import machine
import time

# Define GPIO pins for the HC-SR04 sensor
TRIGGER_PIN = 4
ECHO_PIN = 5

# Define GPIO pins for the LEDs
LED_RED_PIN = 10
LED_YELLOW_PIN = 11
LED_GREEN_PIN = 12

# Initialize GPIO pins for the sensor
trigger = machine.Pin(TRIGGER_PIN, machine.Pin.OUT)
echo = machine.Pin(ECHO_PIN, machine.Pin.IN)

# Initialize GPIO pins for the LEDs
led_red = machine.Pin(LED_RED_PIN, machine.Pin.OUT)
led_yellow = machine.Pin(LED_YELLOW_PIN, machine.Pin.OUT)
led_green = machine.Pin(LED_GREEN_PIN, machine.Pin.OUT)

# Function to measure distance using HC-SR04 sensor
def measure_distance():
    # Send a 10us pulse to the trigger pin to start the measurement
    trigger.high()
    time.sleep_us(10)
    trigger.low()

    # Wait for the echo pin to go high and start the timer
    while echo.value() == 0:
        pass
    start_time = time.ticks_us()

    # Wait for the echo pin to go low and stop the timer
    while echo.value() == 1:
        pass
    end_time = time.ticks_us()

    # Calculate the duration and convert it to distance in centimeters
    duration = time.ticks_diff(end_time, start_time)
    distance = duration / 58  # Speed of sound is approximately 58 microseconds/cm

    return distance

# Function to control LEDs based on the measured distance
def control_leds(distance):
    if distance <= 30:
        led_red.high()
        led_yellow.low()
        led_green.low()
    elif distance <= 50:
        led_red.low()
        led_yellow.high()
        led_green.low()
    else:
        led_red.low()
        led_yellow.low()
        led_green.high()

# Main program loop
while True:
    # Measure distance
    distance = measure_distance()

    # Control LEDs based on distance
    control_leds(distance)

    # Delay for a short period
    time.sleep(0.1)