Introduction

MQTT is an easily used networking protocol designed for IOT (internet of things) applications. It is well suited for controlling hardware devices and for reading sensors across a local network or the internet.

It is a means of communicating between multiple clients. A single server, also known as a broker, manages the network. Clients may include ESP8266, ESP32 and Pyboard D modules and other networked computers. Typical server hardware is a Raspberry Pi or other small Linux machine which may be left running 24/7. Public brokers also exist.

An effective PC client and server is mosquitto.

This repository

This contains two separate projects:

1. A "resilient" asynchronous non-blocking MQTT driver.
2. A means of using a cheap ESP8266 module to bring MQTT to MicroPython platforms which lack a WiFi interface. This is now obsolescent.

1. The "resilient" driver

This is an alternative to the official driver. It has been tested on the following platforms.

1. ESP8266
2. ESP32, ESP32-S2 and ESP32-S3
3. Pyboard D
4. Arduino Nano Connect
5. Raspberry Pi Pico W

The principal features of this driver are:

1. Non-blocking operation for applications using uasyncio.
2. Automatic recovery from WiFi and broker outages.
3. True qos == 1 operation with retransmission.
4. Improved WiFi range because of its tolerance of poor connectivity.

It has the drawback of increased code size which is an issue on the ESP8266. Run as frozen bytecode it uses about 50% of the RAM on the ESP8266. On ESP32 and Pyboard D it may be run as a standard Python module.

mqtt_as documentation.

2. MQTT bridge for generic MicroPython targets

This is obsolescent. It dates from a time when the only WiFi capable MicroPython target was the ESP8266. For all new applications one of the many WiFi-capable targets should be used with mqtt_as.

This comprises an ESP8266 firmware image and a MicroPython driver. The target hardware is linked to an ESP8266 running the firmware image using a 5-wire interface. The driver runs on the target which can then access MQTT. The driver is non-blocking and is designed for applications using uasyncio.

This library is in the bridge directory and is documented

here

It works and is supported, but its days are numbered unless someone reports a definite use case.