4 wheel car forward and backward move and Detect obstragle by using Ultra Sonic Sensor And stop the movement

4_wheel_car_with_Ultra_sen.ino

String readvoice;
String readvoicestore;

const int f_trig =  13;
const int f_echo = 12;
const int b_trig = 11;
const int b_echo = 10;

long duration_f;
int distance_f;

long duration_b;
int distance_b;

void setup() {
  Serial.begin(9600);
  pinMode(f_trig, OUTPUT);
  pinMode(f_echo, INPUT);
  pinMode(b_trig, OUTPUT);
  pinMode(b_echo, INPUT);

  pinMode(9, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(7, OUTPUT);
  pinMode(6, OUTPUT);

}
//-----------------------------------------------------------------------//
void loop() {
  // Serial.println(Serial.read());
  while (Serial.available()) { //Check if there is an available byte to read
    delay(10); //Delay added to make thing stable
    char c = Serial.read(); //Conduct a serial read
    readvoice += c; //build the string- "forward", "reverse", "left" and "right"
  }
  if (readvoice.length() > 0) {
    readvoicestore = readvoice;
  }
  if (readvoicestore.length() > 0) {
    if (readvoicestore == "forward")
    {
      if (distance_f_() < 20) {
        Serial.println("F Stop");
        stop();
        readvoicestore = "stop";
      }
      else if (readvoicestore == "stop") {
        Serial.println("F Stop Function");
        stop();
      }
      else {
        Serial.println("F forword");
        forward();
      }
    }
    else if (readvoicestore == "backward")
    {
      if (distance_b_() < 20) {
        Serial.println("B Stop");
        stop();
        readvoicestore = "stop";
      }
      else if (readvoicestore == "stop") {
        Serial.println("B Stop Function");
        stop();
      } else {
        Serial.println("B backword");
        backward();
      }
    }
    readvoice = "";
    delay(20);
  }
}




int distance_f_() {

  digitalWrite(f_trig, LOW);
  delayMicroseconds(2);

  digitalWrite(f_trig, HIGH);
  delayMicroseconds(10);
  digitalWrite(f_trig, LOW);
  duration_f = pulseIn(f_echo, HIGH);

  distance_f = duration_f * 0.034 / 2;

  return distance_f;
}

int distance_b_() {

  digitalWrite(b_trig, LOW);
  delayMicroseconds(2);

  digitalWrite(b_trig, HIGH);
  delayMicroseconds(10);
  digitalWrite(b_trig, LOW);
  duration_b = pulseIn(b_echo, HIGH);

  distance_b = duration_b * 0.034 / 2;

  return distance_b;
}


void forward() {
  digitalWrite(7, HIGH);
  digitalWrite(9, HIGH);
  digitalWrite(6, LOW);
  digitalWrite(8, LOW);
  delay(20);
}


void backward() {
  digitalWrite(6, HIGH);
  digitalWrite(8, HIGH);
  digitalWrite(7, LOW);
  digitalWrite(9, LOW);
  delay(20);
}

void stop() {
  digitalWrite(6, LOW);
  digitalWrite(8, LOW);
  digitalWrite(7, LOW);
  digitalWrite(9, LOW);
  delay(20);
}