Lesson 1.2.2 Passive Buzzer

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Introduction

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

Components

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.

T-Board NamephysicalwiringPiBCM
GPIO17Pin 11017

Experimental Procedures

Step 1: Build the circuit. 

  • For C Language Users

Step 2: Change directory.

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

Step 3: Compile.

    gcc 1.2.2_PassiveBuzzer.c -lwiringPi

Step 4: Run.

    sudo ./a.out

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

Code

#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");

        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

#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.

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).

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.

        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]):

 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

Step 2: Change directory. 

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

Step 3: Run.

    sudo python3 1.2.2_PassiveBuzzer.py

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

Code

import RPi.GPIO as GPIO
import time

Buzzer = 11

CL = [0, 131, 147, 165, 175, 196, 211, 248]     # Frequency of Bass tone in C major
CM = [0, 262, 294, 330, 350, 393, 441, 495]     # Frequency of Midrange tone in C major
CH = [0, 525, 589, 661, 700, 786, 882, 990]     # Frequency of Treble tone in C major

song_1 = [  CM[3], CM[5], CM[6], CM[3], CM[2], CM[3], CM[5], CM[6], # Notes of song1
            CH[1], CM[6], CM[5], CM[1], CM[3], CM[2], CM[2], CM[3],
            CM[5], CM[2], CM[3], CM[3], CL[6], CL[6], CL[6], CM[1],
            CM[2], CM[3], CM[2], CL[7], CL[6], CM[1], CL[5] ]

beat_1 = [  1, 1, 3, 1, 1, 3, 1, 1,             # Beats of song 1, 1 means 1/8 beat
            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 ]

song_2 = [  CM[1], CM[1], CM[1], CL[5], CM[3], CM[3], CM[3], CM[1], # Notes of song2
            CM[1], CM[3], CM[5], CM[5], CM[4], CM[3], CM[2], CM[2],
            CM[3], CM[4], CM[4], CM[3], CM[2], CM[3], CM[1], CM[1],
            CM[3], CM[2], CL[5], CL[7], CM[2], CM[1]    ]

beat_2 = [  1, 1, 2, 2, 1, 1, 2, 2,             # Beats of song 2, 1 means 1/8 beat
            1, 1, 2, 2, 1, 1, 3, 1,
            1, 2, 2, 1, 1, 2, 2, 1,
            1, 2, 2, 1, 1, 3 ]

def setup():
    GPIO.setmode(GPIO.BOARD)        # Numbers GPIOs by physical location
    GPIO.setup(Buzzer, GPIO.OUT)    # Set pins' mode is output
    global Buzz                     # Assign a global variable to replace GPIO.PWM
    Buzz = GPIO.PWM(Buzzer, 440)    # 440 is initial frequency.
    Buzz.start(50)                  # Start Buzzer pin with 50% duty cycle

def loop():
    while True:
        print ('\n    Playing song 1...')
        for i in range(1, len(song_1)):     # Play song 1
            Buzz.ChangeFrequency(song_1[i]) # Change the frequency along the song note
            time.sleep(beat_1[i] * 0.5)     # delay a note for beat * 0.5s
        time.sleep(1)                       # Wait a second for next song.

        print ('\n\n    Playing song 2...')
        for i in range(1, len(song_2)):     # Play song 1
            Buzz.ChangeFrequency(song_2[i]) # Change the frequency along the song note
            time.sleep(beat_2[i] * 0.5)     # delay a note for beat * 0.5s

def destory():
    Buzz.stop()                 # Stop the buzzer
    GPIO.output(Buzzer, 1)      # Set Buzzer pin to High
    GPIO.cleanup()              # Release resource

if __name__ == '__main__':      # Program start from here
    setup()
    try:
        loop()
    except KeyboardInterrupt:   # When 'Ctrl+C' is pressed, the program destroy() will be  executed.
        destory()

Code Explanation

CL = [0, 131, 147, 165, 175, 196, 211, 248]     # Frequency of Bass tone in C major
CM = [0, 262, 294, 330, 350, 393, 441, 495]     # Frequency of Midrange tone in C major
CH = [0, 525, 589, 661, 700, 786, 882, 990]     # Frequency of Treble tone in C major 

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

song_1 = [  CM[3], CM[5], CM[6], CM[3], CM[2], CM[3], CM[5], CM[6], 
            CH[1], CM[6], CM[5], CM[1], CM[3], CM[2], CM[2], CM[3],
            CM[5], CM[2], CM[3], CM[3], CL[6], CL[6], CL[6], CM[1],
            CM[2], CM[3], CM[2], CL[7], CL[6], CM[1], CL[5] ]

These arrays are the notes of a song.

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 ]

Every sound beat (each number) represents the ⅛ beat, or 0.5s

Buzz = GPIO.PWM(Buzzer, 440)
Buzz.start(50)

Define pin Buzzer as PWM pin, then set its frequency to 440 and Buzz.start(50) is used to run PWM. What’s more, set the duty cycle to 50%.

        for i in range(1, len(song_1)): 
            Buzz.ChangeFrequency(song_1[i]) 
            time.sleep(beat_1[i] * 0.5)  

Run a for loop, then the buzzer will play the notes in the array song_1[] with the beats in the beat_1[] array, .

Now you can hear the passive buzzer playing music.

Phenomenon Picture