long zen = 0;
long zenm = 0;

void setup() {
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  digitalWrite(4, 1);
}

void loop() {
    zen = 50;
        if (zen > zenm ) {
          zenm = zenm + 1;
      digitalWrite(2, HIGH);
      digitalWrite(3, HIGH);
      digitalWrite(4, LOW);
         delayMicroseconds(1);
      digitalWrite(3, LOW);
      delayMicroseconds(1);
      digitalWrite(3, HIGH);
         delayMicroseconds(1);
      digitalWrite(4, HIGH);
        }
        if (zen < zenm) {
          zenm = zenm - 1;
      digitalWrite(2, LOW);
      digitalWrite(3, HIGH);
      digitalWrite(4, LOW);
         delayMicroseconds(1);
      digitalWrite(3, LOW);
      delayMicroseconds(1);
      digitalWrite(3, HIGH);
         delayMicroseconds(1);
      digitalWrite(4, HIGH);
        }
} 

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