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1.2.2 Passive Buzzer
=====================

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

In this lesson, we will learn how to make a passive buzzer play music.

Components
----------

.. image:: img/list_1.2.2.png


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

In this experiment, a passive buzzer, a PNP transistor and a 1k resistor
are used between the base of the transistor and GPIO to protect the
transistor.

When GPIO17 is given different frequencies, the passive buzzer will emit
different sounds; in this way, the buzzer plays music.

.. image:: img/image333.png


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

**Step 1**: Build the circuit.

.. image:: img/image106.png
    :width: 800

**Step 2**: Change directory.

.. raw:: html

   <run></run>

.. code-block::

    cd ~/davinci-kit-for-raspberry-pi/c/1.2.2/

**Step 3**: Compile.

.. raw:: html

   <run></run>

.. code-block::

    gcc 1.2.2_PassiveBuzzer.c -lwiringPi

**Step 4**: Run.

.. raw:: html

   <run></run>

.. code-block::

    sudo ./a.out

The code run, the buzzer plays a piece of music.

.. note::

    If it does not work after running, or there is an error prompt: \"wiringPi.h: No such file or directory\", please refer to :ref:`install_wiringpi_pi5`.

**Code**

.. code-block:: c

    #include <wiringPi.h>
    #include <softTone.h>
    #include <stdio.h>

    #define BuzPin    0

    #define  CL1  131
    #define  CL2  147
    #define  CL3  165
    #define  CL4  175
    #define  CL5  196
    #define  CL6  221
    #define  CL7  248

    #define  CM1  262
    #define  CM2  294
    #define  CM3  330
    #define  CM4  350
    #define  CM5  393
    #define  CM6  441
    #define  CM7  495

    #define  CH1  525
    #define  CH2  589
    #define  CH3  661
    #define  CH4  700
    #define  CH5  786
    #define  CH6  882
    #define  CH7  990

    int song_1[] = {CM3,CM5,CM6,CM3,CM2,CM3,CM5,CM6,CH1,CM6,CM5,CM1,CM3,CM2,
                    CM2,CM3,CM5,CM2,CM3,CM3,CL6,CL6,CL6,CM1,CM2,CM3,CM2,CL7,
                    CL6,CM1,CL5};

    int beat_1[] = {1,1,3,1,1,3,1,1,1,1,1,1,1,1,3,1,1,3,1,1,1,1,1,1,1,2,1,1,
                    1,1,1,1,1,1,3};


    int song_2[] = {CM1,CM1,CM1,CL5,CM3,CM3,CM3,CM1,CM1,CM3,CM5,CM5,CM4,CM3,CM2,
                    CM2,CM3,CM4,CM4,CM3,CM2,CM3,CM1,CM1,CM3,CM2,CL5,CL7,CM2,CM1
                    };

    int beat_2[] = {1,1,1,3,1,1,1,3,1,1,1,1,1,1,3,1,1,1,2,1,1,1,3,1,1,1,3,3,2,3};

    int main(void)
    {
        int i, j;
        if(wiringPiSetup() == -1){ //when initialize wiring failed,print message to screen
            printf("setup wiringPi failed !");
            return 1;
        }

        if(softToneCreate(BuzPin) == -1){
            printf("setup softTone failed !");
            return 1;
        }

        while(1){
            printf("music is being played...\n");
            delay(100);
            for(i=0;i<sizeof(song_1)/4;i++){
                softToneWrite(BuzPin, song_1[i]);   
                delay(beat_1[i] * 500);
            }

            for(i=0;i<sizeof(song_2)/4;i++){
                softToneWrite(BuzPin, song_2[i]);   
                delay(beat_2[i] * 500);
            }   
        }

        return 0;
    }

**Code Explanation**

.. code-block:: c

    #define  CL1  131
    #define  CL2  147
    #define  CL3  165
    #define  CL4  175
    #define  CL5  196
    #define  CL6  221
    #define  CL7  248

    #define  CM1  262
    #define  CM2  294


These frequencies of each note are as shown. CL refers to low note, 
CM middle note, CH high note, 1-7 correspond to the notes C, D, E, F, G, A, B.

.. code-block:: c

    int song_1[] = {CM3,CM5,CM6,CM3,CM2,CM3,CM5,CM6,CH1,CM6,CM5,CM1,CM3,CM2,
                    CM2,CM3,CM5,CM2,CM3,CM3,CL6,CL6,CL6,CM1,CM2,CM3,CM2,CL7,
                    CL6,CM1,CL5};
    int beat_1[] = {1,1,3,1,1,3,1,1,1,1,1,1,1,1,3,1,1,3,1,1,1,1,1,1,1,2,1,1,
                    1,1,1,1,1,1,3};

The array, song_1[] stores a musical score of a song in which beat_1[] 
refers to the beat of each note in the song (0.5s for each beat).

.. code-block:: c

    if(softToneCreate(BuzPin) == -1){
            printf("setup softTone failed !");
            return 1;
        
This creates a software controlled tone pin. You can use any GPIO pin 
and the pin numbering will be that of the wiringPiSetup() function 
you used. The return value is 0 for success. Anything else and you 
should check the global errnovariable to see what went wrong.

.. code-block:: c

    for(i=0;i<sizeof(song_1)/4;i++){
        softToneWrite(BuzPin, song_1[i]);   
        delay(beat_1[i] * 500);
    }

Employ a for statement to play song_1.

In the judgment condition, **i<sizeof(song_1)/4**\ ，“devide by 4” is
used because the array song_1[] is an array of the data type of integer,
and each element takes up four bytes.

The number of elements in song_1 (the number of musical notes) is gotten
by deviding sizeof(song_4) by 4.

To enable each note to play for beat \* 500ms, the function
delay(beat_1[i] \* 500) is called.

The prototype of softToneWrite(BuzPin, song_1[i])：

.. code-block:: c

    void softToneWrite (int pin, int freq);

This updates the tone frequency value on the given pin. The tone 
does not stop playing until you set the frequency to 0.