from machine import Pin, PWM
import time

pwm = PWM(Pin(22))
pwm.freq(1000)

while True:
    # Increase brightness
    for duty in range(0, 65536, 256):
        pwm.duty_u16(duty)
        time.sleep(0.005)  

    # Decrease brightness
    for duty in range(65535, -1, -256): 
        pwm.duty_u16(duty)
        time.sleep(0.005)