from machine import Pin
from utime import sleep

red = Pin(1,Pin.OUT)
yellow = Pin(4,Pin.OUT)
green = Pin(5,Pin.OUT)

while True:
    red.on()
    yellow.off()
    green.off()
    sleep(3.0)
    red.off()
    yellow.on()
    green.off()
    sleep(0.5)
    red.off()
    yellow.off()
    green.on()
    sleep(3.0)