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.. _4.1.9_py_pi5:

4.1.6 Reversing Alarm
======================================

Introduction
-------------

In this project, we will use LCD, buzzer and ultrasonic sensors to make
a reverse assist system. We can put it on the remote control vehicle to
simulate the actual process of reversing the car into the garage.

Required Components
------------------------------

In this project, we need the following components.

.. image:: ../python_pi5/img/4.1.9_reversing_alarm_list.png
    :width: 800
    :align: center

It's definitely convenient to buy a whole kit, here's the link: 

.. list-table::
    :widths: 20 20 20
    :header-rows: 1

    *   - Name	
        - ITEMS IN THIS KIT
        - LINK
    *   - Raphael Kit
        - 337
        - |link_Raphael_kit|

You can also buy them separately from the links below.

.. list-table::
    :widths: 30 20
    :header-rows: 1

    *   - COMPONENT INTRODUCTION
        - PURCHASE LINK

    *   - :ref:`cpn_gpio_board`
        - |link_gpio_board_buy|
    *   - :ref:`cpn_breadboard`
        - |link_breadboard_buy|
    *   - :ref:`cpn_wires`
        - |link_wires_buy|
    *   - :ref:`cpn_resistor`
        - |link_resistor_buy|
    *   - :ref:`cpn_buzzer`
        - \-
    *   - :ref:`cpn_transistor`
        - |link_transistor_buy|
    *   - :ref:`cpn_ultrasonic_sensor`
        - |link_ultrasonic_buy|
    *   - :ref:`cpn_i2c_lcd`
        - |link_i2clcd1602_buy|

Schematic Diagram
--------------------

Ultrasonic sensor detects the distance between itself and the obstacle
that will be displayed on the LCD in the form of code. At the same time,
the ultrasonic sensor let the buzzer issue prompt sound of different
frequency according to different distance value.

============ ======== ======== ===
T-Board Name physical wiringPi BCM
GPIO23       Pin 16   4        23
GPIO24       Pin 18   5        24
GPIO17       Pin 11   0        17
SDA1         Pin 3             
SCL1         Pin 5             
============ ======== ======== ===

.. image:: ../python_pi5/img/4.1.9_reversing_alarm_schematic.png
   :align: center

Experimental Procedures
------------------------

**Step 1:** Build the circuit.

.. image:: ../python_pi5/img/4.1.9_reversing_alarm_circuit.png
    :align: center

**Step 2:** Change directory.

.. raw:: html

   <run></run>

.. code-block::

    cd ~/raphael-kit/python-pi5

**Step 3:** Run.

.. raw:: html

   <run></run>

.. code-block::

    sudo python3 4.1.9_ReversingAlarm_zero.py

As the code runs, ultrasonic sensor module detects the distance to the
obstacle and then displays the information about the distance on
LCD1602; besides, buzzer emits warning tone whose frequency changes with
the distance.

.. note::

    * If you get the error ``FileNotFoundError: [Errno 2] No such file or directory: '/dev/i2c-1'``, you need to refer to :ref:`i2c_config` to enable the I2C.
    * If you get ``ModuleNotFoundError: No module named 'smbus2'`` error, please run ``sudo apt install python3-smbus2``.
    * If the error ``OSError: [Errno 121] Remote I/O error`` appears, it means the module is miswired or the module is broken.
    * If the code and wiring are fine, but the LCD still does not display content, you can turn the potentiometer on the back to increase the contrast.


.. warning::

    If there is an error prompt  ``RuntimeError: Cannot determine SOC peripheral base address``, please refer to :ref:`faq_soc` 

**Code**

.. note::
    You can **Modify/Reset/Copy/Run/Stop** the code below. But before that, you need to go to  source code path like ``raphael-kit/python-pi5``. After modifying the code, you can run it directly to see the effect.

.. raw:: html

    <run></run>

.. code-block:: python

    #!/usr/bin/env python3
    import LCD1602
    import time
    from gpiozero import DistanceSensor, Buzzer

    # Initialize the ultrasonic sensor with GPIO pins
    sensor = DistanceSensor(echo=24, trigger=23)  # Echo pin is GPIO 24, Trigger pin is GPIO 23

    # Initialize the buzzer connected to GPIO pin 17
    buzzer = Buzzer(17)

    def lcdsetup():
        # Initialize the LCD with I2C address and enable backlight
        LCD1602.init(0x27, 1)  # 0x27 is the I2C address of the LCD
        LCD1602.clear()  # Clear the LCD display
        # Display startup messages on LCD
        LCD1602.write(0, 0, 'Ultrasonic Starting')
        LCD1602.write(1, 1, 'By SunFounder')
        time.sleep(2)  # Wait for 2 seconds

    def distance():
        # Calculate and return the distance measured by the sensor
        dis = sensor.distance * 100  # Convert distance to centimeters
        print('Distance: {:.2f} cm'.format(dis))  # Print distance with two decimal places
        time.sleep(0.3)  # Wait for 0.3 seconds before next measurement
        return dis

    def loop():
        # Continuously measure distance and update LCD and buzzer
        while True:
            dis = distance()  # Get the current distance
            # Display distance and handle alerts based on distance
            if dis > 400:  # Check if distance is out of range
                LCD1602.clear()
                LCD1602.write(0, 0, 'Error')
                LCD1602.write(3, 1, 'Out of range')
                time.sleep(0.5)
            else:
                # Display current distance on LCD
                LCD1602.clear()
                LCD1602.write(0, 0, 'Distance is')
                LCD1602.write(5, 1, str(round(dis, 2)) + ' cm')
                # Adjust buzzer frequency based on distance
                if dis >= 50:
                    time.sleep(0.5)
                elif 20 < dis < 50:
                    # Medium distance: medium buzzer frequency
                    for _ in range(2):
                        buzzer.on()
                        time.sleep(0.05)
                        buzzer.off()
                        time.sleep(0.2)
                elif dis <= 20:
                    # Close distance: high buzzer frequency
                    for _ in range(5):
                        buzzer.on()
                        time.sleep(0.05)
                        buzzer.off()
                        time.sleep(0.05)

    try:
        lcdsetup()  # Setup the LCD display
        loop()      # Start the measurement loop
    except KeyboardInterrupt:
        # Turn off buzzer and clear LCD on user interrupt (e.g., Ctrl+C)
        buzzer.off()
    LCD1602.clear()



**Code Explanation**

#. This script utilizes several libraries for its functionality. The ``LCD1602`` library manages the LCD display, while ``time`` provides time-related functions. The ``gpiozero`` library is essential for Raspberry Pi GPIO pin interactions, particularly for operating the DistanceSensor and Buzzer.

   .. code-block:: python

       #!/usr/bin/env python3
       import LCD1602
       import time
       from gpiozero import DistanceSensor, Buzzer

#. The ultrasonic sensor is set up with its echo and trigger pins connected to GPIO pins 24 and 23, respectively. Additionally, a buzzer is connected to GPIO pin 17.

   .. code-block:: python

       # Initialize the ultrasonic sensor with GPIO pins
       sensor = DistanceSensor(echo=24, trigger=23)  # Echo pin is GPIO 24, Trigger pin is GPIO 23

       # Initialize the buzzer connected to GPIO pin 17
       buzzer = Buzzer(17)

#. The initialization of the LCD display involves clearing it and displaying a startup message.

   .. code-block:: python

       def lcdsetup():
           # Initialize the LCD with I2C address and enable backlight
           LCD1602.init(0x27, 1)  # 0x27 is the I2C address of the LCD
           LCD1602.clear()  # Clear the LCD display
           # Display startup messages on LCD
           LCD1602.write(0, 0, 'Ultrasonic Starting')
           LCD1602.write(1, 1, 'By SunFounder')
           time.sleep(2)  # Wait for 2 seconds

#. The ``distance`` function calculates the distance measured by the ultrasonic sensor and outputs it, returning the value in centimeters.

   .. code-block:: python

       def distance():
           # Calculate and return the distance measured by the sensor
           dis = sensor.distance * 100  # Convert distance to centimeters
           print('Distance: {:.2f} cm'.format(dis))  # Print distance with two decimal places
           time.sleep(0.3)  # Wait for 0.3 seconds before next measurement
           return dis

#. The main loop continually measures the distance, updating both the LCD and the buzzer. It handles different distance ranges with specific actions, like displaying error messages or varying buzzer frequencies based on the measured distance.

   .. code-block:: python

       def loop():
           # Continuously measure distance and update LCD and buzzer
           while True:
               dis = distance()  # Get the current distance
               # Display distance and handle alerts based on distance
               if dis > 400:  # Check if distance is out of range
                   LCD1602.clear()
                   LCD1602.write(0, 0, 'Error')
                   LCD1602.write(3, 1, 'Out of range')
                   time.sleep(0.5)
               else:
                   # Display current distance on LCD
                   LCD1602.clear()
                   LCD1602.write(0, 0, 'Distance is')
                   LCD1602.write(5, 1, str(round(dis, 2)) + ' cm')
                   # Adjust buzzer frequency based on distance
                   if dis >= 50:
                       time.sleep(0.5)
                   elif 20 < dis < 50:
                       # Medium distance: medium buzzer frequency
                       for _ in range(2):
                           buzzer.on()
                           time.sleep(0.05)
                           buzzer.off()
                           time.sleep(0.2)
                   elif dis <= 20:
                       # Close distance: high buzzer frequency
                       for _ in range(5):
                           buzzer.on()
                           time.sleep(0.05)
                           buzzer.off()
                           time.sleep(0.05)

#. Upon execution, the script sets up the LCD and enters the main loop. It can be interrupted with a keyboard command (Ctrl+C), which turns off the buzzer and clears the LCD.

   .. code-block:: python

       try:
           lcdsetup()  # Setup the LCD display
           loop()      # Start the measurement loop
       except KeyboardInterrupt:
           # Turn off buzzer and clear LCD on user interrupt (e.g., Ctrl+C)
           buzzer.off()
           LCD1602.clear()