--- title: "Pico MicroPython MQTT Practice: Publish JSON Payloads to EMQX" url: "https://maker.wiznet.io/ruilixin6/projects/pico-micropython-mqtt-practice-publish-json-payloads-to-emqx/" markdown_url: "https://maker.wiznet.io/ruilixin6/projects/pico-micropython-mqtt-practice-publish-json-payloads-to-emqx/md" type: "UCC: User Created Content" author: "FreakStudio" author_url: "https://maker.wiznet.io/ruilixin6/" original_author: "Freakstudio" original_url: "https://f1829ryac0m.feishu.cn/drive/folder/Fh5Eftd3WlbEIIdHGdtcSsIgn7c?from=frl" published: "2026-08-24" language: "en" tags: ["Pico MicroPython MQTT EMQX JSON"] likes: 0 views: 65 comments: 0 source: "WIZnet Makers (https://maker.wiznet.io/)" --- # Pico MicroPython MQTT Practice: Publish JSON Payloads to EMQX > Practical guide for Pico to publish JSON messages to EMQX broker. Original author: Freakstudio (source: https://f1829ryac0m.feishu.cn/drive/folder/Fh5Eftd3WlbEIIdHGdtcSsIgn7c?from=frl) ## Article 【Preliminary Note】The original hardware example in this article was written based on the RP2040. The actual hardware used in this hands-on demonstration features the W55RP20 as the main controller chip. The circuit logic and UF2 flashing operation principles are universally applicable, with only the main controller model differing. The original chip model mentioned in the circuit descriptions below is provided for reference purposes only. ![](https://maker.wiznet.io/upload/ckeditor5/383111824%5F1787564742%2Epng) In the following code, we implement an MQTT client on the Wiznet W5500 module using MicroPython, which can communicate with the MQTT Broker provided by EMQX Cloud. After connecting to the network and initializing the W5500 module, the program connects to the MQTT server and uses a timer to send keep‑alive ping packets to maintain connection status. Afterwards, the client cyclically publishes predefined JSON messages to the specified topic. Finally, after completing all publish operations, it disconnects the MQTT connection and releases resources. The source code below can be found in the provided resource package under `elegance‑devkit v1\Demo\48 ETH_MQTT_Publish`. Sample code: ```plaintext # Python env : MicroPython v1.23.0 on Wiznet W5500 # -*- coding: utf-8 -*- # @Time : 2024/8/9 11:15 AM # @Author : Li Qingshui # @File : main.py # @Description : Implement publish function for MQTT client # ======================================== Import related modules ======================================== # Import hardware‑related modules from machine import Pin,SPI,reset,Timer # Import time‑related modules import time # Import network‑related modules import network # Import socket module for creating and managing network connections from usocket import socket # Import MQTT client from umqttrobust import MQTTClient # Import json encoding library import json # ======================================== Global variables ============================================ # Device IP address ip = '192.168.1.20' sn = '255.255.255.0' gw = '192.168.1.1' dns= '8.8.8.8' # Tuple object for network configuration netinfo=(ip, sn, gw, dns) # MQTT configuration mqtt_params = { 'url': 'broker.emqx.io', # MQTT server address 'port': 1883, # MQTT server port 'clientid': 'FreakStudioDevice', # Local MQTT client ID 'pubtopic': '/FreakStudio/pub', # Publish topic 'pubqos': 0, # Publish QoS level } # Message content to be published msg = { 'clientid' : 'FreakStudioDevice', 'MQTT_Version' : 'v3.1.1', 'Device' : 'raspberry pi pico', 'Name' : 'FreakStudio MQTT Sub Test', } # Encode message content into json format topic_msg = json.dumps(msg) # Record timer execution count timer_count = 0 # MQTT client instance client = None # ======================================== Function definitions ============================================ def w5x00_init() -> network.WIZNET5K: ''' Initialize network.WIZNET5K instance, set static IP and bring‑up network connection. Returns: network.WIZNET5K: Initialized and connected network interface instance. ''' # Declare global variable global netinfo # Initialize SPI object spi = SPI(0, 2_000_000, mosi=Pin(19), miso=Pin(16), sck=Pin(18)) # Instantiate network.WIZNET5K, pass chip‑select pin CS and reset pin RST nic = network.WIZNET5K(spi, Pin(17), Pin(20)) # Activate network interface nic.active(True) try: print("\r\nConfiguring DHCP") # Try to acquire IP, subnet mask, gateway, DNS via DHCP nic.ifconfig('dhcp') except: print("\r\nDHCP fails, use static configuration") # Fallback to static IP configuration on DHCP failure nic.ifconfig(netinfo) # Block until network link becomes available while not nic.isconnected(): time.sleep(1) # Print register debug information print(nic.regs()) # Print applied network parameters print('ip :', nic.ifconfig()[0]) print('sn :', nic.ifconfig()[1]) print('gw :', nic.ifconfig()[2]) print('dns:', nic.ifconfig()[3]) # Return WIZNET5K instance return nic def mqtt_connect() -> MQTTClient: ''' Connect to MQTT server. Returns: MQTTClient: Successfully connected MQTT client instance. ''' global client_id, mqtt_server # Create MQTT client instance, keep‑alive time set to 60 seconds client = MQTTClient(mqtt_params['clientid'], mqtt_params['url'], mqtt_params['port'],keepalive=60) # Connect to MQTT server client.connect() # Print connection success message print('Connected to %s MQTT Broker'%(mqtt_params['url'])) # Return MQTT client instance return client def timer_callback(t: Timer) -> None: ''' Timer callback function for sending ping keep‑alive packets. Args: t (Timer): Timer instance. Returns: None ''' # Declare global variable global timer_count, client # Increment timer counter timer_count = timer_count + 1 # Trigger when counter reaches or exceeds 30 if timer_count >= 30: # Reset timer counter timer_count = 0 # Send MQTT ping packet client.ping() # ======================================== Custom classes ============================================ # ======================================== Initialization ========================================== # 3‑second power‑on delay for hardware stabilization time.sleep(3) # Print debug banner print("FreakStudio : Using WIZNET5K Ethernet Device to connect to MQTT Broker as a Publisher") # Initialize W5500 module nic = w5x00_init() try: # Try connecting to MQTT server client = mqtt_connect() except OSError as e: # Print exception information print('raise exception : {}'.format(e)) # Reconnect and reset upon connection failure client.reconnect() # Create timer instance for periodic MQTT ping packets timer = Timer(-1) # Call timer_callback every 1 second timer.init(freq=1, mode=Timer.PERIODIC, callback=timer_callback) # ======================================== Main program =========================================== # Publish messages 10 times in loop for i in range(10): try: # Publish message to specified topic client.publish(mqtt_params['pubtopic'],topic_msg,qos = mqtt_params['pubqos']) # Print debug information print('Message Published: %s' % topic_msg) # Wait for 3 seconds time.sleep(3) except Exception as e: # Print exception information print("Failed to publish message") print('raise exception : {}'.format(e)) # Disconnect from MQTT server client.disconnect() # Stop timer timer.deinit() ``` Here we set a timer which invokes the callback function every 1 second. When the timer counter reaches 30 (30 seconds elapsed), it sends an MQTT ping packet to the MQTT Broker to sustain the connection. In the main program, it loops 10 times, publishing JSON‑encoded messages to topic `'/FreakStudio/pub'` and printing debug logs each iteration. Overall workflow diagram: ![1.png](http://openwrite.cn/uploads/21597/63806/eae21306-328c-48de-880f-db46cf08e2fe.png) Meanwhile we need to configure MQTTX software to subscribe to topic `'/FreakStudio/pub'`. First establish connection between client and broker. Click the button in the lower‑left corner to quickly subscribe to a Topic. Once subscribed, the client immediately starts receiving incoming messages: ![2.png](http://openwrite.cn/uploads/21597/63806/0ca3b0e3-8071-40b8-8ad5-3444351a35d8.png) Topic parameters are set as shown below: Each Topic gets a random color marker. You may also open the color‑picker to customize marker color. Click the far‑right button at the top of the subscription list to hide the list for more display space. Since Raspberry Pi Pico sends data in JSON format, set message display format to Json: Flash firmware and open serial terminal. You will see output as follows: Inside MQTTX software, the PC client displays received messages for the corresponding topic: You can also click buttons on the left sidebar to view MQTTX connection history records: --- Source: https://maker.wiznet.io/ruilixin6/projects/pico-micropython-mqtt-practice-publish-json-payloads-to-emqx/