Serving sensor data as JSON API in Raspberry Pi - Mini Project: Build & Apply

Serving sensor data as JSON API

📖 Scenario: You have a Raspberry Pi connected to a temperature sensor. You want to share the sensor readings over a simple web API that returns the data in JSON format. This way, other devices or apps can easily get the current temperature.

🎯 Goal: Build a small Python program that reads temperature data from a sensor (simulated), sets up a web server, and serves the sensor data as a JSON response when accessed.

📋 What You'll Learn

Create a dictionary with sensor data including 'temperature' and 'unit'.

Create a variable called 'port' to set the server port number.

Use Flask to create a web server with a route '/' that returns the sensor data as JSON.

Print a message showing the server is running on the specified port.

💡 Why This Matters

🌍 Real World

Sharing sensor data as JSON over a network is common in IoT projects, home automation, and remote monitoring.

💼 Career

Understanding how to serve JSON APIs is important for backend development, embedded systems, and working with connected devices.

1

Create sensor data dictionary

Create a dictionary called sensor_data with these exact entries: 'temperature': 23.5 and 'unit': 'Celsius'.

Raspberry Pi

# Create the sensor_data dictionary with temperature and unit
# Your code here

Hint

Use curly braces to create a dictionary with keys 'temperature' and 'unit'.

2

Set server port variable

Create a variable called port and set it to 5000.

Raspberry Pi

sensor_data = {'temperature': 23.5, 'unit': 'Celsius'}
# Create a variable port and set it to 5000
# Your code here

Hint

Just assign the number 5000 to the variable named port.

3

Create Flask app and route

Import Flask and jsonify from flask. Create a Flask app called app. Define a route for '/' that returns jsonify(sensor_data).

Raspberry Pi

sensor_data = {'temperature': 23.5, 'unit': 'Celsius'}
port = 5000
# Import Flask and jsonify
# Create app = Flask(__name__)
# Define route '/' that returns jsonify(sensor_data)
# Your code here

Hint

Use @app.route('/') to create the route and return the sensor_data as JSON.

4

Run the Flask server and print message

Add the code to run the Flask app with app.run(host='0.0.0.0', port=port). Before running, print f"Server running on port {port}".

Raspberry Pi

from flask import Flask, jsonify

sensor_data = {'temperature': 23.5, 'unit': 'Celsius'}
port = 5000

app = Flask(__name__)

@app.route('/')
def get_sensor_data():
    return jsonify(sensor_data)

# Print server running message and run app
# Your code here

Hint

Use print(f"Server running on port {port}") and then app.run(host='0.0.0.0', port=port).

Practice

1.

What is the main purpose of serving sensor data as a JSON API on a Raspberry Pi?

easy

A. To allow other devices to easily access sensor information in a standard format

B. To store sensor data only on the Raspberry Pi without sharing

C. To convert sensor data into images for display

D. To run heavy calculations on sensor data locally

Solution

1. Step 1: Understand JSON API purpose

   A JSON API provides data in a simple, standard format that other devices can read easily.

2. Step 2: Relate to sensor data sharing

   Serving sensor data as JSON means sharing sensor readings so other devices or apps can use them.

3. Final Answer:

   To allow other devices to easily access sensor information in a standard format -> Option A

4. Quick Check:

   JSON API shares sensor data easily [OK]

Hint: JSON API means sharing data in a simple format [OK]

Common Mistakes:

• Thinking JSON API stores data only locally
• Confusing JSON API with image or video output
• Assuming JSON API does heavy local processing

2.

Which of the following is the correct way to import Flask in a Python script on Raspberry Pi?

?

easy

A. import flask

B. import Flask

C. from Flask import flask

D. from flask import Flask

Solution

1. Step 1: Recall Flask import syntax

   The Flask class is imported from the flask module using: from flask import Flask

2. Step 2: Check options for correct case and syntax

   from flask import Flask matches correct syntax and case; others have wrong case or structure.

3. Final Answer:

   from flask import Flask -> Option D

4. Quick Check:

   Correct Flask import uses 'from flask import Flask' [OK]

Hint: Flask class is imported with 'from flask import Flask' [OK]

Common Mistakes:

• Using wrong capitalization like 'import Flask'
• Importing the whole module without accessing Flask class
• Mixing module and class names incorrectly

3.

What will be the output of this Flask route when accessed?

from flask import Flask, jsonify
app = Flask(__name__)

@app.route('/sensor')
def sensor_data():
    data = {'temperature': 22.5, 'humidity': 60}
    return jsonify(data)

# Assume app is running

medium

A. Error: jsonify not defined

B. {temperature: 22.5, humidity: 60}

C. {"temperature": 22.5, "humidity": 60}

D. ['temperature', 22.5, 'humidity', 60]

Solution

1. Step 1: Understand jsonify output

   jsonify converts Python dict to JSON string with keys in quotes and proper JSON format.

2. Step 2: Match output format

   {"temperature": 22.5, "humidity": 60} shows correct JSON string with keys and values properly formatted.

3. Final Answer:

   {"temperature": 22.5, "humidity": 60} -> Option C

4. Quick Check:

   jsonify returns JSON string with quoted keys [OK]

Hint: jsonify outputs JSON with quoted keys and values [OK]

Common Mistakes:

• Forgetting quotes around keys in JSON output
• Confusing Python dict print with JSON string
• Assuming jsonify returns Python list

4.

Identify the error in this Flask code snippet that serves sensor data as JSON:

from flask import Flask, jsonify
app = Flask(__name__)

@app.route('/data')
def data():
    sensor = {'temp': 25}
    return json.dumps(sensor)

app.run()

medium

A. json.dumps is used instead of jsonify

B. Flask app is not created correctly

C. Route decorator syntax is wrong

D. Missing import for Flask

Solution

1. Step 1: Check JSON response method

   Flask expects jsonify to create proper response with correct headers, not json.dumps.

2. Step 2: Identify error cause

   Using json.dumps returns a string without correct content-type, causing client issues.

3. Final Answer:

   json.dumps is used instead of jsonify -> Option A

4. Quick Check:

   Use jsonify, not json.dumps, for Flask JSON responses [OK]

Hint: Use jsonify for Flask JSON responses, not json.dumps [OK]

Common Mistakes:

• Returning json.dumps output directly in Flask
• Not importing jsonify
• Assuming json.dumps sets response headers

5.

You want to serve live temperature sensor data from a Raspberry Pi using Flask. Which approach correctly updates the JSON response with real sensor readings each time the API is called?

from flask import Flask, jsonify
app = Flask(__name__)

def read_temp_sensor():
    # Returns current temperature reading
    return 24.7

@app.route('/temp')
def temp():
    # Fill in here

app.run()

hard

A. temp = 24.7
return jsonify({'temperature': temp})

B. temp = read_temp_sensor()
return jsonify({'temperature': temp})

C. return jsonify({'temperature': read_temp_sensor})

D. return {'temperature': read_temp_sensor()} # Flask auto converts

Solution

1. Step 1: Call sensor function inside route

   We must call read_temp_sensor() to get current value each time the route is accessed.

2. Step 2: Return JSON response with current value

   Assign the value to a variable and pass it to jsonify to return proper JSON response.

3. Final Answer:

   temp = read_temp_sensor() return jsonify({'temperature': temp}) -> Option B

4. Quick Check:

   Call sensor function and jsonify result each request [OK]

Hint: Call sensor function inside route, then jsonify result [OK]

Common Mistakes:

• Returning function object instead of calling it
• Using fixed value instead of live sensor reading
• Returning dict without jsonify in Flask