arduino executes serial commands only sometimes

Question

I have been trying to make an arduino project which changes the motor directions based on serial input. I have tried everything on google search. the arduino only responds sometimes. I know my board is not fried because the same happens on other boards.

code:

 const int motorApinA = 6;
  const int motorApinB = 7;
  const int motorBpinA = 8;
  const int motorBpinB = 9;
  const int LED_Strip_pos_pin = 2;


void setup() {
  Serial.begin(9600);
  pinMode(motorApinA, OUTPUT);
  pinMode(motorApinB, OUTPUT);
  pinMode(motorBpinA, OUTPUT);
  pinMode(motorBpinB, OUTPUT);
  pinMode(LED_Strip_pos_pin, OUTPUT);
  Serial.write("yay, your code is working");


}

void loop() 
  {
     if (Serial.read() == 'F')
     {
       digitalWrite(motorApinA, HIGH);
       digitalWrite(motorApinB, LOW);
       digitalWrite(motorBpinB, HIGH);
       digitalWrite(motorBpinA, LOW);
       Serial.println("Done!");
     }
     if (Serial.read() == 'B')
     {
       digitalWrite(motorApinB, HIGH);
       digitalWrite(motorApinA, LOW);
       digitalWrite(motorBpinA, HIGH);
       digitalWrite(motorBpinB, LOW);
       Serial.println("Done!");

     }
     if (Serial.read() == 'L')
     {
       digitalWrite(motorApinA, HIGH);
       digitalWrite(motorApinB, LOW);
       digitalWrite(motorBpinA, HIGH);
       digitalWrite(motorBpinB, LOW);
       Serial.println("Done!");

     }
     if (Serial.read() == 'R')
     {
       digitalWrite(motorApinB, HIGH);
       digitalWrite(motorApinA, LOW);
       digitalWrite(motorBpinB, HIGH);
       digitalWrite(motorBpinA, LOW);
       Serial.println("Done!");

     }
     if (Serial.read() == 'S')
     {
       digitalWrite(motorApinA, LOW);
       digitalWrite(motorApinB, LOW);
       digitalWrite(motorBpinB, LOW);
       digitalWrite(motorBpinA, LOW);
       Serial.println("Done!");
     }

     }   

sorry if I asked this on the wrong site :(

Answer 1

Each time you call Serial.read(), it reads the first char in the buffer. Let's say you have a 'B' in your buffer. Unless your program happens to be at if (Serial.read() == 'B'), it doesn't trigger the action you want. You should store a returned value from Serial.read() and evaluate it.

void loop()  {

  char c = Serial.read();

  if (c == 'F') {
    Serial.println("F!");
  }

  if (c == 'B') {
    Serial.println("B!");
  }

  if (c == 'L') {
    Serial.println("L!");
  }

  if (c == 'R') {
    Serial.println("R!");
  }

  if (c == 'S') {
    Serial.println("S!");
  }
}