Networking with MQTT: Make Your Devices Talk

MQTT is the language of IoT. Devices 'publish' messages to topics like garden/soil, and anything 'subscribed' to that topic receives them instantly. Home Assistant, Node-RED and ESPHome all speak it.

Video tutorial

▶ HiveMQWatch on YouTube ↗

Video by HiveMQ, embedded from YouTube. The written steps below are our own and match the parts list.

Mission steps

1. Install the broker

   Install Mosquitto and its command-line clients on the Pi.

2. Subscribe in one window

   Open an SSH session and subscribe to a test topic.

3. Publish in another

   Open a second session and publish a message. It appears instantly in the first window.

4. Secure it for your network

   Mosquitto 2 only accepts local connections by default. To accept other devices, add a listener and a password file — never expose it to the internet without TLS.

5. Publish from Python

   Use the paho-mqtt library to send sensor readings from any script.

Code

sudo apt install -y mosquitto mosquitto-clients
# window 1
mosquitto_sub -h localhost -t lab/test
# window 2
mosquitto_pub -h localhost -t lab/test -m "hello from the pi"

# pip install paho-mqtt (inside your venv)
import paho.mqtt.publish as publish
publish.single("lab/temperature", "24.5", hostname="localhost")

Tip: test every script on the bench before installing it in a moving machine.

Questions