SPI with external devices (sensors, displays) in Embedded C - Mini Project: Build & Apply

SPI Communication with External Devices

📖 Scenario: You are working on a small embedded system that communicates with external devices like sensors and displays using SPI (Serial Peripheral Interface). SPI is a way for your microcontroller to send and receive data to these devices quickly.In this project, you will write simple embedded C code to set up SPI communication, send commands to a sensor, and read data back.

🎯 Goal: Build a simple SPI communication program that initializes SPI, sends a command to a sensor, reads the sensor data, and prints the received value.

📋 What You'll Learn

Create an SPI data buffer with specific command bytes

Define a variable for the number of bytes to send

Write a function to send and receive SPI data

Print the received sensor data

💡 Why This Matters

🌍 Real World

SPI is widely used in embedded systems to connect microcontrollers with sensors, displays, memory chips, and other devices. Understanding SPI helps you build projects like weather stations, smart watches, and home automation devices.

💼 Career

Embedded software engineers often write SPI communication code to interface with hardware components. This skill is essential for developing firmware for IoT devices, automotive systems, and consumer electronics.

1

Create SPI data buffer

Create an array called spi_tx_buffer with these exact bytes: 0xAA, 0xBB, 0xCC. This buffer will hold the command bytes to send to the sensor.

Embedded C

# Create the SPI transmit buffer with command bytes
// Your code here

Need a hint?

Use an array of unsigned char with exactly three values.

2

Define SPI data length

Create an integer variable called spi_data_length and set it to 3, which is the number of bytes to send.

Embedded C

unsigned char spi_tx_buffer[3] = {0xAA, 0xBB, 0xCC};
// Define the length of SPI data to send
// Your code here

Need a hint?

Use an int variable to store the number 3.

3

Write SPI send and receive function

Write a function called spi_transfer that takes a pointer to tx_buffer, a pointer to rx_buffer, and an integer length. Inside the function, use a for loop with variable i from 0 to length - 1 to simulate sending and receiving SPI data by copying each byte from tx_buffer to rx_buffer. This simulates the sensor echoing back the data.

Embedded C

unsigned char spi_tx_buffer[3] = {0xAA, 0xBB, 0xCC};
int spi_data_length = 3;

// Write spi_transfer function below
// Your code here

Need a hint?

Use a for loop to copy bytes from tx_buffer to rx_buffer.

4

Call SPI function and print received data

Declare an array spi_rx_buffer of size 3 to hold received data. Call spi_transfer with spi_tx_buffer, spi_rx_buffer, and spi_data_length. Then use a for loop with variable i from 0 to 2 to print each received byte in hexadecimal format using printf with 0x%X . End with a newline.

Embedded C

unsigned char spi_tx_buffer[3] = {0xAA, 0xBB, 0xCC};
int spi_data_length = 3;

void spi_transfer(unsigned char *tx_buffer, unsigned char *rx_buffer, int length) {
    for (int i = 0; i < length; i++) {
        rx_buffer[i] = tx_buffer[i];
    }
}

// Declare spi_rx_buffer, call spi_transfer, and print received bytes
// Your code here

Need a hint?

Remember to include stdio.h for printf and print each byte in hex.