# Exercise 13(b)
from machine import Pin, time_pulse_us
from time import sleep_ms,sleep_us
from neopixel import NeoPixel

#Define the GPIO lines needed
echo_pin = Pin(18, Pin.IN)
trig_pin = Pin(19, Pin.OUT)

# Initialize 16-element NeoPixel Ring on GPIO pin 14
ring = NeoPixel(Pin(14), 16)

def all_white():
     # set all elements to white
    for i in range(16):
        ring[i] = (255, 255, 255)
        ring.write()

def some_green(number):
     # set some elements to green
    for i in range(number+1):
        ring[i] = (0, 255, 0)
        ring.write()
        for i in range(number,16):  # turn off all unwanted elements
            ring[i] = (0, 0, 0)
            ring.write()

def some_red(number):
     # set some elements to green
    for i in range(number+1):
        ring[i] = (255, 0, 0)
        ring.write()
        for i in range(number,16):  # turn off all unwanted elements
            ring[i] = (0, 0, 0)
            ring.write()

# Ensure the trigger line is zero to begin with
trig_pin.value(0)
sleep_us(10) 

while True:
    trig_pin.value(1)  # signal to output pulses
    sleep_us(10)       # only need a short burst of pulses
    trig_pin.value(0)  # signal to stop pulses

    # determine how long before an echo signal is received
    pulse_duration = time_pulse_us(echo_pin, 1, 1000000)  # Wait for a LOW pulse, 1s timeout
    
    if pulse_duration > -1:
        echo_duration = pulse_duration/2
    
        # calculate the distance in cms
        object_distance = 341 * (echo_duration/1000000)*100
        print(f' The object is {object_distance:.1f} cms away')

        # calculate how many elements need illuminating
        element_number = int(object_distance/12.5)

        if object_distance>200:
            all_white()
        elif object_distance>60 and object_distance<=200:
            some_green(element_number) 
        elif object_distance<=60:
            some_red(element_number)