import time 
from machine import Pin,PWM,ADC
led=PWM(Pin(5))
led.freq(500)
TRIG = Pin(4, Pin.OUT)
ECHO = Pin(2, Pin.IN)

def distance_cm():
    # Send trigger pulse
    TRIG.low()
    time.sleep_us(2)
    TRIG.high()
    time.sleep_us(10)
    TRIG.low()

    # Wait for echo start
    while ECHO.value() == 0:
        signaloff = time.ticks_us()
    # Wait for echo end
    while ECHO.value() == 1:
        signalon = time.ticks_us()

    # Time difference
    timepassed = time.ticks_diff(signalon, signaloff)
    distance = (timepassed * 0.0343) / 2  # Convert to cm
    return distance

# Main loop
while True:
    dist = distance_cm()
    print("Distance: {:.1f} cm".format(dist))

    time.sleep(0.2)
    # Limit distance range (e.g., 2–50 cm)
    if dist > 50:
        dist = 50
    elif dist < 2:
        dist = 2

    # Map distance (2–50 cm) → LED brightness (bright when close)
    duty = int((1 - (dist - 2) / 48) * 65535)
    led.duty_u16(duty)
    time.sleep(0.1)