spidev library usage in Raspberry Pi - Mini Project: Build & Apply

Using the spidev Library to Communicate with SPI Devices on Raspberry Pi

📖 Scenario: You have a Raspberry Pi connected to an SPI device like an ADC or a sensor. You want to send and receive data using the SPI protocol.

🎯 Goal: Build a simple Python program using the spidev library to open the SPI bus, send data, receive data, and close the connection.

📋 What You'll Learn

Create an instance of the spidev.SpiDev() class

Open SPI bus 0, device 0 using open(0, 0)

Set SPI max speed to 1 MHz using max_speed_hz

Send a list of bytes [0x01, 0x02, 0x03] using xfer2()

Print the response received from the SPI device

Close the SPI connection using close()

💡 Why This Matters

🌍 Real World

SPI devices like sensors, ADCs, and displays often connect to Raspberry Pi using SPI. This project shows how to communicate with them.

💼 Career

Embedded systems and IoT developers frequently use SPI communication. Knowing spidev is useful for hardware interfacing jobs.

1

Import spidev and create SPI object

Import the spidev library and create an SPI object called spi using spidev.SpiDev().

Raspberry Pi

# Import spidev and create spi object
# Your code here

Hint

Use import spidev to bring in the library. Then create the SPI object with spi = spidev.SpiDev().

2

Open SPI bus and set speed

Use the spi object to open SPI bus 0, device 0 with open(0, 0). Then set spi.max_speed_hz to 1000000 (1 MHz).

Raspberry Pi

import spidev
spi = spidev.SpiDev()
# Open SPI bus 0, device 0
# Set max speed to 1 MHz
# Your code here

Hint

Use spi.open(0, 0) to open bus 0, device 0. Then set spi.max_speed_hz = 1000000 to set speed.

3

Send and receive data using xfer2

Send the list of bytes [0x01, 0x02, 0x03] using spi.xfer2([0x01, 0x02, 0x03]) and save the response in a variable called response.

Raspberry Pi

import spidev
spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 1000000
# Send bytes [0x01, 0x02, 0x03] and save response
# Your code here

Hint

Use spi.xfer2() to send and receive data. Save the result in response.

4

Print the response and close SPI

Print the response variable using print(response). Then close the SPI connection with spi.close().

Raspberry Pi

import spidev
spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 1000000
response = spi.xfer2([0x01, 0x02, 0x03])
# Print the response
# Close the SPI connection
# Your code here

Hint

Use print(response) to show the data received. Then call spi.close() to end communication.

The actual response may vary depending on your SPI device. For testing, assume it returns [0, 0, 0].

Practice

1. What is the primary purpose of the spidev library on a Raspberry Pi?

easy

A. To communicate with SPI devices by sending and receiving bytes

B. To control the Raspberry Pi's GPIO pins directly

C. To manage Wi-Fi connections on the Raspberry Pi

D. To create graphical user interfaces on the Raspberry Pi

Solution

1. Step 1: Understand the role of spidev

   The spidev library is designed to allow communication with SPI devices by sending and receiving bytes.

2. Step 2: Compare with other options

   Options B, C, and D relate to GPIO, Wi-Fi, and GUI, which are not the main functions of spidev.

3. Final Answer:

   To communicate with SPI devices by sending and receiving bytes -> Option A

4. Quick Check:

   spidev = SPI communication [OK]

Hint: Remember spidev is for SPI device communication only [OK]

Common Mistakes:

• Confusing spidev with GPIO control libraries
• Thinking spidev manages network or GUI tasks
• Assuming spidev handles I2C communication

2. Which of the following is the correct way to open SPI bus 0, device 0 using spidev in Python?

easy

A. spi.connect(0, 0)

B. spi.start(0, 0)

C. spi.init(0, 0)

D. spi.open(0, 0)

Solution

1. Step 1: Recall spidev method to open SPI

   The correct method to open SPI bus and device is open(bus, device).

2. Step 2: Verify method names

   Methods like start, connect, and init are not valid for spidev.

3. Final Answer:

   spi.open(0, 0) -> Option D

4. Quick Check:

   Open SPI with open() method [OK]

Hint: Use spi.open(bus, device) to start SPI communication [OK]

Common Mistakes:

• Using incorrect method names like start or connect
• Confusing open() with init()
• Not specifying both bus and device numbers

3. What will be the output of the following code snippet?

import spidev
spi = spidev.SpiDev()
spi.open(0, 0)
response = spi.xfer2([0x01, 0x02, 0x03])
spi.close()
print(response)

medium

A. [1, 2, 3]

B. [0, 0, 0]

C. A list of bytes received from the SPI device

D. SyntaxError

Solution

1. Step 1: Understand spi.xfer2() behavior

   The xfer2() method sends bytes and returns a list of bytes received from the SPI device.

2. Step 2: Analyze the code output

   The output depends on the connected SPI device's response, so it returns a list of received bytes, not necessarily the same as sent.

3. Final Answer:

   A list of bytes received from the SPI device -> Option C

4. Quick Check:

   xfer2() returns received bytes list [OK]

Hint: xfer2() returns device response bytes list [OK]

Common Mistakes:

• Assuming output equals input list
• Expecting zeros if no device connected
• Thinking code causes syntax error

4. Identify the error in this code snippet using spidev:

import spidev
spi = spidev.SpiDev()
spi.xfer2([0x01, 0x02])
spi.open(0, 0)
spi.close()

medium

A. Not closing SPI device after use

B. Calling xfer2() before opening SPI device

C. Using wrong method name xfer2()

D. Missing import statement

Solution

1. Step 1: Check method call order

   The xfer2() method requires the SPI device to be opened first with open().

2. Step 2: Identify the error

   Here, xfer2() is called before open(), causing a runtime error.

3. Final Answer:

   Calling xfer2() before opening SPI device -> Option B

4. Quick Check:

   Open SPI before xfer2() call [OK]

Hint: Always open SPI before using xfer2() [OK]

Common Mistakes:

• Calling xfer2() before open()
• Forgetting to close SPI device
• Confusing method names

5. You want to send the bytes [0x10, 0x20, 0x30] to an SPI device on bus 1, device 0, at 500000 Hz speed, and receive the response. Which code snippet correctly does this using spidev?

hard

A. spi = spidev.SpiDev()
spi.open(1, 0)
spi.max_speed_hz = 500000
response = spi.xfer2([0x10, 0x20, 0x30])
spi.close()
print(response)

B. spi = spidev.SpiDev()
spi.open(0, 1)
spi.speed = 500000
response = spi.xfer([0x10, 0x20, 0x30])
spi.close()
print(response)

C. spi = spidev.SpiDev()
spi.open(1, 0)
spi.max_speed = 500000
response = spi.xfer2([0x10, 0x20, 0x30])
spi.close()
print(response)

D. spi = spidev.SpiDev()
spi.open(1, 0)
spi.max_speed_hz = 500000
response = spi.transfer([0x10, 0x20, 0x30])
spi.close()
print(response)

Solution

1. Step 1: Check SPI open parameters and speed setting

   Bus 1, device 0 is opened with spi.open(1, 0). Speed is set with spi.max_speed_hz = 500000.

2. Step 2: Verify transfer method and closing

   xfer2() is the correct method to send and receive bytes. The device is closed after communication.

3. Final Answer:

   Correct code snippet with spi.open(1, 0), max_speed_hz, xfer2(), and close() -> Option A

4. Quick Check:

   Use open(1,0), max_speed_hz, xfer2(), close() [OK]

Hint: Set max_speed_hz and use xfer2() after open() [OK]

Common Mistakes:

• Using wrong bus/device numbers
• Setting speed with wrong attribute name
• Using incorrect transfer method name
• Not closing SPI device