from time import sleep
sleep(0.1)

from machine import Pin
Svetodiod = Pin(25, Pin.OUT)

freq = 0.5 #частота
period = 1 / freq #в секундах
prd_on = period * 0.5
prd_off = period - prd_on

while True:
    Svetodiod.on()
    sleep(prd_on)
    Svetodiod.off()
    sleep(prd_off)