Obstacle Detection
==================

This example shows how to use the ultrasonic sensor to detect an obstacle
and sound an alarm, as well as change the EV3 brick light color.

.. code-block:: python

    """ obstacle.py 

    Use the ultrasonic sensor to detect a distance threshold.

    Setup:
        Connect ultrasonic sensor to port number 1.

    """
    # Importing modules and classes
    import time
    import numpy as np
    from pyev3.brick import LegoEV3
    from pyev3.devices import Ultrasonic

    # Defining parameters
    tstop = 10  # Execution loop duration (s)
    talarm = 0.5 # Alarm beeping interval (s)
    distmin = 10 # Minimum distance for alarm (cm)

    # Creating LEGO EV3 objects
    ev3 = LegoEV3()
    usonic = Ultrasonic(ev3, portnum=1, inputmode='distance')

    # Initializing current time stamp and starting clock
    tprev = 0
    tcurr = 0
    tstart = time.perf_counter()
    # Running execution loop
    print('Running for', tstop, 'seconds ...')
    while tcurr <= tstop:
        # Getting current distance to obstacle
        distcurr = usonic.output
        # Checking for distance threshold
        if distcurr < distmin:
            ev3.set_statuslight(color='red')
        else:
            ev3.set_statuslight(color='green')
        # Updating previous time and getting current time (s)
        tprev = tcurr
        tcurr = time.perf_counter() - tstart
        # Sounding alarm every `talarm` seconds if minimum distance is violated
        if (np.floor(tcurr/talarm) - np.floor(tprev/talarm)) == 1:
            print('Distance = ', distcurr)
            if distcurr < distmin:
                ev3.play_tone(volume=20, frequency=880, duration = 0.1)
    print('Done.')
    # Closing brick connection
    ev3.set_statuslight(color='green')
    ev3.close()