Writing commands to I2C device in Raspberry Pi - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the SMBus module needed for I2C communication.

Raspberry Pi

from smbus2 import [1]

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

AI2C

BSMBus

CBus

DDevice

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'I2C' instead of 'SMBus' will cause an import error.

Using 'Bus' alone is not correct because the full class name is SMBus.

The SMBus class from smbus2 is used to communicate over I2C.

2fill in blank

medium

Complete the code to create an SMBus object for I2C bus number 1.

Raspberry Pi

bus = SMBus([1])

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

A1

B0

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using bus 0 may cause errors if the bus is not enabled.

Using bus 2 or 3 is uncommon and may not exist on the device.

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

3fill in blank

hard

Fix the error in the code to write a single byte command 0x20 to the device at address 0x40.

Raspberry Pi

bus.write_byte([1], 0x20)

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

A64

B0x20

C32

D0x40

Attempts:

3 left

💡 Hint

Common Mistakes

Using the command byte as the device address causes communication failure.

Using decimal 32 or 64 instead of hex 0x40 may cause confusion but 0x40 and 64 are equivalent; however, the code expects hex.

The first argument to write_byte is the I2C device address, which is 0x40 in this case.

4fill in blank

hard

Fill both blanks to write a block of data [0x01, 0x02, 0x03] to register 0x10 of device 0x50.

Raspberry Pi

bus.write_i2c_block_data([1], [2], [0x01, 0x02, 0x03])

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

A0x50

B0x10

C0x20

D0x40

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping device and register addresses causes wrong data writes.

Using incorrect addresses will cause the device not to respond.

The first argument is the device address (0x50), the second is the register address (0x10).

5fill in blank

hard

Fill all three blanks to write the value 0xFF to register 0x01 of device 0x60 using write_byte_data.

Raspberry Pi

bus.write_byte_data([1], [2], [3])

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

A0x60

B0x01

C0xFF

D0x10

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up register and data values.

Using wrong device address causes no communication.

The first argument is the device address (0x60), the second is the register (0x01), and the third is the data byte (0xFF).

Practice

1. What is the main purpose of the write_byte_data function in the smbus2 library when working with I2C devices on Raspberry Pi?

easy

A. To open the I2C bus for communication

B. To read a byte of data from the I2C device

C. To send a command and a single byte of data to a specific register of the I2C device

D. To close the I2C bus after communication

Solution

1. Step 1: Understand the function's role

   The write_byte_data function sends a command (register address) and a byte of data to the I2C device.

2. Step 2: Differentiate from other functions

   Reading data uses read_byte_data, and opening/closing the bus uses SMBus() context or methods.

3. Final Answer:

   To send a command and a single byte of data to a specific register of the I2C device -> Option C

4. Quick Check:

   write_byte_data sends command + data [OK]

Hint: Remember: write_byte_data sends command + data [OK]

Common Mistakes:

• Confusing write_byte_data with read_byte_data
• Thinking it opens or closes the bus
• Assuming it sends multiple bytes at once

2. Which of the following is the correct syntax to write the byte value 0x1A to register 0x10 of an I2C device at address 0x20 using smbus2 in Python?

easy

A. bus.write_byte_data(0x20, 0x10, 0x1A)

B. bus.write_byte_data(0x1A, 0x20, 0x10)

C. bus.write_byte(0x20, 0x10, 0x1A)

D. bus.write_byte_data(0x10, 0x20, 0x1A)

Solution

1. Step 1: Identify the parameter order for write_byte_data

   The function signature is write_byte_data(i2c_addr, register, value).

2. Step 2: Match parameters to values

   Address is 0x20, register is 0x10, and value is 0x1A, so call is bus.write_byte_data(0x20, 0x10, 0x1A).

3. Final Answer:

   bus.write_byte_data(0x20, 0x10, 0x1A) -> Option A

4. Quick Check:

   Address, register, value order = D [OK]

Hint: Remember parameter order: address, register, value [OK]

Common Mistakes:

• Swapping address and register parameters
• Using write_byte instead of write_byte_data
• Incorrect number of arguments

3. What will be the output of the following Python code snippet on Raspberry Pi when writing to an I2C device?

from smbus2 import SMBus
bus = SMBus(1)
try:
    bus.write_byte_data(0x50, 0x01, 0xFF)
    print("Write successful")
except Exception as e:
    print(f"Error: {e}")
bus.close()

medium

A. Error: [Errno 121] Remote I/O error

B. No output

C. SyntaxError

D. Write successful

Solution

1. Step 1: Analyze the code flow

   The code opens I2C bus 1, writes byte 0xFF to register 0x01 at device 0x50, then prints success if no error.

2. Step 2: Consider normal operation

   If the device is connected and address is correct, write succeeds and prints "Write successful".

3. Final Answer:

   Write successful -> Option D

4. Quick Check:

   Successful write prints message [OK]

Hint: If no error, print shows success message [OK]

Common Mistakes:

• Assuming error without device connected
• Confusing syntax error with runtime error
• Ignoring bus.close() importance

4. Identify the error in the following code snippet that writes to an I2C device and suggest the fix:

from smbus2 import SMBus
bus = SMBus(1)
bus.write_byte_data(0x40, 0x02)
bus.close()

medium

A. Wrong device address format; use string instead of integer

B. Missing the data byte argument in write_byte_data; add the data byte

C. Incorrect bus number; change SMBus(1) to SMBus(0)

D. bus.close() should be called before write_byte_data

Solution

1. Step 1: Check write_byte_data parameters

   The function requires three arguments: device address, register, and data byte.

2. Step 2: Identify missing argument

   The code only passes two arguments, missing the data byte to write.

3. Final Answer:

   Missing the data byte argument in write_byte_data; add the data byte -> Option B

4. Quick Check:

   write_byte_data needs 3 args [OK]

Hint: write_byte_data always needs 3 arguments [OK]

Common Mistakes:

• Forgetting the data byte argument
• Assuming bus.close() order matters here
• Changing bus number without reason

5. You want to write a sequence of bytes [0x10, 0x20, 0x30] to consecutive registers starting at 0x00 on an I2C device at address 0x60 using smbus2. Which approach correctly achieves this?

hard

A. Use a loop calling write_byte_data(0x60, register, value) for each byte, incrementing register from 0x00

B. Call write_byte_data(0x60, 0x00, [0x10, 0x20, 0x30]) once to write all bytes

C. Use write_byte(0x60, 0x00, 0x10, 0x20, 0x30) to send all bytes at once

D. Write only the first byte with write_byte_data(0x60, 0x00, 0x10) and ignore the rest

Solution

1. Step 1: Understand write_byte_data limitations

   This function writes one byte to one register at a time.

2. Step 2: Write bytes to consecutive registers

   Use a loop to write each byte to registers 0x00, 0x01, 0x02 respectively.

3. Final Answer:

   Use a loop calling write_byte_data(0x60, register, value) for each byte, incrementing register from 0x00 -> Option A

4. Quick Check:

   One byte per register via loop [OK]

Hint: Write bytes one by one in a loop for consecutive registers [OK]

Common Mistakes:

• Trying to write multiple bytes in one write_byte_data call
• Using write_byte incorrectly with multiple bytes
• Ignoring the need to increment register address