from machine import Pin,PWM
from time import sleep

LED = Pin(5,Pin.OUT)
But = Pin(2,Pin.IN)
pwm = PWM (LED)

pwm.freq(1000)

while True:
    if But.value() == 1:
        for duty in range (65536):
            sleep(0.00001)
            pwm.duty_u16(duty)
    if But.value() == 1:
        for duty in range (65536,-1,-1):
            sleep(0.00001)
            pwm.duty_u16(duty)