code from the paper https://cdn.hackaday.io/files/23081987497504/IEEE Project AWAAZ.pdf

bateye-original.c

const int trigPin = 3;
const int echoPin = 2;

void setup()
{
  // initialize serial communication:
  Serial.begin(115200);
}

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

  // The sensor is triggered by a HIGH pulse of 10 or more microseconds.
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  repeat:
  pinMode(trigPin, OUTPUT);
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Read the signal from the sensor: 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(echoPin, INPUT);
  duration = pulseIn(echoPin, HIGH);

  // convert the time into a distance
  cm = microsecondsToCentimeters(duration);

  if( duration>10000)
  {
    goto repeat;
  }

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

  Serial.println();
  int OutputPin=9;
  unsigned int thisPitch = map(cm, 2, 400, 150, 15000);
  // play the pitch:
  tone(OutputPin, thisPitch, 10);
   // delay in between reads for stability
  Serial.print(thisPitch);
  Serial.print(" ");
  delay(5);
}

long microsecondsToCentimeters(long microseconds)
{
  return microseconds / 29 / 2;
}