Publishing sensor data in IOT Protocols - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to publish sensor data to the MQTT broker.

IOT Protocols

client.[1]("sensor/temperature", "22.5")

Drag options to blanks, or click blank then click option'

Apublish

Bconnect

Csubscribe

Ddisconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Using subscribe instead of publish

Trying to connect instead of sending data

The publish method sends data to a topic on the MQTT broker.

2fill in blank

medium

Complete the code to connect the client to the MQTT broker at 'broker.hivemq.com'.

IOT Protocols

client.[1]("broker.hivemq.com", 1883, 60)

Drag options to blanks, or click blank then click option'

Apublish

Bsubscribe

Cconnect

Ddisconnect

Attempts:

3 left

💡 Hint

Common Mistakes

Using publish instead of connect

Trying to disconnect before connecting

The connect method establishes a connection to the MQTT broker.

3fill in blank

hard

Fix the error in the code to publish JSON sensor data correctly.

IOT Protocols

client.publish("sensor/humidity", [1])

Drag options to blanks, or click blank then click option'

Ajson.load({'humidity': 45})

B{'humidity': 45}

C45

Djson.dumps({'humidity': 45})

Attempts:

3 left

💡 Hint

Common Mistakes

Publishing a dictionary directly

Using json.load instead of json.dumps

The data must be converted to a JSON string using json.dumps() before publishing.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that publishes sensor readings above 30.

IOT Protocols

filtered_data = {sensor: value[1] for sensor, value in readings.items() if value [2] 30}

Drag options to blanks, or click blank then click option'

A**2

B>

C<

D*2

Attempts:

3 left

💡 Hint

Common Mistakes

Using exponentiation instead of multiplication

Filtering values less than 30

The comprehension multiplies values by 2 and filters those greater than 30.

5fill in blank

hard

Fill all three blanks to create a dictionary of sensor names in uppercase with values above 50.

IOT Protocols

result = [1]: [2] for [3], [2] in data.items() if [2] > 50

Drag options to blanks, or click blank then click option'

Asensor.upper()

Bvalue

Csensor

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Using data as iteration variable

Using sensor instead of sensor.upper() for keys

The keys are sensor names in uppercase, values are sensor readings, iterating over sensor and value.

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