from machine import Pin
from time import sleep

entry = Pin(4, Pin.IN, Pin.PULL_UP)
exit = Pin(5, Pin.IN, Pin.PULL_UP)

green = Pin(23, Pin.OUT)
red = Pin(22, Pin.OUT)
yellow = Pin(21, Pin.OUT)
blue = Pin(19, Pin.OUT)

cars = 0

def update():
    green.value(cars < 15)
    red.value(cars == 15)

update()

while True:

    if entry.value() == 0:
        if cars < 15:
            cars += 1
            update()
            yellow.value(1)
            sleep(0.3)
            yellow.value(0)
        while entry.value() == 0:
            sleep(0.05)

    if exit.value() == 0:
        if cars > 0:
            cars -= 1
            update()
            blue.value(1)
            sleep(0.3)
            blue.value(0)
        while exit.value() == 0:
            sleep(0.05)