sketch_L298N.ino

#define RightMotorEnable 9
#define RightMotorBackward 7
#define RightMotorForward 8

#define LeftMotorEnable 11
#define LeftMotorBackward 10
#define LeftMotorForward 12

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(LeftMotorEnable,    OUTPUT);
  pinMode(LeftMotorForward,   OUTPUT);
  pinMode(LeftMotorBackward,  OUTPUT);
  pinMode(RightMotorEnable,   OUTPUT);
  pinMode(RightMotorForward,  OUTPUT);
  pinMode(RightMotorBackward, OUTPUT);
  analogWrite(LeftMotorEnable, 255);
  analogWrite(RightMotorEnable, 255);
  digitalWrite(LeftMotorForward, LOW);
  digitalWrite(LeftMotorBackward, LOW);  
  digitalWrite(RightMotorForward, LOW);  
  digitalWrite(RightMotorBackward, LOW);  
}

void loop() {
  const int pin[4] = {LeftMotorForward, LeftMotorBackward, RightMotorForward, RightMotorBackward};
  const int en[4] = {LeftMotorEnable, LeftMotorEnable, RightMotorEnable, RightMotorEnable};
  for (int i = 0; i < 4; i++) {
      analogWrite(en[i], 128);            // slow speed
      digitalWrite(pin[i], HIGH);
      digitalWrite(LED_BUILTIN, HIGH);   // turn the LED on (HIGH is the voltage level)
      delay(1000);                       // wait for a second
      analogWrite(en[i], 255);           // full speed
      delay(1000);                       // wait for a second
      digitalWrite(pin[i], LOW);
      digitalWrite(LED_BUILTIN, LOW);    // turn the LED off by making the voltage LOW
      delay(1000);                       // wait for a second
  }
}