/**
   HC-SR04 Demo
   Demonstration of the HC-SR04 Ultrasonic Sensor
   Date: August 3, 2016

   Description:
    Connect the ultrasonic sensor to the Arduino as per the
    hardware connections below. Run the sketch and open a serial
    monitor. The distance read from the sensor will be displayed
    in centimeters and inches.

   Hardware Connections:
    Arduino | HC-SR04
    -------------------
      5V    |   VCC
      2     |   Trig
      3     |   Echo
      GND   |   GND

   License:
    Public Domain
*/

// Pinos
const int TRIG_PIN = 2;
const int ECHO_PIN = 3;

//  400 cm (23200 us pulse) distancia maxima suportada pelo sensor
// 100 cm (5800 us pulse) distancia segura
// Or over 50 cm (2900 us pulse) distancia de perigo
//2 cm (116 us pulse) distancia minima suportada pelo sensor ou choque
const unsigned int SAFE_DIST =5800;
const unsigned int MAX_DIST =2900;
const unsigned int MIN_DIST = 1000;
const unsigned int ACIDENT_DIST = 500;

void setup() {

  // The Trigger pin will tell the sensor to range find
  pinMode(TRIG_PIN, OUTPUT);
  digitalWrite(TRIG_PIN, LOW);

  //Set Echo pin as input to measure the duration of 
  //pulses coming back from the distance sensor
  pinMode(ECHO_PIN, INPUT);

  // We'll use the serial monitor to view the sensor output
  Serial.begin(9600);
}

void loop() {

  unsigned long t1;
  unsigned long t2;
  unsigned long pulse_width;
  float cm;
//  float inches;

  // Hold the trigger pin high for at least 10 us
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Wait for pulse on echo pin
  while ( digitalRead(ECHO_PIN) == 0 );

  // Measure how long the echo pin was held high (pulse width)
  // Note: the micros() counter will overflow after ~70 min
  t1 = micros();
  while ( digitalRead(ECHO_PIN) == 1);
  t2 = micros();
  pulse_width = t2 - t1;

  // Calculate distance in centimeters and inches. The constants
  // are found in the datasheet, and calculated from the assumed speed
  //of sound in air at sea level (~340 m/s).
  cm = pulse_width / 58.0;
  //inches = pulse_width / 148.0;

  // Print out results
  if ( pulse_width > SAFE_DIST ) {
    Serial.print(cm);
    Serial.print(" cm \t");
    Serial.println("Seguro");
  } 
   else { 
          if ( MIN_DIST < pulse_width < MAX_DIST ) {
    Serial.print(cm);
    Serial.print(" cm \t");
    Serial.println("Cuidado! Perigo de choque!");
      } 
          else {
               //( pulse_width == ACIDENT_DIST );
    Serial.print(cm);
    Serial.print(" cm \t");
    Serial.println("Acidente detectado!");
       }
       
   // Serial.print(inches);
    //Serial.println(" in");
     }
   // Wait at least 3000ms before next measurement
  delay(3000);

}