Thread: Output music tone from piezo buzzer algorithm, NEED HELP!

I am trying to figure out how to write a c program/algorithm that will output music tone (like middle C, C#, D, etc...). I am using an ATMEGA324P chip, and coding in C.

I am trying not to use the PWM functions, so how would I create the wave form of a specific frequency, and output it continuously unless something disturbs it (controlling it from a DIP switch, so one switch will play one note, and another switch will play another note)...

Could someone help?

Thanks

o man,,,that takes me back, The victory music in my first bash at a game..'roulette' Qbasic had a neat 'PLAY ' function i think it was called, it had predefined note lengths and octave arguments so you could interpret your actual musical notation.

One of the first real character based games for me was "Prince of Persia". Fantastic game, and the music you heard coming from the tiny little case speaker, was made extra creepy because of the poor sound quality.

With external speakers, the sound was much better - but not as deliciously creepy.

Haha defo, the spiky, scratchy tone was so dry and immediate, really unsettling, some melodic arpeggio stuff sounds strangely neat tho. Prince of persia, we all loved that guys moves haha

well, I guess I am looking for more of a general answer.

But here is what I am using. ATMEL ATMEGA324P, with AVR Studio 4 as my environment. And basically, I am going to have a piezo buzzer attached to one of the pins.

I have an example code, but I'm just trying to figure out what it means.

Code:

#include <avr/io.h>
#include <util/delay.h>
#include "LCD.h"

#define BUZZER_PORT	PORTA
#define BUZZER_DDR  DDRA
#define BUZZER_PIN  0

// Provide the duration and period of buzzer signal in ms
void BUZZ(float duration, float period)
{
	long int i,cycles;
	float half_period;	// Initialize variables

	cycles=duration/period;	// Compute the number of cycles to loop toggling the pin
	half_period = period/2;	// Compute a half cycle period

	BUZZER_DDR = (1 << BUZZER_PIN) | BUZZER_DDR;	// Set the port for the buzzer output

	for (i=0;i<cycles;i++)	// Toggle the speaker the appropriate number of cycles
	{
		_delay_ms(half_period);							// Wait a half cycle to toggle port pin
		BUZZER_PORT = (1 << BUZZER_PIN) | BUZZER_PORT;	// Set the port pin
		_delay_ms(half_period);							// Wait a half cycle to clear the port pin
		BUZZER_PORT = ~(1 << BUZZER_PIN) & BUZZER_PORT;	// Clear the port pin
	}

	return;		// Return to the main program
}

void Alert(void)
{
	int i;

	for (i=0; i<4; i=i+1)
	{
		BUZZ(75,0.5);					// Output a waveform of 75ms at 2KHz (period of 2KHz is 1/2000=0.5 ms)
		PORTA = 0b00000010 ^ PORTA;		// Toggle the LED pin by XOR (whenever a bit is XORed with 1, it is toggled)
		_delay_ms(75);					// Wait for 75 ms
	}
	return;
}

int main(void)
{
	LCD_INIT();

	DDRA = DDRA | 0b00000010;
	PORTA = PORTA & 0b00000000;

	while(1)
	{
		LCD_COMMAND(LCD_CLEAR_HOME);	// Clear LCD screen, send cursor to start
		_delay_ms(500);					// Wait for 500 ms
		LCD_STRING("Junior Design");	// Write "Juior Design" to LCD
		_delay_ms(500);					// Wait for 500 ms

		LCD_ADDR(0x40);					// Send cursor to address 0x40 (second row)
		LCD_STRING("ATMEL Lecture");	// Write "ATMEL Lecture" to LCD
		_delay_ms(500);					// Wait for 500 ms
		Alert();						// Go to subroutine Alert()
	}	
}

I guess the way they are using it is using the function BUZZ to create a square wave form, with half the period as a high, and half the period as a low, to a whatever pin the buzzer is connected to.

Can someone explain what this is meant for?

Code:

BUZZER_DDR = (1 << BUZZER_PIN) | BUZZER_DDR;

The thing that I am trying to figure out is, that I am using a dip switch to control what music note I want, so how would I make the loop for the sound pulse to run infinitely until another switch is set, or that switch is turned off. The code example shows it as running for a specific amount of time. I suppose would you use a while statement?

Thanks, appreciate all the help.

but what does the (1 << BUZZER_PIN) do? that's what I don't understand

Is there another way to write it to have the same function? I'm just sort of having a hard time visualizing it as that.

Can it be like:

Code:

_delay_ms(half_period);
BUZZER_PORT = 0x01;
_delay_ms(half_period);
BUZZER_PORT = 0x00;

Is there a real advantage or disadvantage between one or the other?

Thanks

Ok, here is my code.

There is 1 warning and it says, statement with no effect...It is for the for loop statement near the end in the main section. Do you know what the problem is?

Code:

*	Project assignment: Hardware problem
 *	Read in an 8 bit port value (DIP switch ) and output a musical note for each corresponding bit ie B0 -> middle C,
 *	B1 -> C#, B2 -> D, etc...If more than one bit is set, chose the lowest note frequency for output and keep the 
 *	synthesizer monophonic.
 *
 */

#include <avr/io.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <util/delay.h>
#include "LCD.h"

#define BUZZER_PORT	PORTA
#define BUZZER_DDR  DDRA
#define BUZZER_PIN  0


int switch_input;				//global variable


void BUZZ(float period)
{
	int new_input;
	float half_period;			
	
	new_input = PIND;							//variable to test old switch_input variable
	half_period = period/2;						// Compute a half cycle period
	
	BUZZER_DDR = (1 << BUZZER_PIN) | BUZZER_DDR;		// Set the port for the buzzer output

	while(new_input == switch_input)
	{
		_delay_ms(half_period);				// Wait a half cycle to toggle port pin
		BUZZER_PORT = (1 << BUZZER_PIN) | BUZZER_PORT;	// Set the port pin as a 1
		_delay_ms(half_period);				// Wait a half cycle to clear the port pin
		BUZZER_PORT = ~(1 << BUZZER_PIN) & BUZZER_PORT;	// Clear the port pin to 0
	
		new_input = PIND;
	}

	return;
}


int main(void)
{	
	DDRD = 0x00;				//PORTD is all input for DIP switch
	DDRA = 0x01;				//PORTA pin 0 is an output for buzzer	
	PORTA = 0x00;				//Set the buzzer pin initially to 0

	int i,count,bit_check;
	float C,C2,D,D2,E,F,F2,G;	

	C = 261.63;			//initialize vairables to specifc frequency (in HZ)
	C2 = 277.18;
	D = 293.66;
	D2 = 311.13;
	E = 329.63;
	F = 349.23;
	F2 = 369.99;
	G = 392.00;


	while(1)
	{
		switch_input = PIND;		//Reads in the DIP switch values and stores in switch_input

LOOP:	switch(switch_input)		//determines which DIP switch is turned ON to play a 
		{							//specific note
			case 0x0:
				BUZZ((1/C)*100);	//Branches to function BUZZ with period of C ((1/261.63)*100 = 3.822 ms)
				break;

			case 0x1:
				BUZZ((1/C2)*100);
				break;

			case 0x2:
				BUZZ((1/D)*100);
				break;

			case 0x3:
				BUZZ((1/D2)*100);
				break;

			case 0x4:
				BUZZ((1/E)*100);
				break;

			case 0x5:
				BUZZ((1/F)*100);
				break;

			case 0x6:
				BUZZ((1/F2)*100);
				break;

			case 0x7:
				BUZZ((1/G)*100);
				break;
	
			default:						//Default case is for if more than one switch is on
										//Check each bit, starting from the lowest bit, to determine
				count = 0;				//which is the lowest switch on.
				for(i=0x01;i<=0x80;i<<1)		//starts at bit 0 stop after bit 7, i shifts left 1 bit
				{
					bit_check = (switch_input & i);		//Masks all bits except for bit i in PIND	

					if(bit_check == i)			//checks if the bit is a 1 or a 0
						break;	
					else
						count = count + 1;		//count used to determine what bit is lowest
				}
				
				switch_input = pow(2,count);			//2^count gives the lowest switch

				goto LOOP;
		}
	}	
}

Thanks

oh so basically the original code changes only the bits you are interested in either using an OR operator to turn something on, and an AND operator to turn something off.

Also, when they have the BUZZER_PIN = 0 in a macro, why don't they automatically use the code like this:

Code:

_delay_ms(half_period);
BUZZER_PORT = 1 | BUZZER_PORT;
_delay_ms(half_period);
BUZZER_PORT = 0 & BUZZER_PORT;

instead of using the (1<<BUZZER_PIN) which is always automatically 0?

Maybe it is good programming techniques?