How to hold output for 10 seconds?

I am using Ultrasonic sensor, LED, and buzzer in my circuit. However, I need the LED to stay on for like 10 seconds or more.

Here is my code

const int trigPin = 9;
const int echoPin = 10;
const int buzzer = 11;
const int ledPin = 13;

long duration;
int distance;
int safetyDistance;


void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(buzzer, OUTPUT);
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}


void loop() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);

  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);

  distance = duration * 0.034 / 2;

  safetyDistance = distance;
  if (safetyDistance <= 5) {
    digitalWrite(buzzer, HIGH);
    digitalWrite(ledPin, HIGH);

  }
  else {
    digitalWrite(buzzer, LOW);
    digitalWrite(ledPin, LOW);
  }

  Serial.print("Distance: ");
  Serial.println(distance);
}

If you don’t mind the program doing nothing for 10 seconds then delay(10000); will do what you want

If you need to do other things during the period then delay() is not the way to do it. Take a look at Using millis() for timing. A beginners guide, Several things at the same time and the BlinkWithoutDelay example in the IDE

Hello
I ´ve add a timer to your sketch.
The sketch is untestet, but well done :slight_smile:

enum {Led};
const unsigned long Duration {10000};
struct TIMER {
  unsigned long timeStamp;
  unsigned long duration;
} timer[] {
  {0,Duration},
};
const int trigPin = 9;
const int echoPin = 10;
const int buzzer = 11;
const int ledPin = 13;
long duration;
int distance;
int safetyDistance;
void startTimer (TIMER &timer) {
  timer.timeStamp= millis();
}
void stopTimer(TIMER &timer) {
  timer.timeStamp= 0;
}
enum {NoEvent,Event};
bool eventTimer(TIMER &timer) {
  return (( millis() - timer.timeStamp >= timer.duration && timer.timeStamp)?Event:NoEvent); 
}
void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(buzzer, OUTPUT);
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}
void loop() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = duration * 0.034 / 2;
  safetyDistance = distance;
  if (safetyDistance <= 5) {
    digitalWrite(buzzer, HIGH);
    digitalWrite(ledPin, HIGH);
    startTimer(timer[Led]); 
  }
  else {
    digitalWrite(buzzer, LOW);
   
  }
  Serial.print("Distance: ");
  Serial.println(distance);
  if (eventTimer(timer[Led])) digitalWrite(ledPin, LOW),stopTimer(timer[Led]); 
}

It worked perfectly. Thank you!