/*

RC Car + Ping sensor code

 */

// this constant won't change.  It's the pin number
// of the sensor's output:
const int pingPin = 7;
const int fowardPin = 13;
const int backwardPin = 12;
const int rightPin = 11;
const int leftPin = 10;

void setup() {
  // initialize serial communication:
  Serial.begin(9600);
  Serial.println("Motor test!");
  pinMode(fowardPin, OUTPUT);
  pinMode(backwardPin, OUTPUT);
  pinMode(leftPin, OUTPUT);
  pinMode(rightPin, OUTPUT);
}

void loop()
{
  // establish variables for duration of the ping, 
  // and the distance result in inches and centimeters:
  long duration, inches, cm;

  // The PING))) is triggered by a HIGH pulse of 2 or more microseconds.
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  pinMode(pingPin, OUTPUT);
  digitalWrite(pingPin, LOW);
  delayMicroseconds(2);
  digitalWrite(pingPin, HIGH);
  delayMicroseconds(5);
  digitalWrite(pingPin, LOW);

  // The same pin is used to read the signal from the PING))): a HIGH
  // pulse whose duration is the time (in microseconds) from the sending
  // of the ping to the reception of its echo off of an object.
  pinMode(pingPin, INPUT);
  duration = pulseIn(pingPin, HIGH);

  // convert the time into a distance
  inches = microsecondsToInches(duration);
  cm = microsecondsToCentimeters(duration);
  
  Serial.print(inches);
  Serial.print("in, ");
  Serial.print(cm);
  Serial.print("cm");
  Serial.println();
  
  delay(100);
  
  if (inches > 10) {
    digitalWrite(fowardPin, HIGH);
  }
  else {
    Serial.println("stop");
    digitalWrite(fowardPin, LOW);
    delay(500);
    Serial.println("backup");
    digitalWrite(backwardPin, HIGH);
    digitalWrite(rightPin, HIGH);
    delay(3000);
    digitalWrite(backwardPin, LOW);
    digitalWrite(rightPin, LOW);
  }
  
}

long microsecondsToInches(long microseconds)
{
  // According to Parallax's datasheet for the PING))), there are
  // 73.746 microseconds per inch (i.e. sound travels at 1130 feet per
  // second).  This gives the distance travelled by the ping, outbound
  // and return, so we divide by 2 to get the distance of the obstacle.
  // See: http://www.parallax.com/dl/docs/prod/acc/28015-PING-v1.3.pdf
  return microseconds / 74 / 2;
}

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;
}