int trigpin =12;
int echopin =11;
int LEDred =10;
int LEDgreen =9;
int buzzerpin =8;

long duration,distance;

void setup() {
  // put your setup code here, to run once:
pinMode(trigpin, OUTPUT);
pinMode(echopin, INPUT);
pinMode(LEDred, OUTPUT);
pinMode(LEDgreen, OUTPUT);
pinMode(buzzerpin, OUTPUT);
Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
digitalWrite(trigpin, LOW);
delayMicroseconds(2);
digitalWrite(trigpin, HIGH);
delayMicroseconds(8);

duration = pulseIn(echopin, HIGH);
distance = duration*0.034/2;

Serial.print("distance: ");
Serial.println(distance);

if (distance>50) {
  digitalWrite(LEDgreen, HIGH);
  digitalWrite(LEDred, LOW);
  noTone(buzzerpin);
}
else {
  digitalWrite(LEDred, HIGH);
  digitalWrite(LEDgreen, LOW);
  tone(buzzerpin,600);
}

}