51单片机 mqtt 代码实现

51单片机是一种常见的嵌入式系统开发平台，可以通过添加网络模块来实现MQTT协议的通信。下面是一个基本的51单片机MQTT代码实现示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "mqtt.h"
#include "eth.h"
#include "lcd.h"
#include "key.h"

#define MQTT_SERVER "mqtt.example.com"
#define MQTT_PORT 1883
#define MQTT_USERNAME "username"
#define MQTT_PASSWORD "password"
#define MQTT_CLIENT_ID "client_id"

#define MQTT_TOPIC "topic"

unsigned char mqtt_buf[MQTT_BUF_LEN];
unsigned char mqtt_readbuf[MQTT_BUF_LEN];

unsigned char mqtt_connect(void)
{
    unsigned char rc = 0;

    MQTTClient("MQTT", 256, mqtt_buf, MQTT_BUF_LEN, mqtt_readbuf, MQTT_BUF_LEN);

    if (MQTTConnect(MQTT_CLIENT_ID, MQTT_USERNAME, MQTT_PASSWORD) != 0) {
        rc = 1;
    }
    return rc;
}

unsigned char mqtt_publish(char *msg)
{
    unsigned char rc = 0;

    if (MQTTConnect(MQTT_CLIENT_ID, MQTT_USERNAME, MQTT_PASSWORD) != 0) {
        rc = 1;
    }
    else {
        MQTTMessage msg;
        msg.qos = QOS0;
        msg.retained = 0;
        msg.payload = msg;
        msg.payloadlen = strlen(msg);
        if (MQTTPublish(MQTT_TOPIC, &msg) != 0) {
            rc = 1;
        }
        MQTTDisconnect();
    }
    return rc;
}

void main(void)
{
    unsigned char rc;
    unsigned char data;

    lcd_init();
    eth_init();
    mqtt_connect();

    while (1) {
        data = key_scan();
        if (data != 0) {
            char msg[16];
            sprintf(msg, "Key pressed: %c", data);
            mqtt_publish(msg);
        }
    }
}

这个例子使用了MQTT库和以太网库来连接MQTT服务器，并使用按键来发布消息。在使用之前需要根据实际情况修改MQTT服务器地址、端口、用户名、密码、客户端ID和主题等参数。