const int DriverA_1 = 14;
const int DriverA_2 = 15;
const int plus_sensor = 2;
const int sense_sensor = A2;
const int minus_sensor = 4;
//const int DriverB_1 = 10;
//const int DriverB_2 = 11;
char key;
char S = 's';
char B = 'b';
char C = 'c';

int value = 0;
int threshold = 100;

void setup() {
  pinMode(DriverA_1, OUTPUT);
  pinMode(DriverA_2, OUTPUT);
  pinMode(plus_sensor, OUTPUT);
  pinMode(sense_sensor, INPUT);
  pinMode(minus_sensor, OUTPUT);

  digitalWrite(plus_sensor, HIGH);
  digitalWrite(minus_sensor, LOW);
  //pinMode(DriverB_1, OUTPUT);
  //pinMode(DriverB_2, OUTPUT);
  Serial.begin(9600);
}

void loop() {  
  if (Serial.available()) {
    key = Serial.read(); 
    if(key == S){
      Serial.print("Start!");
      Serial.println("");
      while (Serial.read()) {
        value = analogRead(sense_sensor);
        Serial.println(value);
        if (value < threshold){
          motor(HIGH, LOW, 150);
        } else {
          motor(HIGH, LOW, 10);
        }
      }      
    } else if (key == B){
      Serial.print("Back!");
      Serial.println("");
      motor(LOW, HIGH, 3000);
      
    } else if (key == C){
      Serial.print("Stop!");
      Serial.println("");
      motor(LOW, LOW, 3000);
    
    }
  }
}

void motor(int a1, int a2, int d){    
  digitalWrite(DriverA_1, a1);
  digitalWrite(DriverA_2, a2);
  delay(d);
  digitalWrite(DriverA_1, a2);
  digitalWrite(DriverA_2, a2);
  delay(d);
}