My first arduino program using HC SRO4, Adafruit Motor Shield 2.3 and an old RC car

Pilot.ino

#include <Wire.h>
#include <Adafruit_MotorShield.h>
#include "utility/Adafruit_MS_PWMServoDriver.h"


// these constants won't change:
const int pinTrig = 13;     // trigger sound with digital pin 13 (yellow)
const int pinEcho = 12;     // green
const int pinLed = 10;      // orange
const int threshold = 100;  // threshold value to decide when the detected sound is a knock or not
const int safeDistance = 10; // min distance 10 cm

int hasBooted = 0;

// Create the motor shield object with the default I2C address
Adafruit_MotorShield AFMS = Adafruit_MotorShield(); 
// Or, create it with a different I2C address (say for stacking)
// Adafruit_MotorShield AFMS = Adafruit_MotorShield(0x61); 

// Select which 'port' M1, M2, M3 or M4. In this case, M1
Adafruit_DCMotor *enigneMain = AFMS.getMotor(4);
// You can also make another motor on port M2
//Adafruit_DCMotor *myOtherMotor = AFMS.getMotor(2);


void setup() {
  pinMode(pinTrig, OUTPUT); // ping
  pinMode(pinEcho, INPUT); // pong
  pinMode(pinLed, OUTPUT);

  AFMS.begin();  // create with the default frequency 1.6KHz
  //AFMS.begin(1000);  // OR with a different frequency, say 1KHz
  
  // Set the speed to start, from 0 (off) to 255 (max speed)
  enigneMain->setSpeed(225);
  enigneMain->run(FORWARD);
  // turn on motor
  enigneMain->run(RELEASE);

  
  Serial.begin(9600);
}

void loop() {

  if(!hasBooted){
    // advertize booting
    shortBlink();
    Serial.println("booted");
  }

  hasBooted = 1;

  if (Serial.available() > 0) {
    // read the incoming byte:
    int incomingByte = Serial.read();

    // say what you got:
    Serial.print("I received: ");
    Serial.println(incomingByte, DEC);
    shortBlink();
  }
  
  
  // establish variables for duration of the ping, 
  // and the distance result in inches and centimeters:
  long duration, cm;

  digitalWrite(pinTrig, LOW);
  delayMicroseconds(2);
  digitalWrite(pinTrig, HIGH);
  delayMicroseconds(10);
  digitalWrite(pinTrig, LOW);

  pinMode(pinEcho, INPUT);
  duration = pulseIn(pinEcho, HIGH);
  
  cm = microsecondsToCentimeters(duration);


  if(isSafe(cm)) {
    enigneMain->run(FORWARD);
  }
  else {
    enigneMain->run(RELEASE);
    Serial.print("proximity alert: ");
    Serial.println(cm);
  }

  // warn if it isn't safe
  warn(!isSafe(cm));

  
  delay(threshold);
}

long microsecondsToCentimeters(long microseconds)
{
  // The speed of sound is 340 m/s or 29 microseconds per centimeter.
  // The ping travels out and back, so to find the distance of the
  // object we take half of the distance travelled.
  return microseconds / 29 / 2;
}

// cm {long} 
// returns a boolean
int isSafe(long cm) {
  if(cm < safeDistance) {
    return 0;
  }
  return 1;
}

// warn: light a red led
// @param {int} st status (use as a boolean)
void warn(int st) {
  if(st == 1) {
    digitalWrite(pinLed, HIGH);
  }
  else {
    digitalWrite(pinLed, LOW);
  }

}

// shortly blinks at lowintensity
void shortBlink() {
  for(int i=0; i < 5; i++) {
    // on at mid intensity
    for(int j=0; j < 100; j++) {
      digitalWrite(pinLed, HIGH);
      delayMicroseconds(50);
      digitalWrite(pinLed, LOW);
      delayMicroseconds(500);
    }
    delay(100);
    digitalWrite(pinLed, LOW);
    delay(100);
  }
}