What I wanted to learn, and why it interested me: [I wanted to create a interaction where I can control the sound of the speaker and play different songs. It interested me because I want to design products like speakers and headphones which by doing this exercise, I believe I can learn the basics of making them. 

Process and reflection: 

[I started this project by experimenting with a simple speaker connected to the Arduino to see if I could produce sound at all. At first I was confused about how the Arduino would actually read music files from the SD card, but after some trial and error I realized that the SD card had to be inserted into the DFPlayer Mini, which handles the decoding of MP3 files. Once that became clear, I chose a song that felt right for my mini DJ set: Harder, Better, Faster, Stronger by Daft Punk. I extracted the sections I wanted into four separate files, and also kept a full version of the song as one additional file. After that, I wired the push buttons and potentiometer, programmed each button to trigger a different file, and used the potentiometer to control volume.

Through this process, I learned not just about wiring and libraries, but also about how modules like the DFPlayer simplify tasks that Arduino alone can’t do. I was surprised by how strict the SD card formatting and file naming rules were, since even small mistakes could stop playback. In the end, I feel proud because I ended up with a working “mini DJ set” that is fun and interactive, and it gave me confidence that I can combine hardware and software to make creative projects.]

/*

    60-223 Intro to Physical Computing, fall 2025

    Domain-specific Skill Building exercise: Mini DJ Set with DFPlayer

    This sketch connects an Arduino Uno to a DFPlayer Mini MP3 module,

    five push buttons, a potentiometer, and a speaker. The potentiometer

    controls volume, while each button plays a different MP3 file

    stored on the SD card. The DFPlayer handles decoding and playback, and

    the Arduino sends serial commands to start or stop songs depending on

    the button pressed. Output is heard through a small speaker wired to the

    DFPlayer's SPK1/SPK2 pins.

    Pin mapping:

    Arduino pin | role         | details

    -----------------------------------------------

    A0            input          potentiometer 

    7             input          push button → plays 0001.mp3

    8             input          push button → plays 0002.mp3

    9             input          push button → plays 0003.mp3

    10            input          push button → plays 0004.mp3

    11            input          push button → plays 0005.mp3

    2             software TX    Arduino TX → DFPlayer RX (via ~1k resistor)

    3             software RX    Arduino RX ← DFPlayer TX

    SPK1/SPK2     output         speaker driven directly by DFPlayer

    Released to the public domain by Russell Sang, October 2025, Codes from ChapGPT5

*/

#include <SoftwareSerial.h>

#include <DFRobotDFPlayerMini.h>

// DFPlayer serial (UNO/Nano)

static const uint8_t PIN_MP3_TX = 2; // Arduino TX -> DFPlayer RX

static const uint8_t PIN_MP3_RX = 3; // Arduino RX <- DFPlayer TX

SoftwareSerial mp3Serial(PIN_MP3_RX, PIN_MP3_TX);

DFRobotDFPlayerMini player;

// I/O

const int POT_PIN = A0;                        // volume control

const uint8_t BTN_PINS[5] = {7, 8, 9, 10, 11}; // five buttons to GND

const uint8_t TRACKS[5]   = {1, 2, 3, 4, 5};   // plays 0001–0005.mp3

// Debounce

int lastBtnReading[5];

int btnStableState[5];

unsigned long lastDebounceTime[5];

const unsigned long DEBOUNCE_MS = 35;

// Volume cache

int lastVol = -1;

void setup() {

  pinMode(POT_PIN, INPUT);

  for (int i = 0; i < 5; i++) {

    pinMode(BTN_PINS[i], INPUT_PULLUP); // button wired to GND

    lastBtnReading[i]   = HIGH;

    btnStableState[i]   = HIGH;

    lastDebounceTime[i] = 0;

  }

  Serial.begin(9600);

  mp3Serial.begin(9600);

  Serial.println(F("Init DFPlayer..."));

  if (!player.begin(mp3Serial)) {

    Serial.println(F("DFPlayer init FAILED. Check wiring & files (0001..0005.mp3 in root)."));

    while (true) { delay(500); }

  }

  Serial.println(F("DFPlayer ready."));

  delay(300);

  // Set initial volume from pot

  int vol = map(analogRead(POT_PIN), 0, 1023, 5, 28);

  player.volume(vol);

  lastVol = vol;

}

void loop() {

  // --- Volume from potentiometer ---

  int vol = map(analogRead(POT_PIN), 0, 1023, 5, 28);

  if (vol != lastVol) {

    player.volume(vol);

    lastVol = vol;

  }

  // --- Buttons: play corresponding track on press ---

  for (int i = 0; i < 5; i++) {

    int reading = digitalRead(BTN_PINS[i]); // LOW when pressed

    if (reading != lastBtnReading[i]) lastDebounceTime[i] = millis();

    if (millis() - lastDebounceTime[i] > DEBOUNCE_MS) {

      if (reading != btnStableState[i]) {

        btnStableState[i] = reading;

        if (btnStableState[i] == LOW) {

          uint8_t trk = TRACKS[i];

          player.stop();

          delay(80);             // give module a moment

          player.play(trk);

          Serial.print(F("Playing 00"));

          Serial.print(trk);

          Serial.println(F(".mp3"));

        }

      }

    }

    lastBtnReading[i] = reading;

  }

  // DFPlayer status feedback

  if (player.available()) {

    uint8_t type = player.readType();

    int value    = player.read();

    // Uncomment for debugging:

    // Serial.print("Evt "); Serial.print(type);

    // Serial.print(" val "); Serial.println(value);

  }

  delay(5);

}