Driving a piezo speaker with a PIC - Revision history

Lynch at 07:43, 16 February 2009

2009-02-16T07:43:40Z

2009-02-14T02:06:47Z

Code

2009-02-14T02:05:44Z

Duty Cycle

2009-02-14T02:03:58Z

Frequency

2009-02-14T02:02:18Z

Duty Cycle

2009-02-14T02:01:11Z

Duty Cycle

2009-02-14T02:00:10Z

Duty Cycle

2009-02-14T02:00:00Z

Duty Cycle

2009-02-14T01:59:16Z

Duty Cycle

2009-02-14T01:58:58Z

Duty Cycle

@@ Line 1: / Line 1: @@
-== Original Assignment ==
-In this project you will use a PWM output of the PIC microcontroller to play tones on a piezo speaker.  Document frequencies that play the basic notes in the musical scale and demonstrate a simple song.
 == Overview ==
 A Pulse Width Modulation ([[Pulse_Width_Modulation|PWM]]) output from a PIC microcontroller can be used to play tones on a piezo speaker.  With this, musical scales and simple songs can be played on the piezo speaker.

@@ Line 63: / Line 63: @@
 <pre>
 /*
-Bobby By, Agatha Lee, Dan Niecestro
+Code written by Bobby By, Agatha Lee, Dan Niecestro 02-2009
 This code uses a PWM signal from PIC 18F4520 to define the frequencies
 that produce the basic notes in one octave of the musical scale,

@@ Line 50: / Line 50: @@
        '''Duty Cycle = 4 * (1/40MHz) * 16 * (scaling value)'''   for 40MHz clock and 1:16 Timer 2.
-Since the pulse width ratio would be at 100% when the duty cycle exceeds the period of PWM, range of duty cycle values that will produce a sound on the piezo speaker depends on the period of the PWM pulses. Duty cycle values of 1~125 will allow us to play all the notes defined in our code. For very small and very high duty cycles, the volume is low.
+Since the pulse width ratio would be at 100% when the duty cycle exceeds the period of PWM, the range of duty cycle values that will produce a sound on the piezo speaker depends on the period of the PWM pulses. Duty cycle values of 1~125 will allow us to play all the notes defined in our code. For very small and very high duty cycles, the volume is low.
 == Circuit ==

@@ Line 10: / Line 10: @@
 PWM was used to provide the alternating voltage to drive the speaker ([http://www.parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/ProductID/106/List/1/Default.aspx?SortField=ProductName,ProductName| Parallax 900-00001]).  The period of the PWM determines the tone that will be played; the duty cycle changes the volume.
-=== Frequency ===
+=== PWM Period ===
 The frequency range of the speaker was limited by the timer used by the PIC to control PWM, which is Timer 2.  First, we determined the PWM frequencies that we could use, which was from about 2kHz to 10kHz.  Setting the lowest frequency as our first note (C), a set of timer scaling values that correspond to frequencies that would play the basic notes of an octave of the [http://en.wikipedia.org/wiki/Diatonic_scale#Theory_of_diatonic_scales diatonic scale] was found.  The period of the PWM is given by the following equation:

@@ Line 45: / Line 45: @@
 set_pwm1_duty(scaling value);
 </pre>
-This does not determine the true duty cycle (i.e. the pulse width ratio = <math>\begin{matrix}\frac{t_{on}}{t_{period}}\end{matrix}</math>) but rather just the length of time that the pulse is held high <math>(t_{on})</math>. This time is given by:
+This duty cycle does not refer to the pulse width ratio = <math>\begin{matrix}\frac{t_{on}}{t_{period}}\end{matrix}</math> but rather the length of time that the pulse is held high <math>(t_{on})</math>. This time is given by:
        '''Duty Cycle = 4 * (1/40MHz) * 16 * (scaling value)'''   for 40MHz clock and 1:16 Timer 2.
-Since the pulse width ratio would equal 1 when the duty cycle exceeds the period of PWM, range of duty cycle values that will produce a sound on the piezo speaker depends on the period of the PWM pulses. Duty cycle values of 1~125 will allow us to play all the notes defined in our code. For very small and very high duty cycles, the volume is low.
+Since the pulse width ratio would be at 100% when the duty cycle exceeds the period of PWM, range of duty cycle values that will produce a sound on the piezo speaker depends on the period of the PWM pulses. Duty cycle values of 1~125 will allow us to play all the notes defined in our code. For very small and very high duty cycles, the volume is low.
 == Circuit ==

← Older revision		Revision as of 02:00, 14 February 2009
Line 49:		Line 49:

	'''Duty Cycle = 4 * (1/40MHz) * 16 * (scaling value)''' for 40MHz clock and 1:16 Timer 2.		'''Duty Cycle = 4 * (1/40MHz) * 16 * (scaling value)''' for 40MHz clock and 1:16 Timer 2.


	Since the pulse width ratio would equal 1 when the duty cycle exceeds the period of PWM, range of duty cycle values that will produce a sound on the piezo speaker depends on the period of the PWM pulses. Duty cycle values of 1~125 will allow us to play all the notes defined in our code. For very small and very high duty cycles, the volume is low.		Since the pulse width ratio would equal 1 when the duty cycle exceeds the period of PWM, range of duty cycle values that will produce a sound on the piezo speaker depends on the period of the PWM pulses. Duty cycle values of 1~125 will allow us to play all the notes defined in our code. For very small and very high duty cycles, the volume is low.

← Older revision		Revision as of 02:00, 14 February 2009
Line 48:		Line 48:


	'''Duty Cycle = 4 * (1/40MHz) * 16 * (scaling value)''' for 40MHz clock and 1:16 Timer 2.		'''Duty Cycle = 4 * (1/40MHz) * 16 * (scaling value)''' for 40MHz clock and 1:16 Timer 2.

@@ Line 47: / Line 47: @@
 This does not determine the true duty cycle (i.e. the pulse width ratio = <math>\begin{matrix}\frac{t_{on}}{t_{period}}\end{matrix}</math>) but rather just the length that the pulse is held high <math>(t_{on})</math>. This length is given by:
+<pre>
-<math>Duty Cycle = 4 * (1/40MHz) * 16 * (scaling value)</math> for 40MHz clock and 1:16 Timer 2.
+'''Duty Cycle = 4 * (1/40MHz) * 16 * (scaling value)'''   for 40MHz clock and 1:16 Timer 2.
+</pre>
 Since the pulse width ratio would equal 1 when the duty cycle exceeds the period of PWM, range of duty cycle values that will produce a sound on the piezo speaker depends on the period of the PWM pulses. Duty cycle values of 1~125 will allow us to play all the notes defined in our code. For very small and very high duty cycles, the volume is low.