from machine import Pin,PWM
from time import sleep_ms
S1 = PWM(Pin(18),freq = 50,duty = 128)
def rotate(servo,degree):
    servo.duty(int(degree*0.54+25.6))
while 1:
    for i in range(0,180,5):
        rotate(S1,i)
        sleep_ms(20)   
    for i in range(180,0,-5):
        rotate(S1,i)
        sleep_ms(20)