Driving a piezo speaker with a PIC

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

Piezoelectric speakers operate by the converse piezoelectric effect: when a voltage is applied across the terminals, the piezoelectric material in the speaker to deflect in one direction. Applying an alternating voltage will cause the material to vibrate, and create a sound.

Circuit

Circuit Diagram

To the right is a simple circuit diagram showing the PIC connected to a Piezo Speaker.

Code

#include <18f4520.h>
#fuses HS,NOLVP,NOWDT,NOPROTECT
#use delay(clock=40000000)
//define timer scaling value for each note
#define C 255 
#define D 231
#define E 205
#define F 192
#define G 175
#define A 150
#define B 123
#define C2 100
//

#define x 14 //total number of notes in song to be played - modify for specific song

//the song to be played is "Twinkle Twinkle Little Star" in this demonstration
int i;
int song [x]={C, C, G, G, A, A, G, F, F, E, E, D, D, C}; //insert notes of song in array
int length[x]={1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 2}; //relative length of each note

void main() {

      setup_ccp1(CCP_PWM); // PWM output on CCP1/RC2, pin 17 
      set_pwm1_duty(30); // demonstrate the use of both PWMs independently


      for (i=0; i<x; i++) { //play x notes inside song array
      
      setup_timer_2(T2_DIV_BY_16, song[i], 16); //set PWM frequency according to entries in song array
      delay_ms(400*length[i]); //each note is played for 400ms*relative length
      setup_timer_2(T2_DIV_BY_16, 1, 16); //short break between notes
      //the PWM frequency set beyond audible range in order to create silence
      delay_ms(50); //to distinguish between consecutive notes
                  
      }
   }

Further Reading

Parallax Piezo Speaker