Training and testing for new users.

Using Arduino Introductory Tutorials
9 
//What does this sketch do?

const int ledPin          = 13;
const int potentiometer   = A0;
unsigned long startTime;

void setup()
{
  pinMode(ledPin, OUTPUT);
}

void loop()
{
  int rate = analogRead(potentiometer);
  rate = map(rate, 0, 1023, 5000, 100);
  checkTime(rate);
}

void checkTime(int interval)
{
  static byte LEDstate = HIGH;
  if (millis() - startTime >= interval)
  {
    startTime = millis();
    digitalWrite(ledPin, LEDstate);
    LEDstate = !LEDstate;
  }
}