byte index = 0;
unsigned long prev = millis();
byte tm = 210;
byte count = 0;

byte tab[][4] = {
    HIGH, HIGH, LOW, LOW,
    LOW, LOW, HIGH, HIGH, 
    HIGH, LOW, LOW, HIGH,
    LOW, HIGH, HIGH, LOW,
};

void setup()
{
    for(byte i = 8; i < 12; i ++)
    {
        pinMode(i, OUTPUT);
    }
}

void loop()
{
    unsigned long curr = millis();
    if(curr - prev < tm)
        return;
    prev = curr;

    for(int i = 0; i < 4; i ++)
    {
        digitalWrite(i+8, tab[i][index]);
    }
    index ++;
    count ++;
    if(count > 10 && tm > 10)
    {
        tm -= 50;
        count  = 0;
    }
        
    if(index >= 4)
        index = 0;
}