Serial Monitor Problem (TX and RX only works after open serial monitor)

[mkmti]

Hello,

I am trying to control the Arduino from a web page without a ethernet shield.
I can communicate with the Arduino (TX and RX working) , however I always have to open the serial monitor first.

How can I communicate with the Arduino without open the serial monitor?

Here is the code:

char c;
void setup()
{
  Serial.begin(9600);
  pinMode(30, OUTPUT);
  pinMode(24, OUTPUT);
  pinMode(26, OUTPUT);
  pinMode(28, OUTPUT);
}

void loop()
{
  if (Serial.available() > 0)
  {
    c = Serial.read();
  }
  else
  {
    delay(100);
  }
  if (c=='a')
  {
    digitalWrite(24, HIGH);
    digitalWrite(26, LOW);
    digitalWrite(28, LOW);
    digitalWrite(30, LOW);
  }

  if (c=='z')
  {
    digitalWrite(26, HIGH);
    digitalWrite(24, LOW);
    digitalWrite(28, LOW);
    digitalWrite(30, LOW);
  
  }

  if (c=='x')
  {
    digitalWrite(26, LOW);
    digitalWrite(24, LOW);
    digitalWrite(28, HIGH);
    digitalWrite(30, LOW);
  }

  if (c=='y')
  {
    digitalWrite(26, LOW);
    digitalWrite(24, LOW);
    digitalWrite(28, LOW);
    digitalWrite(30, HIGH);
  } 
  
  if (c=='p')
  {
    digitalWrite(26, LOW);
    digitalWrite(24, LOW);
    digitalWrite(28, LOW);
    digitalWrite(30, LOW);
  } 
  
  c='\0';
}

Best Regards,
Tiago

[J-M-L]

Hello, do yourself a favour and please read How to get the best out of this forum and modify your post accordingly (including code tags and necessary documentation for your ask).

---

The Arduino opens its serial line.
A program running on your computer needs to connect to the Serial port.
then you just exchange data

how you do this from a web page is another question I guess.. (where we need more info)

[mkmti]

I am sending values from php to the arduino.

<?php
 
$port = fopen("COM6", "w+");

if($port == NULL){
    echo "bad";
}
if ($_POST['estado']=="forward")
{
    echo "forward";
    fwrite($port, "a");
}

The idea, is after clicking in a button made in html sending the value "a" to the arduino.
This is working, I can receive the values and control my OUTPUTS as I want.
However, to make this communication I have to open the serial monitor first. I am not understanding why I have to open the serial monitor to make the TX and RX working.

How do I communicate without open the serial monitor?

Regards,
Tiago

[J-M-L]

@mkmti

$port = fopen("COM6", "w+");

that reboots your arduino each time you ping your PHP script...