from machine import Pin
from time import sleep_ms
led = Pin(12,Pin.OUT)

key = Pin(21,Pin.IN,Pin.PULL_DOWN)

while 1:
    if (key.value() ==1):
        led.on()
        led.value(1)
        sleep_ms(500)
        led.value(0)
        sleep_ms(500)
    else:
        led.off()