Publishing sensor data in IOT Protocols - Mini Project: Build & Apply

Publishing sensor data

📖 Scenario: You have a small temperature sensor device that collects temperature readings every minute. You want to send these readings to a central server using a simple IoT protocol.

🎯 Goal: Build a small program that prepares temperature data and publishes it using a simulated IoT protocol message format.

📋 What You'll Learn

Create a dictionary with sensor data readings

Add a configuration variable for the sensor ID

Format the data into a publishable message string

Print the final message to simulate sending

💡 Why This Matters

🌍 Real World

IoT devices often collect sensor data and send it to servers for monitoring and analysis. Preparing and publishing data in a clear format is essential.

💼 Career

Understanding how to structure and send sensor data is a key skill for IoT developers and DevOps engineers working with connected devices.

1

Create sensor data dictionary

Create a dictionary called sensor_data with these exact entries: 'temperature': 22.5, 'humidity': 45, 'pressure': 1013

IOT Protocols

# Create the sensor_data dictionary with temperature, humidity, and pressure
# Your code here

Hint

Use curly braces to create a dictionary with the exact keys and values.

2

Add sensor ID configuration

Create a variable called sensor_id and set it to the string 'sensor_001'

IOT Protocols

sensor_data = {'temperature': 22.5, 'humidity': 45, 'pressure': 1013}
# Create the sensor_id variable with value 'sensor_001'
# Your code here

Hint

Assign the string 'sensor_001' to the variable sensor_id.

3

Format publish message

Create a variable called publish_message that formats the string as "ID: sensor_001, Data: {'temperature': 22.5, 'humidity': 45, 'pressure': 1013}" using an f-string with sensor_id and sensor_data

IOT Protocols

sensor_data = {'temperature': 22.5, 'humidity': 45, 'pressure': 1013}
sensor_id = 'sensor_001'
# Create publish_message using f-string with sensor_id and sensor_data
# Your code here

Hint

Use an f-string to insert sensor_id and sensor_data into the message string.

4

Print the publish message

Write a print statement to display the publish_message variable

IOT Protocols

sensor_data = {'temperature': 22.5, 'humidity': 45, 'pressure': 1013}
sensor_id = 'sensor_001'
publish_message = f"ID: {sensor_id}, Data: {sensor_data}"
# Print the publish_message
# Your code here

Hint

Use print() to show the publish_message on the screen.

Practice

1. What is the main purpose of publishing sensor data in IoT protocols?

easy

A. To send sensor data to a topic so others can receive it

B. To store sensor data locally on the device

C. To encrypt sensor data before sending

D. To delete old sensor data from the cloud

Solution

1. Step 1: Understand publishing in IoT

   Publishing means sending data from a sensor to a topic so other devices can get it.

2. Step 2: Identify the main goal

   The goal is to share sensor data, not store or delete it locally or encrypt it by default.

3. Final Answer:

   To send sensor data to a topic so others can receive it -> Option A

4. Quick Check:

   Publishing = sending data to topic [OK]

Hint: Publishing means sending data to a topic for others [OK]

Common Mistakes:

• Confusing publishing with storing data locally
• Thinking publishing encrypts data automatically
• Assuming publishing deletes old data

2. Which MQTT publish command syntax is correct for sending temperature data to topic home/livingroom/temp?

easy

A. mqtt.publish('home/livingroom/temp', '22.5')

B. publish('home/livingroom/temp', temperature=22.5)

C. mqtt.publish('home/livingroom/temp')

D. publish('home/livingroom/temp', 22.5)

Solution

1. Step 1: Check MQTT publish method syntax

   The correct syntax uses the client object (e.g., mqtt) and calls publish with topic and message as string.

2. Step 2: Validate options

   mqtt.publish('home/livingroom/temp', '22.5') uses mqtt.publish with topic and string message, which is correct. publish('home/livingroom/temp', 22.5) misses client object, C misses message, B uses invalid keyword argument.

3. Final Answer:

   mqtt.publish('home/livingroom/temp', '22.5') -> Option A

4. Quick Check:

   mqtt.publish(topic, message) = correct syntax [OK]

Hint: Use client.publish(topic, message) with message as string [OK]

Common Mistakes:

• Omitting the client object before publish
• Not providing the message argument
• Using keyword arguments not supported by publish

3. Given this Python MQTT publish code snippet, what will be printed?

import paho.mqtt.client as mqtt
client = mqtt.Client()
client.connect('broker.hivemq.com', 1883)
result = client.publish('sensor/room1/humidity', '45')
print(result.rc)

medium

A. 1

B. 0

C. null

D. Error

Solution

1. Step 1: Understand publish return value

   client.publish returns a MQTTMessageInfo object with rc attribute showing result code: 0 means success.

2. Step 2: Check printed value

   Printing result.rc will print 0 if publish succeeded without error.

3. Final Answer:

   0 -> Option B

4. Quick Check:

   Publish success code = 0 [OK]

Hint: Publish returns rc=0 on success, print result.rc to see it [OK]

Common Mistakes:

• Assuming publish returns null
• Expecting printed message payload
• Confusing rc with error code

4. You wrote this MQTT publish code but no data appears on the subscriber side:

client.publish('sensor/temp', 25)

What is the likely problem?

medium

A. QoS level is missing and defaults to 2

B. The topic name is invalid

C. The message payload must be a string or bytes, not an integer

D. The client must call subscribe before publish

Solution

1. Step 1: Check payload data type

   MQTT publish requires message payload as string or bytes, not integer directly.

2. Step 2: Identify issue with given code

   Passing 25 as integer causes publish to fail silently or send empty data, so subscriber gets nothing.

3. Final Answer:

   The message payload must be a string or bytes, not an integer -> Option C

4. Quick Check:

   Payload must be string/bytes, not int [OK]

Hint: Always convert payload to string or bytes before publishing [OK]

Common Mistakes:

• Sending integer payload without conversion
• Thinking subscribe is needed before publish
• Assuming topic name is invalid without checking

5. You want to publish temperature data that stays available for new subscribers and is delivered reliably. Which MQTT publish options should you set?

hard

A. Set QoS=0 and retain=false

B. Set QoS=0 and retain=true

C. Set QoS=2 and retain=false

D. Set QoS=1 and retain=true

Solution

1. Step 1: Understand QoS levels

   QoS=1 ensures message delivery at least once, making it reliable.

2. Step 2: Understand retain flag

   retain=true keeps the last message on the broker so new subscribers get it immediately.

3. Step 3: Combine for reliable and persistent data

   Setting QoS=1 and retain=true meets both requirements.

4. Final Answer:

   Set QoS=1 and retain=true -> Option D

5. Quick Check:

   QoS=1 + retain=true = reliable & persistent [OK]

Hint: Use QoS=1 and retain=true for reliable, persistent data [OK]

Common Mistakes:

• Using QoS=0 which is unreliable
• Not setting retain so new subscribers miss data
• Confusing QoS=2 as always best choice