from machine import Pin, time_pulse_us , PWM
from time import sleep_us, sleep

# === BUZZER ===
buzzer = PWM(Pin(15))

def tone(freq, duration):
    if freq < 1:
        buzzer.duty(0)
    else:
        buzzer.freq(int(freq))
        buzzer.duty(512)
        sleep(duration)
        buzzer.duty(0)

def silent(t):
    buzzer.duty(0)
    sleep(t)

# === CONFIGURATION ===
TRIGGER_PIN = 26
ECHO_PIN = 25
MAX_DISTANCE_CM = 400
ECHO_TIMEOUT_US = int((MAX_DISTANCE_CM / 0.0343) * 2)

# === SETUP PINS ===
trigger = Pin(TRIGGER_PIN, Pin.OUT)
echo = Pin(ECHO_PIN, Pin.IN)

def check_distance():
    trigger.value(0)
    sleep_us(2)
    trigger.value(1)
    sleep_us(10)
    trigger.value(0)

    pulse = time_pulse_us(echo, 1, ECHO_TIMEOUT_US)
    if pulse < 0:
        return None
    return pulse

def distance_cm():
    pulse_time = check_distance()
    if pulse_time is None:
        return None
    return (pulse_time * 0.0343) / 2


while True:
    d_cm = distance_cm()
    print("Distance:", d_cm, "cm")

    if d_cm is None:
        silent(0.2)
        continue

    if d_cm < 50:
        freq = (50 - d_cm) * 50  # distance → frequency

        # enforce minimum frequency
        if freq < 200:
            freq = 200

        tone(freq, 0.1)

    else:
        silent(0.2)

    sleep(0.05)