from utime import sleep
from machine import Pin, PWM

# duty for servo is between 40 - 115
DUTY_MIN = 40
DUTY_MAX = 115
duty = DUTY_MIN
delta_d = 5

p = Pin(2)
servo = PWM(p, freq=611)

while True:
    servo.duty(duty)
    sleep(1 / 1000)

    duty += delta_d
    if duty >= DUTY_MAX:
        duty = DUTY_MAX
        delta_d = -delta_d
    elif duty <= DUTY_MIN:
        duty = DUTY_MIN
        delta_d = -delta_d