#define sdby 7
#define pwm_a 6
#define ain_1 5
#define ain_2 4
#define led 13
int plus = 5;
int value = 30;

char readchar = '0';

void setup() {
  Serial.begin(9600);

  pinMode(pwm_a, OUTPUT);
  pinMode(ain_1, OUTPUT);
  pinMode(ain_2, OUTPUT);
  pinMode(sdby, OUTPUT);

  pinMode(led, OUTPUT);

  digitalWrite(sdby, HIGH);
}

void loop() {
  while (Serial.available() > 0) {
    readchar = Serial.read();

    if (readchar == '1') {
      digitalWrite(ain_1, LOW);
      digitalWrite(ain_2, HIGH);
      analogWrite(pwm_a, value);
      digitalWrite(led, HIGH);
     // Serial.println("Go forward");
    }

    if (readchar == '2') {
      digitalWrite(ain_1, HIGH);
      digitalWrite(ain_2, LOW);
      analogWrite(pwm_a, value);
      digitalWrite(led, HIGH);
     // Serial.println("Go backwards");
    }
    if (readchar == '3') {
      value += plus;

      if (value >= 100) {
        value = 100;
      }

     // Serial.println(value);
      analogWrite(pwm_a, value);
    }
    if (readchar == '4') {
      value -= plus;

      if (value <= 0) {
        value = 0;
      }

     // Serial.println(value);
      analogWrite(pwm_a, value);
    }

    if (readchar == '5') {
      value = -value;
     // Serial.println("Switch direction");
      analogWrite(pwm_a, value);
    }

    if (readchar == '0') {
      value = 0;
      analogWrite(pwm_a, value);
      digitalWrite(led, LOW);
     // Serial.println("Off");
    }
  }
}