What is SPI and how to use it on Raspberry Pi

In this tutorial, we will see how to use the SPI protocol with a Raspberry Pi to communicate with external high-speed devices.

SPI (Serial Peripheral Interface) is a synchronous serial communication protocol widely used for communication between a microcontroller and peripheral devices, such as sensors, displays, or flash memories.

SPI is known for its high speed and simplicity, making it a popular choice in hardware projects (on the downside, it requires more wires than I2C, for example).

What is SPI?

SPI is a full-duplex communication protocol, meaning data can be sent and received simultaneously. It uses four main lines for communication:

Each follower device has its own select line, allowing the master to communicate with only one follower at a time.

Connecting SPI Devices

The Raspberry Pi has two available SPI ports: SPI0 and SPI1. The SPI0 port is the most commonly used and is available on the following GPIO pins:

If you have multiple follower devices connected to the SPI bus, you must use the select lines (CS) to choose the device you want to communicate with.

Configuring SPI on Raspberry Pi

The Raspberry Pi has native support for SPI through its GPIO (General Purpose Input/Output). To use SPI, we first need to enable it in the system configuration.

After rebooting, you can verify if SPI is enabled by running the following command in the terminal:

If SPI is enabled, you should see something like spi_bcm2835 in the output.

Programming SPI in Python

To interact with SPI devices on Raspberry Pi, we can use the spidev library, which provides a simple interface for working with SPI in Python.

First, install the spidev library by running the following command in the terminal:

Let’s go with a simple example of how to send and receive data via SPI using Python:

import spidev

# Create an instance of SPI
spi = spidev.SpiDev()

# Open the SPI bus (bus 0, device 0)
spi.open(0, 0)

# Set the clock speed (in Hz)
spi.max_speed_hz = 1000000  # 1 MHz

# Send data to the SPI device
data_sent = [0x01, 0x02, 0x03]  # Data to send
data_received = spi.xfer(data_sent)  # Send and receive data

# Print the received data
print("Received data:", data_received)

# Close the SPI connection
spi.close()

Practical Examples

import spidev

# Create an instance of SPI
spi = spidev.SpiDev()

# Open the SPI bus (bus 0, device 0)
spi.open(0, 0)

# Set the clock speed (in Hz)
spi.max_speed_hz = 1000000  # 1 MHz

# Send command to read temperature
command = [0x01]  # Command to read temperature
response = spi.xfer(command)  # Send command and receive response

# Convert the response to temperature
temperature = (response[0] << 8) | response[1]  # Combine the 2 bytes
temperature = temperature / 10.0  # Convert to degrees Celsius

# Print the temperature
print(f"Temperature: {temperature} °C")

# Close the SPI connection
spi.close()