Add initial PlatformIO configuration and main application code

- Created platformio.ini for ESP32 Devkit configuration with DFPlayer Mini library dependency.
- Implemented main application logic in main.cpp, including LED and buzzer control, and MP3 playback functionality using DFMiniMp3 library.
- Added notification class for handling MP3 player events and errors.
- Set up input pins for buttons and output pins for LEDs, with synchronization logic.
- Included basic setup and loop functions to manage state and playback.
- Added README for test directory to outline unit testing purpose and resources.

.gitignore

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+.pio
+.vscode/.browse.c_cpp.db*
+.vscode/c_cpp_properties.json
+.vscode/launch.json
+.vscode/ipch

.vscode/extensions.json

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+{
+    // See http://go.microsoft.com/fwlink/?LinkId=827846
+    // for the documentation about the extensions.json format
+    "recommendations": [
+        "platformio.platformio-ide"
+    ],
+    "unwantedRecommendations": [
+        "ms-vscode.cpptools-extension-pack"
+    ]
+}

.vscode/settings.json

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+{
+    "python.autoComplete.extraPaths": [
+        "${workspaceFolder}/sources/poky/bitbake/lib",
+        "${workspaceFolder}/sources/poky/meta/lib"
+    ],
+    "python.analysis.extraPaths": [
+        "${workspaceFolder}/sources/poky/bitbake/lib",
+        "${workspaceFolder}/sources/poky/meta/lib"
+    ],
+    "files.associations": {
+        "*.dbclient-js": "javascript",
+        "*.conf": "bitbake",
+        "*.inc": "bitbake"
+    }
+}

include/README

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+
+This directory is intended for project header files.
+
+A header file is a file containing C declarations and macro definitions
+to be shared between several project source files. You request the use of a
+header file in your project source file (C, C++, etc) located in `src` folder
+by including it, with the C preprocessing directive `#include'.
+
+```src/main.c
+
+#include "header.h"
+
+int main (void)
+{
+ ...
+}
+```
+
+Including a header file produces the same results as copying the header file
+into each source file that needs it. Such copying would be time-consuming
+and error-prone. With a header file, the related declarations appear
+in only one place. If they need to be changed, they can be changed in one
+place, and programs that include the header file will automatically use the
+new version when next recompiled. The header file eliminates the labor of
+finding and changing all the copies as well as the risk that a failure to
+find one copy will result in inconsistencies within a program.
+
+In C, the convention is to give header files names that end with `.h'.
+
+Read more about using header files in official GCC documentation:
+
+* Include Syntax
+* Include Operation
+* Once-Only Headers
+* Computed Includes
+
+https://gcc.gnu.org/onlinedocs/cpp/Header-Files.html

lib/README

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+
+This directory is intended for project specific (private) libraries.
+PlatformIO will compile them to static libraries and link into the executable file.
+
+The source code of each library should be placed in a separate directory
+("lib/your_library_name/[Code]").
+
+For example, see the structure of the following example libraries `Foo` and `Bar`:
+
+|--lib
+|  |
+|  |--Bar
+|  |  |--docs
+|  |  |--examples
+|  |  |--src
+|  |     |- Bar.c
+|  |     |- Bar.h
+|  |  |- library.json (optional. for custom build options, etc) https://docs.platformio.org/page/librarymanager/config.html
+|  |
+|  |--Foo
+|  |  |- Foo.c
+|  |  |- Foo.h
+|  |
+|  |- README --> THIS FILE
+|
+|- platformio.ini
+|--src
+   |- main.c
+
+Example contents of `src/main.c` using Foo and Bar:
+```
+#include <Foo.h>
+#include <Bar.h>
+
+int main (void)
+{
+  ...
+}
+
+```
+
+The PlatformIO Library Dependency Finder will find automatically dependent
+libraries by scanning project source files.
+
+More information about PlatformIO Library Dependency Finder
+- https://docs.platformio.org/page/librarymanager/ldf.html

platformio.ini

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+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[env:esp32doit-devkit-v1]
+platform = espressif32
+board = esp32doit-devkit-v1
+framework = arduino
+monitor_speed = 115200
+lib_deps = 
+	makuna/DFPlayer Mini Mp3 by Makuna@^1.2.3

src/main.cpp

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+#include <Arduino.h>
+#include <DFMiniMp3.h>
+
+class Mp3Notify;
+
+typedef DFMiniMp3<HardwareSerial, Mp3Notify> DfMp3;
+DfMp3 mp3(Serial2);
+
+constexpr int kDfPlayerRxPin = 16;
+constexpr int kDfPlayerTxPin = 17;
+constexpr unsigned long kDfPlayerBaud = 9600;
+constexpr uint32_t kDfPlayerOnlineTimeoutMs = 2000;
+
+constexpr int kLedPins[] = {18, 19, 21, 22};
+constexpr size_t kLedCount = sizeof(kLedPins) / sizeof(kLedPins[0]);
+
+constexpr int kBuzzerPins[] = {33, 25, 26, 27};
+constexpr size_t kBuzzerCount = sizeof(kBuzzerPins) / sizeof(kBuzzerPins[0]);
+constexpr size_t kPairCount = (kLedCount < kBuzzerCount) ? kLedCount : kBuzzerCount;
+
+constexpr int kResetPin = 23;
+constexpr uint32_t kAdminHoldMillis = 3000;
+constexpr uint32_t kResetReleaseDelayMs = 300;
+
+int gActiveBuzzer = -1;
+bool gAdminMode = false;
+uint32_t gResetPressStartMs = 0;
+
+void setLed(size_t index, bool on)
+{
+    if (index < kLedCount)
+    {
+        digitalWrite(kLedPins[index], on ? HIGH : LOW);
+    }
+}
+
+void setAllLeds(bool on)
+{
+    for (int pin : kLedPins)
+    {
+        digitalWrite(pin, on ? HIGH : LOW);
+    }
+}
+
+void syncLedsToButtons()
+{
+    for (size_t i = 0; i < kPairCount; ++i)
+    {
+        const bool pressed = (digitalRead(kBuzzerPins[i]) == LOW);
+        setLed(i, pressed);
+    }
+    for (size_t i = kPairCount; i < kLedCount; ++i)
+    {
+        setLed(i, false);
+    }
+}
+
+class Mp3Notify
+{
+public:
+    static void PrintlnSourceAction(DfMp3_PlaySources source, const char *action)
+    {
+        if (source & DfMp3_PlaySources_Sd)
+        {
+            Serial.print("SD Card, ");
+        }
+        if (source & DfMp3_PlaySources_Usb)
+        {
+            Serial.print("USB Disk, ");
+        }
+        if (source & DfMp3_PlaySources_Flash)
+        {
+            Serial.print("Flash, ");
+        }
+        Serial.println(action);
+    }
+    static void OnError([[maybe_unused]] DfMp3 &mp3, uint16_t errorCode)
+    {
+        // see DfMp3_Error for code meaning
+        Serial.println();
+        Serial.print("Com Error ");
+        Serial.println(errorCode);
+    }
+    static void OnPlayFinished([[maybe_unused]] DfMp3 &mp3, [[maybe_unused]] DfMp3_PlaySources source, uint16_t track)
+    {
+        Serial.print("Play finished for #");
+        Serial.println(track);
+        // No automatic restart; playback only occurs on the first buzzer press.
+    }
+    static void OnPlaySourceOnline([[maybe_unused]] DfMp3 &mp3, DfMp3_PlaySources source)
+    {
+        PrintlnSourceAction(source, "online");
+    }
+    static void OnPlaySourceInserted([[maybe_unused]] DfMp3 &mp3, DfMp3_PlaySources source)
+    {
+        PrintlnSourceAction(source, "inserted");
+    }
+    static void OnPlaySourceRemoved([[maybe_unused]] DfMp3 &mp3, DfMp3_PlaySources source)
+    {
+        PrintlnSourceAction(source, "removed");
+    }
+};
+
+void setup()
+{
+    Serial.begin(9600);
+    Serial.println("Booting...");
+
+    for (int pin : kLedPins)
+    {
+        pinMode(pin, OUTPUT);
+        digitalWrite(pin, LOW);
+    }
+
+    for (int pin : kBuzzerPins)
+    {
+        pinMode(pin, INPUT_PULLUP);
+    }
+
+    pinMode(kResetPin, INPUT_PULLUP);
+
+    syncLedsToButtons();
+
+    mp3.begin(kDfPlayerRxPin, kDfPlayerTxPin, kDfPlayerBaud);
+    mp3.setComRetries(1);
+
+    delay(200);
+    mp3.reset(false);
+    delay(1200);
+
+    for (size_t i = 0; i < kPairCount; ++i)
+    {
+        if (kBuzzerPins[i] == kDfPlayerRxPin || kBuzzerPins[i] == kDfPlayerTxPin)
+        {
+            Serial.print("WARNING: buzzer pin conflicts with DF serial: index ");
+            Serial.println(i);
+        }
+    }
+
+    const uint32_t waitStart = millis();
+    while (!mp3.isOnline() && (millis() - waitStart) < kDfPlayerOnlineTimeoutMs)
+    {
+        mp3.loop();
+        delay(1);
+    }
+
+    const bool playerOnline = mp3.isOnline();
+    if (playerOnline)
+    {
+        uint16_t version = mp3.getSoftwareVersion();
+        Serial.print("version ");
+        Serial.println(version);
+
+        uint16_t volume = mp3.getVolume();
+        Serial.print("volume ");
+        Serial.println(volume);
+        mp3.setVolume(24);
+
+        const uint16_t count = mp3.getTotalTrackCount(DfMp3_PlaySource_Sd);
+        Serial.print("files ");
+        Serial.println(count);
+
+        Serial.println("ready.");
+    }
+    else
+    {
+        Serial.println("DFPlayer did not come online.");
+    }
+}
+
+void loop()
+{
+    mp3.loop();
+
+    const bool resetPressed = (digitalRead(kResetPin) == LOW);
+    if (resetPressed && gResetPressStartMs == 0)
+    {
+        gResetPressStartMs = millis();
+        mp3.stop();
+    }
+
+    if (resetPressed && !gAdminMode && (millis() - gResetPressStartMs) > kAdminHoldMillis)
+    {
+        gAdminMode = true;
+        setAllLeds(true);
+    }
+
+    if (!resetPressed && gResetPressStartMs != 0)
+    {
+        if (gAdminMode)
+        {
+            gAdminMode = false;
+            setAllLeds(false);
+            gActiveBuzzer = -1;
+        }
+        else if (gActiveBuzzer != -1)
+        {
+            setLed(static_cast<size_t>(gActiveBuzzer), false);
+            gActiveBuzzer = -1;
+        }
+        gResetPressStartMs = 0;
+        delay(kResetReleaseDelayMs);
+    }
+
+    if (gActiveBuzzer == -1 && !gAdminMode)
+    {
+        for (size_t i = 0; i < kPairCount; ++i)
+        {
+            if (digitalRead(kBuzzerPins[i]) == LOW)
+            {
+                gActiveBuzzer = static_cast<int>(i);
+                for (size_t j = 0; j < kLedCount; ++j)
+                {
+                    setLed(j, (j == i));
+                }
+                mp3.playMp3FolderTrack(static_cast<uint16_t>(i + 1));
+                break;
+            }
+        }
+        if (gActiveBuzzer == -1)
+        {
+            syncLedsToButtons();
+        }
+    }
+    else if (!gAdminMode && gActiveBuzzer >= 0)
+    {
+        setLed(static_cast<size_t>(gActiveBuzzer), true);
+    }
+
+    delay(1);
+}

src/main.cpp.old

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+// Cleaned up and fixed to use SoftwareSerial on D4 (RX) and D1 (TX)
+
+#include <Arduino.h>
+#include <SoftwareSerial.h>
+#include <DFMiniMp3.h>
+
+class Mp3Notify;
+
+// Use a DFPlayer variant that doesn't require ACKs on all commands
+// to avoid blocking on modules that don't ACK reset.
+typedef DFMiniMp3<SoftwareSerial, Mp3Notify, Mp3ChipIncongruousNoAck> DfMp3;
+// DFPlayer wiring: DF TX -> D4 (GPIO2), DF RX -> D1 (GPIO5)
+// Important: Do NOT use GPIO1/GPIO3 for DFPlayer if you want USB Serial.
+// SoftwareSerial args are (rx, tx) from ESP8266 perspective.
+SoftwareSerial mp3Serial(/*rx =*/D4, /*tx =*/D1);
+DfMp3 dfmp3(mp3Serial);
+
+// NOTE: These GPIO numbers currently map to GPIO0, GPIO1, GPIO2, GPIO3.
+// Adjust to your wiring; avoid using GPIO1 (TX0) and GPIO2 (D4) if used by DFPlayer.
+const int buzzerPins[4] = {0, 1, 2, 3};  // FIXME: update to match your wiring
+const int ledPins[4] = {14, 12, 13, 15}; // D5–D8
+const int resetPin = 16;                 // D0
+
+int activeBuzzer = -1;
+bool adminMode = false;
+unsigned long resetPressStart = 0;
+
+class Mp3Notify
+{
+public:
+  static void PrintlnSourceAction(DfMp3_PlaySources source, const char *action)
+  {
+    if (source & DfMp3_PlaySources_Sd)
+    {
+      Serial.print("SD Card, ");
+    }
+    if (source & DfMp3_PlaySources_Usb)
+    {
+      Serial.print("USB Disk, ");
+    }
+    if (source & DfMp3_PlaySources_Flash)
+    {
+      Serial.print("Flash, ");
+    }
+    Serial.println(action);
+  }
+  static void OnError([[maybe_unused]] DfMp3 &mp3, uint16_t errorCode)
+  {
+    Serial.println();
+    Serial.print("Com Error ");
+    Serial.println(errorCode);
+  }
+  static void OnPlayFinished([[maybe_unused]] DfMp3 &mp3, [[maybe_unused]] DfMp3_PlaySources source, uint16_t track)
+  {
+    Serial.print("Play finished for #");
+    Serial.println(track);
+
+    track += 1;
+    if (track > 3)
+    {
+      track = 1;
+    }
+    dfmp3.playMp3FolderTrack(track);
+  }
+  static void OnPlaySourceOnline([[maybe_unused]] DfMp3 &mp3, DfMp3_PlaySources source)
+  {
+    PrintlnSourceAction(source, "online");
+  }
+  static void OnPlaySourceInserted([[maybe_unused]] DfMp3 &mp3, DfMp3_PlaySources source)
+  {
+    PrintlnSourceAction(source, "inserted");
+  }
+  static void OnPlaySourceRemoved([[maybe_unused]] DfMp3 &mp3, DfMp3_PlaySources source)
+  {
+    PrintlnSourceAction(source, "removed");
+  }
+};
+
+void setup()
+{
+  Serial.begin(9600);
+  Serial.println("Booting...");
+
+  mp3Serial.begin(9600);
+  Serial.println("After mp3Serial begin");
+
+  dfmp3.begin();
+  dfmp3.setComRetries(1); // reduce blocking if no response
+  Serial.println("After dfmp3 begin");
+
+  delay(200); // let DFPlayer settle
+
+  dfmp3.reset();
+  // many DFPlayer clones need >1s after reset before responding reliably
+  delay(1200);
+  Serial.println("After dfmp3 reset");
+
+  for (int i = 0; i < 4; i++)
+  {
+    pinMode(buzzerPins[i], INPUT_PULLUP);
+    pinMode(ledPins[i], OUTPUT);
+    digitalWrite(ledPins[i], LOW);
+  }
+  pinMode(resetPin, INPUT_PULLUP);
+
+  // Warn about potential pin conflicts with DFPlayer serial (D4/D1)
+  for (int i = 0; i < 4; i++)
+  {
+    if (buzzerPins[i] == D4 || buzzerPins[i] == D1)
+    {
+      Serial.print("WARNING: buzzer pin conflicts with DF serial: index ");
+      Serial.println(i);
+    }
+  }
+
+  uint16_t version = dfmp3.getSoftwareVersion();
+  Serial.print("version ");
+  Serial.println(version);
+
+  uint16_t volume = dfmp3.getVolume();
+  Serial.print("volume ");
+  Serial.println(volume);
+  dfmp3.setVolume(24);
+
+  uint16_t count = dfmp3.getTotalTrackCount(DfMp3_PlaySource_Sd);
+  Serial.print("files ");
+  Serial.println(count);
+
+  Serial.println("starting...");
+
+  dfmp3.playMp3FolderTrack(1);
+}
+
+void loop()
+{
+  // Process DFPlayer callbacks
+  dfmp3.loop();
+
+  if (digitalRead(resetPin) == LOW && resetPressStart == 0)
+  {
+    resetPressStart = millis();
+  }
+
+  if (digitalRead(resetPin) == LOW && !adminMode && millis() - resetPressStart > 3000)
+  {
+    adminMode = true;
+    for (int i = 0; i < 4; i++)
+    {
+      digitalWrite(ledPins[i], HIGH);
+    }
+  }
+
+  if (digitalRead(resetPin) == HIGH && resetPressStart != 0)
+  {
+    if (adminMode)
+    {
+      adminMode = false;
+      for (int i = 0; i < 4; i++)
+      {
+        digitalWrite(ledPins[i], LOW);
+      }
+      activeBuzzer = -1;
+    }
+    else if (activeBuzzer != -1)
+    {
+      digitalWrite(ledPins[activeBuzzer], LOW);
+      activeBuzzer = -1;
+    }
+    resetPressStart = 0;
+    delay(300);
+  }
+
+  if (activeBuzzer == -1 && !adminMode)
+  {
+    for (int i = 0; i < 4; i++)
+    {
+      if (digitalRead(buzzerPins[i]) == LOW)
+      {
+        activeBuzzer = i;
+        for (int j = 0; j < 4; j++)
+        {
+          digitalWrite(ledPins[j], j == i ? HIGH : LOW);
+        }
+        break;
+      }
+    }
+  }
+}

test/README

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+
+This directory is intended for PlatformIO Test Runner and project tests.
+
+Unit Testing is a software testing method by which individual units of
+source code, sets of one or more MCU program modules together with associated
+control data, usage procedures, and operating procedures, are tested to
+determine whether they are fit for use. Unit testing finds problems early
+in the development cycle.
+
+More information about PlatformIO Unit Testing:
+- https://docs.platformio.org/en/latest/advanced/unit-testing/index.html