ESP32 MicroPython

022 – ESP32 MicroPython: MQTT Part 2: Subscribe

George Bantique

In the previous tutorial, I demonstrate the use of MQTT protocol by sending DHT sensor readings to Thingspeak as MQTT broker while the ESP32 serves as MQTT client. The act of MQTT client sending data to MQTT broker is called MQTT publish.

Now in this tutorial, I will demonstrate the other direction of MQTT communication which is MQTT subscribe where a client is waiting for a message from a broker. A client that subscribes to a certain topic will receive a data update from the broker when a new publish data is received from a certain publishing client.

Now to demonstrate that, I will be needing 3 components which are:

  1. A publishing client
  2. A broker and
  3. A subscribe client

BILL OF MATERIALS:

  1. ESP32 development board.
  2. 0.96 OLED display
 

HARDWARE INSTRUCTION:

  1. Connect the OLED VCC pin to ESP32 3.3V pin.
  2. Connect the OLED GND pin to ESP32 GND pin.
  3. Connect the OLED SCL pin to ESP32 D22 pin.
  4. Connect the OLED SDA pin to ESP32 D21 pin.
 

VIDEO DEMONSTRATION:

 

CALL TO ACTION:

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Thank you and have a good days ahead.

See you,

– George Bantique | tech.to.tinker@gmail.com

 

SOURCE CODE:

1. Basic demonstration of handling MQTT Subscribe message data payload:

# **************************************#  
#  MQTT in MicroPython with Thingspeak  #  
# **************************************#  
# Author: George Bantique               #  
#         TechToTinker Youtube Channel  #  
#         TechToTinker.blogspot.com     #  
#         tech.to.tinker@gmail.com      #  
# Date: Dec.13, 2020                    #  
# Please feel free to modify the code   #  
# according to your needs.              #  
# **************************************# 

# **************************************#  
# Load necessary libraries  
import machine  
import network  
import wifi_credentials  
from umqtt.robust import MQTTClient  
import ssd1306  
import time  
import os  
import sys 


# **************************************#  
# Objects:  
led = machine.Pin(2,machine.Pin.OUT)  
scl = machine.Pin(22, machine.Pin.OUT, machine.Pin.PULL_UP)  
sda = machine.Pin(21, machine.Pin.OUT, machine.Pin.PULL_UP)  
i2c = machine.I2C(scl=scl, sda=sda, freq=400000)  
oled = ssd1306.SSD1306_I2C(128, 64, i2c, addr=0x3C) 

# **************************************#  
# Configure the ESP32 wifi as STAtion.  
sta = network.WLAN(network.STA_IF)  
if not sta.isconnected():  
  print('connecting to network...')  
  sta.active(True)  
  #sta.connect('wifi ssid', 'wifi password')  
  sta.connect(wifi_credentials.ssid, wifi_credentials.password)  
  while not sta.isconnected():  
    pass  
print('network config:', sta.ifconfig()) 

# **************************************#  
# Callback function, it is the function  
# that will be called when a new msg  
# is received from MQTT broker  
def call_back_function(topic, msg):  
    oled.fill(0)  
    oled.text(msg.decode().strip("'n"), 5, 5)  
    oled.show()  
    print((topic, msg)) 
        
# **************************************#  
# Global variables and constants  
UNIQUE_CLIENT_ID = "ab06f0c1-1319-44bc-9534-04caea40af81"  
THINGSPEAK_URL = b"mqtt.thingspeak.com"   
THINGSPEAK_USERNAME = b'mwa0000020270097'  
THINGSPEAK_MQTT_API_KEY = b'AWP9SRI6ED9ONGBO'  
THINGSPEAK_CHANNEL_ID = b'1250656'  
THINGSPEAK_CHANNEL_READ_API_KEY = b'TVRCWGZKKOVC2MQR'  
TOPIC_SUB = bytes("channels/{:s}/subscribe/fields/field1/{:s}"
                  .format(THINGSPEAK_CHANNEL_ID,
                          THINGSPEAK_CHANNEL_READ_API_KEY),
                  'utf-8')  

# **************************************#  
# MQTT client configuration:  
# 1.Create the MQTT client      
client = MQTTClient(client_id = UNIQUE_CLIENT_ID,   
                    server = THINGSPEAK_URL,   
                    user = THINGSPEAK_USERNAME,   
                    password = THINGSPEAK_MQTT_API_KEY,   
                    ssl = False)  
# 2.Set the callback function  
client.set_callback(call_back_function)  
# 3.Connect to MQTT broker  
try:  
    client.connect()  
except Exception as e:  
    machine.reset  
# 4.Subscribe to a specific topic      
client.subscribe(TOPIC_SUB)  

# **************************************#  
# Main loop  
while True:  
    try:  
        #client.wait_msg() #blocking  
        client.check_msg() #non-blocking  
    except KeyboardInterrupt:  
        print('Ctrl-C pressed...exiting')  
        client.disconnect()  
        sys.exit()
 

2. How to use MQTT Subscribe message as command for controlling something:

# **************************************# 
#  MQTT in MicroPython with Thingspeak  # 
# **************************************# 
# Author: George Bantique               # 
#         TechToTinker Youtube Channel  # 
#         TechToTinker.blogspot.com     # 
#         tech.to.tinker@gmail.com      # 
# Date: Dec.13, 2020                    # 
# Please feel free to modify the code   # 
# according to your needs.              # 
# **************************************# 

# **************************************# 
# Load necessary libraries 
import machine 
import network 
import wifi_credentials 
from umqtt.robust import MQTTClient 
import ssd1306 
import time 
import os 
import sys 

# **************************************# 
# Objects: 
led = machine.Pin(2,machine.Pin.OUT) 
scl = machine.Pin(22, machine.Pin.OUT, machine.Pin.PULL_UP) 
sda = machine.Pin(21, machine.Pin.OUT, machine.Pin.PULL_UP) 
i2c = machine.I2C(scl=scl, sda=sda, freq=400000) 
oled = ssd1306.SSD1306_I2C(128, 64, i2c, addr=0x3C) 

# **************************************# 
# Configure the ESP32 wifi as STAtion. 
sta = network.WLAN(network.STA_IF) 
if not sta.isconnected(): 
  print('connecting to network...') 
  sta.active(True) 
  #sta.connect('wifi ssid', 'wifi password') 
  sta.connect(wifi_credentials.ssid, wifi_credentials.password) 
  while not sta.isconnected(): 
    pass 
print('network config:', sta.ifconfig()) 

# **************************************# 
# Callback function, it is the function 
# that will be called when a new msg 
# is received from MQTT broker 
def call_back_function(topic, msg): 
     global message 
     oled.fill(0) 
     message = msg.decode().strip("'n") 
     oled.text(message, 5, 5) 
     oled.show() 
     print((topic, msg)) 
 
# **************************************# 
# Global variables and constants 
UNIQUE_CLIENT_ID = "ab06f0c1-1319-44bc-9534-04caea40af81" 
THINGSPEAK_URL = b"mqtt.thingspeak.com"  
THINGSPEAK_USERNAME = b'mwa0000020270097' 
THINGSPEAK_MQTT_API_KEY = b'AWP9SRI6ED9ONGBO' 
THINGSPEAK_CHANNEL_ID = b'1250656' 
THINGSPEAK_CHANNEL_READ_API_KEY = b'TVRCWGZKKOVC2MQR' 
TOPIC_SUB = bytes("channels/{:s}/subscribe/fields/field1/{:s}"
                  .format(THINGSPEAK_CHANNEL_ID,
                          THINGSPEAK_CHANNEL_READ_API_KEY),
                  'utf-8') 
message = "" 

# **************************************# 
# MQTT client configuration: 
# 1.Create the MQTT client object    
client = MQTTClient(client_id = UNIQUE_CLIENT_ID,  
                    server = THINGSPEAK_URL,  
                    user = THINGSPEAK_USERNAME,  
                    password = THINGSPEAK_MQTT_API_KEY,  
                    ssl = False) 
# 2.Set the callback function 
client.set_callback(call_back_function) 
# 3.Connect to MQTT broker 
try: 
    client.connect() 
except Exception as e: 
    machine.reset 
# 4.Subscribe to a specific topic     
client.subscribe(TOPIC_SUB) 

# **************************************# 
# Main loop 
while True: 
    try: 
        client.wait_msg() #blocking 
        #client.check_msg() #non-blocking 
         
        if message == 'led ON': 
            led.on() 
            print('led is now ON') 
        elif message == 'led OFF': 
            led.off() 
            print('led is now OFF') 
        elif message == 'oled WHITE': 
            oled.invert(1) 
            print('oled is now black on WHITE') 
        elif message == 'oled BLACK': 
            oled.invert(0) 
            print('oled is now white on BLACK') 
             
    except KeyboardInterrupt: 
        print('Ctrl-C pressed...exiting') 
        client.disconnect() 
        sys.exit()
 

REFERENCES AND CREDITS:

Thingspeak: thingspeak.com

3 thoughts on “022 – ESP32 MicroPython: MQTT Part 2: Subscribe”

  1. Hi,
    I try to set Thinkspeak. But there is not MQTT API KEY on My Profile page.
    I try to find some document like https://ww2.mathworks.cn/help/thingspeak/use-desktop-mqtt-client-to-publish-to-a-channel.html
    to set MQTT device on ThingSpeak, and key in the CLIENT_ID, password(MQTT_API_KEY)
    But it still show error message like below:
    Traceback (most recent call last):
    File "", line 91, in
    File "umqtt/simple.py", line 215, in check_msg
    File "umqtt/robust.py", line 44, in wait_msg
    File "umqtt/robust.py", line 24, in reconnect
    File "umqtt/simple.py", line 110, in connect
    MQTTException: 5

    Reply

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