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mqtt - MQTT 订阅

问题描述

有人可以帮我处理这段代码吗？

目标是在有效载荷的值 > 1000 时触发 Led。

它是基于 esp8266mqtt PubSub 客户端示例的 MQTT 订阅代码。我将使用它来订阅来自 CO2sensor 的主题

我试图修改它的一部分，但我认为它对数据类型或错误条件做了一些事情？

#include <ESP8266WiFi.h>
#include <PubSubClient.h>

// Update these with values suitable for your network.

const char *ssid = "xxx";
const char *password = "xxx";
const char *mqtt_server = "xxxx";

WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
int value = 0;
int led = D4;

void setup_wifi()
{

  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED)
  {
    delay(500);
    Serial.print(".");
  }

  randomSeed(micros());

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void callback(char *topic, byte *payload, unsigned int length)
{
  Serial.print("Message arrived [");
  Serial.print(topic);
  Serial.print("] ");
  for (int i = 0; i < length; i++)
  {
    Serial.print((char)payload[i]);
  }
  Serial.println();

  // Switch on the LED if value of C02 is above 1000
  i = atoi (payload); //convert string to integer
  if ( i > 1000)      // comparison
  {
    digitalWrite(led, HIGH); // Turn the LED on 
  }
  else
  {
    digitalWrite(led, LOW); // Turn the LED off 
  }
}

void reconnect()
{
  // Loop until we're reconnected
  while (!client.connected())
  {
    Serial.print("Attempting MQTT connection...");
    // Create a random client ID
    String clientId = "ESP8266Client-";
    clientId += String(random(0xffff), HEX);
    // Attempt to connect
    if (client.connect(clientId.c_str()))
    {
      Serial.println("connected");
      // Once connected, publish an announcement...
      //client.publish("outTopic", "Test");
      // ... and resubscribe
      client.subscribe("my/sensors/co2");
    }
    else
    {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void setup()
{
  pinMode(led, OUTPUT); // Initialize the BUILTIN_LED pin as an output
  Serial.begin(115200);
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
}

void loop()
{
  if (!client.connected())
  {
    reconnect();
  }
  client.loop();
}

亲切的问候

你好，这是我发布的：

void pubMessage() {
      char message[16];    
      snprintf(message, sizeof(message), "%d", co2);
      client.publish("my/sensors/co2", message);
      delay(30000);

标签： mqttsubscriptionpayload

解决方案

首先，您将第一个字节payload转换为字符。

由于它只是第一个字节，它的最大值为 256。

其次，您将该 1 个字节的值与字符串进行比较'1000'

在不确切知道您要发布的内容的情况下，很难告诉您如何修复它。

如果您要发布一个表示数字的字符串，那么您需要先对其进行解析，atoi()然后再与整数1000而不是字符串进行比较。

如果它是一个字节值，那么您需要在进行比较之前从传入的字节数组中读取正确的值。

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