from machine import Pin
from time import sleep_us, sleep, ticks_us, ticks_diff
 
# Define the velocity of sound
soundVelocity=340
 
# Define led, Trigger and echo pins
triggerPin = Pin(14,Pin.OUT)
echoPin = Pin(17,Pin.IN)
led = Pin(21, Pin.OUT)

print("Start Measuring distance")
# Start an endless loop
while True:
# Set the Trigger pin to LOW
    triggerPin.off()
    sleep_us(5)
# Make a 10 microSeconds HIGH pulse
    triggerPin.on()
    sleep_us(10)
    triggerPin.off()
# Wait for the echo pin to get to ON status
    while (echoPin.value() == 0):
        pass
# Start measuring the time
    startTime = ticks_us()
# Wait for the echo pin to get to OFF status
    while (echoPin.value() == 1):
        pass
# Stop measuring the time
    stopTime = ticks_us()
# Calculate the time for the echo to arrive
    echoTime = ticks_diff(stopTime,startTime)
# Calculate the distance 
    distance = echoTime*soundVelocity/2/10000
# Print the distance
    print("Distance: %5.1f" % (distance),"cm")
 
    if (distance<20):
        led.on()
    sleep(0.2)