【ESP32 物聯網實戰 09】遙控：遠端反向控制，透過 MQTT 操作實體繼電器

今天，我們要來打通雙向通訊的最後一哩路：利用 MQTT 的訂閱 (Subscribe) 功能，讓 ESP32 即時監聽來自雲端的指令，並透過繼電器 (Relay) 去安全地控制 110V 的實體電器，實現真正的遠端遙控！

3. ESP32 實作：訂閱 MQTT 遠端指令

import time
import network
from machine import Pin
from umqtt.simple import MQTTClient

relay = Pin(13, Pin.OUT)
relay.value(0) 

SSID = "Your_WiFi_SSID"
PASSWORD = "Your_WiFi_Password"
CLIENT_ID = "esp32_relay_control_01"  
BROKER = "broker.emqx.io"
TOPIC_CONTROL = "tpcu/iot/classA/fan" 

wlan = network.WLAN(network.STA_IF)
wlan.active(True)
wlan.connect(SSID, PASSWORD)
while not wlan.isconnected():
    time.sleep(0.5)

def on_message_received(topic, msg):
    topic_str = topic.decode("utf-8")
    msg_str = msg.decode("utf-8").upper() 
    
    print(f"收到來自主題 [{topic_str}] 的訊息: {msg_str}")
    
    if msg_str == "ON":
        relay.value(1) 
        print("💡 繼電器開啟！風扇/電燈運轉...")
    elif msg_str == "OFF":
        relay.value(0)  
        print("🚫 繼電器關閉！風扇/電燈停止...")
    else:
        print("收到未知指令。")

client = MQTTClient(CLIENT_ID, BROKER)
client.set_callback(on_message_received)
client.connect()
client.subscribe(TOPIC_CONTROL)
print(f"成功連線 Broker 並訂閱主題，等待指令中...")

try:
    while True:
        client.check_msg()
        time.sleep(0.1) 
except KeyboardInterrupt:
    client.disconnect()