// Distance Alert Using Ultrasonic Sensor/ISD1820/Arduino
// by RG Innovations 
// This sketch can work with ATtiny85 and Arduino UNO, MEGA, etc...
// This example code is in the public domain.


#define trigPin 3 //HCSR05 Trigger set to pin 3
#define echoPin 2 // HCSR05 Echo set to Pin 5
#define LED_PIN 4 // LED light set to Pin 4
#define ISD_PIN 5 // ISD1820 module PE Pin
#define DISTANCE 30 // Distance value to check in CM
#define trigPin1 6 //HCSR05 Trigger set to pin 3
#define echoPin1 7
#define trigPin2 8 //HCSR05 Trigger set to pin 3
#define echoPin2 9

long duration, duration1, duration2, cm;

void setup() 
{ 
  pinMode(LED_PIN, OUTPUT);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  digitalWrite(LED_PIN, LOW);  
} 
 
 
void loop() 
{ 

  //sending the trigger pulse, starting with LOW for a clean pulse
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);

digitalWrite(trigPin1, LOW);
delayMicroseconds(2);
digitalWrite(trigPin1, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin1, LOW);

digitalWrite(trigPin2, LOW);
delayMicroseconds(2);
digitalWrite(trigPin2, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin2, LOW);
//setting up the input pin, and receiving the duration in uS
pinMode(echoPin, INPUT);
duration = pulseIn(echoPin, HIGH);
// convert the pulse travel time into a distance

pinMode(echoPin1, INPUT);
duration1 = pulseIn(echoPin, HIGH);

pinMode(echoPin2, INPUT);
duration2 = pulseIn(echoPin, HIGH);


cm = microsecondsToCentimeters(Min(duration, duration1, duration2) );
  
      
      if (cm<=DISTANCE){
        digitalWrite(LED_PIN, HIGH);
        digitalWrite(ISD_PIN, HIGH);
        delay (200);        
        digitalWrite(ISD_PIN, LOW);
        delay (4800);
        digitalWrite(LED_PIN, LOW);
      }
      
delay(100);

} 


long microsecondsToCentimeters(long microseconds)
{
// The speed of sound is 340 m/s (29 us/cm)
return microseconds / 29 / 2;
}

int Min(int a, int b, int c)
{
  if(a > b && c >b)
  return b;
  else if( a<c && a< b)
  return a;
  else if(c<a && c<b)
  return c;

}