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.. _py_reversing_aid:

7.10 Reversing Aid
======================

This project uses an LED, a buzzer and an ultrasonic module to create a reversing assist system.
We can put it on a remote control car to simulate the the actual process of reversing a car into a garage.


**Schematic**

|sch_reversing_aid|



**Wiring**

|wiring_reversing_aid| 


**Code**

.. note::

    * Open the ``7.10_reversing_aid.py`` file under the path of ``euler-kit/micropython`` or copy this code into Thonny, then click "Run Current Script" or simply press F5 to run it.

    * Don't forget to click on the "MicroPython (Raspberry Pi Pico)" interpreter in the bottom right corner. 

    * For detailed tutorials, please refer to :ref:`open_run_code_py`.



.. code-block:: python


    import machine
    import time
    import _thread


    buzzer = machine.Pin(15, machine.Pin.OUT)
    led = machine.Pin(14, machine.Pin.OUT)

    TRIG = machine.Pin(17,machine.Pin.OUT)
    ECHO = machine.Pin(16,machine.Pin.IN)

    dis = 100

    def distance():
        timeout=10000*5/340 
        TRIG.low()
        time.sleep_us(2)
        TRIG.high()
        time.sleep_us(10)
        TRIG.low()
        timeout_start = time.ticks_ms() # For timeout, re-read distance
        while not ECHO.value():
            waiting_time = time.ticks_ms()
            if waiting_time - timeout_start > timeout:
                return -1
        time1 = time.ticks_us()
        while ECHO.value():
            waiting_time = time.ticks_ms()
            if waiting_time - timeout_start > timeout:
                return -1
        time2 = time.ticks_us()
        during = time.ticks_diff(time2 ,time1)
        return during * 340 / 2 / 10000

    def ultrasonic_thread():
        global dis
        while True:
            dis = distance()

    _thread.start_new_thread(ultrasonic_thread, ())

    def beep():
        buzzer.value(1)
        led.value(1)
        time.sleep(0.1)
        buzzer.value(0)
        led.value(0)
        time.sleep(0.1)

    intervals = 10000000
    previousMills=time.ticks_ms()
    time.sleep(1) 

    while True:
        if dis<0:
            pass
        elif dis <= 10:
            intervals = 300
        elif dis <= 20:
            intervals =500
        elif dis <=50:
            intervals =1000
        else:
            intervals = 2000
        if dis!=-1:
            print ('Distance: %.2f' % dis)
            time.sleep_ms(100)

        
        currentMills=time.ticks_ms()
        
        if time.ticks_diff(currentMills,previousMills)>=intervals:
            beep()
            previousMills=currentMills
        
* As soon as the program runs, the ultrasonic sensor will continuously read the distance to the obstacle in front of you, and you will be able to see the exact distance value on the shell.
* The LED and buzzer will change the frequency of blinking and beeping depending on the distance value, thus indicating the approach of the obstacle.
* The :ref:`py_ultrasonic` article mentioned that when the ultrasonic sensor works, the program will be paused.
* To avoid interfering with the LED or buzzer timing, we created a separate thread for ranging in this example.