from machine import Pin, time_pulse_us
import time

SOUND_SPEED=340 
TRIG_PULSE_DURATION_US=10

trig_pin = Pin(15, Pin.OUT) 
echo_pin = Pin(14, Pin.IN)  

while True:
    # Prepare the signal
    trig_pin.value(0)
    time.sleep_us(5)

    # Create a 10 microseconds pulse
    trig_pin.value(1)
    time.sleep_us(TRIG_PULSE_DURATION_US)
    trig_pin.value(0)

    ultrasonic_duration = time_pulse_us(echo_pin, 1, 30000) # Return the propation time of the wave in 10 microseconds

    # Included to handle the negative error that might occur if the object is not in range    
    if ultrasonic_duration > 0:
        distance_cm = SOUND_SPEED * ultrasonic_duration / 20000
        print(f"Distance : {distance_cm} cm")
    else:
        print("Out of range or sensor error")

    time.sleep_ms(500)

# QUICK NOTES ABOUT THE SIMULATION
# I included the two resistors (as voltage dividers) as a precautionary measure
# for when building real-world projects. The echo pin from the HC-SR04 produces 5V 
# but the Raspberry Pi operates with ~3.3V. In a real-world project, without the resistor,
# I would risk frying my board. So the resistors (1K and 2K ohms) prevent this by dissipating
# some of that so the board and the sensor work without risk of damaging each other.