Publishing sensor data in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this sensor data publishing code?

Consider this Python code running on a Raspberry Pi that reads a temperature sensor and publishes the data to a server. What will be printed when the code runs?

Raspberry Pi

import time

def read_temperature():
    return 25.5

def publish_data(temp):
    print(f"Publishing temperature: {temp}°C")

for _ in range(2):
    temp = read_temperature()
    publish_data(temp)
    time.sleep(1)

A Publishing temperature: 25.5°C

B

Publishing temperature: 25.5°C
Publishing temperature: 25.5°C

C Error: time.sleep is not defined

D

Publishing temperature: 25°C
Publishing temperature: 25°C

💡 Hint

Look at the loop and how many times the print happens.

The loop runs twice, each time reading the temperature 25.5 and printing it. So the output is printed two times.

🧠 Conceptual

intermediate

Which protocol is commonly used to publish sensor data from Raspberry Pi?

When sending sensor data from a Raspberry Pi to a cloud server, which protocol is most commonly used for lightweight, reliable messaging?

A MQTT

B HTTP

C FTP

D SMTP

💡 Hint

Think about a protocol designed for small devices and low bandwidth.

MQTT is a lightweight messaging protocol designed for IoT devices like Raspberry Pi to publish sensor data efficiently.

🔧 Debug

advanced

What error does this sensor publishing code raise?

Analyze the following code snippet that tries to publish sensor data. What error will it raise when run?

Raspberry Pi

import paho.mqtt.client as mqtt

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

sensor_value = 42
client.publish("sensor/data", sensor_value)
client.disconnect()

print("Data published")

A AttributeError: 'Client' object has no attribute 'publish'

B ConnectionRefusedError

C No error, prints 'Data published'

D TypeError: a bytes-like object is required, not 'int'

💡 Hint

Check the data type expected by the publish method.

The publish method expects a string or bytes payload. Passing an integer causes a TypeError.

📝 Syntax

advanced

Which option correctly publishes JSON sensor data using MQTT?

Given a Raspberry Pi sensor reading, which code snippet correctly publishes the data as JSON to an MQTT topic?

Raspberry Pi

import json
import paho.mqtt.client as mqtt

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

sensor_data = {"temperature": 22.5, "humidity": 60}

# Publish code here

client.disconnect()

A client.publish("sensor/data", json.dumps(sensor_data))

B client.publish("sensor/data", str(sensor_data))

C client.publish("sensor/data", sensor_data)

D client.publish("sensor/data", json.load(sensor_data))

💡 Hint

Think about how to convert a dictionary to a string format suitable for transmission.

json.dumps converts the dictionary to a JSON string, which is the correct format for publishing.

🚀 Application

expert

How many messages are published by this Raspberry Pi sensor script?

Consider this Python script that reads sensor data and publishes it every 2 seconds for 5 iterations. How many MQTT publish messages will be sent?

Raspberry Pi

import time
import paho.mqtt.client as mqtt

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

for i in range(5):
    temp = 20 + i
    client.publish("sensor/temperature", str(temp))
    time.sleep(2)

client.disconnect()

A 0

B 10

C 1

D 5

💡 Hint

Count how many times the loop runs and publishes.

The loop runs 5 times, publishing once each iteration, so 5 messages are sent.