTE_DS2 78
#define NOTE_E2  82
#define NOTE_F2  87
#define NOTE_FS2 93
#define NOTE_G2  98
#define NOTE_GS2 104
#define NOTE_A2  110
#define NOTE_AS2 117
#define NOTE_B2  123
#define NOTE_C3  131
#define NOTE_CS3 139
#define NOTE_D3  147
#define NOTE_DS3 156
#define NOTE_E3  165
#define NOTE_F3  175
#define NOTE_FS3 185
#define NOTE_G3  196
#define NOTE_GS3 208
#define NOTE_A3  220
#define NOTE_AS3 233
#define NOTE_B3  247
#define NOTE_C4  262
#define NOTE_CS4 277
#define NOTE_D4  294
#define NOTE_DS4 311
#define NOTE_E4  330
#define NOTE_F4  349
#define NOTE_FS4 370
#define NOTE_G4  392
#define NOTE_GS4 415
#define NOTE_A4  440
#define NOTE_AS4 466
#define NOTE_B4  494
#define NOTE_C5  523
#define NOTE_CS5 554
#define NOTE_D5  587
#define NOTE_DS5 622
#define NOTE_E5  659
#define NOTE_F5  698
#define NOTE_FS5 740
#define NOTE_G5  784
#define NOTE_GS5 831
#define NOTE_A5  880
#define NOTE_AS5 932
#define NOTE_B5  988
#define NOTE_C6  1047
#define NOTE_CS6 1109
#define NOTE_D6  1175
#define NOTE_DS6 1245
#define NOTE_E6  1319
#define NOTE_F6  1397
#define NOTE_FS6 1480
#define NOTE_G6  1568
#define NOTE_GS6 1661
#define NOTE_A6  1760
#define NOTE_AS6 1865
#define NOTE_B6  1976
#define NOTE_C7  2093
#define NOTE_CS7 2217
#define NOTE_D7  2349
#define NOTE_DS7 2489
#define NOTE_E7  2637
#define NOTE_F7  2794
#define NOTE_FS7 2960
#define NOTE_G7  3136
#define NOTE_GS7 3322
#define NOTE_A7  3520
#define NOTE_AS7 3729
#define NOTE_B7  3951
#define NOTE_C8  4186
#define NOTE_CS8 4435
#define NOTE_D8  4699
#define NOTE_DS8 4978

You can add that before your main program but in order to make everything a tad tidier, I followed this guide. Basically, I made my own header file “pitches.h” defining all this constants. Now all I have to do is call it in the program. With that, we’re all set up to compose our Christmas song. I choosed, “We Wish You a Merry Christmas”, because I feel it welcomes guests a little bit better then “I Saw Mommy Kissing Santa Claus”. I used this as a reference for the song.

Here’s the whole code for the main program:

#include "pitches.h"
int ledOpen = 11;
int ledClose = 13;
int switchReed = 9;
const int buzzer = 7; 

void setup() {
  pinMode(ledOpen, OUTPUT);
  pinMode(ledClose, OUTPUT);
  pinMode(switchReed, INPUT);
  pinMode(buzzer, OUTPUT); // Set buzzer - pin 9 as an output

  Serial.begin(9600);
}

void loop() {

  if (digitalRead(switchReed) == HIGH) {
    digitalWrite(ledOpen, LOW);
    digitalWrite(ledClose, HIGH);
  }
  else {
    digitalWrite(ledOpen, HIGH);
    digitalWrite(ledClose, LOW);
    int melody[] = {
      NOTE_C4,
      NOTE_F4, NOTE_F4, NOTE_G4, NOTE_F4, NOTE_E4,
      NOTE_D4, NOTE_D4, NOTE_D4,
      NOTE_G4, NOTE_G4, NOTE_A4, NOTE_G4, NOTE_F4,
      NOTE_E4, NOTE_E4, NOTE_E4,
      NOTE_A4, NOTE_A4, NOTE_B4, NOTE_A4, NOTE_G4,
      NOTE_F4, NOTE_D4, NOTE_C4, NOTE_C4,
      NOTE_D4, NOTE_G4, NOTE_E4,
      NOTE_F4
    };

    // note durations: 4 = quarter note, 8 = eighth note, etc.:
    int noteDurations[] = {
      4,
      4, 8, 8, 8, 8,
      4, 4, 4,
      4, 8, 8, 8, 8,
      4, 4, 4,
      4, 8, 8, 8, 8,
      4, 4, 8, 8,
      4, 4, 4,
      2
    };

    for (int thisNote = 0; thisNote < 30; thisNote++) {

      // to calculate the note duration, take one second divided by the note type.
      //e.g. quarter note = 1000 / 4, eighth note = 1000/8, etc.
      int noteDuration = 1000 / noteDurations[thisNote];
      tone(5, melody[thisNote], noteDuration);

      // to distinguish the notes, set a minimum time between them.
      // the note's duration + 30% seems to work well:
      int pauseBetweenNotes = noteDuration * 1.30;
      delay(pauseBetweenNotes);
      // stop the tone playing:
      noTone(5);
    }
  }
}

That’s it! Only thing left to do is preparing how to answer your guests asking how this device wplays a christmas song every time they come in. Again, stay tuned on Learn for fun projects like this. I did an analysis on the basic arduino schematic diagram previously, you might want to check it out. Merry Christmas, and keep creating!

What you’ll need:

Magnetic Reed Switches

Power Supply

Making the Speakers Sing

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