Serial Monitor: Initial sent command ignored, successive commands are fine

Projects Programming
1

Hello.

This issue is more of a slight bother than a problem, though I would like to be sure I am doing things properly.

I am new to Arduino, though my first little projects have been extremely fun and educational. I am now moving on to a more complicated project and am in the early stages of development. I am now working with a mobile platform and have cobbled together a little program to assist in the testing of motors. The code changes the platform's direction using a keyboard, and it has been enormously helpful.

My little, tiny, eeny weeny issue is that when I open the Serial Monitor and send my first command, the instruction seems to be ignored. All successive commands work flawlessly, though this initial hiccup is causing me worry that I am making a mistake somewhere.

This is the program as it stands (I have used two pieces of publicly available code that were fiddled, nibbled, and expanded into something that works for me):

// Control a USB connected 4WD mobile platform from a keyboard via the Serial Monitor in the Arduino IDE.
// w - forward
// z - backwards
// a - left
// s - right
// q - stop

const int speed = 200;  // Speed setting from 1 (slow) to 255 (fast)
int incomingByte;       // A variable to read incoming serial data into

void setup() {
  // Initialize serial communication:
  Serial.begin(9600);
  // Setup Channel A
  pinMode(12, OUTPUT); //Initiates Motor Channel A pin
  pinMode(9, OUTPUT); //Initiates Brake Channel A pin
  // Setup Channel B
  pinMode(13, OUTPUT); //Initiates Motor Channel A pin
  pinMode(8, OUTPUT);  //Initiates Brake Channel A pin
}

void loop() {
  if (Serial.available() > 0) {
    incomingByte = Serial.read();
    if (incomingByte == 'w') {
      // Forward
      digitalWrite(13, HIGH);
      digitalWrite(8, LOW); 
      analogWrite(11, speed); 
      digitalWrite(12, LOW);
      digitalWrite(9, LOW);
      analogWrite(3, speed);
    }
    if (incomingByte == 'z') {
      // Backward
      digitalWrite(13, LOW); 
      digitalWrite(8, LOW);
      analogWrite(11, speed);
      digitalWrite(12, HIGH);
      digitalWrite(9, LOW); 
      analogWrite(3, speed); 
    }
    if (incomingByte == 's') {
      // Hard right
      digitalWrite(13, LOW); 
      digitalWrite(8, LOW); 
      analogWrite(11, speed); 
      digitalWrite(12, LOW); 
      digitalWrite(9, LOW);   
      analogWrite(3, speed);   
    }
    if (incomingByte == 'a') {
      // Hard left
      digitalWrite(13, HIGH); 
      digitalWrite(8, LOW);   
      analogWrite(11, speed);  
      digitalWrite(12, HIGH);  
      digitalWrite(9, LOW);   
      analogWrite(3, speed);    
    }
    if (incomingByte == 'q') {
      // Stop
      digitalWrite(8, HIGH);  //Engage the Brake for Channel A
      digitalWrite(9, HIGH);  //Engage the Brake for Channel B
    }
  }
}

Does anyone spot an error I have made that would be causing this little glitch? (Any other criticisms of this code would be welcome as well, I love learning from my mistakes.)

Thank you so much for any help, suggestions, or advice.

2

The problem is probably nothing to do with your code, but to do with the fact that when you open the serial console the Arduino reboots. There is a short delay while it goes through the bootloader process, after which it will be able to accept serial commands fine. If your first command is sent while it's still rebooting, then it will be ignored.

Add a capacitor (>10µF) between the RESET and GND pins on the Arduino to stop it rebooting when you connect to serial.

3

You're a hero, majenko.

Thank you so much for taking the time to help, it is appreciated.