Publishing sensor data in Raspberry Pi

Introduction

We publish sensor data to share information from sensors with other devices or systems. This helps us monitor and react to changes in the environment.

You want to send temperature readings from a Raspberry Pi to a cloud server.

You need to share humidity data with a mobile app in real-time.

You want to log sensor data remotely for later analysis.

You want to trigger alerts when sensor values cross a limit.

You want to connect multiple sensors and send their data to a dashboard.

Syntax

Raspberry Pi

import paho.mqtt.client as mqtt
import time

# Setup MQTT client
client = mqtt.Client()
client.connect("broker.hivemq.com", 1883, 60)

# Function to publish sensor data
def publish_sensor_data(topic, data):
    client.publish(topic, data)

# Example usage
sensor_topic = "home/room1/temperature"
sensor_value = "23.5"
publish_sensor_data(sensor_topic, sensor_value)

# Disconnect after publishing
client.disconnect()

This example uses MQTT protocol to publish data.

You need an MQTT broker to send data through.

Examples

Simple publish of temperature data to a topic.

Raspberry Pi

import paho.mqtt.client as mqtt

client = mqtt.Client()
client.connect("broker.hivemq.com", 1883, 60)

# Publish temperature data
client.publish("home/room1/temperature", "22.0")
client.disconnect()

Publishing empty data to check how receiver handles it.

Raspberry Pi

import paho.mqtt.client as mqtt

client = mqtt.Client()
client.connect("broker.hivemq.com", 1883, 60)

# Publish empty data (edge case)
client.publish("home/room1/temperature", "")
client.disconnect()

Publishing data with degree symbol to show encoding support.

Raspberry Pi

import paho.mqtt.client as mqtt

client = mqtt.Client()
client.connect("broker.hivemq.com", 1883, 60)

# Publish data with special characters
client.publish("home/room1/temperature", "23.5°C")
client.disconnect()

Sample Program

This program connects to an MQTT broker, publishes three temperature readings one by one, and then disconnects.

Raspberry Pi

import paho.mqtt.client as mqtt
import time

# Connect to MQTT broker
client = mqtt.Client()
client.connect("broker.hivemq.com", 1883, 60)

# Simulate sensor data
sensor_topic = "home/room1/temperature"
sensor_values = [22.5, 22.7, 22.9]

print("Publishing sensor data:")
for sensor_value in sensor_values:
    print(f"Publishing {sensor_value} to topic {sensor_topic}")
    client.publish(sensor_topic, str(sensor_value))
    time.sleep(1)  # wait 1 second between publishes

client.disconnect()
print("Disconnected from broker.")

Important Notes

Publishing sensor data usually takes O(1) time per message.

Memory use is small, mostly for the message and connection.

Common mistake: forgetting to connect or disconnect the MQTT client.

Use publishing when you want to send data out; use subscribing when you want to receive data.

Summary

Publishing sensor data shares sensor readings with other devices.

Use MQTT protocol to send data easily from Raspberry Pi.

Always connect before publishing and disconnect after.