So confused by TX RX serial communication!

Projects Programming
2

Every time this bit of code executes:

  if(Serial.available() > 0)
  {
    received = Serial.read();
    Serial.print("Received: ");
    Serial.print(received);
    Serial.println();

Your it will be printed out, and then loop back in and be read because TX and RX are connected.

I bet if you look up your numbers on an ascii table, they will represent the letters "Received".

You are also essentially sending 14 bytes for every one read which means you will quickly overrun the serial buffer and start loosing packets (think exponential growth in the number being sent).

You either need a second Serial port to talk to the Arduino serial monitor, or use something like an LED to verify the loop back.
Here is a possible (quickly written) example:

int sent = 19;
int received = 0;

void setup()
{
  Serial.begin(9600);
  pinMode(13,OUTPUT);
}

void loop()
{
  delay(2000);
  Serial.println(sent);
  
  if(Serial.available() > 0)
  {
    received = Serial.read();
    if (recieved == '1'){
      while(Serial.available == 0); //wait for the second byte
      recieved = Serial.read();
      if (recieved == '9'){
        //Recieved 19, so blink the light to show it was recieved successfully
        digitalWrite(13,HIGH);
        delay(1000);
        digitalWrite(13,LOW);
        delay(1000);     
      }
    }
  }
}