void setup() { //The 8-pin ATTinys (25/45/85) all have 5 usable digital output pins 0-4 pinMode(1, OUTPUT); } void loop() { digitalWrite(1, HIGH); //Set the LED pins to HIGH. This gives power to the LED and turns it on delay(1000); // Wait for a half a second digitalWrite(1, LOW); // Set the LED pins to LOW. This turns it off delay(1000); // Wait for a half second }