51 MCU peripherals: buzzer

  Buzzer

A buzzer is a device that converts an electrical signal into a sound signal , It is often used to generate the key tone of the device 、 Alarm tone and other prompt signals .

Buzzer can be divided into active buzzer and passive buzzer according to driving mode ：

Active buzzer ： Internal oscillation source , Connect the positive and negative poles to the DC voltage, that is, the continuous sound , Fixed frequency ;

Passive buzzer ： No internal oscillation source , The oscillation controller is required to provide an oscillation pulse , Adjust the frequency of the oscillation pulse , It can make sounds of different frequencies ;

The specific principle of buzzer can be consulted by yourself , All in all , What you need to know is , There are two pieces of metal inside the buzzer , When positive and negative electrodes are added , Will adsorb together and produce collision , Make a sound . When one of the buzzer pin electrodes is fixed , When the current between positive and negative phases is applied to the other pin , Will produce a certain frequency of vibration , To make different sounds .

The tone of sound can be controlled by frequency , The higher the frequency is. , The louder the voice .

The sound size is determined by the hardware , Unable to write code to control the sound size .

Look at the schematic

The triode here is used to amplify the pin current of MCU , It has reached the level of being able to drive the buzzer .

There will be J8 Receive P2.0 Interface , And provide a certain frequency signal .

Code implementation

demand ： Make a dripping sound , The frequency is 500Hz, Then the clock cycle is 2ms, So every 1ms Change the level state .

I tried it first , I don't know if it's OK to keep high level ：P20 = 1; No sound was heard .

The frequency is 500Hz Try again ：

/**
  *@file    buzzer.c
  *@author  Timi
  *@date    2022.07.23
  */
#include <reg51.h>

sbit P20 = P2^0;

#define AIM_COUNTER(time) (65536 - (time) * 1000 / 1)

        
// Function entrance 
void main(void)
{   
    TMOD = 0x01;
    TL0 = (AIM_COUNTER(50) % 256);
    TH0 = (AIM_COUNTER(50) / 256);
    TR0 = 1;
    ET0 = 1;
    EA = 1;
    
    while(1);
}

/**
  *@brief    Let the buzzer ring 
  *@param[in]
  *@param[out] 
  *@return
  */
void EnableBuzzer() interrupt 1 using 1
{
    TL0 = (AIM_COUNTER(1) % 256);
    TH0 = (AIM_COUNTER(1) / 256);
    
    P20 = ~P20;
}

This situation , The buzzer keeps ringing . But what I want is Didi's voice . How to adjust it ？

My idea is , Ring for a while , Then stop for a while , Then ring for a while , Stop for a while , If it goes back and forth .

The code prototype is as follows ：

/**
  *@file    buzzer.c
  *@author  Timi
  *@date    2022.07.23
  */
#include <reg51.h>

#define uchar unsigned char 
#define AIM_COUNTER(time) (65536 - (time) * 1000 / 1)

sbit P20 = P2^0;
static uchar count = 0;

void Delay500ms(void);

// Function entrance 
void main(void)
{   
    TMOD = 0x01;
    TL0 = (AIM_COUNTER(50) % 256);
    TH0 = (AIM_COUNTER(50) / 256);
    TR0 = 1;
    ET0 = 1;
    EA = 1;
    
    while(1);
}

/**
  *@brief    Let the buzzer ring 
  *@param[in]
  *@param[out] 
  *@return
  */
void EnableBuzzer(void) interrupt 1 using 1
{
    TL0 = (AIM_COUNTER(1) % 256);
    TH0 = (AIM_COUNTER(1) / 256);
    
    P20 = ~P20;         // The above three codes realize 500Hz Vibration of frequency 
    
    if(count++ == 100)  // Per vibration 100 Tentatively after times 500ms
    {
        P20 = 0;
        Delay500ms();
        count = 0;
    }
}

void Delay500ms(void)   // error  0us
{
    uchar a,b,c;
    
    for(c = 205; c > 0; c--)
        for(b = 116; b > 0; b--)
            for(a = 9; a > 0; a--);
}

Although it can realize the function , But I still used for loop Delay, The pause time is not accurate .

I want to use a timer , however , Use timer in timer , Don't you just nest loops ？ More complicated , And easy to make mistakes . therefore , How to solve this problem ？

The solution code is as follows ：

/**
  *@file    buzzer.c
  *@author  Timi
  *@date    2022.07.23
  */
#include <reg51.h>

#define u32 unsigned int
#define AIM_COUNTER(time) (65536 - (time) * 1000 / 1)

sbit P20 = P2^0;

static u32 count = 1;

// Function entrance 
void main(void)
{   
    TMOD = 0x01;
    TL0 = (AIM_COUNTER(50) % 256);
    TH0 = (AIM_COUNTER(50) / 256);
    TR0 = 1;
    ET0 = 1;
    EA = 1;
    
    while(1);
}

/**
  *@brief    Let the buzzer ring 
  *@param[in]
  *@param[out] 
  *@return
  */
void EnableBuzzer(void) interrupt 1 using 1
{
    TL0 = (AIM_COUNTER(1) % 256); //500Hz The frequency of 
    TH0 = (AIM_COUNTER(1) / 256);
    
    if(count >= 1 && count <=250)
    {
        P20 = ~P20;
    }
    else if(count >= 251 && count <= 1000)  // You can control how long it rings by the ratio of the numbers in these two places , How long does it stop 
    {
        // Do nothing ;
    }
    else
    {
        count = 0;
    }
    count++;
}

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