from machine import Pin
import utime

trigger = Pin(26, Pin.OUT)
echo = Pin(27, Pin.IN)
red_led = Pin(18,Pin.OUT)
yellow_led = Pin(5,Pin.OUT)
green_led = Pin(17,Pin.OUT)

def ultra():
    trigger.off()
    utime.sleep_us(2)
    trigger.on()
    utime.sleep_us(5)
    trigger.off()
    while echo.value() == 0:
        signal_off = utime.ticks_us()
    while echo.value() == 1:
        signal_on = utime.ticks_us()
    try:
        time_passed = signal_on - signal_off
    except NameError:
        return 0
    return time_passed/58

while True:
    distance = ultra()
    print(f"Distance from object is {distance:6.2f}cm.")
    utime.sleep(1)
    if distance < 5:
        red_led.on()
        green_led.off()
        yellow_led.off()
    elif 20 > distance > 5:
        yellow_led.on()
        red_led.off()
        green_led.off()
    elif 60 > distance > 20:
        green_led.on()
        yellow_led.off()
        red_led.off()