#define trigPin 21
#define echoPin 16
float distanceCm;
void setup() {
Serial.begin (9600);
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
}
void loop() {
long duration, distance;
digitalWrite(trigPin, LOW);
delayMicroseconds(10);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
duration = pulseIn(echoPin, HIGH);
distanceCm = duration * 0.034 / 2;
Serial.print(distanceCm);
Serial.println(" cm");
delay(500);
}