/***********************************************************************
* Arduino Nano "Sketch" for DustDetector
* Ultrasonic Sensor HC-SR04 
* mark and paste into Arduino IDE
***********************************************************************/
// DEFINE NANO PIN NUMBERS
#define  TrigPin    9
#define  EchoPin   10
#define  AlertPin   3
#define  DISTANCE   8 // SETS DISTANCE, IN INCHES, FROM TOP DOWN TO DUST PILE

/*F**********************************************************************
*
**********************************************************************/
void 
setup() 
{
    pinMode( TrigPin, OUTPUT);                  // SETS TRIGPIN AS AN OUTPUT
    pinMode( AlertPin, OUTPUT);
    pinMode( EchoPin, input);                    // SETS ECHOPIN AS AN input
    digitalWrite( AlertPin, LOW );
}
/*F**********************************************************************
*
**********************************************************************/
void 
loop() 
{
    int    dist;
    long   dur;

    digitalWrite( TrigPin, LOW );                  // MAKE SURE TRIGPIN IS LO
    delayMicroseconds( 2 );
    digitalWrite( TrigPin, HIGH );                        // SET TRIGPIN HIGH 
    delayMicroseconds( 10 );                                    // WAIT 10 US
    digitalWrite( TrigPin, LOW );                           // SET TRIGPIN LO
    dur = pulseIn( EchoPin, HIGH);    // RD ECHOPIN, RTRN ECHO TRAVEL TIME US
    dist = dur / 148;    // CALC DIST: INCHES (SOUND TRAVEL 1" IN 148US)
    if( dist < DISTANCE )
        digitalWrite( AlertPin, HIGH );                      // TURN ON ALERT
    else
        digitalWrite( AlertPin, LOW );                      // TURN OFF ALERT
    delay( 1000 );                             // 1 SECOND OVERALL CYCLE TIME
}