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.. _per_reversing_system:

2.11 Reversing System
==========================

For this project we used an ultrasonic module and an active buzzer to create a reversing alarm system. The ultrasonic module is used to detect the distance, and the buzzer emits different frequencies of alarm sounds depending on the distance.

* :ref:`cpn_bb`
* :ref:`cpn_led`
* :ref:`cpn_res`
* :ref:`cpn_ultrasonic`
* :ref:`cpn_transistor`
* :ref:`cpn_buzzer`

**Wiring**

|reversing_system0|


* The Echo and Trig pins of the ultrasonic module are connected to GP15 at the same time, so that the ultrasonic module sends and receives signals from GP15.
* The middle pin of the transistor connected to the buzzer is connected to GP14 through a 1kΩ resistor.

**Code**

.. note::

    * You can refer to the image below to write code by dragging and dropping. 
    * Import ``2.11_reversing_system.png`` from the path of ``euler-kit\piper``. For detailed tutorials, please refer to :ref:`import_code_piper`.


|reversing_system|

* After connecting Pico, click the **Start** button and the code starts to run.
* When the ultrasonic detection distance is less than 5cm, the buzzer emits a sharp sound (0.1s).
* When the detection distance is between 5~10cm, the buzzer emits a slightly slow sound (0.5s).
* When the detection distance is greater than 10cm, there is a sound prompt every 1 second.


**How it Works?**


|reversing_system1|

Read the distance (in cm) of the ultrasonic detection, and store it in the variable [distance].

|reversing_system2|

When distance is less than or equal to 5, set the variable intervals to 0.1s. The variable [intervals] is the interval between buzzer sounds.

|reversing_system3|

When distance is greater than 5 and less than or equal to 10, set the [intervals] to 0.5s.

|reversing_system4|

When distance is greater than 10, set the [intervals] time to 1s.

|reversing_system5|

Finally, make the buzzer sound every [intervals] seconds.