Connecting two arduino boards by SPI

[bud2024]

master arduino code

#include <SPI.h> // Include SPI library

#define LED 7          // LED connected to Pin 7
#define BUTTON 2       // Button connected to Pin 2

int buttonState;
int x;

void setup() {
  Serial.begin(115200);                // Start Serial communication
  pinMode(BUTTON, INPUT);              // Set button pin as input
  pinMode(LED, OUTPUT);                // Set LED pin as output
  
  SPI.begin();                         // Start SPI as Master
  SPI.setClockDivider(SPI_CLOCK_DIV8); // Set SPI clock to 2MHz (16MHz/8)
  digitalWrite(SS, HIGH);              // Deselect the Slave by setting SS HIGH
}

void loop() {
  byte masterSend, masterReceive;

  // Read the button state
  buttonState = digitalRead(BUTTON);

  // Set value to send based on button state
  if (buttonState == HIGH) {
    x = 1;
  } else {
    x = 0;
  }

  // Start communication with the Slave
  digitalWrite(SS, LOW);              // Select the Slave
  masterSend = x;                     
  masterReceive = SPI.transfer(masterSend); // Send and receive data
  digitalWrite(SS, HIGH);             // Deselect the Slave

  // Set LED state based on the received value
  if (masterReceive == 1) {
    digitalWrite(LED, HIGH);          // Turn on LED
    Serial.println("Master LED ON");
  } else {
    digitalWrite(LED, LOW);           // Turn off LED
    Serial.println("Master LED OFF");
  }

  delay(1000); // Wait for 1 second
}

slave arduino code

#include <SPI.h> // Include SPI library

#define LED 7 // LED connected to Pin 7
#define BUTTON 2 // Button connected to Pin 2

volatile boolean received;
volatile byte slaveReceive, slaveSend;
int buttonState;
int x;

void setup() {
Serial.begin(115200); // Start Serial communication
pinMode(BUTTON, INPUT); // Set button pin as input
pinMode(LED, OUTPUT); // Set LED pin as output
pinMode(MISO, OUTPUT); // Set MISO as output for SPI

SPCR |= _BV(SPE); // Enable SPI in Slave mode
SPI.attachInterrupt(); // Enable SPI interrupt
received = false; // Reset received flag
}

ISR(SPI_STC_vect) {
slaveReceive = SPDR; // Read the received data
received = true; // Set received flag
}

void loop() {
if (received) { // Check if data is received
received = false; // Reset received flag

// Set LED state based on received value
if (slaveReceive == 1) {
  digitalWrite(LED, HIGH);   // Turn on LED
  Serial.println("Slave LED ON");
} else {
  digitalWrite(LED, LOW);    // Turn off LED
  Serial.println("Slave LED OFF");
}

// Read the button state
buttonState = digitalRead(BUTTON);

// Set value to send based on button state
if (buttonState == HIGH) {
  x = 1;
} else {
  x = 0;
}

slaveSend = x;
SPDR = slaveSend;            // Send data back to Master

}

delay(1000); // Wait for 1 second
}

help me to identify the issues.
It doesnt show anything in serial monitor

[pert]

I moved your topic to an appropriate forum category @bud2024 .

In the future, please take some time to pick the forum category that best suits the subject of your topic. There is an "About the _____ category" topic at the top of each category that explains its purpose.

This is an important part of responsible forum usage, as explained in the "How to get the best out of this forum" guide. The guide contains a lot of other useful information. Please read it.

Thanks in advance for your cooperation.

[LarryD]

• Your 1k switch resistor is shorted out.

• Your switches should be wired to GND as S3 below.
  You will then need to use this in setup( ) pinMode(BUTTON, INPUT_PULLUP);
  NOTE: A closed/pushed switch will read as a LOW.