10. Μέτρηση απόστασης ultrasonic + buzzer

// this constant won't change. It's the pin number of the sensor's output:
const int pingPin = 7;
int const buzzPin = 2;


void setup() {
// initialize serial communication:
Serial.begin(9600);
pinMode(buzzPin, OUTPUT); // buzz pin is output to control buzzering
}

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


Serial.print(cm);
Serial.print("cm");
Serial.println();


// if distance less than 0.5 meter and more than 0 (0 or less means over range) 
if (cm <= 50 && cm >= 0) {
// Buzz
digitalWrite(buzzPin, HIGH);
digitalWrite(buzzPin, LOW);
delay(10*cm);
digitalWrite(buzzPin, HIGH);
} else {
// Don't buzz
digitalWrite(buzzPin, LOW);
}
// Waiting 60 ms won't hurt any one


delay(100);
}


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;
}