Arduino SPI communication protocol and interfacing with SPI devices

The SPI (Serial Peripheral Interface) protocol is another widely used communication protocol for interfacing with sensors, displays, and other devices that can be connected to an Arduino board. SPI uses a four-wire bus consisting of a serial data line (MOSI), a serial clock line (SCK), a slave select line (SS), and a serial data line for receiving data (MISO) to transmit data between devices.

Here’s an overview of how to use the SPI protocol with an Arduino board:

1. Initialize the SPI communication: To use the SPI protocol, you first need to initialize the SPI library in the Arduino code using the SPI.begin() function. This function sets up the Arduino board as an SPI master device.

#include 

void setup() {
  SPI.begin(); // Initialize the SPI communication
}

2. Interfacing with SPI devices: To interface with an SPI device, you need to know its SPI mode, clock frequency and slave select pin. To communicate with an SPI device, use the SPI.beginTransaction() function to set the SPI mode, clock frequency and slave select pin, followed by the SPI.transfer() function to send and receive data to and from the device.

Here’s an example code to read the temperature from a MAX31855 thermocouple sensor using the SPI protocol:

#include 

#define SS_PIN 10 // MAX31855 slave select pin
#define CLK_PIN 13 // SPI clock pin
#define DO_PIN 12 // MAX31855 data out pin

void setup() {
  SPI.begin(); // Initialize the SPI communication
  pinMode(SS_PIN, OUTPUT); // Set the slave select pin as output
  digitalWrite(SS_PIN, HIGH); // Deselect the MAX31855
  Serial.begin(9600); // Initialize the serial communication
}

void loop() {
  byte data[4];
  digitalWrite(SS_PIN, LOW); // Select the MAX31855
  delayMicroseconds(1);
  SPI.beginTransaction(SPISettings(500000, MSBFIRST, SPI_MODE0)); // Set the SPI mode and clock frequency
  for (int i = 0; i < 4; i++) {
    data[i] = SPI.transfer(0x00); // Send dummy data and read data from the MAX31855
  }
  SPI.endTransaction(); // End the SPI transaction
  digitalWrite(SS_PIN, HIGH); // Deselect the MAX31855
  int16_t temperature = ((data[0] << 8) | data[1]) >> 4; // Combine the bytes and convert to temperature in Celsius
  float celsius = temperature * 0.25;
  Serial.print("Temperature: ");
  Serial.print(celsius);
  Serial.println(" C");
  delay(1000); // Wait for 1 second
}

3. Using SPI displays: SPI displays, such as TFT displays, can be interfaced with an Arduino board using libraries such as Adafruit_ILI9341 or TFT_eSPI. These libraries provide functions to initialize the display, set the cursor position, and display text or graphics.

Here’s an example code to display text on a TFT display using the Adafruit_ILI9341 library:

#include 
#include 
#include 

#define TFT_CS 10
#define TFT_DC 9
#define TFT_RST 8
Adafruit_ILI9341 tft = Adafruit_ILI9341(TFT_CS, TFT_DC, TFT_RST);

void setup() {
  tft.begin(); // Initialize the TFT display
  tft.fillScreen(ILI9341_BLACK); // Clear the display
  tft.setCursor(0, 0); // Set the cursor position
  tft.setTextSize(2); // Set the text size
  tft.setTextColor(ILI9341_WHITE); // Set the text color
  tft.println("Hello, world!"); // Display the text
}

void loop() {
  // Do nothing
}

Overall, the SPI protocol is a powerful tool for interfacing with a wide range of sensors, displays, and other devices that can be connected to an Arduino board, and enables a variety of applications that involve sensing, display, and control.