#define ECHO_PIN 2
#define TRIG_PIN 3
void setup() {
 Serial.begin(115200);
 pinMode(LED_BUILTIN, OUTPUT);
 pinMode(TRIG_PIN, OUTPUT);
 pinMode(ECHO_PIN, INPUT);
 }
float readDistanceCM() {
 digitalWrite(TRIG_PIN, LOW);
 delayMicroseconds(2);
 digitalWrite(TRIG_PIN, HIGH);
 delayMicroseconds(10);
 digitalWrite(TRIG_PIN, LOW);
 int duration = pulseIn(ECHO_PIN, HIGH);
 return duration * 0.034 / 2;
 }
void loop() {
 float distance = readDistanceCM();
 bool isNearby = distance < 100;
 digitalWrite(LED_BUILTIN, isNearby);
 Serial.print("Measured distance: ");
 Serial.println(readDistanceCM());
 delay(100);
}