from machine import Pin, PWM
from time import sleep

# Set up PWM Pin
led = Pin(20, Pin.OUT)
led_pwm = PWM(led)
#duty_step = 129 

#Set PWM frequency
frequency = 5000
led_pwm.freq (frequency)


while True:
   for i in range (0, 65536, 6553):
        led_pwm.duty_u16(i)
        sleep(0.5)