smbus2 library for I2C in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this smbus2 read_byte code?

Consider this Python code snippet using smbus2 to read a byte from an I2C device at address 0x20 on bus 1:

from smbus2 import SMBus

with SMBus(1) as bus:
    data = bus.read_byte(0x20)
print(data)

Assuming the device returns the byte 0x5A, what will be printed?

Raspberry Pi

from smbus2 import SMBus

with SMBus(1) as bus:
    data = bus.read_byte(0x20)
print(data)

A 90

B 0x5A

C b'\x5A'

D Error: SMBus object has no attribute 'read_byte'

💡 Hint

Remember that read_byte returns an integer representing the byte value.

The read_byte method returns the byte as an integer. The hexadecimal 0x5A equals decimal 90, so print(data) outputs 90.

🧠 Conceptual

intermediate

Which smbus2 method writes a block of bytes to a device?

You want to send multiple bytes at once to an I2C device using smbus2. Which method should you use?

A write_byte_data(addr, cmd, val)

B write_byte(addr, val)

C write_block_data(addr, cmd, vals)

D read_block_data(addr, cmd)

💡 Hint

Look for a method that explicitly mentions writing a block of data.

write_block_data sends a list of bytes (vals) to the device at addr starting at register cmd. Other methods write single bytes or read data.

🔧 Debug

advanced

Why does this smbus2 code raise an IOError?

Examine this code snippet:

from smbus2 import SMBus

bus = SMBus(1)
value = bus.read_byte_data(0x50, 0x10)
bus.close()
print(value)

It raises an IOError when run. What is the most likely cause?

A The bus number 1 is invalid on Raspberry Pi

B The SMBus object was not opened with a context manager

C The <code>read_byte_data</code> method requires a third argument

D The device at address 0x50 is not connected or not responding

💡 Hint

Consider hardware connection and device presence on the I2C bus.

An IOError usually means the device at the given address did not acknowledge the request. This often happens if the device is disconnected or powered off.

📝 Syntax

advanced

Which option correctly writes a single byte using smbus2?

Choose the correct syntax to write the byte 0x1F to register 0x05 of a device at address 0x30 using smbus2:

A bus.write_byte_data(0x30, 0x05, 0x1F)

B bus.write_byte(0x30, 0x05, 0x1F)

C bus.write_byte_data(0x30, 0x1F)

D bus.write_byte_data(0x05, 0x30, 0x1F)

💡 Hint

Remember the order of parameters: device address, register, then value.

write_byte_data takes three arguments: device address, register address, and the byte value to write. Option A matches this order and syntax.

🚀 Application

expert

How many bytes are read by this smbus2 block read?

Given this code snippet:

from smbus2 import SMBus

with SMBus(1) as bus:
    data = bus.read_i2c_block_data(0x40, 0x00, 6)
print(len(data))

What is the output of print(len(data))?

A 0

B 6

C 1

D Raises TypeError

💡 Hint

The third argument to read_i2c_block_data specifies how many bytes to read.

The method read_i2c_block_data reads the specified number of bytes (6 here) from the device starting at register 0x00. The returned list length is 6.