How to send data from nodemcu to arduino mega using serial communication?

I am trying to set up two-way communication between nodemcu and Arduino mega using serial i.e nodemcu send some particular data to Arduino and after receiving it Arduino responds it with another data particularly a string or integer. Is there any way to do it?

Have a look at the examples in Serial Input Basics - simple reliable ways to receive data. There is also a parse example to illustrate how to extract numbers from the received text.

The technique in the 3rd example will be the most reliable. It is what I use for Arduino to Arduino and Arduino to PC communication.

You can send data in a compatible format with code like this (or the equivalent in any other programming language)

Serial.print('<'); // start marker
Serial.print(value1);
Serial.print(','); // comma separator
Serial.print(value2);
Serial.println('>'); // end marker

…R

Here's where I started... extremely helpful.

"http://gammon.com.au/i2c"

1. Build the following hardware setup between NodeMCU1.0 and MEGA. NodeMCU communicates with it SM1 uisng UART Port; it uses software UART port (SUART Port) to communicates with UART1 Port of MEGA.

2. NodeMCU sends 1234 to MEGA.

#include<SoftwareSerial.h>
SoftwareSerial SUART(4, 5);  //D2, D1 = SRX, STX
char recStr[10] = "";
char ourStr[8] = "Arduino";
bool flag1 = false;

void setup()
{
  Serial.begin(115200);
  SUART.begin(115200);
}

void loop()
{
  SUART.print("<1234>"); //sending 1234
  Serial.println("<1234>");

   //--add codes as needed to capture string coming from MEGA
  delay(1000);
}

3. MEGA receives 1234 from NodeMCU and then sends the string - Arduino - to NodeMCU.

char recStr[10] = "";

void setup()
{
  Serial.begin(115200);
  Serial1.begin(115200);
}

void loop()
{
  byte n = Serial1.available();
  if (n != 0)
  {
    Serial1.readBytesUntil('>', recStr, 10);
    int x = atoi(recStr + 1);
    if (x == 1234)
    {
      char recStr[10] = "";      
      Serial.println("Received 1234 from Node; now sending - Arduino - to Node...!");
      Serial1.println("<Arduino>");
    }
  }
}

espMega-1x.png