Communication Between Two Arduino

Method Serial Communication

Example 1

In Example 1 Arduino Mega Having 4 Uart And Arduino Uno Having One Uart But We Need Two Uart in Arduino Uno So We need to Created Virtual Uart So See in Serial Port Moniter What data is Received.

The Serial Communication is Depended on Uart. As Many Uart Required To Send And Received Data Information Between Arduino Boards

Processing Algorithm

Circuit Diagram

Programming Code
Arduino Mega Code

int flag_led = 0;
void setup() {
  Serial.begin(9600);
  Serial1.begin(9600);
}

void loop() {
  if (Serial.available() > 0)
  {
    while (Serial.available() > 0) {
      flag_led = Serial.read() - '0';
    }
  }
  Serial1.print(flag_led);
  Serial.print(flag_led);
  Serial.println("-send-");
  delay(1000);
}

Arduino Uno Code

#define Ledpin 8
int recived = 0;

#include <SoftwareSerial.h>
//RX = digital pin 10, TX = digital pin 11
SoftwareSerial virtualPort(10, 11);

void setup() {
  Serial.begin(9600);
  pinMode(Ledpin, OUTPUT);
  virtualPort.begin(9600);
}

void loop() {
  if(virtualPort.available()){
    while (virtualPort.available() > 0) {
      recived = virtualPort.read()-'0';
    }
  }
  Serial.print(recived);
  Serial.println("--recived--");
  if (recived == 1) {
    digitalWrite(Ledpin, HIGH);
  } else {
    digitalWrite(Ledpin, LOW);
  }
  delay(1000);
}

Result

Example 2

In Example 2 Arduino Mega  And Arduino Uno Not Use Serial Port Moniter so we use TX0 & RX0. During Upload Code Disconnect RX TX wires if You Connect Them And Try to Upload it is Impossible to upload Code so It better u dissconnect wires before Upload it.

Processing Algorithm

Circuit Diagram

Programming Code
Arduino Mega Code

int flag_led = 0;
#define Buttonpin 7
void setup() {
  Serial.begin(9600);
  pinMode(Buttonpin, INPUT);
}

void loop() {
  if(digitalRead(Buttonpin)){
    flag_led = 1;
    }else{
    flag_led =0;
   }
  Serial.print(flag_led);
  delay(1000);
}

Arduino Uno Code

#define Ledpin 8
int recived = 0;

void setup() {
  Serial.begin(9600);
  pinMode(Ledpin, OUTPUT);
}

void loop() {  
  if(Serial.available()){
    while (Serial.available() > 0) {
      recived=0;
      recived = Serial.read()-'0';
    }
  }
  if (recived == 1) {
    digitalWrite(Ledpin, HIGH);
  } else {
    digitalWrite(Ledpin, LOW);
  }
  delay(100);
}

Result