import machine
import time

TRIG_PIN = machine.Pin(20, machine.Pin.OUT)
ECHO_PIN = machine.Pin(21, machine.Pin.IN)
BUZZER_PIN = machine.Pin(15, machine.Pin.OUT)
LED_PIN = machine.Pin(14, machine.Pin.OUT)

def send_trigger_pulse():
    TRIG_PIN.low()
    time.sleep_us(2)
    TRIG_PIN.high()
    time.sleep_us(10)
    TRIG_PIN.low()

def get_echo_pulse_duration():
    pulse_duration = machine.time_pulse_us(ECHO_PIN, 1, 30000)  # Timeout set to 30ms (maximum range)
    return pulse_duration

def distance_in_cm(pulse_duration):
    # Speed of sound at sea level is approximately 343 meters per second (or 34300 cm/s)
    # Distance = Speed * Time / 2 (since the sound traveled to the object and back)
    distance = (pulse_duration / 2) * 0.0343
    return distance

def alert():
    for _ in range(4):  # Repeat the alert beep 4 times
        BUZZER_PIN.on()
        LED_PIN.on()
        time.sleep(0.25)  # Beep and LED on duration (half a second)
        BUZZER_PIN.off()
        LED_PIN.off()
        time.sleep(0.25)  # Pause between beeps

def main():
    while True:
        send_trigger_pulse()
        pulse_duration = get_echo_pulse_duration()
        distance = (pulse_duration / 2) * 0.0343
        
        if distance <= 15:
            alert()  # Alert beep sound and LED blinking
        else:
            LED_PIN.off()  # Turn off the LED if distance is greater than 15 cm
        
        print("Distance: {:.2f} cm".format(distance))
        time.sleep(1)

if __name__ == "__main__":
    main()