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Lesson 12 Passive Buzzer
============================

**Introduction**
---------------------

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

**Newly Added Components**
------------------------------

.. image:: media_pi/image227.png
    :width: 800
    :align: center

**Schematic Diagram**
--------------------------

The base pin(b pin) of the transistor is connected to pin11, the
collector pin(c pin) to the cathode pin of the buzzer, and the emitter
pin(e pin) to GND. The anode of the buzzer is connected to 5 v power
supply. When pin11 inputs high voltage, the transistor will be switched
on, and the collector will output low level. When there is a level
difference between the two pins of the buzzer, the buzzer rings. When
pin11 inputs low power level, the transistor is cut off, and the
collector is at high level, and both ends of the buzzer are at high
level, so the buzzer is silent.

.. image:: media_pi/image228.png
    :width: 800
    :align: center

.. image:: media_pi/image256.png
    :width: 800
    :align: center

**Build the Circuit**
-------------------------

.. image:: media_pi/image147.png
    :width: 800
    :align: center

**For C Language Users**
-------------------------

**Command**
^^^^^^^^^^^^^^^^^^^

**1.** Go to the folder of the code.

.. raw:: html

    <run></run>

.. code-block::

    cd /home/pi/electronic-kit/for-raspberry-pi/c/Lesson_12_PassiveBuzzer

**2.** Compile the code.

.. raw:: html

    <run></run>

.. code-block::

    gcc 12_PassiveBuzzer.c -lwiringPi

**3.** Run the executable file.

.. raw:: html

    <run></run>

.. code-block::

    sudo ./a.out

Now, the buzzer automatically plays music on a loop.

.. 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:`C code is not working?`.

**Code**
^^^^^^^^^

.. code-block:: C

    #include <wiringPi.h>  
    #include <softTone.h>  
    #include <stdio.h>  
      
    #define BuzPin    0  
      
    #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[] = {CH5,CH2,CM6,CH2,CH3,CH6,0,CH3,CH5,CH3,CM6,CH2,0};   
    int beat[] = {1,1,1,1,1,1,2,1,1,1,1,1,3};  
      
    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");         
            for(int i=0;i<sizeof(song)/4;i++){  
                softToneWrite(BuzPin, song[i]);   
                delay(beat[i] * 250);  
            }     
        }  
        return 0;  
    }   

**Code Explanation**
^^^^^^^^^^^^^^^^^^^^^

.. code-block:: C

    #include <softTone.h> 

WiringPi includes a software-driven sound handler capable 
of outputting a simple tone/square wave signal on any of 
the Raspberry Pi’s GPIO pins. To maintain a low CPU usage, 
the minimum pulse width is 100μS. That gives a maximum frequency 
of 1/0.0002 = 5000Hz. Within these limitations, simple tones on a 
high impedance speaker or piezo sounder is possible.

.. code-block:: C

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

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

.. code-block:: C

    23.int song[] = {CH5,CH2,CM6,CH2,CH3,CH6,0,CH3,CH5,CH3,CM6,CH2,0};    
    24.int beat[] = {1,1,1,1,1,1,2,1,1,1,1,1,3};  

Define a section of music and the corresponding beat. 
The number in **beat[]** refers to the beat of each note in the 
**song** (0.5s for each beat).

.. code-block:: C

 35.    if(softToneCreate(BuzPin) == -1){  

**softToneCreate( )** 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. This is used to determine whether it is successful 
for the software to control tone pin; if it fails, it will not execute the program.

.. code-block:: C

    42.        for(int i=0;i<sizeof(song)/4;i++){  
    43.            softToneWrite(BuzPin, song[i]);   
    44.            delay(beat[i] * 250);  
    45.        }

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** (the number of musical notes) is gotten by deviding **sizeof(song)** 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.

**For Python Language Users**
-----------------------------

**Command**
^^^^^^^^^^^^

**1.** Go to the folder of the code.

.. raw:: html

    <run></run>

.. code-block::

    cd /home/pi/electronic-kit/for-raspberry-pi/python

**2.** Run the code.

.. raw:: html

    <run></run>

.. code-block::

    sudo python3 12_PassiveBuzzer.py

Now, the buzzer automatically plays music on a loop.

**Code**

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


.. raw:: html

    <run></run>

.. code-block:: python

    import RPi.GPIO as GPIO  
    import time  
      
    Buzzer = 17  
      
    CL = [0, 131, 147, 165, 175, 196, 211, 248]        # Frequency of Low C notes  
    CM = [0, 262, 294, 330, 350, 393, 441, 495]        # Frequency of Middle C notes  
    CH = [1, 525, 589, 661, 700, 786, 882, 990]        # Frequency of High C notes  
      
    song = [    CH[5], CH[2], CM[6], CH[2], CH[3], CH[6],CH[0], CH[3], # Notes of song  
                CH[5], CH[3], CM[6], CH[2],CH[0]]  
      
    beat = [    1,1,1,1,1,1,2,1,1,1,1,1,3    ]  
      
    def setup():  
        GPIO.setmode(GPIO.BCM)          
        GPIO.setup(Buzzer, GPIO.OUT)      
        global Buzz                           
              
                              
      
    def loop():  
        while True:  
            print ('\n    Playing song...')  
            for i in range(1, len(song)):          
                if  song[i] == 1 :  
                    time.sleep(beat[i] *0.25)  
                else:    
                    Buzz = GPIO.PWM(Buzzer, song[i])     
                    Buzz.start(50)  
                    time.sleep(beat[i] * 0.25)         
                    Buzz.stop()  
            time.sleep(1)             # Wait a second for next song.  
              
    def destory():  
        Buzz.stop()                      
        GPIO.output(Buzzer, LOW)          
        GPIO.cleanup()                  
      
    if __name__ == '__main__':        # Program start from here  
        setup()  
        try:  
            loop()  
        except KeyboardInterrupt:     # When 'Ctrl+C' is pressed, the child program destroy() will be  executed.  
            destory()  

**Code Explanation**
^^^^^^^^^^^^^^^^^^^^

.. code-block::

    6.CL = [0, 131, 147, 165, 175, 196, 211, 248]
    7.CM = [0, 262, 294, 330, 350, 393, 441, 495]
    8.CH = [1, 525, 589, 661, 700, 786, 882, 990]

These are the frequencies of each note. The first 0 is to 
skip **CL[0]** so that the number **CL[1]-CL[7]** corresponds to the 
CDEFGAB of the note.

.. code-block::

    10.int song[] = {CH5,CH2,CM6,CH2,CH3,CH6,0,CH3,CH5,CH3,CM6,CH2,0};    
    13.int beat[] = {1,1,1,1,1,1,2,1,1,1,1,1,3};  

Define a section of music and the corresponding beats. 
The number in **beat[]** refers to the beat of each note 
in the **song** (0.5s for each beat).

.. code-block::

    29.    Buzz = GPIO.PWM(Buzzer, song[i])     
    30.    Buzz.start(50) 

Define pin Buzzer as PWM pin, then set its frequency to 786(song[0]) 
and **Buzz.start(50)** is used to run PWM. What’s more, 
set the duty cycle to 50%.

.. code-block::

    22. def loop():  
    23.    while True:  
    24.        print ('\n    Playing song...')  
    25.        for i in range(1, len(song)):          
    26.            if  song[i] == 1 :  
    27.                time.sleep(beat[i] *0.25)  
    28.            else:    
    29.                Buzz = GPIO.PWM(Buzzer, song[i])     
    30.                Buzz.start(50)  
    31.                time.sleep(beat[i] * 0.25)         
    32.                Buzz.stop() 
    33.   time.sleep(1)               

Play music in the while loop. As i increases gradually, the buzzer 
plays following the note in song[].

**Phenomenon Picture**
--------------------------

.. image:: media_pi/image148.jpeg
    :width: 800
    :align: center