#define ECHOPIN 2
#define TRIGPIN 4
#define LED_RED 12
#define LED_YELLOW 14
#define LED_GREEN 26
long khoangTGian, khoangCach;
void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(TRIGPIN, OUTPUT);
  pinMode(LED_RED, OUTPUT);
  pinMode(LED_YELLOW, OUTPUT);
  pinMode(LED_GREEN, OUTPUT);
  pinMode(ECHOPIN, INPUT);
}

void loop() {
  digitalWrite(TRIGPIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIGPIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIGPIN, LOW);

  khoangTGian = pulseIn(ECHOPIN, HIGH);
  khoangCach = khoangTGian / 58.2;
  String hienThi = String(khoangCach);

  Serial.print("Khoảng cách: ");
  Serial.print(hienThi);
  Serial.println(" cm");

  if (khoangCach <= 100) {
    digitalWrite(LED_RED, HIGH);
    digitalWrite(LED_YELLOW, LOW);
    digitalWrite(LED_GREEN, LOW);
  } else if (khoangCach > 100 && khoangCach <= 300) {
    digitalWrite(LED_RED, LOW);
    digitalWrite(LED_YELLOW, HIGH);
    digitalWrite(LED_GREEN, LOW);
  } else {
    digitalWrite(LED_RED, LOW);
    digitalWrite(LED_YELLOW, LOW);
    digitalWrite(LED_GREEN, HIGH);
  }
  delay(1000);
}