SPI with display modules in Raspberry Pi

Introduction

SPI helps the Raspberry Pi talk quickly to display screens. It sends pictures and text fast so you can see them right away.

You want to show sensor data on a small screen connected to your Raspberry Pi.

You are building a weather station and need to display temperature and humidity.

You want to create a simple game or clock on a tiny display.

You need a fast way to update graphics on a screen without delays.

Syntax

Raspberry Pi

import spidev

spi = spidev.SpiDev()
spi.open(bus, device)
spi.max_speed_hz = speed

spi.xfer2(data_bytes)

spi.close()

bus and device select the SPI channel on the Raspberry Pi.

xfer2() sends a list of bytes to the display and receives bytes back.

Examples

This example opens SPI bus 0, device 0, sets speed, sends a command byte to turn off the display, then closes SPI.

Raspberry Pi

import spidev

spi = spidev.SpiDev()
spi.open(0, 0)  # Use SPI bus 0, device 0
spi.max_speed_hz = 500000

spi.xfer2([0xAE])  # Send command to turn off the display

spi.close()

This sends a command byte followed by pixel data bytes to the display.

Raspberry Pi

import spidev

spi = spidev.SpiDev()
spi.open(0, 0)
spi.max_speed_hz = 1000000

# Send multiple bytes to draw pixels
spi.xfer2([0x40, 0xFF, 0x00, 0xFF])

spi.close()

Sample Program

This program opens SPI, sends commands to turn off the display, clears it by sending zeros, then turns it back on. It prints a message when done.

Raspberry Pi

import spidev
import time

spi = spidev.SpiDev()
spi.open(0, 0)  # SPI bus 0, device 0
spi.max_speed_hz = 800000

# Simple example: initialize display and clear screen
# Commands depend on your display module

# Turn display off
spi.xfer2([0xAE])
# Clear display (send zeros)
spi.xfer2([0x00] * 128)
# Turn display on
spi.xfer2([0xAF])

print("Display initialized and cleared.")

spi.close()

Important Notes

Always check your display's datasheet for the right command bytes.

Use proper wiring: connect MOSI, SCLK, CS, and power pins correctly.

Remember to close SPI after use to free the device.

Summary

SPI lets Raspberry Pi send commands and data fast to display modules.

Use spidev library to open SPI, send bytes, and close it.

Commands and data bytes depend on your specific display hardware.

Practice

1. What is the main purpose of using SPI with display modules on a Raspberry Pi?

easy

A. To power the display module

B. To connect the Raspberry Pi to the internet

C. To store files on the Raspberry Pi

D. To send commands and data quickly to the display

Solution

1. Step 1: Understand SPI role

   SPI is a communication protocol used to send data between devices quickly.

2. Step 2: Connect SPI to display modules

   On Raspberry Pi, SPI sends commands and data to control display modules efficiently.

3. Final Answer:

   To send commands and data quickly to the display -> Option D

4. Quick Check:

   SPI = fast data transfer to display [OK]

Hint: SPI is for fast data transfer to devices like displays [OK]

Common Mistakes:

• Confusing SPI with internet connection
• Thinking SPI stores files
• Assuming SPI powers devices

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

easy

A. spi = spidev.SpiDev(); spi.open(0, 0)

B. spi = spidev.open(1, 0)

C. spi = spidev.open(0, 0)

D. spi = spidev.SpiDev.open(0, 0)

Solution

1. Step 1: Recall spidev usage

   spidev requires creating an SpiDev object first, then calling open(bus, device).

2. Step 2: Check syntax correctness

   spi = spidev.SpiDev(); spi.open(0, 0) correctly creates spi = spidev.SpiDev() then calls spi.open(0, 0).

3. Final Answer:

   spi = spidev.SpiDev(); spi.open(0, 0) -> Option A

4. Quick Check:

   spidev object then open() method [OK]

Hint: Create SpiDev object before calling open() [OK]

Common Mistakes:

• Calling spidev.open() directly without object
• Using wrong bus or device numbers
• Using incorrect method syntax

3. What will be the output of this Python code snippet using spidev?

import spidev
spi = spidev.SpiDev()
spi.open(0, 0)
response = spi.xfer2([0xAA, 0x55])
spi.close()
print(response)

medium

A. [170, 85]

B. Depends on the connected SPI device response

C. An error because xfer2 needs a string

D. [0, 0]

Solution

1. Step 1: Understand xfer2 function

   spi.xfer2 sends bytes and returns the response bytes from the SPI device.

2. Step 2: Recognize device dependency

   The returned list depends on the connected device's response, so output varies.

3. Final Answer:

   Depends on the connected SPI device response -> Option B

4. Quick Check:

   SPI response varies by device [OK]

Hint: SPI transfer output depends on device response [OK]

Common Mistakes:

• Assuming output equals input bytes
• Thinking xfer2 requires string input
• Expecting fixed output without device

4. You wrote this code to send a command to your SPI display but it raises an AttributeError:

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

What is the error and how to fix it?

medium

A. spidev has no open() function; create SpiDev object first

B. xfer2() requires a string, not a list

C. spi.close() should be called before xfer2()

D. Bus number 0 is invalid on Raspberry Pi

Solution

1. Step 1: Identify AttributeError cause

   spidev module does not have open() function; open() is method of SpiDev object.

2. Step 2: Correct usage of spidev

   Create spi = spidev.SpiDev() first, then call spi.open(0, 0) to fix error.

3. Final Answer:

   spidev has no open() function; create SpiDev object first -> Option A

4. Quick Check:

   Use SpiDev() object before open() [OK]

Hint: Always create SpiDev() object before open() [OK]

Common Mistakes:

• Calling spidev.open() directly
• Passing wrong data type to xfer2()
• Closing SPI before transfer

5. You want to send a command byte 0xA5 followed by data bytes [0x01, 0x02, 0x03] to an SPI display using spidev. Which code correctly sends the command first, then the data, assuming spi is already opened?

hard

A. spi.writebytes([0xA5, 0x01, 0x02, 0x03])

B. spi.xfer2([0xA5, 0x01, 0x02, 0x03])

C. spi.xfer2([0xA5]); spi.xfer2([0x01, 0x02, 0x03])

D. spi.writebytes([0xA5]); spi.writebytes([0x01, 0x02, 0x03])

Solution

1. Step 1: Understand command and data separation

   Many SPI displays require sending command and data separately to distinguish them.

2. Step 2: Check code options

   spi.xfer2([0xA5]); spi.xfer2([0x01, 0x02, 0x03]) sends command byte first, then data bytes in separate calls, matching typical display protocol.

3. Final Answer:

   spi.xfer2([0xA5]); spi.xfer2([0x01, 0x02, 0x03]) -> Option C

4. Quick Check:

   Separate command and data transfers [OK]

Hint: Send command and data in separate SPI transfers [OK]

Common Mistakes:

• Sending command and data in one transfer
• Using writebytes() which may not return response
• Not separating command from data