​

int low = 10;

int high = 9;

​

void setup() {

  pinMode(0, OUTPUT);

  pinMode(1, OUTPUT);

  pinMode(2, OUTPUT); 

}

​

int on_time = 20; //in ms

int refresh_rate = 1; // per second

int pins = 3;

int off_time = (1000 / (refresh_rate * (pins + 1))) - on_time; //in ms

​

void loop() {

   for (int pin = 0; pin <= pins; pin++) {

    digitalWrite(pin, HIGH);

    delay(on_time);

    digitalWrite(pin, LOW); 

    delay(off_time);