const int M1_IN1 = 5; 
const int M1_IN2 = 6; 
const int M2_IN1 = 8; 
const int M2_IN2 = 9; 

void setup() {

  Serial.begin(115200);
  while (!Serial) {
    delay(100); 
  }

  pinMode(M1_IN1, OUTPUT);
  pinMode(M1_IN2, OUTPUT);
  pinMode(M2_IN1, OUTPUT);
  pinMode(M2_IN2, OUTPUT);

  motor1_coast();
  motor2_coast();

  delay(3000);
}

void loop() {  // testing motor features (reverse / forward / brake / coast)

  motor1_forward();
  delay(2000);

  motor1_brake();
  delay(1000);

  motor1_reverse();
  delay(2000);

  motor1_coast();
  delay(2000);

  motor2_forward();
  delay(2000);

  motor2_brake();
  delay(1000);

  motor2_reverse();
  delay(2000);

  motor2_coast();
  delay(2000);

  motor1_forward();
  motor2_forward();
  delay(2000);

  motor1_brake();
  motor2_brake();
  delay(2000);
  
  motor1_coast();
  motor2_coast();
  delay(5000);
}

// motor functions defined

void motor1_forward() {
  digitalWrite(M1_IN1, HIGH);
  digitalWrite(M1_IN2, LOW);
}

void motor1_reverse() {
  digitalWrite(M1_IN1, LOW);
  digitalWrite(M1_IN2, HIGH);
}

void motor1_brake() {
  digitalWrite(M1_IN1, HIGH);
  digitalWrite(M1_IN2, HIGH);
}

void motor1_coast() {
  digitalWrite(M1_IN1, LOW);
  digitalWrite(M1_IN2, LOW);
}

void motor2_forward() {
  digitalWrite(M2_IN1, HIGH);
  digitalWrite(M2_IN2, LOW);
}

void motor2_reverse() {
  digitalWrite(M2_IN1, LOW);
  digitalWrite(M2_IN2, HIGH);
}

void motor2_brake() {
  digitalWrite(M2_IN1, HIGH);
  digitalWrite(M2_IN2, HIGH);
}

void motor2_coast() {
  digitalWrite(M2_IN1, LOW);
  digitalWrite(M2_IN2, LOW);
}