Read multiple char from USART

Question

int i, j;
char data;
int flag=0;

void loop() 
{
if(Serial.available() > 0){
    data  = Serial.read();
    flag=0;
  }

  if (data == 'd' && 'b') {
    digitalWrite(cONOF, HIGH);
  } else if (data == 't' && 'w') {
    digitalWrite(cONOF, LOW);
  }


  if (data == 'y' && 'w') {
    digitalWrite(start, HIGH);
    delay(2000);
    digitalWrite(start, LOW);
  }


  if (data == 'e' && 'r' && 'h' && 'i') {
    for (i=0;i<10;i++) {
      digitalWrite(horn, HIGH);
      delay(100);
      digitalWrite(horn, LOW);
      delay(100);
    }
    for (j=0;j<10;j++) {
      digitalWrite(horn, HIGH);
      delay(500);
      digitalWrite(horn, LOW);
      delay(500);
    }
    digitalWrite(horn, LOW);
  }

}

I want to read data from the USART where the messages have more than one character. I tried the code above but it doesn't work well. For example, I want to send the message 'db' to turn the output on, but just sending 'd' also turns it on, how do I fix this?

geometrikal · Accepted Answer · 2014-08-03 04:44:42Z

1

You need split the reading into two processes - storing the characters and checking if they are the right message.

To store the characters for example:

String message = "";

void loop() 
{
while(Serial.available()) {
    char b = Serial.read();

    if (b == '\r') {
        processMessage();
        message = "";
    }
    else {
        message += b;
    }
}
}

The process might look like

void processMessage() {

    if (message == "fb") {
         foo();
    }
    else if (message == "bf") {
         bar();
    }
}

I just use the Messenger library usually. But note you have to change WProgram.h to Arduino.h in Messenger.cpp to get it to work.

answered Aug 3, 2014 at 4:44

geometrikal

2,92516 silver badges21 bronze badges

ohh yaaa thx broder :) it works... perfect

Nasuha
– Nasuha

2014-08-06 04:42:43 +00:00
Commented Aug 6, 2014 at 4:42
Just be careful, in the code I posted if the string gets too big you could run out of memory. Might be wise to count the characters going in and stop adding em if it gets too long. Please accept my answer if its all good :P

geometrikal
– geometrikal

2014-08-06 09:54:41 +00:00
Commented Aug 6, 2014 at 9:54

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