MQTT 远程控制

MQTT 远程控制

概述

本节介绍如何通过 MQTT 协议远程控制 ESP32 音频播放器。学习完成后，您将能够：

• 设计音频控制的 MQTT Topic 结构
• 实现 MQTT 订阅以接收控制命令
• 将 MQTT 消息与音频播放逻辑关联
• 发布播放状态和元数据回 MQTT

前置要求

在开始本节之前，请确保：

• 已掌握 MQTT 协议基础
• 音频基本播放功能正常工作
• Mosquitto 或 EMQX Broker 已运行
• PubSubClient 库已安装

MQTT Topic Design

Control Topics

Topic	数据类型	功能	说明
factory/broadcast/control	JSON	综合控制	包含所有控制命令
factory/broadcast/play	String	播放控制	”play” / “stop” / “pause” / “resume”
factory/broadcast/station	Integer	切换电台	电台索引号 (0-3)
factory/broadcast/volume	Integer	音量控制	0-250
factory/broadcast/mute	Boolean	静音切换	true / false

Status Topics

Topic	数据类型	功能	说明
factory/broadcast/status	JSON	播放器状态	当前状态、音量、电台
factory/broadcast/streamtitle	String	当前曲目	电台当前播放的曲目标题
factory/broadcast/streameinfo	String	流信息	比特率、格式等

Topic Design Principles

factory/broadcast/{command}

分层说明：
factory      → 工厂级前缀
broadcast    → 广播系统
{command}    → 具体命令

MQTT Control Implementation

Complete MQTT Control Sketch

#include <Arduino.h>
#include <WiFi.h>
#include <PubSubClient.h>
#include <AudioOutputI2S.h>
#include <AudioGeneratorMP3.h>
#include <AudioFileSourceICYStream.h>

// WiFi 配置
const char* ssid = "您的WiFi名称";
const char* password = "您的WiFi密码";

// MQTT 配置
const char* mqttServer = "192.168.1.100";
const int mqttPort = 1883;
const char* mqttUser = "node_red";
const char* mqttPassword = "node_red";
const char* deviceID = "esp32_broadcast_01";

// Topic 定义
const char* topicPlay = "factory/broadcast/play";
const char* topicStation = "factory/broadcast/station";
const char* topicVolume = "factory/broadcast/volume";
const char* topicMute = "factory/broadcast/mute";
const char* topicStatus = "factory/broadcast/status";
const char* topicStreamTitle = "factory/broadcast/streamtitle";

// I2S 引脚
#define I2S_BCLK  26
#define I2S_LRCK  25
#define I2S_DIN   22

// 电台列表
const char* stationNames[] = {"News", "Music", "Pop", "Classic"};
const char* stationURLs[] = {
  "http://stream1.example.com:8000/news",
  "http://stream2.example.com:8000/music",
  "http://stream3.example.com:8000/pop",
  "http://stream4.example.com:8000/classic"
};
const int stationCount = 4;
int currentStation = 0;

// 音频对象
AudioGeneratorMP3* mp3;
AudioFileSourceICYStream* file;
AudioOutputI2S* output;

// 音量管理
int currentVolume = 128;
bool isMuted = false;
int previousVolume = 128;

// MQTT 客户端
WiFiClient wifiClient;
PubSubClient mqttClient(wifiClient);

// 状态发布
void publishStatus() {
  StaticJsonDocument<256> doc;
  doc["device"] = deviceID;
  doc["station"] = currentStation;
  doc["station_name"] = stationNames[currentStation];
  doc["volume"] = currentVolume;
  doc["muted"] = isMuted;
  doc["playing"] = mp3 ? mp3->isRunning() : false;
  doc["wifi_rssi"] = WiFi.RSSI();

  char buffer[256];
  serializeJson(doc, buffer);
  mqttClient.publish(topicStatus, buffer);
}

// 音量设置
void setVolume(int vol) {
  currentVolume = constrain(vol, 0, 250);
  output->SetVolume(currentVolume);
  isMuted = false;
  publishStatus();
}

// 静音切换
void toggleMute() {
  if (isMuted) {
    currentVolume = previousVolume;
    output->SetVolume(currentVolume);
    isMuted = false;
  } else {
    previousVolume = currentVolume;
    output->SetVolume(0);
    isMuted = true;
  }
  publishStatus();
}

// 切换电台
void switchStation(int stationIndex) {
  if (stationIndex < 0 || stationIndex >= stationCount) return;

  if (mp3 && mp3->isRunning()) mp3->stop();
  if (file) file->close();

  currentStation = stationIndex;
  file->open(stationURLs[currentStation]);
  mp3->begin(file, output);

  mqttClient.publish(topicStreamTitle, stationNames[currentStation]);
  publishStatus();
}

// MQTT 回调处理
void mqttCallback(char* topic, byte* payload, unsigned int length) {
  String message;
  for (unsigned int i = 0; i < length; i++) {
    message += (char)payload[i];
  }

  Serial.printf("收到消息: [%s] %s\n", topic, message.c_str());

  if (strcmp(topic, topicPlay) == 0) {
    if (message == "play") {
      switchStation(currentStation);
    } else if (message == "stop") {
      if (mp3 && mp3->isRunning()) mp3->stop();
    } else if (message == "pause") {
      if (mp3 && mp3->isRunning()) mp3->stop();  // 简单实现：停止
    }
  }
  else if (strcmp(topic, topicStation) == 0) {
    int station = message.toInt();
    switchStation(station);
  }
  else if (strcmp(topic, topicVolume) == 0) {
    int vol = message.toInt();
    setVolume(vol);
  }
  else if (strcmp(topic, topicMute) == 0) {
    if (message == "true" || message == "1") {
      if (!isMuted) toggleMute();
    } else {
      if (isMuted) toggleMute();
    }
  }
}

// MQTT 重连
void reconnectMQTT() {
  while (!mqttClient.connected()) {
    Serial.print("尝试 MQTT 连接...");
    if (mqttClient.connect(deviceID, mqttUser, mqttPassword)) {
      Serial.println("已连接");

      // 订阅控制 Topic
      mqttClient.subscribe(topicPlay);
      mqttClient.subscribe(topicStation);
      mqttClient.subscribe(topicVolume);
      mqttClient.subscribe(topicMute);

      // 发布在线状态
      mqttClient.publish(topicStatus, "{\"device\":\"" +
                         String(deviceID) + "\",\"status\":\"online\"}");
    } else {
      Serial.printf("失败 (rc=%d)，5秒后重试\n", mqttClient.state());
      delay(5000);
    }
  }
}

void setup() {
  Serial.begin(115200);

  // 连接 WiFi
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(1000);
    Serial.print(".");
  }
  Serial.println("\nWiFi 已连接");

  // 初始化音频
  output = new AudioOutputI2S();
  output->SetPinout(I2S_BCLK, I2S_LRCK, I2S_DIN);
  output->SetVolume(currentVolume);
  output->begin();

  mp3 = new AudioGeneratorMP3();
  file = new AudioFileSourceICYStream();

  // 初始电台
  file->open(stationURLs[currentStation]);
  mp3->begin(file, output);

  // MQTT 配置
  mqttClient.setServer(mqttServer, mqttPort);
  mqttClient.setCallback(mqttCallback);
}

void loop() {
  // MQTT 保活
  if (!mqttClient.connected()) {
    reconnectMQTT();
  }
  mqttClient.loop();

  // 音频播放循环
  if (mp3->isRunning()) {
    if (!mp3->loop()) {
      mp3->stop();
      Serial.println("播放结束，5秒后重连");
      delay(5000);
      switchStation(currentStation);
    }
  }

  // 定期更新流标题
  static unsigned long lastTitleCheck = 0;
  if (millis() - lastTitleCheck > 15000) {
    lastTitleCheck = millis();
    if (file && file->getStreamTitle()) {
      mqttClient.publish(topicStreamTitle, file->getStreamTitle());
    }
    publishStatus();
  }
}

MQTT Control Flow

Control Flow Diagram

Node-RED Dashboard / Mobile App
        │
        │ MQTT Publish
        ▼
   Mosquitto Broker
        │
        │ Topic: factory/broadcast/play
        ▼
   ESP32 (PubSubClient)
        │
        │ mqttCallback()
        ▼
   ESP32 Audio Controller
        │
        ├── play → mp3->begin(file, output)
        ├── stop → mp3->stop()
        ├── station → switchStation(index)
        ├── volume → output->SetVolume(n)
        └── mute → toggleMute()

Stream Title Publishing

Metadata Publishing

// 定期检查并发布流元数据
void publishStreamMetadata() {
  if (!file) return;

  // 获取流标题（当前歌曲/节目名）
  const char* title = file->getStreamTitle();
  if (title && strlen(title) > 0) {
    mqttClient.publish(topicStreamTitle, title);
    Serial.printf("当前播放: %s\n", title);
  }

  // 获取流信息（比特率、格式等）
  const char* info = file->getStreamInfo();
  if (info && strlen(info) > 0) {
    mqttClient.publish("factory/broadcast/streaminfo", info);
  }
}

Pre-sales Key Points

MQTT Control Capabilities

控制能力	实现方式	买家价值
远程开关	MQTT 播放/停止命令	”可远程启停车间广播”
音源切换	MQTT 电台索引命令	”可切换不同播放内容”
音量调节	MQTT 音量值	”可远程调节音量”
状态监控	MQTT 状态发布	”可实时查看设备状态”
元数据显示	MQTT 曲目标题	”可显示当前播放内容”

Summary

本节介绍了通过 MQTT 远程控制 ESP32 音频播放器：

1. Topic 设计：使用 factory/broadcast/{command} 层级结构
2. 控制命令：播放/停止、切换电台、音量调节、静音
3. 状态发布：定期推送设备状态和流元数据
4. 回调处理：MQTT 消息触发音频控制函数