int trigpin=11;
int echopin=12;
int ledPin=9;
long duration, cm, inches;
void setup() {
Serial.begin(9600);
pinMode(trigpin, OUTPUT);
pinMode(echopin, INPUT);
 
pinMode(ledPin, OUTPUT);
digitalWrite(ledPin, LOW);
}

void loop() {
  digitalWrite(trigpin,LOW);
  delayMicroseconds(5);
  digitalWrite(trigpin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigpin, LOW);

  pinMode(echopin, INPUT);
  duration=pulseIn(echopin, HIGH);

  cm=(duration/2)/29.1;
  inches=(duration/2)/74;

  Serial.print(inches);
  Serial.print("in, ");
  Serial.print(cm);
  Serial.print("cm");
  Serial.println();
 
  
  if (cm<4)
  {
  delay(250);
  digitalWrite(ledPin, HIGH);
  delay(100);
  digitalWrite(ledPin, LOW);
  delay(100);
  }
  









}