from machine import Pin, PWM
import time

servo = PWM(Pin(0), freq=50, duty_u16=0)

while True:
    servo.duty_u16(3277)     # 0°
    time.sleep_ms(500)
    servo.duty_u16(4915)    # 90°
    time.sleep_ms(500)
    servo.duty_u16(6553)    # 180°
    time.sleep_ms(500)
    servo.duty_u16(4915)    # 90°
    time.sleep_ms(500)