51 single chip microcomputer buzzer

The principle of buzzer sound is that the current passes through the electromagnetic coil, which makes the electromagnetic coil generate a magnetic field to drive the vibration membrane to make sound. Therefore, a certain current is required to drive it. The current output by the IO pin of the microcontroller is small, and the TTL level output by the microcontroller basically cannot drive the buzzer. Therefore, a current amplification circuit is needed. The role of the transistor is to drive, and the driving current is amplified by the transistor, so that the buzzer can make a sound.

The difference between active buzzer and passive buzzer:

The "source" here does not refer to the power supply. It refers to the oscillation source. In other words, the active buzzer has an oscillation source inside, so it will buzz as soon as it is powered on. The  passive buzzer
does not have an oscillation source inside, so it cannot be made to buzz if a DC signal is used. It must be driven by a 2K~5K square wave. 
Active buzzers are often more expensive than passive ones because they have multiple oscillation circuits inside. 
The advantages of passive buzzers are: 1. Cheap, 2. The sound frequency is controllable, and the "Doremi Fasolaxi" effect can be produced. 3. In some special cases, it can reuse a control port with the LED. The advantages of active buzzers are: convenient program control.

Routine, reference from the Internet.

  1 /************************************************ ************************  

  2 [File Name] C51 Music Program (August Osmanthus)  

  3 [Function] Playing music through microcontroller  

  4   

  5/************************************************ ************************/   

  6 #include    

  7 #include    

  8 //This example uses 89C52, the crystal oscillator is 11.0592MHZ    

  9 // Regarding how to compile music code, it is actually very simple. You can see the following code.    

 10 //The frequency constant is the pitch in musical terms, and the beat constant is the number of beats in musical terms;    

 11 //So take out the music score and try to edit it!    

 12 

 13 sbit Beep = P1^5 ; 

 14    

 15 unsigned char n=0; //n is the beat constant variable    

 16 unsigned char code music_tab[] ={   

 17 0x18, 0x30, 0x1C, 0x10, //Format: frequency constant, beat constant, frequency constant, beat constant,    

 18 0x20, 0x40, 0x1C , 0x10,   

 19 0x18, 0x10, 0x20 , 0x10,   

 20 0x1C, 0x10, 0x18, 0x40,   

 21 0x1C, 0x20, 0x20 , 0x20,   

 22 0x1C, 0x20, 0x18, 0x20,   

 23 0x20, 0x80, 0xFF , 0x20,   

 24 0x30, 0x1C, 0x10, 0x18,   

 25 0x20, 0x15, 0x20 , 0x1C,   

 26 0x20, 0x20, 0x20 , 0x26,   

 27 0x40, 0x20, 0x20 , 0x2B,   

 28 0x20, 0x26, 0x20 , 0x20,   

 29 0x20, 0x30, 0x80, 0xFF,   

 30 0x20, 0x20, 0x1C , 0x10,   

 31 0x18, 0x10, 0x20, 0x20,   

 32 0x26, 0x20, 0x2B , 0x20,   

 33 0x30, 0x20, 0x2B , 0x40,   

 34 0x20, 0x20, 0x1C , 0x10,   

 35 0x18, 0x10, 0x20, 0x20,   

 36 0x26, 0x20, 0x2B , 0x20,   

 37 0x30, 0x20, 0x2B , 0x40,   

 38 0x20, 0x30, 0x1C , 0x10,   

 39 0x18, 0x20, 0x15 , 0x20,   

 40 0x1C, 0x20, 0x20 , 0x20,   

 41 0x26, 0x40, 0x20 , 0x20,   

 42 0x2B, 0x20, 0x26 , 0x20,   

 43 0x20, 0x20, 0x30, 0x80,   

 44 0x20, 0x30, 0x1C , 0x10,   

 45 0x20, 0x10, 0x1C , 0x10,   

 46 0x20, 0x20, 0x26 , 0x20,   

 47 0x2B, 0x20, 0x30, 0x20,   

 48 0x2B, 0x40, 0x20, 0x15,   

 49 0x1F, 0x05, 0x20, 0x10,   

 50 0x1C, 0x10, 0x20, 0x20,   

 51 0x26, 0x20, 0x2B , 0x20,   

 52 0x30, 0x20, 0x2B , 0x40,   

 53 0x20, 0x30, 0x1C , 0x10,   

 54 0x18, 0x20, 0x15 , 0x20,   

 55 0x1C, 0x20, 0x20 , 0x20,   

 56 0x26, 0x40, 0x20 , 0x20,   

 57 0x2B, 0x20, 0x26 , 0x20,   

 58 0x20, 0x20, 0x30, 0x30,   

 59 0x20, 0x30, 0x1C , 0x10,   

 60 0x18, 0x40, 0x1C , 0x20,   

 61 0x20, 0x20, 0x26 , 0x40,   

 62 0x13, 0x60, 0x18, 0x20,   

 63 0x15, 0x40, 0x13 , 0x40,   

 64 0x18, 0x80, 0x00   

 65 };   

 66    

 67 void int0() interrupt 1 //Use interrupt 0 to control the beat    

 68 {TH0=0xd8;   

 69 TL0=0xef;   

 70 n--;   

 71 }   

 72    

 73 void delay (unsigned char m) //Control frequency delay    

 74 {   

 75 unsigned i=3*m;   

 76 while(--i);   

 77 }   

 78    

 79 void delayms(unsigned char a) // millisecond delay subroutine    

 80 {   

 81 while(--a); //Use while(--a) Do not use while(a--); You can compile and see the assembly result to know!    

 82 }   

 83    

 84 void main()   

 85 { unsigned char p,m; //m is the frequency constant variable    

 86 unsigned char i=0;   

 87 TMOD&=0x0f;   

 88 TMOD|=0x01;   

 89 TH0=0xd8;TL0=0xef;   

 90 IE=0x82;   

 91 play:   

 92 while(1)   

 93 {   

 94 a: p=music_tab[i];   

 95 if(p==0x00) { i=0, delayms(1000); goto play;} //If the end character is encountered, delay 1 second and go back to the beginning and play again    

 96 else if(p==0xff) { i=i+1;delayms(100),TR0=0; goto a;} //If a rest is encountered, delay 100ms and continue to pick the next note    

 97 else {m=music_tab[i++], n=music_tab[i++];} //Get the frequency constant and beat constant    

 98 TR0=1; //Start timer 1    

 99 while(n!=0) Beep=~Beep,delay(m); //Wait for the beat to finish, output audio through P1 port (multi-channel is possible!)    

100 TR0=0; //Turn off timer 1    

101 }   

102 }