print("Hello, ESP32!")
from machine import Pin
import time
import utime

# Pin setup
trig = Pin(5, Pin.OUT)
echo = Pin(18, Pin.IN)

led_red = Pin(12, Pin.OUT)
led_yellow = Pin(14, Pin.OUT)
led_green = Pin(27, Pin.OUT)

def get_distance():
    # Trigger the ultrasonic sensor
    trig.off()
    utime.sleep_us(2)
    trig.on()
    utime.sleep_us(10)
    trig.off()
    
    # Initialize start_time and end_time to avoid unbound variable errors
    start_time = 0
    end_time = 0

    # Measure the time it takes for echo to go high and low
    while echo.value() == 0:
        start_time = utime.ticks_us()
    while echo.value() == 1:
        end_time = utime.ticks_us()

    # Calculate the duration and distance
    duration = utime.ticks_diff(end_time, start_time)
    distance = (duration * 0.0343) / 2  # Convert time to distance
    return distance

while True:
    distance = get_distance()
    if distance <= 100:  # <= 1 meter
        led_red.on()
        led_yellow.off()
        led_green.off()
    elif distance <= 200:  # <= 2 meters
        led_red.off()
        led_yellow.on()
        led_green.off()
    else: 
        led_red.off()
        led_yellow.off()
        led_green.on()
    
    time.sleep(0.5)