Implementing SPI Communication for Arduino

Hello everyone, Rabbit Brother is back! Today we are going to learn a super practical communication method – SPI communication. It’s like a “highway” between Arduino and peripherals, allowing data transfer to be fast and stable. Whether dealing with SD cards, displays, or various sensor modules, SPI is a great tool. Let Rabbit Brother guide you through SPI communication!

SPI (Serial Peripheral Interface) is a synchronous serial communication protocol. Sounds fancy, right? It’s actually a way for Arduino to “chat” with external devices. It uses 4 lines for communication:

• MOSI (Master Out Slave In): The line for the master device to send data

• MISO (Master In Slave Out): The line for the master device to receive data

• SCK (Serial Clock): The clock signal line

• SS (Slave Select): The line to select the slave device

Tip: You can imagine SPI as a conversation between a waiter (master device) and a customer (slave device) in a restaurant. MOSI is the waiter speaking, MISO is the customer responding, SCK is the metronome controlling the rhythm of the conversation, and SS is the waiter choosing which customer to serve.

We need to include the SPI library and initialize it. Let’s take a look at the most basic code framework:

#include <SPI.h>
void setup() {
// Initialize SPI communication
SPI.begin();
// Set communication speed to 4MHz
SPI.setClockDivider(SPI_CLOCK_DIV4);
// Set data mode
SPI.setDataMode(SPI_MODE0);
// Set bit order (MSB first)
SPI.setBitOrder(MSBFIRST);
}
void loop() {
// Code to send and receive data
}

Now let’s see a practical example of how to communicate with an SD card using SPI:

#include <SPI.h>
#include <SD.h>
const int chipSelect = 10;  // CS pin for the SD card
void setup() {
Serial.begin(9600);
// Initialize SD card
if (!SD.begin(chipSelect)) {
Serial.println("SD card initialization failed!");
return;
}
Serial.println("SD card initialized successfully!");
// Write to file
File dataFile = SD.open("test.txt", FILE_WRITE);
if (dataFile) {
dataFile.println("Rabbit Brother teaches you Arduino!");
dataFile.close();
Serial.println("File written successfully!");
}
}
void loop() {
// Empty loop
}

Notes:

1. The SS pin is digital pin 10 on most Arduino boards

2. Different devices may require different clock speeds, check the device manual

3. Remember to connect power and ground correctly

When you need to control multiple SPI devices, you can do it like this:

const int device1_cs = 10;
const int device2_cs = 9;
void setup() {
pinMode(device1_cs, OUTPUT);
pinMode(device2_cs, OUTPUT);
// Initialize to high, not selected

digitalWrite(device1_cs, HIGH);
digitalWrite(device2_cs, HIGH);
SPI.begin();
}
void sendToDevice1(byte data) {
digitalWrite(device1_cs, LOW);  // Select device 1
SPI.transfer(data);            // Send data
digitalWrite(device1_cs, HIGH); // Deselect
}
void sendToDevice2(byte data) {
digitalWrite(device2_cs, LOW);  // Select device 2
SPI.transfer(data);            // Send data
digitalWrite(device2_cs, HIGH); // Deselect
}

1. Using an oscilloscope to observe SPI signals is a good way to troubleshoot

2. When communication errors occur, first check the wiring and timing

3. If data transmission is unstable, consider lowering the clock speed

1. Try connecting an LED dot matrix module using SPI to display a smiley face

2. Consider: Why is SPI faster than I2C in transmission speed?

3. Challenge: Implement a program to control two SPI devices simultaneously

Friends, today’s Arduino learning journey ends here! Remember to write code, and feel free to ask Rabbit Brother in the comments if you have any questions. Wishing everyone a happy learning experience, and may your Arduino skills improve steadily!