Arduino Nano: LED brightness with HC-SR04 ultrasonic distance sensor

hcsr04LEDBrightness.ino

//Reference: https://howtomechatronics.com/tutorials/arduino/ultrasonic-sensor-hc-sr04/
const int ledPin = 9;
const int trigPin = 8;
const int echoPin = 4;

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

void loop() {
  digitalWrite(trigPin, LOW); //to make sure that the trigPin is clear
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW); //after this, 8 cycle sonic burst will be sent out
  
  long duration_us = pulseIn(echoPin, HIGH);
  int distanceRaw_cm = 0.034*duration_us/2;
  int distance_cm = constrain(distanceRaw_cm, 0, 30);
  Serial.print(distance_cm);
  
  int brightness = map(distance_cm, 0, 30, 255, 0);
  Serial.print(", ");
  Serial.println(brightness);
  analogWrite(ledPin, brightness);
}