const unsigned long Interval = 1000;
unsigned long previousMillis = 0;

int randNum()
{
  static int previousNum = -1000;
  int rand_Num;
  do
  {
    rand_Num = random(0, 9);
  } while (rand_Num == previousNum);
  return previousNum = rand_Num;
}

void setup()
{
  Serial.begin(9600);
  randomSeed(analogRead(A0));
}

void loop()
{
  unsigned long currentMillis = millis();
  if (currentMillis - previousMillis >= Interval)
  {
    previousMillis = currentMillis;
    Serial.println(randNum());
  }
}