2.11 Passive Buzzer

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Overview

In this lesson, you will get to know about passive buzzer. As a type of electronic buzzer with an integrated structure, passive buzzer is supplied by DC power, widely used in computer, alarm, electronic toy, telephone, timer and other electronic products or voice devices.

Components Required

Component Introduction

Buzzers can be categorized as active and passive ones (see the following picture). Turn the buzzer so that its pins are facing up, and the buzzer with a green circuit board is a passive buzzer, while the one enclosed with a black tape is an active one.

The difference between an active buzzer and a passive buzzer:

The difference between an active buzzer and a passive buzzer is: An active buzzer has a built-in oscillating source, so it will make sounds when electrified. But a passive buzzer does not have such source, so it will not beep if DC signals are used; instead, you need to use square waves whose frequency is between 2K and 5K to drive it. The active buzzer is often more expensive than the passive one because of multiple built-in oscillating circuits.

The following is the electrical symbol of a buzzer. It has two pins with positive and negative poles. With a + in the surface represents the anode and the other is the cathode.

You can check the pins of the buzzer, the longer one is the anode and the shorter one is the cathode. Please don’t mix them up when connecting, otherwise the buzzer will not make sound.

Fritzing Circuit

In this example, what we use to drive the buzzer is the pin 9. We get the cathode of the Buzzer to GND, and the anode to the digital pin 9.

Schematic Diagram

Code

#include "pitches.h"
int melody[] = 
{
  NOTE_C4, NOTE_G3, NOTE_G3, NOTE_A3, NOTE_G3, 0, NOTE_B3, NOTE_C4
};

int noteDurations[] = 
{
  4, 8, 8, 4, 4, 4, 4, 4
};

void setup() 
{
  for (int thisNote = 0; thisNote < 8; thisNote++) 
  {
    int noteDuration = 1000 / noteDurations[thisNote];
    tone(9, melody[thisNote], noteDuration);
    int pauseBetweenNotes = noteDuration  * 1.30;
    delay(pauseBetweenNotes);
    noTone(9);
  }
}

void loop() 
{
  // no need to repeat the melody.
}

At the time when you finish uploading the codes to the Mega2560 board, you can hear a melody containing seven notes.

Code Analysis

There are two points needing your attention:

①tone() & noTone(): This function is used to control the sound of the passive buzzer directly and its prototype is as follows:

void tone(int pin, unsigned int frequency)
void tone(int pin, unsigned int frequency, unsigned long duration)

Generates a square wave of the specified frequency (and 50% duty cycle) on a pin (so as to make the passive buzzer vibrate to make sound). A duration can be specified, otherwise the wave continues until a call to noTone(). The pin can be connected to a piezo buzzer or other speaker to play tones.

Only one tone can be generated at a time. If a tone is already playing on a different pin, the call to tone() will have no effect. If the tone is playing on the same pin, the call will set its frequency.

Use of the tone() function will interfere with PWM output on pins 3 and 11 (on boards other than the Mega).

It is not possible to generate tones lower than 31Hz.

pin: The Arduino pin on which to generate the tone.

frequency: The frequency of the tone in hertz.

duration: The duration of the tone in milliseconds (optional)

void noTone(int pin)

Stops the generation of a square wave triggered by tone(). Has no effect if no tone is being generated.

pin: The Arduino pin on which to generate the tone.

Having known the two functions, you may grasp the codes—the installation of the array melody[] and the array noteDurations[] is the preparation of the subsequently several times of calling of the function tone() and the changing of tone and duration in the loop for better effect of music play.

②pitches.h: The code uses an extra file, pitches.h. This file contains all the pitch values for typical notes. For example, NOTE_C4 is middle C. NOTE_FS4 is F sharp, and so forth. This note table was originally written by Brett Hagman, on whose work the tone() command was based. You may find it useful whenever you want to make musical notes.

#include "pitches.h"

Note: There is already a pitches.h file in this sample program. If we put it together with the main code in one folder, the successive steps of installing pitches.h can be omitted.

After you open the code 2.11passiveBuzzer, if you cannot open the pitches.h code, you can just install one manually. The steps are as follows:

To make the pitches.h file, either click on the button just below the serial monitor icon and choose “New Tab”, or use Ctrl+Shift+N.

Then paste in the following code and save it as pitches.h:

/*****************
 Public Constants
 *****************/
#define NOTE_B0  31
#define NOTE_C1  33
#define NOTE_CS1 35
#define NOTE_D1  37
#define NOTE_DS1 39
#define NOTE_E1  41
#define NOTE_F1  44
#define NOTE_FS1 46
#define NOTE_G1  49
#define NOTE_GS1 52
#define NOTE_A1  55
#define NOTE_AS1 58
#define NOTE_B1  62
#define NOTE_C2  65
#define NOTE_CS2 69
#define NOTE_D2  73
#define NOTE_DS2 78
#define NOTE_E2  82
#define NOTE_F2  87
#define NOTE_FS2 93
#define NOTE_G2  98
#define NOTE_GS2 104
#define NOTE_A2  110
#define NOTE_AS2 117
#define NOTE_B2  123
#define NOTE_C3  131
#define NOTE_CS3 139
#define NOTE_D3  147
#define NOTE_DS3 156
#define NOTE_E3  165
#define NOTE_F3  175
#define NOTE_FS3 185
#define NOTE_G3  196
#define NOTE_GS3 208
#define NOTE_A3  220
#define NOTE_AS3 233
#define NOTE_B3  247
#define NOTE_C4  262
#define NOTE_CS4 277
#define NOTE_D4  294
#define NOTE_DS4 311
#define NOTE_E4  330
#define NOTE_F4  349
#define NOTE_FS4 370
#define NOTE_G4  392
#define NOTE_GS4 415
#define NOTE_A4  440
#define NOTE_AS4 466
#define NOTE_B4  494
#define NOTE_C5  523
#define NOTE_CS5 554
#define NOTE_D5  587
#define NOTE_DS5 622
#define NOTE_E5  659
#define NOTE_F5  698
#define NOTE_FS5 740
#define NOTE_G5  784
#define NOTE_GS5 831
#define NOTE_A5  880
#define NOTE_AS5 932
#define NOTE_B5  988
#define NOTE_C6  1047
#define NOTE_CS6 1109
#define NOTE_D6  1175
#define NOTE_DS6 1245
#define NOTE_E6  1319
#define NOTE_F6  1397
#define NOTE_FS6 1480
#define NOTE_G6  1568
#define NOTE_GS6 1661
#define NOTE_A6  1760
#define NOTE_AS6 1865
#define NOTE_B6  1976
#define NOTE_C7  2093
#define NOTE_CS7 2217
#define NOTE_D7  2349
#define NOTE_DS7 2489
#define NOTE_E7  2637
#define NOTE_F7  2794
#define NOTE_FS7 2960
#define NOTE_G7  3136
#define NOTE_GS7 3322
#define NOTE_A7  3520
#define NOTE_AS7 3729
#define NOTE_B7  3951
#define NOTE_C8  4186
#define NOTE_CS8 4435
#define NOTE_D8  4699
#define NOTE_DS8 49

Phenomenon Picture