ArduinoUltrasonicFunFor Ages: 0-100

This is a simple project. It uses an Arduino UNO and a HC-SR04

int trigPin = 11;
int echoPin = 12;
long duration,cm,inches;
void setup() {
 // put your setup code here, to run once:
 Serial.begin(9600);
 pinMode(trigPin,OUTPUT);
 pinMode(echoPin,INPUT);
 pinMode(2,OUTPUT);
}
void loop() {
 // put your main code here, to run repeatedly:
 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 < 20){
   digitalWrite(2,HIGH);
   delay(50);
   digitalWrite(2,LOW);
   delay(50);
 }
 delay(100);
}