#include <LiquidCrystal_I2C.h>
#define PIN_ECHO 2
#define PIN_TRIG 3
#define LED 12
int min_wert = 10; // Schwell-Wert unter dem LED permanent leuchtet
int max_wert = 100; // Schwell-Wert ab dem LED permanent ausgeschaltet ist
int us_wert, cm;

LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
  lcd.clear();
  lcd.setCursor(3,0);
  lcd.print("Entfernung:");
  lcd.setCursor(8,1);
  lcd.print("cm");
  pinMode(PIN_TRIG, OUTPUT);
  pinMode(PIN_ECHO, INPUT);
  pinMode(LED, OUTPUT);
  //us_wert = pulseIn(PIN_ECHO, HIGH);
}

void loop() {
  // put your main code here, to run repeatedly:
  lcd.setCursor(5,1);
  digitalWrite(PIN_TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(PIN_TRIG, LOW);
  delayMicroseconds(10);
  us_wert = pulseIn(PIN_ECHO, HIGH);
  cm = (us_wert/(2*29.1));
  Serial.print(us_wert);
  Serial.print(" - ");
  Serial.println(cm);
  if (cm < 100) {
    lcd.print(" ");
    if (cm < 10) {
      lcd.print(" ");
    }
  }
  lcd.print(cm);
  delay(200);

  if(cm<=min_wert) {
    digitalWrite(LED, HIGH);
  } else if (cm >= max_wert) {
    digitalWrite(LED, LOW);
  } else {
    digitalWrite(LED, HIGH);
    delay(cm);
    digitalWrite(LED, LOW);
    delay(cm);
  }

}