//'Buffer'/'NOT' logical gate!
#define pin1 (4)
#define pin2 (5)
#define pin3 (6)
#define pin4 (7)

//Pins of the gate...
void setup(){
  randomSeed(analogRead(A1));
  pinMode(pin1, OUTPUT);
  pinMode(pin2, OUTPUT);
  pinMode(pin3, OUTPUT);
  pinMode(pin4, OUTPUT);
}
void loop(){
  //HIGH - 'Buffer' & LOW - 'NOT'
  digitalWrite(pin1, random(2));
  digitalWrite(pin2, random(2));
  digitalWrite(pin3, random(2));
  digitalWrite(pin4, random(2));
  delay(500);
}