https://medium.com/kidstronics/bridging-all-sensors-together-pitbot-ca8803bf9cb

_29_HC-SR04_SimpleTest_01.ino

/*  Project: LEGO Episode # 29
 *   Bridging All Sensors Together — Pitbot
 *   Collecting All Codes for the Final Act of Giving Behaviors to Robot
 *   
 *   INO file: _29_HC-SR04_SimpleTest_01.ino
 *   
 *   date: 9/01/19
 *  
 *  code by: https://forum.arduino.cc
 *  hardware by: Arduino IDE 1.8.9
 * 
 *  Description: There is no easy way more simple than that sketch to test right away HC-SR04!
 *               Please oepn Serial Monitor at 9600 bps:)
 *  
 *  Visit: https://medium.com/jungletronics
 *  
 *  Tutorial: https://medium.com/kidstronics/bridging-all-sensors-together-pitbot-ca8803bf9cb
 *  License: CC-SA 3.0, feel free to use this code however you'd like.
 *  Please improve upon it! Let me know how you've made it better.
 */
/*
  HC-SR04 Ping distance sensor]
  VCC to arduino 5v GND to arduino GND
  Echo to Arduino pin 13 Trig to Arduino pin 12
*/

int echoPin = 13; 
int trigPin = 12; 

void setup() { 
  Serial.begin (9600); 
  pinMode(trigPin, OUTPUT); 
  pinMode(echoPin, INPUT); 
} 

void loop() { 
  int duration, cm; 
  digitalWrite(trigPin, LOW); 
  delayMicroseconds(20); 
  digitalWrite(trigPin, HIGH); 
  delayMicroseconds(20); 
  digitalWrite(trigPin, LOW); 
  duration = pulseIn(echoPin, HIGH); 
  cm = duration / 29 / 2;
/* Sound velocity=29cm/microsec,
   then divide by 2 because of the return time 
*/
  Serial.print(cm); 
  Serial.println(" cm"); 
  delay(500); 
}