from machine import Pin, Timer
from utime import sleep

time_elapsed = 0

def scheduler(timer):
    global time_elapsed
    time_elapsed += 1
    print(time_elapsed)

def light_red():
    led_red.on()
    led_yellow.off()
    led_green.off()

def light_yellow():
    led_red.off()
    led_yellow.on()
    led_green.off()

def light_green():
    led_red.off()
    led_yellow.off()
    led_green.on()


led_red = Pin(4, Pin.OUT)
led_red.off()

led_yellow = Pin(5, Pin.OUT)
led_yellow.off()

led_green = Pin(18, Pin.OUT)
led_green.off()


timer = Timer(0)
timer.init(period=1000, mode=Timer.PERIODIC, callback=scheduler)


while True:
    pass