#define TRIG_PIN 14
#define ECHO_PIN 21
#define LED 16
float duration_us, distance_cm;


void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(14, OUTPUT);
  pinMode(21, INPUT);
  pinMode(16, OUTPUT);
  
}

void loop() {
  digitalWrite(14, HIGH);
  delayMicroseconds(10);
  digitalWrite(14, LOW);
  duration_us = pulseIn(21, HIGH);
  distance_cm = 0.017 * duration_us;
  if (distance_cm < 100) {digitalWrite(16, HIGH);
  }else{digitalWrite(16, LOW);
  }
Serial.print("distanceA:");
Serial.print(distance_cm);
Serial.println(" cm     ");
delay(10);
}