DC piezo buzzer volume control

1/*
2 Fade
3
4 This example shows how to fade an buzzer on pin XX
5  using the analogWrite() function.
6
7 The analogWrite() function uses PWM, so  if
8 you want to change the pin you're using, be
9 sure to use another PWM capable  pin. On most
10 Arduino, the PWM pins are identified with 
11 a "~" sign, like  ~3, ~5, ~6, ~9, ~10 and ~11.
12
13 This example code is in the public domain.
14  */
15
16/*
17 * following cut from https://playground.arduino.cc/Main/TimerPWMCheatsheet  
18How to adjust Arduino PWM frequencies by macegr in this forum post http://forum.arduino.cc/index.php?topic=16612#msg121031
19
20Pins  11 and 3: controlled by timer 2 in phase-correct PWM mode (cycle length = 510)
21
22Setting   Divisor   Frequency
230x01      1       31372.55
240x02      8       3921.16
250x03      32      980.39
260x04      64      490.20   <--DEFAULT
270x05      128     245.10
280x06      256     122.55
290x07      1024    30.64
30
31TCCR2B = (TCCR2B & 0b11111000)  | <setting>;
32
33All frequencies are in Hz and assume a 16000000 Hz system clock.
34
35*/
36
37int  buzzer = 11;           // the PWM pin the buzzer is attached to
38int volume =  0;          // how loud the buzzer is
39int fadeAmount = 5;     // how many points  to fade the buzzer volume by
40
41int duty_cycle = 127;         // 0-255 so 50%  = 127 approx
42
43int setting=0x01;
44
45// the setup routine runs once when  you press reset:
46void setup() {
47
48    TCCR2B = TCCR2B & 0b11111000 | setting;//to  adjust divider for timer
49    
50  // declare buzzer pin to be an output:
51  pinMode(buzzer, OUTPUT);
52}
53
54// the loop routine runs over and over again  forever:
55void loop() {
56  // set the volume of pin 9:
57  analogWrite(buzzer,  volume);
58
59  // change the volume for next time through the loop:
60  volume  = volume + fadeAmount;
61
62  // reverse the direction of the fading at the ends  of the fade:
63  if (volume <= 0 || volume >= 255) {
64    fadeAmount = -fadeAmount;
65  }
66  // wait for 100 milliseconds to see the volume effect
67  delay(100);
68}
69