int t =50; //мілісекунди

void setup() {
for (int i=1; i<=8; i++)
{
  pinMode(i, OUTPUT);
}
}

void loop() {
  for (int i=2; i<=8; i++)
  {
    digitalWrite(i,HIGH);
      delay(t);
    digitalWrite(i+1,HIGH);
      delay(t);
    digitalWrite(i+2,HIGH);
      delay(t);
    digitalWrite(i,LOW);
      delay(t);
    digitalWrite(i+1,LOW);
      delay(t);
}  

for(int i=8; i>=2; i--)
  {
    digitalWrite(i,HIGH);
      delay(t);
    digitalWrite(i-1,HIGH);
      delay(t);
    digitalWrite(i-2,HIGH);
      delay(t);
    digitalWrite(i,LOW);
      delay(t);
    digitalWrite(i-1,LOW);
      delay(t);
  }


}