from time import sleep_ms
from servo import Servo
my_servo = Servo(pin_id=28) 
while True:  
  my_servo.write(90)
  sleep_ms(500)
  my_servo.write(0)
  sleep_ms(500)
  my_servo.write(180)
  my_servo.write(90)
  sleep_ms(500)
  my_servo.write(90)
  sleep_ms(500)