Reading sensor data over I2C in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the I2C library.

Raspberry Pi

import [1]

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

Asmbus2

Brandom

Ctime

Dos

Attempts:

3 left

💡 Hint

Common Mistakes

Importing unrelated modules like random or os.

Forgetting to import the I2C communication library.

We use the smbus2 library to communicate over I2C on Raspberry Pi.

2fill in blank

medium

Complete the code to create an I2C bus object.

Raspberry Pi

bus = smbus2.SMBus([1])

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

A0

B1

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using bus number 0 which may not be enabled.

Using bus numbers higher than 1 without checking hardware.

On Raspberry Pi, I2C bus 1 is commonly used for sensor communication.

3fill in blank

hard

Fix the error in reading a byte from the sensor at address 0x48.

Raspberry Pi

data = bus.read_byte_data([1], 0x00)

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

A0x48

B0x00

C0x04

D0x49

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong I2C address causing no response or errors.

Confusing register address with device address.

The sensor's I2C address is 0x48, so we must use that address to read data.

4fill in blank

hard

Fill both blanks to read two bytes and combine them into a 16-bit value.

Raspberry Pi

high = bus.read_byte_data(0x48, [1])
low = bus.read_byte_data(0x48, [2])
value = (high << 8) | low

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

A0x00

B0x01

C0x02

D0x03

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect register addresses causing wrong data.

Mixing up high and low byte registers.

Register 0x00 is usually the high byte and 0x01 the low byte for sensor data.

5fill in blank

hard

Fill all three blanks to convert the raw sensor value to temperature in Celsius.

Raspberry Pi

if value & [1]:
    value = value - [2]
temperature = value * [3]

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

A0x8000

B65536

C0.0078125

D0x7FFF

Attempts:

3 left

💡 Hint

Common Mistakes

Ignoring sign bit causing wrong negative temperature.

Using wrong scale factor leading to incorrect Celsius values.

The highest bit (0x8000) indicates negative temperature in two's complement. We subtract 65536 to convert. The scale factor 0.0078125 converts raw units to Celsius.

Practice

1. What is the main purpose of using the I2C protocol on a Raspberry Pi when working with sensors?

easy

A. To communicate with multiple sensors using unique addresses

B. To increase the Raspberry Pi's processing speed

C. To power the sensors directly from the Raspberry Pi

D. To store sensor data permanently on the Raspberry Pi

Solution

1. Step 1: Understand I2C communication basics

   I2C allows multiple devices to connect using unique addresses on the same bus.

2. Step 2: Identify the role of I2C with sensors

   The Raspberry Pi uses I2C to talk to sensors by addressing each one uniquely.

3. Final Answer:

   To communicate with multiple sensors using unique addresses -> Option A

4. Quick Check:

   I2C = Multiple devices, unique addresses [OK]

Hint: I2C uses addresses to talk to many devices [OK]

Common Mistakes:

• Thinking I2C increases processing speed
• Confusing communication with power supply
• Assuming I2C stores data permanently

2. Which Python library is commonly used on Raspberry Pi to read data from an I2C sensor?

easy

A. pygame

B. smbus

C. matplotlib

D. requests

Solution

1. Step 1: Recall common Python libraries for hardware

   For I2C communication on Raspberry Pi, the smbus library is standard.

2. Step 2: Eliminate unrelated libraries

   pygame is for games, matplotlib for plotting, requests for web requests, so they don't fit.

3. Final Answer:

   smbus -> Option B

4. Quick Check:

   Python I2C library = smbus [OK]

Hint: Use smbus for I2C sensor communication [OK]

Common Mistakes:

• Choosing pygame or matplotlib for sensor reading
• Confusing web libraries with hardware libraries

3. Given this Python code snippet reading from an I2C sensor, what will be printed?

import smbus
bus = smbus.SMBus(1)
address = 0x48
value = bus.read_byte_data(address, 0x00)
print(value)

medium

A. The string 'value' printed literally

B. An error because SMBus(1) is invalid

C. The I2C address 0x48 printed as decimal

D. The byte value stored at register 0x00 of device 0x48

Solution

1. Step 1: Understand the code's function

   The code reads one byte from register 0x00 of the device at I2C address 0x48.

2. Step 2: Identify the output of print(value)

   It prints the numeric byte value read from that register, not the address or a string.

3. Final Answer:

   The byte value stored at register 0x00 of device 0x48 -> Option D

4. Quick Check:

   read_byte_data returns register byte value [OK]

Hint: read_byte_data reads register value, not address [OK]

Common Mistakes:

• Thinking SMBus(1) is invalid (it's correct for Raspberry Pi)
• Confusing address with data value
• Expecting string output instead of number

4. What is wrong with this code snippet for reading I2C sensor data?

import smbus
bus = smbus.SMBus(0)
address = 0x40
data = bus.read_byte_data(address, 0x01)
print(data)

medium

A. read_byte_data requires three arguments, missing one

B. The address 0x40 is invalid for I2C devices

C. SMBus(0) is incorrect; Raspberry Pi usually uses bus 1

D. print(data) should be print(bus.read_byte_data)

Solution

1. Step 1: Check SMBus bus number

   On Raspberry Pi, I2C bus 1 is standard; bus 0 is usually invalid or unused.

2. Step 2: Verify other code parts

   Address 0x40 is valid, read_byte_data takes two arguments, and print(data) is correct.

3. Final Answer:

   SMBus(0) is incorrect; Raspberry Pi usually uses bus 1 -> Option C

4. Quick Check:

   Use SMBus(1) on Raspberry Pi [OK]

Hint: Use SMBus(1) for Raspberry Pi I2C bus [OK]

Common Mistakes:

• Using SMBus(0) instead of SMBus(1)
• Thinking I2C addresses like 0x40 are invalid
• Misunderstanding read_byte_data arguments

5. You want to read temperature data from a sensor at I2C address 0x5A which stores temperature in two registers: 0x07 (MSB) and 0x08 (LSB). How do you correctly combine these bytes to get the temperature value in Python?

hard

A. temp = (bus.read_byte_data(0x5A, 0x07) << 8) | bus.read_byte_data(0x5A, 0x08)

B. temp = bus.read_byte_data(0x5A, 0x07) + bus.read_byte_data(0x5A, 0x08)

C. temp = bus.read_byte_data(0x5A, 0x08) << 8 | bus.read_byte_data(0x5A, 0x07)

D. temp = bus.read_byte_data(0x5A, 0x07) * bus.read_byte_data(0x5A, 0x08)

Solution

1. Step 1: Understand byte order for temperature

   MSB is the high byte, so shift it left by 8 bits to make space for LSB.

2. Step 2: Combine MSB and LSB correctly

   Use bitwise OR to combine shifted MSB with LSB for full 16-bit value.

3. Final Answer:

   temp = (bus.read_byte_data(0x5A, 0x07) << 8) | bus.read_byte_data(0x5A, 0x08) -> Option A

4. Quick Check:

   Combine MSB << 8 with LSB using OR [OK]

Hint: Shift MSB 8 bits left, OR with LSB to combine bytes [OK]

Common Mistakes:

• Adding bytes instead of bitwise OR
• Swapping MSB and LSB order
• Multiplying bytes instead of combining bits