from time import sleep
from machine import Pin, PWM

pwm = PWM(Pin(1))
pwm.freq(50)

while True:
    for position in range(1000,9000,50):
        pwm.duty_u16(position)
        sleep(0.01)
    for position in range(9000,1000,-50):
        pwm.duty_u16(position)
        sleep(0.01)