//include the serial communication library
#include <SoftwareSerial.h>
SoftwareSerial Serial_sonar(0, 1); // rx, tx

//define variables and pin numbers
#define echoPin 9 // echo conencted to PB1
#define trigPin 10 // trigger connected to PB0

long duration, distance; 

//serial communication and pins for input and output
void setup() 
{
Serial_sonar.begin(9600);
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT); 
}

// the actual program loop
void loop() {
  //send the pulse
digitalWrite(trigPin, LOW); 
delayMicroseconds(1000); //each 1 sec we send a pulse
digitalWrite(trigPin, HIGH);
delayMicroseconds(10); 
digitalWrite(trigPin, LOW);

//we measuse the time 
duration = pulseIn(echoPin, HIGH);

//formula for cm feedback. The sound speed is 340m/s = 29us/cm.
//we divide the pulse time by 58, the time that the pulse takes to go and come back. 
distance = duration/58; 

//send the information to the Serial Monitor
Serial_sonar.print(distance);
Serial_sonar.println(" cm");
delay(1000);
}