from time import sleep
from machine import Pin, PWM, ADC

MIN = 500
MAX = 2500
MAX = 65535
a = MAX - MIN
b = ADC(Pin(28))
pwm = PWM(Pin(27))
pwm.freq(50)
pwm.duty_ns(500000)

while True:
  duty_us = (b.read_u16()*a/65535)+MIN
  pwm.duty_ns(int(duty_us*1000))
  sleep(0.05)