int trig = 2;
int echo = 3;

int led1 = 4;
int led2 = 5;
int led3 = 6;

void setup() {
  pinMode(trig, OUTPUT);
  digitalWrite(trig, LOW);
  pinMode(echo, INPUT);
  pinMode(led1, OUTPUT);
  digitalWrite(led1, LOW);
  pinMode(led2, OUTPUT);
  digitalWrite(led2, LOW);
  pinMode(led3, OUTPUT);
  digitalWrite(led3, LOW);
  Serial.begin(9600);
}

void loop() {
  double duration, cm;
  
  digitalWrite(trig, LOW);
  delayMicroseconds(2);
  digitalWrite(trig, HIGH);
  delayMicroseconds(5);
  digitalWrite(trig, LOW);
  
  duration = pulseIn(echo, HIGH);
  
  cm = duration / 29 / 2;
  
  digitalWrite(led1, ((cm >= 10) ? HIGH : LOW));
  digitalWrite(led2, ((cm >= 20) ? HIGH : LOW));
  digitalWrite(led3, ((cm >= 30) ? HIGH : LOW));
  
  Serial.print("time: ");
  Serial.println(duration);
  Serial.print("cm:   ");
  Serial.println(cm);
  
  delay(100);
}