上一篇写到了获取DHT11的数据，这次我们要通过MQTT下发指令，解析后获取DHT11传感器数据后，通过MQTT发送到服务端。

准备工作

模块联网请参考前面的文章，MQTT服务端需要提前准备好，我们假设通过两个TOPIC来实现命令监听和数据发布：

命令监听TOPIC：b'cat/esp32/01'

数据发送TOPIC：b'iot/esp32/01'

参考代码

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import utime
from machine import Pin
import dht
from umqtt.simple import MQTTClient
import ujson

SERVER = 'your_mqtt_server'
CLIENT_ID = 'esp32_dg_01'
TOPIC = b'cat/esp32/01'

RESPONSE_TOPIC = b'iot/esp32/01'

sensor = dht.DHT11(Pin(18))

client = MQTTClient(CLIENT_ID, SERVER)


def read_sensor():
  global temp, hum
  temp = hum = 0
  try:
    sensor.measure()
    temp = sensor.temperature()
    hum = sensor.humidity()
    if (isinstance(temp, float) and isinstance(hum, float)) or (isinstance(temp, int) and isinstance(hum, int)):
      msg = (b'{0:3.1f},{1:3.1f}'.format(temp, hum))

      # uncomment for Fahrenheit
      #temp = temp * (9/5) + 32.0

      hum = round(hum, 2)
      return(msg)
    else:
      return('Invalid sensor readings.')
  except OSError as e:
    return('Failed to read sensor.')

def mqtt_callback(topic, msg):
    print('topic: {}'.format(topic))
    print('msg: {}'.format(msg))
    print(topic)
    print(msg)
    print(bytes.decode(msg))
    if TOPIC == topic:
        obj = ujson.loads(bytes.decode(msg))
        print(obj["cmd"])
        if obj["cmd"] == "dht":
            sensor_readings = read_sensor()
            print(sensor_readings)
            print(temp)
            print(hum)
            print('{{"temp":{0:.2f}, "hum":{1:.2f}}}'.format(temp, hum))
            client.publish(RESPONSE_TOPIC, '{{"temp":{0:.2f}, "hum":{1:.2f}}}'.format(temp, hum))
        else:
           print("Unkown Command") 
    else:
        print("Other Topic")

client.set_callback(mqtt_callback)
client.connect()

client.subscribe(TOPIC)


while True:
  client.check_msg()
  utime.sleep(1)

实测

MQTT发送指令（并通过另外的TOPIC返回数据）：

模块接收到指令并获取数据后发送：