The Crypt of Vital Breath

This challenge has been solved in the framework of the Arduino Days 2025 organised in Benin.

Project Overview

You step cautiously into an ancient crypt, where the air is heavy and laden with an eerie silence. Before you, a stone altar covered with forgotten symbols. In the center lies a mysterious artifact that seems to be asleep: a small crystal connected to a strange sound box. You approach it and read the inscription engraved on the stone: “Only the breath of the stars will reveal the melody.” Suddenly, a faint glow emanates from the crystal. It's an ancient sensor, designed to react to ambient temperature. But the burning air of the crypt has sealed it in a state of dormancy. You understand then: if you can cool the artifact by blowing on it, it will reveal its sacred song...

How it works :

How the challenge works

• The DHT11 sensor measures temperature continuously.
• If Temperature < 22°C → The system detects the abnormality.
• The buzzer activates to play the "Frère Jacques ” melody to indicate that the challenge has been solved.
• If the temperature is high, nothing happens.

Bonus operation

• Limited Time Mode: The temperature must drop below 22°C in less than 30 seconds, otherwise the crypt closes and the melody is lost!
• Mystic Sound Mode: Adds a second, hidden melody that can only be played at 20°C or below.
• Ancient Clues Mode: Displays live temperature on the serial monitor to help adventurers adjust their breath.
• Reverse Mode: The Sacred Flame Test: Modifies the code to detect a high temperature (e.g. rubbing the sensor with your fingers to raise it to 30°C and trigger another melody).

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Hardware List

Component	Model	Quantity
Arduino Card	Arduino UNO	1
Temperature Sensor	DHT11	1
Buzzer	Passive Buzzer	1
Breadboard	-	1
Jumpers	Several

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Technical Specifications

Arduino UNO board

• Microcontroller : ATmega328P
• Operating voltage : 5V
• Recommended input voltage : 7-12V
• Max current per I/O pin : 40 mA
• Clock frequency: 16 MHz

DHT11 Temperature Sensor

• Supply voltage : 3.3V - 5V
• Temperature range : 0°C to 50°C
• Accuracy: ±2°C
• Humidity range: 20% to 90% RH

Passive Buzzer

• Operating voltage: 3.3V - 5V
• Nominal current: 10-30 mA
• Resonance frequency: ~2 kHz

Breadboard

• Max current per row : 1A
• Max voltage: 300V

Jumpers

• Max current supported : 1-3A
• Length : 10-30 cm

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Software and Programming

• Software: Arduino IDE
• Programming language: Arduino (C++)

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Schematics

Project electrical diagram

Project synoptic diagram

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Arduino codes

Arduino Challenge Code

#include <dht11.h>

#define DHT11PIN 7
#define SPEAKER_PIN 8

dht11 DHT11;

// Fréquences des notes en Hz
#define NOTE_DO  262
#define NOTE_RE  294
#define NOTE_MI  330
#define NOTE_FA  349
#define NOTE_SOL 392
#define NOTE_LA  440

// Mélodie "Frère Jacques"
int melody[] = {
  NOTE_DO, NOTE_RE, NOTE_MI, NOTE_DO,
  NOTE_DO, NOTE_RE, NOTE_MI, NOTE_DO,
  NOTE_MI, NOTE_FA, NOTE_SOL,
  NOTE_MI, NOTE_FA, NOTE_SOL
};

// Durées des notes (en ms)
int noteDurations[] = {500, 500, 500, 500, 500, 500, 500, 500, 500, 500, 1000, 500, 500, 1000};

void playMelodyFJ() {
  int length = sizeof(melody) / sizeof(melody[0]);
  for (int i = 0; i < length; i++) {
    tone(SPEAKER_PIN, melody[i], noteDurations[i]);
    delay(noteDurations[i] * 1.30);
  }
}

void setup() {
  Serial.begin(9600);
  pinMode(SPEAKER_PIN, OUTPUT);
}

void loop() {
  float temperature = (float) DHT11.temperature;
  Serial.print("Température (°C) : ");
  Serial.println(temperature, 2);
  delay(1000);

  if (temperature < 22) {
    playMelodyFJ();
  } else {
    noTone(SPEAKER_PIN);
  }
}

Bonus Arduino code

#include <dht11.h>
#define DHT11PIN 7
#define SPEAKER_PIN 8

dht11 DHT11;

// Fréquences des notes en Hz
#define NOTE_DO  262
#define NOTE_RE  294
#define NOTE_MI  330
#define NOTE_FA  349
#define NOTE_SOL 392
#define NOTE_LA  440

// Mélodie de "Frère Jacques"
int melody[] = {
  NOTE_DO, NOTE_RE, NOTE_MI, NOTE_DO,
  NOTE_DO, NOTE_RE, NOTE_MI, NOTE_DO,
  NOTE_MI, NOTE_FA, NOTE_SOL,
  NOTE_MI, NOTE_FA, NOTE_SOL,
  NOTE_SOL, NOTE_LA, NOTE_SOL, NOTE_FA, NOTE_MI, NOTE_DO,
  NOTE_SOL, NOTE_LA, NOTE_SOL, NOTE_FA, NOTE_MI, NOTE_DO,
  NOTE_DO, NOTE_SOL, NOTE_DO,
  NOTE_DO, NOTE_SOL, NOTE_DO
};

// Durées des notes (en ms)
int noteDurations[] = {
  500, 500, 500, 500,
  500, 500, 500, 500,
  500, 500, 1000,
  500, 500, 1000,
  250, 250, 250, 250, 500, 500,
  250, 250, 250, 250, 500, 500,
  250, 250, 500,
  250, 250, 500
};

// Fréquences des notes
#define NOTE1_DO  262
#define NOTE1_RE  294
#define NOTE1_MI  330
#define NOTE1_FA  349
#define NOTE1_SOL 392
#define NOTE1_LA  440
#define NOTE1_SI  494
#define NOTE1_DO_HIGH  523  // Do de l'octave supérieure

// Mélodie "Happy Birthday"
int melody1[] = {
  NOTE1_SOL, NOTE1_SOL, NOTE1_LA, NOTE1_SOL, NOTE1_DO_HIGH, NOTE1_SI,
  NOTE1_SOL, NOTE1_SOL, NOTE1_LA, NOTE1_SOL, NOTE1_RE, NOTE1_DO_HIGH,
  NOTE1_SOL, NOTE1_SOL, NOTE1_SOL, NOTE1_MI, NOTE1_DO_HIGH, NOTE1_SI, NOTE1_LA,
  NOTE1_FA, NOTE1_FA, NOTE1_MI, NOTE1_DO_HIGH, NOTE1_RE, NOTE1_DO_HIGH
};

// Durées des notes (plus rapides)
int noteDurations1[] = {
  300, 300, 600, 600, 600, 900,
  300, 300, 600, 600, 600, 900,
  300, 300, 300, 300, 300, 300, 600,
  300, 300, 300, 300, 600, 900
};


// Fréquences des notes
#define NOTE2_DO  262
#define NOTE2_RE  294
#define NOTE2_MI  330
#define NOTE2_FA  349
#define NOTE2_SOL 392
#define NOTE2_LA  440
#define NOTE2_SI  494

// Mélodie "Au clair de la lune"
int melody2[] = {
  NOTE2_DO, NOTE2_RE, NOTE2_MI, NOTE2_RE, NOTE2_DO,
  NOTE2_MI, NOTE2_RE, NOTE2_RE, NOTE2_DO, NOTE2_DO,
  NOTE2_RE, NOTE2_MI, NOTE2_RE, NOTE2_DO, NOTE2_MI,
  NOTE2_RE, NOTE2_RE, NOTE2_DO, NOTE2_RE, NOTE2_RE,
  NOTE2_RE, NOTE2_LA, NOTE2_LA, NOTE2_RE, NOTE2_DO,
  NOTE2_SI, NOTE2_LA, NOTE2_SOL, NOTE2_DO, NOTE2_DO,
  NOTE2_RE, NOTE2_MI, NOTE2_RE, NOTE2_DO, NOTE2_MI,
  NOTE2_RE, NOTE2_RE, NOTE2_DO
};

// Durées des notes (en millisecondes)
int noteDurations2[] = {
  500, 250, 250, 250, 700, // Première phrase
  250, 250, 250, 250, 700, // Deuxième phrase
  250, 250, 250, 250, 250, // Troisième phrase
  250, 250, 250, 250, 700, // Quatrième phrase
  250, 250, 250, 250, 700, // Cinquième phrase
  250, 250, 250, 250, 700, // Sixième phrase
  250, 250, 250, 250, 700, // Septième phrase
  250, 250, 250, 250, 1000  // Huitième phrase
};


void playMelodyAU() {
  int length = sizeof(melody2) / sizeof(melody2[0]);
  for (int i = 0; i < length; i++) {
    tone(SPEAKER_PIN, melody2[i], noteDurations2[i]);
    delay(noteDurations2[i] * 1.30); // Pause entre les notes
    float temperature = (float) DHT11.temperature;
    Serial.print("Temperature (C): ");
    Serial.println(temperature, 2);
    if (temperature < 30 ){
      loop(); 
    }
  }
}

void playMelodyHB() {
  int length = sizeof(melody1) / sizeof(melody1[0]);
  for (int i = 0; i < length; i++) {
    tone(SPEAKER_PIN, melody1[i], noteDurations1[i]);
    delay(noteDurations1[i] * 1.20); // Pause réduite entre les notes
  }
}

void playMelodyFJ() {
  int length = sizeof(melody) / sizeof(melody[0]);
  for (int i = 0; i < length; i++) {
    tone(SPEAKER_PIN, melody[i], noteDurations[i]);

    delay(noteDurations[i] * 1.30); // Petite pause entre les notes
  }
   // Pause avant de rejouer la mélodie
}

void playMelody1() {
  int length = sizeof(melody) / sizeof(melody[0]);
  for (int i = 0; i < length; i++) {
    tone(SPEAKER_PIN, melody[i], noteDurations[i]);

    delay(noteDurations[i] * 1.30); // Petite pause entre les notes
    float temperature = (float) DHT11.temperature;
    Serial.print("Temperature (C): ");
    Serial.println(temperature, 2);
    if (temperature <= 20 ){
      playMelodyHB();
      break; 
    }
    
  } 
}


void setup() {
  Serial.begin(9600);
  pinMode(SPEAKER_PIN, OUTPUT);
}

void loop() {
   float temperature = (float) DHT11.temperature;
  Serial.print("Temperature (C): ");
  Serial.println(temperature, 2);
  delay(1000);

  if (temperature < 22) {
    playMelody1();
  } 
  else if (temperature >= 30 ){
    playMelodyAU();
  }
  else {
    noTone(SPEAKER_PIN);
  }

  // 
}

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