import machine
import time


# Define pins for HC-SR04 sensor
TRIG_PIN = machine.Pin(14, machine.Pin.OUT)
ECHO_PIN = machine.Pin(12, machine.Pin.IN)

# Define pin for the relay connected to LED
RELAY_PIN = machine.Pin(13, machine.Pin.OUT)

# Function to measure distance using HC-SR04
def measure_distance():
    # Send a 10us pulse to the trigger pin
    TRIG_PIN.off()
    time.sleep_us(2)
    TRIG_PIN.on()
    time.sleep_us(10)
    TRIG_PIN.off()

    # Initialize variables to hold pulse start and end time
    pulse_start = 0
    pulse_end = 0

    # Wait for the echo pin to go high (pulse start)
    while ECHO_PIN.value() == 0:
        pulse_start = time.ticks_us()

    # Wait for the echo pin to go low (pulse end)
    while ECHO_PIN.value() == 1:
        pulse_end = time.ticks_us()

    # Ensure we have valid values for pulse_start and pulse_end
    if pulse_start and pulse_end:
        # Calculate pulse duration
        pulse_duration = time.ticks_diff(pulse_end, pulse_start)
        # Calculate distance in cm (speed of sound is 34300 cm/s)
        distance = (pulse_duration * 0.0343) / 2
        return distance
    else:
        # Return an invalid distance if measurement failed
        return -1

# Threshold distance to control the LED (in cm)
DISTANCE_THRESHOLD = 100

while True:
    # Measure the current distance
    distance = measure_distance()
    
    # If the distance is valid and less than the threshold, control the relay
    if distance != -1:
        print("Distance: {:.2f} cm".format(distance))
        
        # If the distance is less than the threshold, turn ON the LED (activate relay)
        if distance < DISTANCE_THRESHOLD:
            RELAY_PIN.on()  # Activate relay (LED ON)
            print('Turned ON Led')
        else:
            RELAY_PIN.off()  # Deactivate relay (LED OFF)
            print('Turned OFF Led')
    # Wait for a second before measuring again
    time.sleep(1)