from machine import Pin
import time
LED_PIN = 15
led = Pin(LED_PIN, Pin.OUT)
start_timer = time.ticks_ms()
print(start_timer)

while True:
  if time.ticks_diff(time.ticks_ms(), start_timer) > 500:
    led.value(not led.value())
    start_timer = time.ticks_ms()
  print(".", end="")