5. MQTT-Based Edge Communication o Setup publisher/subscriber model for edge-to-cloud communication

REQUIRED LIBRARY (on Raspberry Pi)

pip install Adafruit-DHT

FINAL IMPROVED CODE (LED + DHT11 via MQTT)

import time
import RPi.GPIO as GPIO
import paho.mqtt.client as mqtt
import board
import adafruit_dht

# ---------------- GPIO SETUP ----------------
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)

LED_PIN = 18
GPIO.setup(LED_PIN, GPIO.OUT)

# ---------------- DHT11 SETUP ----------------
dhtDevice = adafruit_dht.DHT11(board.D4)

# ---------------- MQTT SETUP ----------------
BROKER = "192.168.0.161"
TOPIC_CMD = "led/cmd"
TOPIC_STATUS = "led/status"
TOPIC_DHT = "sensor/dht11"

# ---------------- STATE ----------------
led_state = False   # change detector

# ---------------- CALLBACKS ----------------
def on_connect(client, userdata, flags, rc):
    print("Connected:", rc)
    client.subscribe(TOPIC_CMD)

def on_message(client, userdata, msg):
    global led_state
    payload = msg.payload.decode().lower()
    print("MQTT:", payload)

    # -------- OFF → ON (CHANGE SIGNAL) --------
    if payload == "on" and not led_state:
        led_state = True
        GPIO.output(LED_PIN, GPIO.HIGH)
        client.publish(TOPIC_STATUS, "ON")

        # ---- READ DHT11 ONCE ----
        try:
            temperature = dhtDevice.temperature
            humidity = dhtDevice.humidity

            if temperature is not None and humidity is not None:
                data = f"Temp={temperature}C Humidity={humidity}%"
                client.publish(TOPIC_DHT, data)
                print("DHT:", data)

        except RuntimeError as error:
            print("DHT error:", error)

    # -------- ON → OFF (CHANGE SIGNAL) --------
    elif payload == "off" and led_state:
        led_state = False
        GPIO.output(LED_PIN, GPIO.LOW)
        client.publish(TOPIC_STATUS, "OFF")

def on_disconnect(client, userdata, rc):
    print("Disconnected")

# ---------------- MQTT CLIENT ----------------
client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message
client.on_disconnect = on_disconnect

client.connect(BROKER, 1883, 60)
client.loop_forever()

Example Output

MQTT: on
DHT: Temp=28C Humidity=65%
DHT: Temp=28C Humidity=64%
MQTT: off

Case02

import time
from time import sleep
import os,sys
import RPi.GPIO as GPIO
import paho.mqtt.client as paho

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
LED_PIN=18  #define LED pin
GPIO.setup(LED_PIN,GPIO.OUT)   # Set pin function as output


def on_connect(self, mosq, obj, rc):
        self.subscribe("led", 0)
    
def on_message(mosq, obj, msg):
    #print(msg.topic + " " + str(msg.qos) + " " + str(msg.payload))
    if(msg.payload.decode().lower() == 'on'):    
        print("LED on")
        #sleep(5)
        GPIO.output(LED_PIN, 1)  #LED ON
        sleep(0.2)
    elif(msg.payload.decode().lower() == 'off'): 
        print("LED off") 
        #sleep(5)
        GPIO.output(LED_PIN,0)   # LED OFF
        sleep(0.2)

def on_publish(mosq, obj, mid):
    #print("mid: " + str(mid))
    pass

    
def on_subscribe(mosq, obj, mid, granted_qos):
    print("Subscribed: " + str(mid) + " " + str(granted_qos))



mqttc = paho.Client()                        # object declaration
# Assign event callbacks
mqttc.on_message = on_message                          # called as callback
mqttc.on_connect = on_connect
mqttc.on_publish = on_publish
mqttc.on_subscribe = on_subscribe

mqttc.connect('192.168.0.161', 1883)

rc = 0
flag = 0
flag1 = 0
while True:
    input_state=bool(GPIO.input(18))
    rc = mqttc.loop()
    if flag==0:
        mqttc.publish("led",'Status :'+str(GPIO.input(18)))
        flag=1
    if input_state==False:
        if flag1==0:
            print('Button Not Pressed')
            flag1=1
            flag=0
    elif input_state==True:
        if flag1==1:
            print('Button Pressed')
            flag1=0
            flag=0

Testing From OnBard raspberry Pi(192.168.0.161)

import time
from time import sleep
import os,sys
import RPi.GPIO as GPIO
import paho.mqtt.client as paho

GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
LED_PIN=18  #define LED pin
GPIO.setup(LED_PIN,GPIO.OUT)   # Set pin function as output
GPIO.output(LED_PIN,0)

GPIO.output(LED_PIN,1) #On
GPIO.output(LED_PIN,0) #OFF

Using MQTT Msg Publish

On Way Case 

pi@raspberrypi:~ $ mosquitto_pub -h 192.168.0.161 -t led -m "on"
pi@raspberrypi:~ $ mosquitto_pub -h 192.168.0.161 -t led -m "oN"
pi@raspberrypi:~ $ mosquitto_pub -h 192.168.0.161 -t led -m "On"
pi@raspberrypi:~ $ mosquitto_pub -h 192.168.0.161 -t led -m "ON"

OFF Way Case

pi@raspberrypi:~ $ mosquitto_pub -h 192.168.0.161 -t led -m "off"
pi@raspberrypi:~ $ mosquitto_pub -h 192.168.0.161 -t led -m "Off"
pi@raspberrypi:~ $ mosquitto_pub -h 192.168.0.161 -t led -m "oFf"
pi@raspberrypi:~ $ mosquitto_pub -h 192.168.0.161 -t led -m "OFF"