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How to MQTT Client Example (MicroPython)

This program demonstrates how to configure the W55RP20-S2E board as an MQTT Client (OP=5) using a Raspberry Pi Pico (Host) via UART or SPI. It connects to an MQTT broker, subscribes to a specific topic, and publishes messages to the network.

Step 1: Prepare software

The following software is required to run and test the MicroPython example.

• Thonny : An integrated development environment for MicroPython. used to write, upload, and run code.
• MQTT Broker: A server to mediate messages (e.g., Mosquitto installed on your PC).

Step 2: Prepare hardware

1. Connect GPIO13 according to the selected UART/SPI mode of the W55RP20 EVB Pico, as illustrated below.

2. Connect the Raspberry Pi Pico and the W55RP20 EVB Pico using jumper wires as shown below, depending on the selected UART/SPI mode.

• Important Note on Mode Switching: In this example setup, GPIO 13 of the W55RP20 EVB Pico is physically connected to GPIO 13 of the Raspberry Pi Pico. The Host Pico sets the mode (High/Low) automatically based on the software configuration.
• If you change the MODE in the code (e.g., UART ↔ SPI): You MUST reset both boards (Raspberry Pi Pico and W55RP20 EVB Pico) to ensure the mode is switched and recognized correctly.

If UART mode :

If SPI mode :

3. Connect the Raspberry Pi Pico to your PC (desktop or laptop) using a 5-pin Micro USB cable.

4. Connect the W55RP20 EVB Pico to your PC (desktop or laptop) using a USB Type-C cable.

Step 3: Setup Example

• Raspberry Pi Pico (Master) : Getting started with Raspberry Pi Pico (MicroPython)

Please refer to the link below to install the MicroPython firmware on the Raspberry Pi Pico.

• W55RP20 EVB Pico : Getting started with W55RP20 EVB Pico

Please refer to the link below for instructions on how to use the W55RP20 S2E.

Step 4: Upload Code

• Raspberry Pi Pico

Open Thonny IDE and connect to the Raspberry Pi Pico. Upload the following driver and example files to the Pico's storage.

Required Files:

1. w55rp20_s2e_uart.py (Required for UART mode)
2. w55rp20_s2e_spi.py (Required for SPI mode)

Example Application Files (Choose one to test):

• 08_mqtt_client.py (The main application)

Configuration: Before running an example, open the Python file you intend to use and modify the User Configuration section at the top.

# 08_mqtt_client.py
#
# MQTT Client example (Supports both SPI and UART modes):
# - Configure the module as MQTT client (OP=5) + DHCP
# - Connect to broker, subscribe to topic, and handle incoming messages
#
# Select mode by changing the MODE variable below.

import time

# -------------------------------------------------------------------------
# Configuration
# -------------------------------------------------------------------------
MODE     = "uart"  # Set to "spi" or "uart"
USE_DHCP = True    # True: DHCP (IM=1), False: Static IP (IM=0)

# MQTT Broker Settings
BROKER_HOST = "192.168.11.2"
BROKER_PORT = "1883"
CLIENT_ID   = "w55rp20_mpy_client"
SUB_TOPIC   = "w55rp20/sub"
PUB_TOPIC   = "w55rp20/pub"
PUB_MESSAGE = "Hello from W55RP20-S2E"
KEEP_ALIVE  = 30

# Network Configuration
LOCAL_IP    = "192.168.11.100"  # Local IP (Used when USE_DHCP=False)
SUBNET_MASK = "255.255.255.0"   # Subnet Mask (Used when USE_DHCP=False)
GATEWAY     = "192.168.11.1"    # Gateway (Used when USE_DHCP=False)
DNS_SERVER  = "8.8.8.8"         # DNS Server (Used when USE_DHCP=False)
.
.

Step 5: Testing with Mosquitto (PC Side)

Follow these steps to set up your PC as the MQTT environment.

1. Start the Mosquitto Broker

Open a terminal on your PC and start the broker.

Note: On Windows, you may need to navigate to C:\Program Files\mosquitto.

# Start broker with verbose logging to see connections
mosquitto -v

# Start broker with verbose logging to see connections
mosquitto -v

2. Monitor Incoming Messages (Subscribe)

Open a second terminal. This will show you the messages sent from the Pico.

# Listen for messages from the Pico
mosquitto_sub -h localhost -t w55rp20/pub

# Listen for messages from the Pico
mosquitto_sub -h localhost -t w55rp20/pub

3. Send Messages to the Pico (Publish)

Open a third terminal. Use this to send a command to the Pico.

# Send a message to the Pico
mosquitto_pub -h localhost -t w55rp20/sub -m "Hello from PC"

# Send a message to the Pico
mosquitto_pub -h localhost -t w55rp20/sub -m "LED_ON"

Step 6: Run

Pico (Thonny):

• Open 08_mqtt_client.py.
• Run the script (F5).

PC (Verify Publish):

• Check the second terminal on your PC. 
• You should see "Hello from W55RP20-S2E"

Pico (Thonny) : Verify Subscribe

• Use the third terminal command to send a message.
• In the Thonny shell, you should see [RX] w55rp20/sub : Hello from PC.