SQLite database for sensor data in Raspberry Pi - Mini Project: Build & Apply

SQLite database for sensor data

📖 Scenario: You have a Raspberry Pi connected to a temperature sensor. You want to store the temperature readings in a small database so you can analyze them later.

🎯 Goal: Create a simple SQLite database on the Raspberry Pi to store sensor data. You will create the database, add a configuration for the sensor ID, insert temperature readings, and finally display the stored data.

📋 What You'll Learn

Create an SQLite database connection

Create a table for sensor readings

Store sensor ID in a variable

Insert temperature readings into the database

Retrieve and display all stored readings

💡 Why This Matters

🌍 Real World

Storing sensor data in a database on a Raspberry Pi helps keep track of environmental conditions over time for analysis or alerts.

💼 Career

Many IoT and embedded systems jobs require working with small databases like SQLite to manage sensor or device data efficiently.

1

Create SQLite database and table

Write code to import sqlite3, connect to a database file named sensor_data.db, and create a table called readings with columns id (integer primary key autoincrement), sensor_id (text), temperature (real), and timestamp (text). Use conn as the connection variable and cursor as the cursor variable.

Raspberry Pi

import sqlite3

# Connect to SQLite database sensor_data.db
conn = sqlite3.connect('sensor_data.db')
cursor = conn.cursor()

# Create readings table
# Your code here

Hint

Use sqlite3.connect() to connect and cursor.execute() to create the table.

2

Set sensor ID configuration

Create a variable called sensor_id and set it to the string 'sensor_01' to identify the sensor.

Raspberry Pi

import sqlite3

conn = sqlite3.connect('sensor_data.db')
cursor = conn.cursor()
cursor.execute('''CREATE TABLE IF NOT EXISTS readings (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    sensor_id TEXT,
    temperature REAL,
    timestamp TEXT
)''')
conn.commit()

# Set sensor_id variable
# Your code here

Hint

Just assign the string 'sensor_01' to the variable sensor_id.

3

Insert a temperature reading

Write code to insert a new reading into the readings table using cursor.execute(). Use the sensor_id variable, temperature value 23.5, and timestamp string '2024-06-01 12:00:00'. Commit the change with conn.commit().

Raspberry Pi

import sqlite3

conn = sqlite3.connect('sensor_data.db')
cursor = conn.cursor()
cursor.execute('''CREATE TABLE IF NOT EXISTS readings (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    sensor_id TEXT,
    temperature REAL,
    timestamp TEXT
)''')
conn.commit()

sensor_id = 'sensor_01'

# Insert a temperature reading
# Your code here

Hint

Use parameter substitution with ? placeholders and a tuple of values.

4

Display all stored readings

Write code to select all rows from the readings table using cursor.execute() and fetch all results with cursor.fetchall(). Then print each row on its own line.

Raspberry Pi

import sqlite3

conn = sqlite3.connect('sensor_data.db')
cursor = conn.cursor()
cursor.execute('''CREATE TABLE IF NOT EXISTS readings (
    id INTEGER PRIMARY KEY AUTOINCREMENT,
    sensor_id TEXT,
    temperature REAL,
    timestamp TEXT
)''')
conn.commit()

sensor_id = 'sensor_01'

cursor.execute('INSERT INTO readings (sensor_id, temperature, timestamp) VALUES (?, ?, ?)', (sensor_id, 23.5, '2024-06-01 12:00:00'))
conn.commit()

# Retrieve and print all readings
# Your code here

Hint

Use cursor.execute('SELECT * FROM readings') and cursor.fetchall(). Then print each row.

Practice

1. What is the main purpose of using SQLite on a Raspberry Pi for sensor data?

easy

A. To send sensor data directly to the cloud

B. To control the sensor hardware directly

C. To store sensor readings locally without needing a separate database server

D. To display sensor data on a web page automatically

Solution

1. Step 1: Understand SQLite's role on Raspberry Pi

   SQLite is a lightweight database that runs locally without needing a separate server.

2. Step 2: Connect SQLite to sensor data storage

   It stores sensor readings on the Raspberry Pi itself, making data management easy and offline.

3. Final Answer:

   To store sensor readings locally without needing a separate database server -> Option C

4. Quick Check:

   SQLite stores data locally = B [OK]

Hint: SQLite stores data locally on Pi, no extra server needed [OK]

Common Mistakes:

• Confusing SQLite with cloud services
• Thinking SQLite controls hardware
• Assuming SQLite automatically displays data

2. Which of the following is the correct Python code snippet to create a table named sensors with columns id (integer primary key), name (text), and value (real)?

easy

A. cursor.execute('CREATE TABLE sensors (id INTEGER PRIMARY KEY, name TEXT, value REAL)')

B. cursor.execute('CREATE sensors TABLE (id INT, name STRING, value FLOAT)')

C. cursor.execute('MAKE TABLE sensors (id PRIMARY KEY, name TEXT, value REAL)')

D. cursor.execute('CREATE TABLE sensors id INTEGER, name TEXT, value REAL')

Solution

1. Step 1: Check SQL syntax for table creation

   The correct SQL command is CREATE TABLE followed by table name and column definitions in parentheses.

2. Step 2: Match Python sqlite3 syntax

   Python uses cursor.execute() with a valid SQL string. cursor.execute('CREATE TABLE sensors (id INTEGER PRIMARY KEY, name TEXT, value REAL)') matches correct SQL and Python syntax.

3. Final Answer:

   cursor.execute('CREATE TABLE sensors (id INTEGER PRIMARY KEY, name TEXT, value REAL)') -> Option A

4. Quick Check:

   Correct SQL CREATE TABLE syntax = D [OK]

Hint: Use 'CREATE TABLE table_name (columns)' inside cursor.execute() [OK]

Common Mistakes:

• Using wrong SQL keywords like MAKE TABLE
• Incorrect column types like STRING instead of TEXT
• Missing parentheses around columns

3. Given this Python code snippet using sqlite3 on Raspberry Pi:

import sqlite3
conn = sqlite3.connect('data.db')
cursor = conn.cursor()
cursor.execute('CREATE TABLE IF NOT EXISTS sensors (name TEXT, value REAL)')
cursor.execute("INSERT INTO sensors VALUES ('temp', 23.5)")
cursor.execute('SELECT * FROM sensors')
rows = cursor.fetchall()
print(rows)

What will be the output?

medium

A. [('temp', 23.5)]

B. []

C. SyntaxError

D. None

Solution

1. Step 1: Understand table creation and insertion

   The table 'sensors' is created if not exists, then a row ('temp', 23.5) is inserted.

2. Step 2: Fetch all rows and print

   The SELECT query fetches all rows, which includes the inserted row, so print outputs [('temp', 23.5)].

3. Final Answer:

   [('temp', 23.5)] -> Option A

4. Quick Check:

   Inserted row fetched = [('temp', 23.5)] [OK]

Hint: Inserted data appears in fetchall() output as list of tuples [OK]

Common Mistakes:

• Forgetting to insert data before SELECT
• Expecting empty list if table exists
• Confusing fetchall() output format

4. This Python code tries to insert sensor data but causes an error:

cursor.execute('CREATE TABLE sensors (name TEXT, value REAL)')
cursor.execute('INSERT INTO sensors (name, value) VALUES (?, ?)', ('humidity'))
conn.commit()

What is the error and how to fix it?

medium

A. Error: SQL syntax error; fix by removing parentheses in VALUES

B. Error: Missing second value in tuple; fix by adding a second value like ('humidity', 45.0)

C. Error: Table sensors does not exist; fix by creating table first

D. Error: commit() missing; fix by adding conn.commit()

Solution

1. Step 1: Identify parameter mismatch in INSERT

   The VALUES clause expects two values, but only one ('humidity') is given as a tuple missing a second element.

2. Step 2: Fix by providing both values

   Provide a tuple with two elements, e.g., ('humidity', 45.0), to match the two columns.

3. Final Answer:

   Error: Missing second value in tuple; fix by adding a second value like ('humidity', 45.0) -> Option B

4. Quick Check:

   Parameter count matches columns = C [OK]

Hint: Tuple for parameters must match number of placeholders [OK]

Common Mistakes:

• Passing single string instead of tuple with two values
• Ignoring commit() after insert
• Wrong SQL syntax in INSERT statement

5. You want to store sensor readings with a timestamp in SQLite on Raspberry Pi. Which table schema and insertion code correctly store sensor name, value, and current time using Python's sqlite3?

hard

A. CREATE TABLE readings (name TEXT, value REAL, time TEXT); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, 'CURRENT_TIMESTAMP')")

B. CREATE TABLE readings (name TEXT, value REAL, time INTEGER); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, CURRENT_TIMESTAMP)")

C. CREATE TABLE readings (name TEXT, value REAL, time INTEGER); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, datetime('now'))")

D. CREATE TABLE readings (name TEXT, value REAL, time TEXT); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, datetime('now', 'localtime'))")

Solution

1. Step 1: Choose correct table schema for timestamp

   Use TEXT type for time column to store datetime strings, which SQLite supports well.

2. Step 2: Insert current local time correctly

   Use SQLite function datetime('now', 'localtime') to get current local timestamp as text.

3. Step 3: Match insertion code with schema

   CREATE TABLE readings (name TEXT, value REAL, time TEXT); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, datetime('now', 'localtime'))") uses TEXT time column and inserts with datetime('now', 'localtime'), which is correct.

4. Final Answer:

   CREATE TABLE readings (name TEXT, value REAL, time TEXT); cursor.execute("INSERT INTO readings VALUES ('temp', 22.1, datetime('now', 'localtime'))") -> Option D

5. Quick Check:

   Local timestamp stored as TEXT = A [OK]

Hint: Use datetime('now', 'localtime') for current local time in SQLite [OK]

Common Mistakes:

• Using CURRENT_TIMESTAMP without quotes in Python
• Storing time as INTEGER without conversion
• Ignoring localtime adjustment for timestamps