'Serial1' was not declared in this scope

Question

Trying to do serial communication between 2 Arduino Unos.

Code:

#include <SoftwareSerial.h>
int ledPin = 13;
int board; // 1 = Uno. 2 = Mega.
int on_off; // 1 = On. 0 = Off.
int buzzerPin = 9;
int Ack_tx = 2; //Acknowledgement tx.
int rec;
void setup()
{
 Serial.begin(9600); // start serial communication at 9600bps
 Serial1.begin(9600); // start serial1 communication at 9600bps
 pinMode(ledPin, OUTPUT);
 pinMode(buzzerPin, OUTPUT);
 Serial.flush();
 Serial1.flush();
} // End Setup
void loop()
{
 Serial.println("Enter Uno=1/Mega=0 ..."); //Select board
 // if(!Serial){ board = Serial.read();}
 while(Serial.available()==0) { // Wait for User to Input Data
 }
 board = Serial.parseInt(); //Read the data the user has input
 Serial.println("Enter LED On=1/Off=0 ..."); //Select On or Off
 while (Serial.available()==0) { // Wait for User to Input Data
 }
 on_off = Serial.parseInt();
 Serial.println();
 switch (board) {
 case 0: //Mega board
 if (on_off == 1) digitalWrite(ledPin, HIGH); //Select Uno LED On
 else digitalWrite(ledPin, LOW); //Select Uno LED Off
 break; //End Case
 case 1: //Uno board
 //Serial.println("Off to Uno...");
 //Send on_off info to Uno
 Serial1.write(on_off/256); //Send the Quotient or "how many times" value
 Serial1.write(on_off%256); //Send the Modulo or Remainder.
 delay(50); //Wait for the serial port.
 while(Serial1.available()<2) //Wait for 2 bytes to arrive
 {
 //do nothing
 } //End While
 byte b1=Serial1.read(); //Read Upper byte
 byte b2=Serial1.read(); //Read Lower byte
 rec=(b1*256)+b2; 
 if (rec == Ack_tx) tone(buzzerPin, 300, 300); //Ack_tx from Uno
 break;
 } //End Switch Case
} 

Error:

Arduino: 1.8.5 (Windows 10), Board: "Arduino/Genuino Uno"
C:\Users\Akshit\Documents\Arduino\sketch_mar06a\sketch_mar06a.ino: In function 'void setup()':
sketch_mar06a:13: error: 'Serial1' was not declared in this scope
 Serial1.begin(9600); // start serial1 communication at 9600bps
 ^
C:\Users\Akshit\Documents\Arduino\sketch_mar06a\sketch_mar06a.ino: In function 'void loop()':
sketch_mar06a:51: error: 'Serial1' was not declared in this scope
 Serial1.write(on_off/256); //Send the Quotient or "how many times" value
 ^
Multiple libraries were found for "SoftwareSerial.h"
 Used: C:\Program Files (x86)\Arduino\hardware\arduino\avr\libraries\SoftwareSerial
 Not used: C:\Program Files (x86)\Arduino\libraries\SoftwareSerial
exit status 1
'Serial1' was not declared in this scope
This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

This is a very basic problem I know, but nothing on the internet is helping.

• Ignacio Vazquez-Abrams: Why do you think "Serial1" should exist?
• Aki: I picked this code off of the internet. I feel it should exist because we would need one serial for communication with the serial monitor of computer and a second one for the actual serial communication between the two arduinos Pls correct me if I am wrong.
• Ignacio Vazquez-Abrams: So... you saw it in random code and thought it would work everywhere?
• Aki: The code made sense to me. Couldnt think of any changes to make.. Ill try the answer given by Majenko
• gre_gor: @Aki An Uno has only one hardware serial interface (Serial). What do you expect Serial1 to be?

Answer 1

The Uno has no Serial1. It only has one serial port, called Serial. To use Serial1 you will need a bigger board such as a Mega2560, or define it as a SoftwareSerial port and use two other IO pins of your choice for it, though at lower baud rates than Serial can run at.

• mustafatorun: I have arduino micro, and I can use serial (form comunication pc )and serial1 (form com. wifi module).

Answer 2

You import the SoftwareSerial library but you however never instance an object of the SoftwareSerial class.

You just need to add the line

 SoftwareSerial Serial1(10, 11); // RX, TX

after including the library header (taken from here)

This now creates an object Serial1 on which the operations down there should work the same as with a real hardware serial (API-wise).

Side note: Careful with the wiring. You are using this Serial1 emulated UART to communicate between the boards, so if you're using above pin numbers (D10 = RX, D11 =TX) then you must connected D10 (Board1) -> D11 (Board2), D11 (Board1) -> D10 (Board2), i.e. RX->TX, TX->RX.