#define relay 13
long duration = 1000;
long interval = 3000;
void setup()
{
Serial.begin(9600);
pinMode(relay, OUTPUT);
}
void loop()
{
static bool state;
static unsigned long time;
if((millis() — time) > (state ? duration : interval))
{
state = !state;
digitalWrite(relay, state);
time = millis();
}
}